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General Biology Notes 1
laurenrachelmiller
- Collectively, hydrogen bonds hold a substance together (water is attracted to water).
- Cohesion due to hydrogen bonding contributes to the transport of water and dissolved nutrients against gravity in plants
Four emergent properties of water that contribute to Earth's suitability for life
- Cohesive behavior
- Ability to moderate temperature
- Expansion upon freezing
- Versatility as a solvent
-The clinging of one substance to another
- A measure of how difficult it is to stretch or break the surface of a liquid
- Water has a greater surface tension than most other liquids and is related to cohesion
Moderation of Temperature by Water
- Water moderates air temperature by absorbing heat from air that is warmer and releasing the stored heat to air that is cooler
- Measure of heat intensity that represents the average kinetic energy of the molecules, regardless of volume
Specific Heat
- The amount of heat that must be absorbed or lost for 1g of that substance to change its temperature by 1 degree Celsius
High Specific Heat of Water
- Relative to other materials, water will change its temperature less when it absorbs or loses a given amount of heat (water resists changing its temperature)
- Also plays a role in stabilizing ocean temperatures, creating a favorable environment for marine life
- The quantity of heat a liquid must absorb for 1g of it to be converted from the liquid to the gaseous state
- As a liquid evaporates, the surface of the liquid that remains behind cools down
- Contributes to the stability of temperature in lakes and ponds and also provides a mechanism that prevents terrestrial organisms from overheating
Water's greatest density
- Is reached at 4 degrees Celsius and then begins to expand as the molecules move faster
Hydration Shell
- Sphere of water molecules around each dissolved ion
Human Lysozyme
- Water soluble protein that is found in tears and saliva that has antibacterial action
Colloid
- Substances can be hydrophilic without actually dissolving--a stable suspension of fine particles in a liquid
pH of a solution
- The negative logarithm (base 10) of the Hydrogen ion concentration
Internal pH of most living cells
- Is close to 7
- Allows biological fluids to maintain a relatively constant pH despite the addition of acids or bases
- It is a substance that minimizes the changes in the concentration of Hydrogen and Hydroxide ions in a solution
- Most buffer solutions contain a weak acid and its corresponding base, which combine reversible with hydrogen ions
Structural Isomer
- Differ in covalent arrangements of their atoms
Cis-trans isomers (geometric isomers)
- Carbons have covalent bonds to the same atoms, but these atoms differ in their spatial arrangements due to the inflexibility of double bonds
- Isomers that are mirror images of each other and differ in shape due to the presence of an asymmetric carbon, one that is attached to four different atoms or groups of atoms
Critically important large molecules of all living things
- Carbohydrates, lipids, proteins, and nucleic acids
Macromolecules
- Carbohydrates, proteins, and nucleic acids
- A long molecule consisting of many similar or identical building blocks linked by covalent bonds
- Carbohydrates, proteins, and nucleic acids are polymers
- The repeating units that serve as the building blocks of a polymer
- Specialized macromolecules that speed up chemical reactions
- They regulate metabolism by acting as catalysts, chemical agents that selectively speed up chemical reactions without being consumed by the reaction
- Include both sugars and polymers of sugars
Simplest Carbohydrates
- Monosaccharides or simple sugars (these are the monomers from which more complex carbohydrates are constructed)
- Generally have molecular formulas that are some multiple of the unit CH2O.
- Glucose is the most common monosaccharide and is a major nutrient for cells and can serve as raw material for the synthesis of amino acids and fatty acids
Trademarks of a sugar
- Molecule that ranges from 3 to 7 carbons long with a carbonyl group and multiple hydroxyl groups
- Depending on the location of the carbonyl group, the sugar is either an aldose or a ketose
- Glucose is an aldose and fructose is a ketose
Disaccharide
- Consists of two monosaccharides joined by a glycosidic linkage (a covalent bond formed between two monosaccharides by a dehydration reaction)
Common Disaccharides
- Maltose (made from two molecules of glucose), Lactose (made from a glucose and a galactose molecule), and the most prevalent disaccharide Sucrose (made from glucose and fructose)
Polysaccharides
- Polymers with a few hundred thousand monosaccharides joined by glycosidic linkages
Starch (a storage plant polysaccharide)
- As a polymer of alpha glucose monomers, it is stored as granules within cellular structures known as plastids (which include chloroplasts)
- Synthesizing starch enables plants to stockpile glucose
- Most animals, including humans, have enzymes that can hydrolyze plant starch, making glucose an available nutrient for cells
- Found in potato tubers, grains, wheat, maize, and rice
- The simplest form of starch, amylose, is unbranched (helical shape)
Glycogen (a storage animal polysaccharide)
- A polymer of glucose that is similar to amylopectin (a more complex form of starch) but it is more extensively branched
- Humans and other vertebrates store glycogen in liver and muscle cells
Cellulose (structural polysaccharide)
- A major component of the tough walls that enclose plant cells and it is the most abundant organic compound on earth. - Cellulose is a polymer of glucose, but in cellulose all of the glucose monomers are in the beta configuration
- Straight shape, parallel cellulose molecules held together are grouped into units called microfibrils
- Humans do not have the enzymes to digest beta linkages
Chtin (structural polysaccharide)
- The carbohydrate used by arthropods (insects, spiders, and crustaceans) to build their exoskeletons
- Pure chitin is leathery and flexible, but it is hardened when encrusted with calcium carbonate
- Chitin has beta linkages and the glucose monomer has a nitrogen containing appendage
Most biologically important types of lipids
- Fats, phospholipids, and steroids
- An alcohol where each of its three carbons bears a hydroxyl group
- Has a long carbon skeleton usually 16 or 18 carbon atoms in length and has a carboxyl group
Triacylglycerol (or triglyceride/fat)
- Three fatty acid molecules are joined to one glycerol molecule by three ester linkages
Unsaturated fatty acid
- Has one or more double bonds; nearly all double bonds in naturally occurring fatty acids are cis double bonds
- Fats of plants and fish are generally unsaturated
- Unsaturated fats can have trans double bonds and these may contribute to atherosclerosis
Saturated fatty acid
- Has single bonds, most animal fats are saturated
Major function of fats
- Energy storage (a gram of fat storage stores twice as much energy as a gram of a polysaccharide)
Phospholipid
- Has only two fatty acids attached to a glycerol rather than three--the third hydroxyl group is joined to a phosphate group which has a negative electrical charge in the cell
- Lipids characterized by a carbon skeleton consisting of four fused rings
- Common component of animal cell membranes and is the precursor from which other steroids are synthesized
- In vertebrates, cholesterol is synthesized in the liver and obtained from the diet
- Consists of one or more polypeptides, each folded and coiled into a specific three-dimensional structure
- Account for more than 50% of the dry mass of most cells
- Proteins can speed up chemical reactions and also play a role in defense, storage, transport, cellular communication, movement, or structural support.
- All unbranched polymers constructed from 20 amino acids
Polypeptides
- Polymers of amino acids
- An organic molecule possessing both an amino group and a carboxyl group
Functions of Proteins
- Enzymatic (pepsin, digestion), defensive (antibodies), storage (casein, milk protein), transport (hemoglobin, blood), hormonal (insulin, pancreas), receptor (nerve cell receptors), contractile and motor (actin and myosin, muscle), and structural (keratin, hair)
Peptide Bond Formation
- When two amino acids are positioned so that the carboxyl group of one is adjacent to the amino group of the other, they can become joined by a dehydration reaction that forms a covalent bond
- Note that one end of a polypeptide chain has a free amino group, while the opposite end has a free carboxyl group
Two Protein Types
- Many proteins are roughly spherical (globular proteins; Collagen and Hemoglobin)
- Fibrous proteins are shaped like long fibers
Four levels of protein structure
- All proteins share three superimposed levels of structure, known as primary, secondary, and tertiary structures
Primary Structure
- A linked series of amino acids with a unique sequence
- Determines a proteins shape
- Coils and folds are the result of hydrogen bonds between the repeating constituents of the polypeptide backbone (not the amino acid side chains)
- Alpha helix: A delicate coil held together by hydrogen bonding between every four amino acid
- Beta Pleated Sheet: Two or more strands of the polypeptide chain lying side by side (called beta strands) are connected by hydrogen bonds between parts of the two parallel proteins
Tertiary Structure
- The overall shape of a polypeptide resulting from interactions between the side chains of the various amino acids
- Hydrophobic interaction: As a polypeptide folds into its function shape, amino acids with hydrophobic side chains usually end up in clusters at the core of the protein, out of contact with water
- Covalent bonds called disulfide bridges may further reinforce the shape of a protein (Disulfide bridges form where two cysteine monomers, which have sulfhydryl groups on their side chains are brought close together by the folding of the protein
Quaternary Structure
- Some proteins consist of two or more polypeptide chains aggregated into one functional macromolecule
Sickle-Cell Disease
- An inherited blood disorder that is caused by the substitution of one amino acid (valine) for the normal one (glutamic acid) at a particular position on the primary structure of hemoglobin
- Abnormal hemoglobin molecules change shape and crystallize into sickles
Denaturation
- If the pH, salt concentration, or temperature (excessive heat) are altered, the weak chemical bonds and interactions within a protein may be destroyed--causing it to unravel and lose its native shape
- Most proteins become denatured if they are transferred from an aqueous environment to a nonpolar solvent (the polypeptide chain refolds so that its hydrophobic regions face outward)
- Some proteins can return to its functional shape when the denaturing agent is removed
Chaperonins
- Crucial to the folding process because these are protein molecules that assist in the proper folding of other proteins
- Don't specify the final structure of a polypeptide
- Keep new polypeptides segregated from "bad influences" in the cytoplasmic environment while it folds spontaneously
Role of DNA
- DNA provides directions for its own replication, directs RNA synthesis, and through RNA, controls protein synthesis
- Each gene along a DNA molecule directs synthesis of messenger RNA (mRNA)
Nucleic Acids
- Polymers made of monomers called nucleotides
Polynucleotide
- Nucleic acids are macromolecules that exist as polymers
- Each monomer has only one phosphate group
- Monomers of polynucleotides
- Composed of a nitrogenous base, a pentose sugar, and one or more phosphate groups
- Portion of a nucleotide without any phosphate groups is called a nucleoside
Nitrogenous Bases (Pyrimidine)
- One six membered ring of carbon and nitrogen atoms
- Cytosine (C), Thymine (T), and Uracil (U)
- Uracil is only found in RNA and Thymine is only found in DNA
Nitrogenous Bases (Purine)
- Larger, with a six-membered ring fused to a five membered ring
- Adenine (A) and Guanine (G)
Phosphodiester Linkage
- Adjacent nucleotides are joined by a phosphodiester linkage, which consists of a phosphate group that links the sugars of two nucleotides
- Results in a backbone with a repeating pattern of sugar-phosphate units (nitrogenous bases are not a part of the backbone)
The linear order in a gene
- Two free ends of the polymer are distinctly different from each other (one end has a phosphate attached to a 5' carbon, and the other end has a hydroxyl group on a 3' carbon)
RNA Structure
- Ribose sugar
- Exists as a single polynucleotide chain
- Complementary base pairing can occur between two parts of two RNA molecules or even between two stretches of nucleotides in the same RNA molecule
- In RNA Adenine pairs with Uracil
DNA Structure
- Deoxyribose sugar
- DNA molecules have two polynucleotides (or strands) that spiral around an imaginary axis, forming a double helix
- The two sugar-phosphate backbones run in opposite 5' --> 3' directions (antiparallel)
- Sugar-phosphate backbones are on the outside of the helix, and the nitrogenous bases are paired in the interior of the helix
- The two strands are held together by hydrogen bonds between the paired nitrogenous bases
- Adenine always pairs with Thymine and Guanine always pairs with Cytosine
- The two strands of the double helix are said to be complementary to each other
Selective Permeability
Exhibited by the plasma membrane: allows some substances to cross more easily than others
Staple Ingredients of Membranes
- Lipids and proteins (although carbohydrates are also important)
- Having both a hydrophilic region and a hydrophobic region (phospholipid and membrane proteins)
Fluid Mosaic Model
- The membrane is a fluid structure with a "mosaic" of various proteins embedded in or attached to a double layer (bilayer) of phospholipids
Fluidity of Membranes
- Membrane is held together primarily by hydrophobic interactions, which are much weaker than covalent bonds
- Lipids (rapidly) and some proteins (are much larger than lipids and move more slowly) can shift about laterally in the plane of the membrane
Influences on the Fluidity of Membranes
- Remains fluid as temperature decreases until finally the phospholipids settle into a closely packed arrangement and the membrane solidifies
- Will remain fluid to a lower temperature if it is rich in phospholipids with unsaturated hydrocarbon tails
- At high temperatures cholesterol makes the membrane less fluid by restraining phospholipid movement
- Because cholesterol also hinders the close packing of phospholipids, it lowers the temperature required for the membrane to solidify
- Membranes must be fluid to work properly
Six Major Functions of Proteins in the Plasma Membrane
- Transport
- Enzymatic activity
- Signal transduction
- Cell-cell recognition
- Intercellular joining
- Attachment to the cytoskeleton and extracellular matrix
Integral Proteins
- Penetrate the hydrophobic interior of the lipid bilayer
- Majority are transmembrane proteins, which span the membrane
- Hydrophobic regions of an integral protein consist of one or more stretches of nonpolar amino acids, usually coiled into alpha helics
- Some proteins have a hydrophilic channel through their center that allows passage of hydrophilic substances
Peripheral Proteins
- Not embedded in the lipid bilayer at all; they are appendages loosely bound to the surface of the membrane (often to exposed parts of integral proteins)
Cell-Cell Recognition
- A cell's ability to distinguish one type of neighboring cell from another, is crucial to the functioning of an organism
- Cells recognize other cells by binding to molecules, often containing carbohydrates, on the extracellular surface of the plasma membrane
Glycolipids
- Membrane carbohydrates are usually short, branched chains of fewer than 15 sugar units
- Covalently bonded carbohydrates to lipids
Glycoproteins
- Covalently bonded to proteins
Synthesis of Membrane
- Membrane is built by the endoplasmic reticulum and Golgi apparatus
1) Membrane proteins and lipids are synthesized in the ER. Carbohydrates are added to the transmembrane proteins, making them glycoproteins. The carbohydrates portions may the be modified
2) Inside the Golgi apparatus, the glycoproteins undergo further carbohydrate modification, and lipids acquire carbohydrates, becoming glycolipids
- The glycoproteins, glycolipids, and secretory proteins are transported in vesices to the plasma membrane
- As vesicles fuse with the plasma membrane, the outside face of the vesicle becomes continuous with the inside (cytoplasmic) face of the plasma membrane. This releases the secretory proteins from the cell, a process called exocytosis and positions the carbohydrates of membrane glycoproteins and glycolipids on the extracellular face of the plasma membrane
Lipid Bilayer Permeability
- Nonpolar molecules, such as hydrocarbons, carbon dioxide, and oxygen, are hydrophobic and can dissolve
- Polar molecules such as glucose (other sugars) and water pass only slowly
- A charged atom or molecule and its surrounded shell of water
Transport Proteins
- Hydrophilic substances can avoid contact with the lipid bilayer by passing through transport proteins
- Channel proteins function by have a hydrophilic channel that certain molecules or atomic ions use as a tunnel through the membrane (channel proteins that transport ions are called ion channels)
- Carrier proteins hold onto their passengers and change shape in a way that shuttles them across the membrane (these are the transport proteins that move solutes against their concentration gradients)
Aquaporins
- Channel proteins that facilitate the passage of water molecules
- The movement of molecules of any substance so that they spread out evenly into the available space (spontaneous process, needs no input of energy)
- In the absence of other forces, a substances will diffuse from where it is more concentrated to where it is less concentrated
- Any substance will diffuse down its own concentration gradient, the region along which the density of a chemical substance increases or decreases
Passive Transport
- The diffusion of a substance across a biological membrane (cell does not have to expend energy to make it happen)
- Water diffuses across the membrane from the region of lower solute concentration (higher free water concentration) to that of higher solute concentration (lower free water concentration) until the solute concentrations on both sides of the membrane are equal
- The diffusion of free water across a selectively permeable membrane, whether artificial or cellular
Tonicity
- The ability of a surrounding solution to cause a cell to gain or lose water
- If there is a higher concentration of nonpenetrating solutes in the surrounding solution, water will tend to leave the cell (and vice versa)
Isotonic
- If a cell without a wall is immersed in an environment that is isotonic to the cell there will be no net movement of water across the plasma membrane
Hypertonic
- A cell in a hypertonic solution will lose water, shrivel, and most likely die
Hypotonic
- If a cell is placed in a solution that is hypotonic to the cell, water will enter the cell faster than it leaves, and the cell will swell and lyse (burst)
- A cell wall without rigid walls can tolerate neither excessive uptake nor excessive loss of water
Osmoregulation
- Organisms that lack rigid cells walls must have other adaptations for osmoregulation, the control of solute concentrations and water balance
Turgid
- Cells of plants, prokaryotes, fungi, and some protists are surrounded by walls
- Relatively inelastic wall will expand only so much before it exerts a back pressure on the cell (turgor pressure)
- Turgid (very firm): Is the healthy state for most plant cells
- If a plant's cells and their surroundings are isotonic, there is no net tendency for water to enter
Plasmolysis
- As the plant cell (bacteria and fungi) shrivels, its plasma membrane pulls away from the wall and this phenomenon, plasmolysis, causes the plant to wilt and can lead to plant death
Facilitated Diffusion
- Many polar molecules and ions impeded by the lipid bilayer of the membrane diffuse passively with the help of transport proteins
- Does not alter the direction of transport
Gated Channels
- Many ion channels function as gated channels, which open or close in response to a stimulus
- For some gated channels, the stimulus is electrical
- Other gated channels open or close when a specific substance other than the one to be transported bind to the channel
- To pump a solute across a membrane against its gradient requires work, the cell must expend energy
- Active transport may be necessary in cases where electrical forces due to the membrane potential oppose the simple diffusion of an ion down its concentration gradient
Sodium-Potassium Pump
1) Cytoplasmic Na+ binds to the sodium-potassium pump. The affinity for Na+ is high when the protein has this shape
2) Na+ binding stimulates phosphorylation by ATP
3) Phosphorylation leads to a change in protein shape, reducing its affinity for Na+, which is released outside
4) The new shape has a high affinity for K+, which binds on the extracellular side and triggers release of the phosphate group
5) Loss of the phosphate group restores the protein's original shape, which has a lower affinity for K+
6) K+ is released; affinity for Na+ is high again, and the cycle repeats
- The sodium-potassium pump appears to be the major electrogenic pump of animal cells
Membrane Potential
- All cells have voltages across their plasma membranes
- Cytoplasmic side of the membrane is negative in charge relative to the extracellular side because of an unequal distribution of anions and cations on the two sides
- The voltage across a membrane
- Membrane potential favors passive transport of cations into the cell and anions out of the cell
- Two forces drive the diffusion of ions across a membrane creating an electrochemical gradient: chemical force (the ion's concentration gradient) and an electrical force (the effect of the membrane potential
Electrogenic Pump
- A transport protein that generates voltage across a membrane
- The main electrogenic pump of plants, fungi, and bacteria is a proton pump which actively transports protons out of the cell (transfers positive charge from the cytoplasm to the extracellular solution)
Cotransport
- A single ATP-powered pump that transports a specific solute can indirectly drive the active transport of several other solutes in a mechanism
- Another transport protein, a contransporter separate from the pump, can couple the downhill diffusion of this substance to the uphill transport of a second substance against its own concentration (or electrochemical) gradient
Exocytosis
- Large molecules, such as proteins and polysaccharides, as well as larger particles, generally cross the membrane in bulk by mechanisms that involve packaging in vesicles (these processes require energy)
- Cell secretes certain biological molecules by the fusion of vesicles with the plasma membrane
- A transport vesicle that has budded from the Golgi apparatus moves along microtubules of the cytoskeleton to the plasma membrane
- When the vesicle membrane and plasma membrane come into contact, specific proteins rearrange the lipid molecules of the two bilayers so that the two membranes fuse
- The contents of the vesicle then spill to the outside of the cell, and the vesicle membrane becomes part of the plasma membrane
Endocytosis (3 types)
- A small area of the plasma membrane sinks inward to form a pocket
- As the pocket deepens, it pinches in, forming a vesicle containing material that had been outside the cell
Phagocytosis
- Cell engulfs a particle by wrapping pseudopodia around it and packaging it within a membranous sac called a food vacuole
- Particle will be digested after the food vacuoule fuses with a lysosome containing hydrolytic enzymes
Pinocytosis
- The cell gulps droplets of extracellular fluid into tiny vesicles
Receptor-Mediated Endocytosis
- Enables the cell to acquire bulk quantities of specific substances, even though those substances may not be very concentrated in the extracellular fluid
- Embedded in the membrane are proteins with specific receptor sites exposed to the extracellular fluid, to which specific substances bind
- The receptor proteins then cluster in regions of the membrane called coated pits, which are lined on their cytoplasmic side by a fuzzy layer of coat proteins (next, each coated pit forms a vesicle containing the ligand molecules)
- After the ingested material is liberated from the vesicle, the emptied receptors are recycled to the plasma membrane by the same vesicle
- The totality of an organism's chemical reactions
- Manages the material and energy resources of the cell
Metabolic Pathway
- Begins with a specific molecule, which is then altered in a series of defined steps, resulting a certain product (each step of the pathway is catalyzed by a specific enzyme)
Catabolic Pathway
- Some metabolic pathways release energy by breaking down complex molecules to simpler compounds
- A major pathway of catabolism is cell respiration
- Downhill
- Exergonic pathway
Anabolic Pathway
- These pathways consume energy to build complicated molecules from simpler ones; they are sometimes called biosynthetic pathways
- Synthesis of amino acid from simpler molecules and the synthesis of a protein from amino acids
- Uphill
- The study of how energy flows through living organisms
- The study of the energy transformations that occur in a collection of matter
First Law of Thermodynamics (principle of conservation of energy)
- The energy of the universe is constant: Energy can be transferred and transformed, but it cannot be created or destroyed
- A measure of disorder or randomness in a system
Second Law of Thermodynamics
- Every energy transfer or transformation increases the entropy of the universe
- For a process to occur spontaneously, it must increase the entropy of the universe
- The entropy of a particular system, such as an organism, may actually decrease as long as the total entropy of the universe (the system plus its surroundings) increases
- A process that can occur without an input of energy
- DeltaG = DeltaH - TDeltaS
- DeltaG has a negative value for all spontaneous processes
- Processes that have a positive or zero deltaG are never spontaneous
Energy Coupling
- The use of an exergonic process to drive an endergonic one
- ATP is responsible for mediating most energy coupling in cells, and in most cases it acts as the immediate source of energy that powers cellular work
Structure of ATP
- Contains ribose with adenine and a chain of three phosphate groups
- Hydrolysis gives ADP
Three Types of Cellular Work
- Chemical, transport, and mechanical
Phosphorylated Intermediate
- Recipient with a phosphate from ATP covalently bonded to it
- The reactant an enzyme acts on
Enzyme Substrate Complex
- The enzyme binds to its substrate (or substrates, when there are two or more reactants) forming an enzyme substrate complex
Active Site
- Only a restricted region of the enzyme molecule actually binds to the substrate
- Typically a pocket or groove on the surface of the enzyme where catalysis occurs
Induced Fit
- Specificity of an enzyme is attributed to a compatible fit between the shape of its active site and the shape of the substrate
- As the substrate enters the active site, the enzyme changes shape slightly due to interactions between the substrate's chemical groups and chemical groups on the side chains of the amino acids that form the active site
- Brings chemical groups of teh active site into positions that enhance their ability to catalyze the chemical reaction
Catalysis in the Enzyme's Active Site
1) Substrates enter active site; enzyme changes shape such that its active site enfolds the substrates (induced fit)
2) Substrates are held in active site by weak interactions, such as hydrogen bonds and ionic bonds
3) Active site can lower EA and speed up a reaction by: acting as a template for substrate orientation, stressing the substrates and stabilizing the transition state, providing a favorable microenvironment and/or, participating directly in the catalytic reaction
4) Substrates are converted to products
5) Products are released
6) Active site is available for two new substrate molecules
Conditions that Effect Enzyme Activity
- Temperature, pH, and chemicals
- Increasing temperature increases the rate of enzymatic reaction up to a certain point
- Optimal pH values most enzymes fall in the range of pH 6-8
- Many enzymes require nonprotein helpers for catalytic activity (may be bound tightly to the enzyme as permanent residents, or they may bind loosely and reversible along with the substrate)
- The cofactors of some enzymes are inorganic, such as the metal atoms Zinc, Iron, and Copper in ionic form
Coenzymes
- Organic cofactors
Enzyme Inhibitor
- Certain chemicals selectively inhibit the action of specific enzymes
- If the inhibitor attaches to the enzyme by covalent bonds, inhibition is usually irreversible
Competitive Inhibitors
- Many enzyme inhibitors bind to the enzyme by weak interactions, in which case inhibition is reversible
- Some reversible inhibitors resemble the normal substrate molecule and compete for admission into the active site
- Competitive inhibitors reduce the productivity of enzymes by blocking substrates from entering active sites
- Can be overcome by increasing the concentration of substrate
Noncompetitive Inhibitors
- Don't directly compete with the substrate to bind to the enzyme at the active site
- Impede enzymatic reactions by binding to another part of the enzyme that causes the enzyme molecule to change its shape in such a way that the active site become less effective at catalyzing the conversion of substrate to a product
- These regulatory molecules change an enzyme's shape and the functioning of its active site by binding to a site elsewhere on the molecule, via noncovalent interactions
- Describes any case in which a protein's function at one site is affected by the binding of a regulatory molecule to a separate site
- May result in either inhibition or stimulation
- Constructed from two or more subunits, each composed of a polypeptide chain with its own active site (oscillates between a catalytically active and inactive shape)
- Activating/inhibiting regulatory molecule binds to a regulatory site (allosteric site), often located where subunits join
- Binding of an activator to an allosteric site stablizes the shape that has functional active sites
- Binding of an inhibitor stabilizes the inactive form of the enzyme
Cooperativity
- This mechanism amplifies the response of enzymes to substrates: One substrate molecule primes an enzyme to act on additional substrate molecules more readily
- Considered allosteric regulation because binding of the substrate to one active site affects catalysis in another active site
Feedback Inhibition
- A metabolic pathway is switched off by the inhibitory binding of its end product to an enzyme that acts early in the pathway
- Prevents a cell from wasting chemical resources
Enzyme Locations
- A team of enzymes for several steps of a metabolic pathway are assembled into a multienzyme complex (this arrangement facilitates the sequence of reactions, with the product from the first enzyme becoming the substrate for an adjacent enzyme in the complex, and so on, until the end product is released
- Others are in solution within particular membrane enclosed eukaryotic organelles
Limits on the range of animal forms
- Physical laws that govern strength, maximum size, diffusion, movement, and heat exchange limit the range of animal forms
Cellular Exchange
- Exchange occurs as substances dissolved in an aqueous solution move across the plasma membrane of each cell
- The rates of exchange for nutrients, waste products, and gases are proportional to membrane surface area, whereas the amount of material that must be exchanged to sustain life is proportional to cell volume
Simple Body Plans that Maximize Exposure to Surrounding Medium
- Hydras that have gastrovascular cavities
- Another common body plan that maximizes exposure to the surrounding medium is a flat shape
- A thin, flat shape places most cells of the worm in direct contact with its particular environment--the nutrient-rich intestinal fluid of a vertebrate host
Internal Exchange Surfaces in Humans
- Digestive, respiratory, and circulatory systems each have an area more than 25 times that of skin
Interstitial Fluid
- Space between cells filled with fluid
- Exchange between the interstitial fluid and the circulatory fluid enables cells throughout the body to obtain nutrients and get rid of wastes
Hierarchical Organization of Body Plans
- Cells are organized into tissues, groups of cells with a similar appearance and a common function
- Different types of tissues are further organized into functional units called organs (simplest animals, such as sponges, lack organs or even true tissues)
- Groups of organs that work together and provide an additional level of organization and coordination and make up an organ system
Four main types of animal tissues
- Epithelial, connective, muscle, and nervous
Epithelial Tissue Basic Structure, Function, and Characteristics
- Occurring as sheets of cells, epithelial tissues cover the outside of the body and line organs and cavities within the body
- Two forms occur in the human body:
(1) Covering and lining and epithelium - Forms the outer layer of the skin; lines open cavities of the digestive and respiratory systems; covers the walls of organs of the closed ventral body cavity.
(2) Glandular epithelium - Surrounds glands within the body. All glands are made up of epithelial cells.
- Because epithelial cells are closely packed, often with tight junctions, they function as a barrier against mechanical injury, pathogens, and fluid loss.
- Epithelium has two names (the first name indicates the number of cell layers, the second describes the shape of its cell)
(1) Simple epithelia - Consist of a single cell layer (found where absorption, secretion, and filtration occur).
(2) Stratified epithelia -Are composed of two or more cell layers stacked on top of each other (typically found in high abrasion areas where protection is needed).
- All epithelial cells have six sides but they vary in height.
- Epithelial tissues have five main characteristics:
(1) Polarity
(2) Specialized contacts
(3) Supported by connective tissue
(4) Avascular and innervated
(5) Regeneration
(2) Glandular epithelium - Surrounds glands within the body.
- Because epithelial cells are closely packed, often with tight junctions, they function as a barrier against mechanical injury, pathogens, and fluid loss
- Functions of epithelial cells include:
(1) Secretion: Secretion is the movement of material from one point to another chemicals, or a secreted chemical substance from a cell or gland. The classical mechanism of cell secretion is via secretory portals at the cell plasma membrane called porosomes.
(2) Selective absorption: The process of absorbing or assimilating substances into cells or across the tissues and organs through diffusion or osmosis, as in absorption of nutrients by the digestive system, or absorption of drugs into the bloodstream.
(3) Protection: This involves the skin (i.e. protection from wear and tear, drying, or excess moisture).
(4) Transcellular transport: Transcellular transport involves the transportation of solutes by a cell through a cell. Epithelial cells use primary and secondary active transport, often in conjunction with passive diffusion through ion channels, to produce transcellular transport across epithelial tissues.
(5) Sensing: Relates to the extracellular environment.
Simple Cuboidal Epithelium
- Dice shaped cells specialized for secretion
- Makes up the epithelium of kidney tubules and many glands
Simple Columnar Epithelium
- The large, brick-shaped cells of simple columnar epithelia are often found where secretion or active absorption is important (in the intestines)
Simple Squamous Epithelium
- The single layer of platelike cells that functions in the exchange of material by diffusion
- Thin and leaky, lines blood vessels and the air sacs of the lungs
Pseudostratified Columnar Epithelium
- A single layer of cells varying in height
- Ciliated cells forms a mucous membrane that lines portions of the respiratory tract
Stratified Squamous Epithelium
- Multilayered and regenerates rapidly
- Commonly found on surface subject to abrasion, such as the outer skin and the linings of the mouth, anus and vagina
Connective Tissue Structure and Function
- Consists of sparse population of cells scattered through an extracellular matrix, holds many tissues and organs together and in place
- Matrix generally consists of a web of fibers embedded in a liquid, jellylike, or solid foundation
- Numerous cells are in the matrix called fibroblasts (secrete fiber proteins) and macrophages (which engulf foreign particles and any cell debris by phagocytosis)
Three Types of Connective Tissue
- Collagenous fibers provide strength and flexibility (fibrous connective tissue found in tendons and ligaments and cartilage)
- Reticular fibers join connective tissue to adjacent tissues
- Elastic fibers make tissues elastic
Loose Connective Tissue
- The most widespread connective tissue in the vertebrate
- Binds epithelia to underlying tissues and holds organs in place
- Includes are three types of connective tissue
- Adipose tissue is a specialized loose connective tissue that stores fat in adipose cells distributed throughout its matrix (pads and insulates)
Muscle Tissue Structure and Function
- All muscle cells consist of filaments containing the proteins actin and myosin, which together enable muscles to contract
- Attached to bones by tendons, skeletal muscle, or striated muscle, is responsible for voluntary movements
- Consists of bundles of long cells called muscle fibers
Smooth Muscle
- Lacks striations
- Found in the walls of the digestive tract, urinary bladder, arteries, and other internal organs
- Spindle shaped cells
- Responsible for involuntary body activities
Cardiac Muscle
- Forms the contractile wall of the heart
- Striated muscle
- Cardiac muscle has fibers that interconnect via intercalated disks, which relay signals from cell to cell and help synchronize heart contraction
Nervous Tissue Structure and Function
- Function in the receipt, processing, and transmission of information
- Contains nervous tissue or neurons or nerve cells which transmit nerve impulses as well as support cells called glia
- Signaling molecules (called hormones) reach all locations in the body
- Only cells that have receptors for a particular hormone respond
- Hormones are relatively slow acting and the effects of hormones are often long-lasting because hormones remain in the bloodstream for seconds, minutes, or even hours
- Well suited for coordinating gradual changes that affect the entire body such as growth and development, reproduction, metabolic processes, and digestion
- Neurons transmit signals called nerve impulses, between specific locations in the body
- Each nerve impulse travels to specific target cells along dedicated communication lines consisting mainly of axons
- Four types of cells can receive nerve impulses: neurons, muscle cells, endocrine cells, and exocrine cells
- Information is conveyed by the pathway the signal takes
- Transmission is extremely fast, nerve impulses take only a fraction of a second to reach the target and last only a fraction of a second
- Well suited for directing immediate and rapid responses (good for controlling fast locomotion)
- An animal uses internal mechanisms to control internal change in the face of external fluctuation
- An animal allows its internal condition to change in accordance with external change in the variable
- Homeostasis (a dynamic equilibrium) is the maintenance of internal balance where animals maintain a relatively constant internal environment even when the external environment changes significantly
- An animal achieves homeostasis :
1) By maintaining a variable (such as body temperature or solute concentration) at or near a particular value (set point)
2) Fluctuations in the variable above or below the set point serve as the stimulus detected by a receptor, or sensor
3) Upon receiving a signal from the sensor, a control center generates output that triggers a response, a physiological activity that helps return the variable to the set point
- A control mechanism that reduces the stimulus
- Major factor of homeostasis
- A control mechanism that amplifies the stimulus
- Doesn't play a major role in homeostasis
- Helps drive processes to completion
- In all animals (and plants too) certain cyclic alterations in metabolism reflect a circadian rhythm, a set of physiological changes that occur roughly every 24 hours
- One way in which the normal range of homeostasis can change
- It is the gradual process by which an animal adjusts to changes in its external environments
- The process by which animals maintain an internal temperature within a tolerable range
- For every ten degree celcius decrease in temperature the rates of most enzyme mediated reactions decrease two to three fold
- Increases in temperature speed up reactions but cause some proteins to denature
Endothermic
- Birds, mammals, a few nonavian reptiles, some fish, and many insect species (bees and moths, body temperature depends on flight muscles) are warmed mostly by heat generated by metabolism
- Can maintain a stable body temperature even in the face of large fluctuations in the environmental temperature
- Control heat exchange by regulating blood flow
- Only endotherms develop fever
Ectothermic
- Amphibians, lizards, snakes, turtles, many fish, and most invertebrates gain most of their heat from external sources
- Generally need to consume much less food then endotherms of equivalent size (an advantage if food supplies are limited)
- Some ectotherms control heat exchange by regulating blood flow
- Control body temperature mainly by behavior (positioning body toward or away from sun)
- Acclimitization often includes adjustments at the cellular level
Poikilotherm
- An animal whose body temperature varies with its environment
Homeotherm
- Has a relatively constant body temperature
Four Physical Processes of Heat Exchange
- Radiation is the emission of electromagnetic waves by all objects warmer than absolute zero
- Evaporation is the removal of heat from the surface of a liquid that is losing some of its molecules as gas
- Convection is the transfer of heat by the movement of air or liquid past a surface
- Conduction is the direct transfer of thermal motion (heat) between molecules of objects in contact with each other
- The outer covering of the body, consisting of the skin, hair and nails (claws or hooves in some species)
- Major thermoregulatory adaptation in mammals and birds
- Reduces the flow of heat between an animal and its environment
- Sources of insulation include hair, feathers, and layers of fat formed by adipose tissue
Circulatory Adaptations
- Many animals alter the amount of blood (and hence heat) flowing between their body core and their skin
- Vasodilation warms the skin and increases the transfer of body heat to the environment by radiation, conduction, and convection
- Vasoconstriction reduces blood flow and heat transfer by decreasing the diameter of superficial vessels
Countercurrent Exchange
- In many birds, mammals, certain sharks, fish and insects, reducing heat loss from the body relies on countercurrent exchange
- The transfer of heat (or solutes) between fluids that are flowing in opposite directions
- Arteries and veins are located adjacent to each other
Thermogenesis
- Endotherms can vary heat production to match changing rates of heat loss
- Increased by such muscle activity as moving or shivering
- (nonshivering thermogenesis) In some mammals, certain hormones can cause mitochondria to increase their metabolic activity and produce heat instead of ATP
- Brown fat: Located in the neck and between shoulders--specialized for rapid heat production
Hypothalamus and Thermostatic Function
- Sensors for thermoregulation are concentrated in a brain region called the hypothalamus
- A group of nerve cells in the hypothalamus functions as thermostat responding to body temperatures outside a normal range by activating mechanisms that promote heat loss or gain
Metabolic Rate
- The amount of energy an animal uses in a unit of time (the sum of all the energy used in biochemical reactions over a given time interval)
Three Ways of Determining Metabolic Rate
- Monitoring an animal's rate of heat loss using a calorimeter
- The amount of oxygen consumed or carbon dioxide produced by an animal's cellular respiration
- (for longer periods) Recording the rate of food consumption, the energy content of the food per gram of protein or carbohydrate, and the chemical energy lost in waste products
Basal Metabolic Rate (Endotherm)
- The minimum metabolic rate of a nongrowing endotherm that is at rest, has an empty stomach, and is not experiencing stress
- Measured under a "comfortable" temperature range--a range that requires no generation or shedding of heat above the minimum
Standard Metabolic Rate (Ectotherm)
- The minimum metabolic rate of ectotherms is determined at specific temperature because changes in the environmental temperature alter body temperature and therefore metabolic
- Rate of fasting, nonstressed ectotherm at rest at a particular temperature is called its standard metabolic rate
- Lower energetic requirement of ectothermy is readily apparent
Influences on Metabolic Rate
- Whether an animal is an endotherm/ectotherm, age, sex, size, activity, temperature, and nutrition
Metabolic Rate and Size
- Metabolic rate remains roughly proportional to body mass to the three quarter power
- Smaller animal's higher metabolic rate per gram demands a higher rate of oxygen delivery and has a higher breathing rate, blood volume, and heart rate and must consume more food per unit of body mass
Metabolic Rate and Activity
- Metabolic rate an animal can sustain is inversely related to the duration of activity
- Average daily rate of energy consumption is 2 to 4 times BMR or SMR
Energy Budgets
- For many animals, locomotion and other activities are a major part of the energy budget
- A physiological state of decreased activity and metabolism, is an adaption that enables animals to save energy while avoiding difficult and dangerous conditions
- All endotherms that exhibit daily torpor are relatively small
- Long term torpor that is an adaptation to winter cold and food scarcity
- Body temperature declines as its body thermostat is turned down (temperature reduction may be dramatic)
- In some organisms the circadian clock ceases operation during hibernation
Estivation
- Slow metabolism and inactivity of estivation, or summer torpor, enables animals to survive long periods of high temperatures and scarce water supplies
An Adequate Diet Must Satisfy Three Nutritional Needs
- Chemical energy for cellular processes
- Organic building blocks for macromolecules
- Essential nutrients
- Materials that an animal's cells require but cannot synthesize
- Must be obtained from dietary resources
Four Classes of Essential Nutrients
- Essential amino acids
- Essential fatty acids
- Vitamins
- Minerals
- Animals require 20 amino acids to make proteins
- Majority of animal species have the enzymes to synthesize about half of these amino acids, as long as their diet includes sulfur and organic nitrogen
- Remaining amino acids must be obtained from food in prefabricated form
- Most animals, including humans, require eight amino acids in their diet (infants also need a ninth, histidine)
- Proteins in animal products such as meat, eggs, and cheese are complete (they provide all the essential amino acids)
- Plant proteins are incomplete being deficient in one or more essential amino acids
- Animals produce the enzymes to synthesize most, but not all of the fatty acids they need
- Fatty acids that can't be made are certain fatty acids that are unsaturated
- Organic molecules that have diverse functions and are required in the diet in very small amounts
- 13 vitamins have been identified for humans
- Dietary minerals are inorganic nutrients, such as iron and sulfur, that are usually required in small amounts
- Ingesting large amounts of some minerals can upset homeostatic balance and impair health
- A diet that lacks one or more essential nutrients or consistently supplies less chemical energy than the body requires
- Most common type of malnutrition is a diet that provides insufficient amounts of one or more essential amino acids causes protein deficiency
Undernutrition
- A diet that fails to provide adequate sources of chemical energy
- The body uses up stored carbohydrates and fat and the begins breaking down its own proteins for fuel; muscles begin to decrease in size; and the brain may become protein-deficient
Four Stages of Food Processing
- Ingestion
- Digestion
- Elimination
- The act of feeding or eating
- Food is broken down into molecules small enough for the body to absorb
- Mechanical digestion precedes chemical digestion typically
- The animal's cells absorb small molecules such as amino acids and simple sugars
- Completes the process as undigested material passes out of the digestive system
Intracellular Digestion
- Food vacuoles--cellular organelles in which hydrolytic enzymes break down food--are the simplest digestive compartments
- Begins after a cell engulfs solid food by phagocytosis or liquid food by pinocytosis
- Newly formed food vacuoles fuse with lysosymes, organelles containing hydrolytic enzymes
- Fusion of organelles brings food in contact with the enzymes allowing digestion to occur safely within a compartment enclosed by a protective membrane
Suspension Feeders
- Many aquatic animals are suspension feeders, which eat small organisms or food particles suspended in the water
Filter Feeders
- Many aquatic animals are filter feeders--they move water through a filtering structure to obtain food
Substrate Feeders
- Animals that live in or on their food source
Fluid Feeders
- Suck nutrient rich fluid from a living host
Bulk Feeders
- Most animals, including humans, are bulk feeders, which eat relatively large pieces of food
Gastrovascular Cavity
- Many animals with relatively simple body plans have a digestive compartment with a single opening
- This pouch functions in digestion as well as in the distribution of nutrients throughout the body
Digestion in a Carnivorous Hydra
1) Digestion enzymes are released from a gland cell
2) Food particles are broken down by enzymes
3) Food particles are engulfed and digested in food vacuoles
Alimentary Canal
- A digestive tube extending between two openings, a mouth and an anus
Earthworm Digestive System
Grasshopper Digestive System
Bird Digestive System
Mammalian Digestive System Diagram
- The digestive system consists of the alimentary canal, three pairs of salivary glands, the pancreas, the liver and the gallbladder
Peristalsis
- Food is pushed along the alimentary canal by peristalsis, alternating waves of contraction and relaxation of the smooth muscles lining the canal
Sphincters
- At some of the junctions between specialized compartments, the muscular layer forms ringlike valves called sphincters that regulate the passage of material between compartments
- Ingestion and the initial steps of digestion occur in the oral cavity
- Mechanical digestion begins as teeth grind food
- The presence of food stimulates a nervous reflex that causes the salivary glands to deliver saliva ducts to the oral cavity
Salivary Amylase
- Hydrolyzes starch and glycogen (a glucose polymer from animals) into smaller polysaccharides and the disaccharide maltose
Mucus
- A viscous mixture of water, salts, cells, and slippery glycoproteins called mucins
- Mucus in saliva protects the lining of the mouth from abrasion and lubricates food for easier swallowing
- Help prevent tooth decay by neutralizing acid
Antimicrobial Agents
- Protect against bacteria that enter the mouth with food (lysozyme)
- Manipulated food into a ball
Swallowing Reflex and Esophageal Peristalsis
1) When a person is not swallowing, the esophageal sphincter muscle is contracted, the epiglottis is up, and the glottis is open, allowing air to flow through the trachea to the lungs
2) The swallowing reflex is triggered when a bolus of food reaches the pharynx
3) The larynx, the upper part of the respiratory tract, moves upward and the epiglottis tips over the glottis, preventing food from entering the trachea
4) The esophageal sphincter relaxes, allowing the bolus to enter the esophagus
5) After the food has entered the esophagus, the larynx moves downward and opens the breathing passage
6) Waves of muscular contraction move the bolus through teh esophagus to the stomach
- Throat region that opens into the esophagus (connects to the stomach) and the trachea (windpipe)
Epiglottis
- Flap of cartilage that covers the glottis
Glottis
- The vocal cords and the opening between them
Muscle in Esophagus
- Striated muscle is situated at the top of the esophagus and is active during swallowing
- The rest of the esophagus uses smooth muscle which functions in peristalsis
Stomach Location and Diagram
- Located just below the diaphragm, stores food, and begins digestion of proteins
Stomach Secretion
- The stomach secretes a digestive fluid called gastric juice and mixes this secretion with the food through a churning action
- Mixture of ingested food and digestive juice is called chyme
Two Components of Gastric Juice that Carry out Chemical Digestion
- HCl (makes pH about 2, which denatures proteins and exposes their peptide bonds)
- A protease called pepsin (protein digesting enzyme that breaks peptide bonds to form smaller polypeptides)
- Parietal cells secrete by hydrogen and chloride ions, which form HCl
- Using an ATP - driven pump, the parietal cells expel hydrogen ions into the lumen
- The hydrogen ions combine with chloride ions that diffuse into the lumen through specific membrane channels of the parietal cells
- Chief cells release pepsin into the lumen in an inactive form called pepsinogen
- HCl converts pepsinogen to active pepsin by clipping off a small portion of the molecule and exposing its active site
- After HCl converts a small amount of pepsinogen to pepsin--pepsin begins to help activate the remaining pepsinogen
Interior Surface of the Stomach
- Highly folded and dotted with pits leading into tubular gastric glands
Mucous Cells
- Secrete mucus, which lubricates and protects the cells lining the stomach
Stomach Sphincters
- Most of the time, the stomach is closed off at both ends
- The sphincter between the esophagus and the stomach normally opens only when a bolus arrives
- The sphincter located where the stomach opens to the small intestine helps regulate passage into the small intestine, allowing only one squirt of chyme at a time
- Occurs in the oral cavity, pharynx, and esophagus
- Polysaccharides (starch, glycogen) are turned into smaller polysaccharides by salivary amylase
- Disaccharides (sucrose, lactose) are turned into Maltose by salivary amylase
- In the small intestine, pancreatic amylase converts the polysaccharides to disaccharides
- Enzymes from epithelium in the small intestine convert the remaining disaccharides into monosaccharides
- In the stomach, pepsin breaks down proteins into small polypeptides
- In the small intestine, pancreatic trypsin and chymotrypsin cleave bonds adjacent to certain amino acids to make smaller polypeptides--pancreatic carboxypeptidase makes still smaller peptides
- Enzymes from epithelium of small intestine (dipeptidases, carboxypeptidases, and aminopeptidases) split off one amino acid at a time, working from opposite ends of a polypeptide to make amino acids
Nucleic Acid Digestion
- In the small intestine, DNA and RNA broken down by pancreatic nucleases form nucleotides
- Enzymes from epithelium of small intestine (nucleotidases) form nucelosides and nucleosidases and phosphatases form nitrogenous bases, sugars, and phosphates
Fat Digestion
- In the small intestine, pancreatic lipase, converts fat into glycerol, fatty acids, monoglycerides
- Most enzymatic hydrolysis of the macromolecules from food occurs in the small intestine
- In humans, the small intestine is the longest compartment of the alimentary canal
Pancreas (digestion)
- Aids chemical digestion by producing an alkaline solution rich in bicarbonate as well as several enzymes
- Bicarbonate neutralizes the acidity of chyme and acts as a buffer
- Proteases are secreted into the duodenum in inactive forms
Duodenum
- The first 10 inches of the small intestine
- Chyme from the stomach mixes with digestive juices from the pancreas, liver and gallbladder as well as from gland cells of the intestinal wall itself
Liver (digestion)
- Digestion of fats and other lipids begins in the small intestine and relies on the production of bile (a mixture of substance made in the liver)
- Bile contains bile salts, which act as emulsifiers that aid in digestion and absorption or lipids
- Bile is stored and concentrated in the gallbladder
- Bile production aids livers in the regulation and destruction of red blood cells that are no longer fully functional
Remaining Regions of Small Intestine
- Jejunum and ileum
- Function mainly in the absorption of nutrients and water
Nutrient Absorption in Small Intestine Diagram
Villi
- Large folds in the lining encircle the intestine and are studded with finger-like projections
Microvilli
- Each epithelial cell of a villus has on its apical surface many microscopic projections that are exposed to the intestinal lumen
- Gives the small intestine an enormous surface area that greatly increases the rate of nutrient absorption
Facilitated Diffusion (Digestion)
- Fructose moves by facilitated diffusion down its concentration gradient from the lumen of the small intestine into the epithelial cells
Active Transport (Digestion)
- Amino acids, small peptides, vitamins, and most glucose molecules are pumped against concentration gradients by the epithelial cells of the villus
Hepatic Portal Vein
- The capillaries and veins that carry nutrient rich blood away from the villi all converge into the hepatic portal vein, a blood vessel that leads directly to the liver
- Allows the liver to regulate the distribution of nutrients to the rest of the body
- Allows the liver to remove toxic substances before the blood circulates broadly
Hydrolysis of Fat by Lipase/Absorption of Fats
1) In the lumen, triglycerides exposed on the surface of fat droplets are subject to enzymatic hydrolysis. The enzyme lipase breaks the triglycerides down to fatty acids and monoglycerides
2) After diffusing into epithelial cells, monoglycerides and fatty acids are reformed into tryglycerides (some glycerol and fatty acids pass directly into capillaries)
3) Triglycerides are incorporated into water-soluble globules called chylomicrons
4) Chylomicrons leave epithelial cells by exocytosis and enter lacteals (lymphatic vessel at the core of each villus), where they are carried away by the lymph and later pass into large veins
Large Intestine
- The alimentary canal ends with the large intestine, which includes the colon, cecum and rectum
- The small intestine connects to the large intestine at a T-shaped junction
- One arm of the T-shaped junction, which leads to the rectum and anus
- Recovers water that has entered the alimentary canal as the solvent of digestive juices
- 90% of water is reabsorbed into the small intestine and colon
- Water is reabsorbed by osmosis when ions are pumped out of the lumen of the colon
- Feces become increasingly solid as they are moved along the colon by peristalsis
Cecum
- Pouch shaped part of the T-shaped junction is important for fermenting ingested material, especially in animals that eat a large amount of plant material
- A finger-like extension of the human cecum, has a minor and dispensable role in immunity
- Terminal portion of the large intestine where feces are stored until they can be eliminated
- Between the rectum and anus are two sphincters, the inner one being involuntary and the outer one being voluntary
Stomach Adaptations
- Large expandable stomachs are common in carnivorous vertebrates
Intestinal Adaptations
- In general, herbivores and omnivores have longer alimentary canals relative to their size than do carnivores
Digestive Adaptations
- Mutualistic symbiosis; a mutually beneficial interaction between two species
- Location of mutualistic microbes in alimentary canals varies on the type of herbivore
Ruminant Digestion
- Most elaborate adaptations for an herbivorous diet have evolved in the ruminant animals (deer, sheep, and cattle)
1) Rumen. When the cow first chews and swallows a mouthful of grass, boluses enter the rumen
2) Reticulum. Some boluses also enter the reticulum. In both the rumen and the reticulum, mutualistic prokaryotes and protists go to work on the cellulose-rich meal. As by-products of their metabolism, the microorganisms secrete fatty acids. The cow periodically regurgitates and rechews the cud, which further breaks down the fibers, making them more accessible to further microbial action
3) Omasum. The cow then reswallows the cud, which moves to the omasum, where water is removed
4) Abomasum. The cud, containing great numbers of microorganisms, finally passes to the abomasum for the digestion by the cow's own enzymes
Regulation of Digestion
- A branch of the nervous system called the enteric division, which is dedicated to the digestive organs, regulates these events as well as peristalsis in the small and large intestines
- The endocrine system also plays a critical role in controlling digestion
1) As food arrives at the stomach, it stretches the stomach walls, triggering release of the hormone gastrin. Gastrin circulates via the bloodstream back to the stomach, which it stimulates production of gastric juices
2) Chyme eventually passes from the stomach to the duodenum. The duodenum responds to amino acids or fatty acids in the chyme by releasing the digestive hormones cholecystokinin and secretin. Cholecystokinin (CKK) stimulates the release of digestive enzymes from the pancreas and of bile from the gallbladder. Secretin stimulates the pancreas to release bicarbonate, which neutralizes chyme
3) If the chyme is rich in fats, the high levels of secretin and CCK released act on the stomach to inhibit peristalsis and secretion of gastric juices, thereby slowing digestion
Regulation of Energy Storage
- First sites used for energy storage are liver and muscle cells
- In these cells, excess energy from the diet is stored in glycogen and any additional excess energy is usually stored in fat in adipose cells
- Adipose tissue provides the most space efficient way for the body to store large amounts of energy
Glucose Homeostasis
- The pancreatic hormones insulin and glucagon maintain glucose homeostasis by tightly regulating the synthesis and breakdown of glycogen
- The liver is the key site for glucose homeostasis
- When insulin levels rise after a carbohydrate-rich meal, glucose entering the liver in the hepatic portal vein is used to synthesize glycogen
- Between meals, when blood in the hepatic portal vein has a much lower glucose concentration, glucagon stimulates the liver to break down glycogen, releasing glucose into the blood
Overnourishment
- The consumption of more calories than the body needs for normal metabolism, causes obesity, the excessive accumulation of fat
Obesity can cause:
- Type 2 diabetes
- Cancer of the colon and breast
- Cardiovascular disease
Appetite Regulating Hormones
- Secreted by the stomach wall, grhelin is one of the signals that triggers feelings of hunger
- A rise in blood sugar level after a meal stimulates the pancreas to secrete insulin (also suppresses appetite by acting on the brain)
- Produce by adipose tissue, leptin suppresses appetite (when the amount of body fat decreases, leptin levels fall, and appetite increases)
- The hormone PYY, secreted by the small intestine after meals, acts as an appetite suppressant that counters grhelin
- Systemic arteries transport oxygenated blood from the heart to the rest of the body
- Pulmonary arteries transport deoxygenated blood from the heart to the lungs
- Composed of a small lumen, an innermost layer of endothelium, a middle layer of smooth muscle and elastic fibers (typically thickest layer) and, and outer layer of connective tissue and elastic fibers
- Very thick, strong, and elastic in order to withstand and maintain high blood pressures
- Signals from the sympathetic nervous system and hormones circulating in the blood act on the smooth muscle in arteries
Arteriole
- Functions as an arterial bridge to complete the systemic circuit of sending oxygenated blood throughout the body
- Major function is to regulate blood pressure by constriction and dilation of vessels in order to assist the transfer of blood into capillaries at a low blood pressure
- Smallest of the true arteries
- Signals from the sympathetic nervous system and hormones circulating in the blood act on the smooth muscle in arterioles
- Aid in circulation by ensuring that oxygenated blood is supplied throughout the body by acting as a bridge between veins and arteries
- Critical to the exchange of substances between the blood and the interstitial fluid (takes place across the walls of capillaries)
o Some substances are carried across the capillary wall in vesicles that form on one side by endocytosis and release their contents on the opposite side by exocytosis
o Small molecules, such as O2 and CO2, diffuse across the endothelial cells or, in some tissues, through microscopic pores in the capillary walls
o Porous openings in fenestrated capillaries provide the route for the transport of small solutes such as sugars, salts, and urea, as well as bulk flow of fluid into tissues driven by blood pressure within the capillary
- Smallest (about one cell layer thick) and most numerous type (there are networks of capillaries throughout the body called capillary beds/capillaries have the largest total cross-sectional area) type of main blood vessel
- Very thin (with sometimes porous) walls constructed from an inner layer of endothelium and the basal lamina
- Very low blood pressure is needed with capillaries and this can be regulated by rings of smooth muscle located at the entrance to capillary beds called Precapillary Sphincters or by contraction/dilation of the smooth muscle in an arteriole
- Movement of fluid between the capillaries and surrounding tissues is controlled by blood pressure (which tends to drive fluid out of the capillaries, this is the stronger force so there is a net loss of fluid) and the presence of blood proteins (which tends to pull fluid back, osmotic pressure)
Venule
- Allow deoxygenated blood to return from the capillary beds and for the blood to drain into veins
- Venules are extremely porous so that fluid and blood cells can move easily from the bloodstream through their walls.
- Constructed from an inner endothelium, a middle layer of muscle and elastic tissue (poorly developed in order to have thinner walls than arterioles), and an outer layer of fibrous connective tissue. The middle layer is poorly developed so that venules have thinner walls than arterioles. They are extremely porous so that fluid and blood cells can move easily from the bloodstream through their walls
- Systemic veins transport deoxygenated blood back to the heart
- Pulmonary veins transport oxygenated blood to the left atrium of the heart
- Composed of a thin, wide lumen, an innermost layer of endothelium, a middle layer of smooth muscle and elastic fibers and, and outer layer of connective tissue and elastic fibers
- Rhythmic contractions of smooth muscles in the walls of veins aid in the movement of the blood
- The contraction of skeletal muscles during exercise squeezes blood through the veins toward the heart
- The change in pressure within the thoracic cavity during inhalation causes the venae cavae and other large veins near the heart to expand and fill with blood
Lymphatic System
- A network of tiny vessels intermingled among capillaries of the cardiovascular system (fluid lost by capillaries is called lymph)
- Along a lymph vessel are organs called lymph nodes which play an important role in the body's defense
Components of Blood
- Plasma ( 55%)
- Cellular Elements (45%)
Components of Plasma
- Water: solvent for carrying other substances
- Ions (sodium, potassium, calcium, magnesium, chloride, bicarbonate): Osmotic balance, pH buffering, and regulation of membrane permeability
- Plasma proteins: Albumin (osmotic balance, pH buffering), fibrinogen (clotting), and immunoglobulins (antibodies)
- Substances transported by blood: Nutrients (such as glucose, fatty acids, and vitamins), waste products of metabolism, respiratory gases, and hormones
Components of Cellular Elements
- Leukocytes (white blood cells): Basophils, lymphocytes, eosinophils, monocytes, and neutrophils, function in defense and immunity
- Platelets: Pinched off cytoplasmic fragments of specialized bone marrow cells that have no nuclei, function in blood clotting
- Erythrocytes (red blood cells): Biconcave, mature mammalian erythrocytes lack nuclei and mitochondria in order to have more space for hemoglobin (ATP is produced by anaerobic metabolism) and functions in the transport of O2 and some CO2
Process of Blood Clotting
- A break in a blood vessel wall exposes proteins that attract platelets and intitiate coagulations, the conversion of liquid components of blood to a solid clot
- The coagulant circulates in an inactive form called fibrinogen
- In response to a broken blood vessel, platelets release clotting factors that trigger reactions leading to the formation of thrombin, and enzyme that converts fibrinogen to fibrin
- Newly formed fibrin aggregates into threads that form the framework of the clot (thrombins also activates a factor that catalyzes the formation of more thrombin, driving clotting to completion through positive feedback
- Sometimes clots (thrombus) form within a blood vessel, blocking the flow of blood
- A negative-feedback mechanism, sensitive to the amount of O2 reaching the body's tissues via the blood, controls erythrocyte production
- If the tissues do not receive enough O2, the kidneys synthesize and secrete this hormone that stimulates erythrocyte production
- Cholesterol metabolism and inflammation play central roles
Process of Atherosclerosis
1) Lipoproteins such as LDL enter the lining of the artery and aggregate, leading to engulfment by immune cells called macrophages. Uptake of these lipoproteins by macrophages leads to the generation of lipid-rich foam cells
2) Secretion of extracellular matrix components increases lipoprotein aggregation. T lymphocytes enter the growing plaque, causing chronic inflammation. Smooth muscle cells from the lining of the artery also enter the plaque
3) Smooth muscle cells form a fibrous cap separating the plaque from the blood. Within the plaque, foam cells die, releasing the cellular debris and cholesterol. If the plaque ruptures, a blood clot can form within the artery
4) If the plaque continues to grow but does not rupture, the artery becomes increasingly obstructed
Heart Attack (Myocardial Infarction)
- Damage or death of cardiac muscle tissue resulting from blockage of one or more coronary arteries, which supply oxygen-rich blood to the heart muscle
- Death of nervous tissue in the brain due to a lack of Oxygen
- The uptake of molecular O2 from the environment and the discharge of CO2 to the environment
- Cells that carry out gas exchange must be in contact with an aqueous solution so respiratory surfaces are always moist
- The net result of diffusion at gas exchange surfaces: A gas always diffuses from a region of higher partial pressure to a region of lower partial pressure
Respiratory Surfaces
- The movement of CO2 and O2 across moist respiratory surfaces takes place entirely by diffusion
- Rate of diffusion is proportional to the surface area across which it occurs and inversely proportional to the square of the distance through which molecules must move (gas exchange is fast when the area of diffusion is large and the path for diffusion is short)
- Respiratory surfaces tend to be large and thin
Respiratory of Simple Animals
- In sponges, cnidarians, and flatworms every cell in the body is close enough to the external environment that gases can diffuse quickly between all cells and the environment
Skin (respiratory organ)
- Serves as a respiratory organ in some animals including earthworms and some amphibians (can only survive for extended periods in moist places)
Three Main Respiratory Organs
- Gills
- Tracheae
- Lungs
- Movement of the respiratory medium over the respiratory surface
- Maintains the partial pressure gradients of O2 and CO2 (in fish)
Gills and Respiration
- Gills are outfoldings of the body surface that are suspended in the water
- Most gill-bearing animals either move their gills through the water or move water over their gills
- Arrangement of capillaries in fish gills allows for countercurrent exchange (this process maximizes gas exchange efficiency because blood flows in the direction opposite to that of water passing over the gills)
Tracheal Systems in Insects
- Made up of air tubes that branch throughout the body, is one variation of an internal respiratory surface
- Tracheal system brings air within a short distance of virtually every body cell in an insect and can transport O2 and CO2 without the participation of the animal's open circulatory system
Lungs (basic info)
- Localized respiratory organs
- Typically subdivided into numerous pockets
- Most reptiles (all birds) and all mammals depend entirely on lungs for gas exchange
- System of branching ducts conveys air to the lungs, which are located in the thoracic activity
Mammalian Respiratory System Diagram
Nasal Cavity
- Air enters through the nostrils and is then filtered by hairs, warmed, humidified, and sampled for odors as it flows through a maze of spaces in the nasal cavity
- Leads to the pharynx (an intersection where the paths for air and food cross)
- When food is swallowed, the larynx (the upper part of the respiratory tract) moves upward and tips the epiglottis over the glottis (the opening of the trachea), but the rest of the time, the glottis is open, enabling breathing
Vocal Cords
- Air passes into the trachea
- Cartilage reinforcing the walls of both the larynx and the trachea keeps this part of the airway open
- Sounds are produced when muscles in the larynx are tensed, stretching the cords so they vibrate
- Branches into two bronchi (one leading to each lung)
- Within the lung the bronchi branch repeatedly into finer and finer tubes called bronchioles
Epithelium Lining (respiratory system)
- Lines the major branches with cilia and thin film of mucus
- The mucus traps dust, pollen and other particulate contaminants
- The beating cilia move the mucus upward to the pharynx, where it can be swallowed into the esophagus
Alveoli
- Gas exchange in mammals occurs in alveoli
- Air sacs clustered at the tips of the tiniest bronchioles
- Oxygen in the air entering the alveoli dissolves in the moist film lining their inner surfaces and rapidly diffuses across the epithelium into a web of capillaries that surrounds each alveolus
- Net diffusion of carbon dioxide occurs in the opposite direction, from the capillaries across the epithelium of the alveolus and into the air space
- Lack cilia or significant air currents to remove particles from their surface, alveoli are highly susceptible to contamination so white blood cells patrol alveoli, engulfing foreign particles
- Subject to surface tension (surfactant)
- Alternating inhalation and exhalation of air
Amphibian Breathing
- Frog ventilates its lungs by positive pressure breathing, inflating the lungs with forced air flow
1) Muscles lower the floor of an amphibian's oral cavity, drawing in air through its nostrils
2) With nostrils and mouth closed, the floor of the oral cavity rises, forcing air down the trachea
3) During exhalation, air is forced back out by the elastic recoil or the lungs and by compression of the muscular body wall
Bird Breathing
- When birds breath, they pass air over the gas exchange surface in only one direction
- Incoming fresh air does not mix with air that has already carried out gas exchange
- Birds use eight or nine air sacs situated on either side of the lungs (do not function directly in gas exchange, function as bellows that keep air flowing through the lungs)
- The sites of gas exchange in bird lungs are tiny channels called parabronchi
- Passage of air through the entire system--lungs and air sacs--requires two cycles of inhalation and exhalation
Mammalian Breathing
- Mammals employ negative pressure breathing--pulling, rather than pushing, air into their lungs
- Muscle contraction actively expands the thoracic cavity, mammals lower air pressure in their lungs below that of the air outside of their body (inhalation)
- During exhalation (passive) the muscles controlling the thoracic cavity relax, and the volume of the cavity is reduced
- Increased air pressure in the alveoli forces air up the breathing tubes and out of the body
- The volume of air inhaled and exhaled with each breath
- The tidal volume during maximal inhalation and exhalation
- The air that remains after a forced exhalation
- As humans age, their lungs lose their resilience and residual volume increases at the expense of vital capacity
Medulla Oblongata (regulation of breathing)
- Neurons responsible for regulating the breathing are in the medulla oblongata, near the base of the brain
- Neural circuits in the medulla form a breathing control center that establishes the breathing rhythm
- Medulla uses the pH of the surrounding tissue fluid as an indicator of blood CO2 concentration. (CO2 is the main determinant of the pH of cerebrospinal fluid)
- Increased metabollic activity increases pH by increasing the CO2 concentration in the blood
Coordination of Circulation and Gas Exchange
- Blood flowing through the alveolar capillaries has a lower PO2 and a higher PCO2 than the air in the alveoli (as a result, CO2 diffuses down its partial pressure gradient from the blood to the air in the alveoli)
Respiratory Pigments
- Animals transport most of their O2 bound to these proteins
- Respiratory pigments circulate with the blood or hemolymph and are often contained within specialized cells
- Pigments greatly increase the amount of O2 that can be carried in the circulatory fluid
- Vertebrate hemoglobin consists of four polypeptide chains, each with a cofactor called a heme group that has an iron atom at its center
- Each iron atom binds one molecule of O2, hence, a single hemoglobin molecule can carry four molecules of O2
- Hemoglobin binds O2 reversible, loading O2 in the lungs or gills and unloading it in other parts of the body
Carbon Dioxide Transport in the Blood
1) Carbon dioxide produced by body tissues diffuses into the interstitial fluid and the plasma
2) Over 90% of the CO2 diffuses into red blood cells, leaving only 7% in the plasma as dissolved CO2
3) Some CO2 is picked up and transported by hemoglobin
4) However, most CO2 reacts with water in red blood cells, forming carbonic acid, a reaction catalyzed by carbonic anhydrase contained within red blood cells
5) Carbonic acid dissociates into a bicarbonate ion and a hydrogen ion
6) Hemoglobin binds most of the hydrogen ion from carbonic acid, preventing the hydrogen ion from acidifying the blood and thus preventing the Bohr shift
7) Most of the bicarbonate ion diffuses into the plasma, where it is carried in the bloodstream to the lungs
8) In the lungs, bicarbonate diffuses from the plasma into red blood cells, combining with hydrogen ions released from hemoglobin and forming carbonic acid
9) Carbonic acid is converted back to CO2 and water. CO2 is also unloaded from hemoglobin
10) CO2 diffuses into the plasma and the interstitial fluid
11) CO2 diffuses into the alveolar space, from which it is expelled during exhalation. The reduction of CO2 concentration in the plasma drives the breakdown of carbonic acid into CO2 and water in the red blood cells, a reversal of the reaction that occurs near body tissues
Myoglobin
- Diving mammals also have a high concentration of an oxygen storing protein called myoglobin in their muscles
- Breakdown of nitrogenous molecules releases ammonia, a very toxic compound
- This is the process that rids the body of nitrogenous metabolites and other metabolic waste products
Osmolarity
- When two solutions separated by the membrane differ in osmotic pressure
Osmoconformer
- Isomotic (when two solutions separated by a selectively permeable membrane have the same osmolarity) with surroundings
- Most marine invertebrate are osmoconformers (isosmotic with sea water)
Osmoregulator
- Controls internal osmolarity independent of that of its environment
- Many marine vertebrate and only some marine invertebrate are osmoregulators
Stenohaline
- Most animals cannot tolerate substantial changes in external osmolarity
Euryhaline
- These animals can survive large fluctuations in external osmolarity
- A few aquatic invertebrates that live in temporary ponds and films of water around soil particles can lose almost all of their body water and survive
- These animals enter a dormant state when their habitats dry up, an adaptation called anhydrobiosis (tardigrades, better known as water bears are a good example)
Four Ways Most Land Animals Lose Water
- Urine, feces, across their skin, and from the surfaces of gas exchange organs
Transport Epithelia
- In most animals, osmoregulation and metabolic waste disposal rely on transport epithelia (one or more layers of epithelial cells specialized for moving particular solutes in controlled amounts in specific directions)
- Typically arranged into complex tubular networks with extensive surface areas
- Some transport epithelia face the outside environment directly, while others line channels connected to the outside by an opening on the body surface
- Most common in aquatic species
- Being highly soluble, ammonia molecules easily pass through membranes and are readily lost by diffusion to the surrounding water
- Mammals, most adult amphibians, sharks, and some marine bony fish and turtles mainly excrete urea
- Produced in the vertebrate liver, urea is the product of a metabolic cycle that combines ammonia with carbon dioxide
- Can be safely stored and transported through the circulatory system
- Animals must expend energy to produce urea from ammonia
- Insects, land snails, and many reptiles, including birds, excrete uric acid as their primary nitrogenous waste
- Relatively nontoxic and does not dissolve readily in water
- Can be excreted as a semi-solid pate with very little water loss
- Uric acid is more energetically expensive to produce than urea, requiring considerable ATP synthesis from ammonia
Four Excretory Processes
1) Filtration: The excretory tubule collects a filtrate from the blood. Water and solutes are forced by blood pressure across the selectively permeable membranes of a cluster of capillaries and into the excretory tube
2) Reabsorption: The transport epithelium reclaims valuable substances from the filtrate and returns them to the body fluids
3) Secretion: Other substances such as toxins and excess ions, are extracted from body fluids and added to the contents of the excretory tubule
4) Excretion: The altered filtrate (urine) leaves the system and the body
Protonephridia
- Flat worms have excretory systems which form a network of dead-end tubules that are connected to external openings, branch throughout the flatworm body, which lacks a coelom (or body cavity)
- Cellular units called flame bulbs cap the branches of each protonephridium
Metanephridia
- Most annelids, such as earthworms, have excretory organs that collect fluid directly from the coleom
- Have both excretory and osmoregulatory functions
Malpighian Tubes
- Insects and other terrestrial arthropods have organs that remove nitrogenous wastes and that also function in osmoregulation
Kidney Diagram
Ureter
- Urine produced by each kidney exits through two ducts
Urinary Bladder
- The two ureters drain into a common sac
- Urine is expelled from the bladder through a tube
Outer Renal Cortex and Inner renal medulla
- Both regions are supplied with blood by a renal artery and rained by a renal vein
- Within the cortex and medulla lie tightly packed excretory tubules and associated blood vessels
Inner Renal Pelvis
- Collects urine from the excretory tubules and passes it to the urinary bladder
Nephrons
- Weaving back and forth across the renal cortex and medulla are the functional units of the vertebrate kidney
Cortical Nephrons
- 85% of the kidney's nephrons
- Reach only a short distance into the medulla
Juxtamedullary Nephrons
- Extend deep into the medulla
- Essential for the production of urine that is hyperosmotic to body fluids (a key adaptation for water conservation in mammals)
Nephron Diagram
Glomerulus
- Each nephron consists of a single long tubule as well as a ball of capillaries
Bowman's Capsule
- The blind end of the tubule forms a cup-shaped swelling around the glomerulus
Proximal Tubule
- Reabsorption in the proximal tubule is critical for the recapture of ions, water, and valuable nutrients from the huge volume of filtrate
- NaCl in the filtrate diffuses into the cells of the transport epithelium, where Na+ is actively transported into the interstitial fluid
- This transfer of positive charge out of the tubule drives the passive transport of Cl-, as well as the movement of more Na+ from the lumen into the cells of the tubule wall by facilitated diffusion and cotransport mechanisms
- As salt moves from the filtrate to the interstitial fluid, water follows by osmosis (the salt and water then diffuse from the interstitial fluid into the peritubular capillaries)
- Glucose, amino acids, potassium ions, and other essential substances are also actively or passively transported from the filtrate to the interstitial fluid and then into the peritubular capillaries
- Processing of filtrate in the proximal tubule helps maintain a relatively constant pH in body fluids
- Cells of the transport epithelium secrete H+ into the lumen of the tubule but also synthesize and secrete ammonia, which acts a a buffer to trap H+ in the form of ammonium ions
- The more acidic the filtrate, the more ammonia the cells produce and secrete (a mammal's urine usually contains some ammonia from this source)
- The proximal tubules also reabsorb about 90% of the buffer bircarbonate from the filtrate, contributing further to pH balance in body fluids
- Material to be excreted become concentrated (many wastes leave the body fluids during the nonselective filtration process and remain in the filtrate while water and salts are reabsorbed)
Descending limb of the loop of Henle
- Reabsorption of water continues as the filtrate moves into the descending limb of the loop of Henle
- Numerous water channels formed by aquaporin proteins make the transport epithelium freely permeable to water
- There are almost no channels for salt and other small solutes, resulting in very low permeability for theses substances
- In order for water to move out of the tubule vy osmosis, the interstitial fluid bathing the tubule must be hyperosmotic to the filtrate
- Osmolarity of the interstitial fluid increases progressively from the outer cortex to the inner medulla of the kidney
- Flitrate loses water--and therefore its solute concentration increases
Ascending limb of the loop of Henle
- Has transport epithelium studded with ion channels, but no water channels
- This membrane is impermeable to water
- Two specialized regions: a thin segment near the loop tip and a thick segment adjacent to the distal tubule
- As filtrate ascends in the thin segment, NaCl, which became concentrated in the descending limb, diffuses out of the permeable tubule into the interstitial fluid (helps maintain the osmolarity of the interstitial fluid in the medulla)
- In the thick segment, NaCl is actively transported by the epithelium into the interstitial fluid
- As a result of losing salt but not water, the filtrate becomes progressively more dilute as it moves up to the cortex
Distal Tuble
- Plays a key role in regulating the K+ and NaCl concentration of body fluids
- Involves variation in the amount of K+ secreted into the filtrate as well as the amount of NaCl reabsorbed from the filtrate
- The distal tubule contributes to pH regulation by controlled secretion of H+ and reabsorption of bircarbonate
Collecting Duct
- Carries the filtrate through the medulla to the renal pelvis
- Transport epithelium of the nephron and collect duct processes the filtrate, forming the urine
- One of this epithelium's most important tasks is reabsorption of solutes and water
- About 99% of the water and nearly all of the sugars, amino acids, vitamins, and other organic nutrients are reabsorbed into the blood, leaving only about 1.5 L of urine to be transported to the bladder
- Hormonal control of permeability and transport determines the extent to which urine becomes concentrated
- When the kidneys are conserving water, aquaporin channels in the collect duct allow water molecules to cross the epithelium (epithelium remains impermeable to salt, and in the renal cortex, to urea)
- In the inner medulla, the duct becomes permeable to urea (because of the high urea concentration in the filtrate at this point, some urea diffuses out of the duct and into the interstitial fluid)
- Net result is urine that is hyperosmotic to the general body fluids
- In producing dilute urine, the kidney actively reabsorbs salts without allowing water to follow by osmosis (epithelium lacks water channels)
- Although isosmotic to the inner medulla's interstitial fluid, the urine is hyperosmotic to blood and interstitial fluid elsewhere in the body
Afferent Arteriole
- Each nephron is supplied with blood by an afferent arteriole, an offshoot of the renal artery that branches and forms the capillaries of the glomerulus
Efferent Arteriole
- The capillaries of the glomerulus converge as they leave the flomerulus, forming an efferent arteriole
Peritubular Capillaries
- Branches of this efferent arteriole form the peritubular capillaries, which surround the proximal and distal tubules
- Other branches extend downward and form the vasa recta, hairpin-shaped capillaries that serve the renal medulla, including the long loop of Henle of juxtamedullary nephrons
- The vasa recta can supply the kidney with nutrients and other important substances carried by the blood without interfering with the osmolarity gradient in the inner and outer medulla
Countercurrent Multiplier Systems
- The loop of Henle has several qualities of a countercurrent system by expending energy to actively transport NaCl from the the filtrate in the upper part of the ascending limb of the loop
- Countercurrent systems, which expend energy to create concentration gradients, are called countercurrent multiplier systems
- Maintains the a high solute concentration in the interior of the kideny, enabling the kidney to form concentrated urine
Antidiuretic Hormone (Vasopressin)
- ADH is produced in the hypothalamus and stored in the posterior pituitary gland
- Osmoreceptor cells in the hypothalamus monitor the osmolarity of blood and regulate release of ADH from the posterior pituitary
- When ADH reaches the kidney, its main targets are the collecting ducts (the ADH brings about changes that makes the epithelium more permeable to water)
- As osmolarity of the blood subsides, a negative feed-feedback mechanism reduces the activity of osmoreceptor cells and ADH secretion is reduced
- A reduction in the blood osmolary below the set point, a large volume of water taken in, decreases ADH secretion to a very low level (results in a decrease in water reabsorption so there is a discharge of dilute urine)
1) ADH binds to membrane receptor
2) Receptor activates cAMP second messenger system
3) Vesicles with aquaporin water channels are inserted into membrane lining lumen of collecting duct
4) Aquaporin channels enhance reabsorption of water from collecting duct into interstitial fluid
Renin-Angiotensin-Aldosterone System
- Second regulatory mechanism that helps maintain homeostasis by acting on the kidney
Juxtaglomerular Apparatus
- A specialized tissue consisting of cells of and around the afferent arteriole that supplies blood to the glomerulus
- When blood pressure or blood volume in the afferent arteriole that supplies blood to the glomerulus drops , the JGA release the enzyme renin
- Renin initiates a sequence of chemical reactions that cleave a plasma called angiotensin II
- Angiotensin II raises blood pressure by constricting areterioles, which decreases blood flow to many capillaries (it also stimulates the adrenal glands to release a hormone called aldosterone)
Aldosterone
- This hormone acts on the nephrons' distal tubules and collecting duct, making them reabsorb more Na+ and water, the increasing blood blood volume and pressure
Atrial Natriuretic Peptide
- Opposes the RAAS
- The walls of the atria of the heart release ANP in response to an increase in blood volume and pressure. ANP inhibits the release of renin from the IGA, inhibits NaCl reabsorption by the collecting ducts, and reduces aldosterone release from the adrenal glands
- These actions lower blood volume and pressure
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Coben and Boyer revolutionized genetics by producing recombinant [DNA/RNA].
List four specific ways in which fishes are adapted for aquatic life.
Test your vocabulary by matching each term to its definition, as identified by its preceding letter code. A. A graphical representation of the numbers, energy, or biomass at each trophic level in an ecosystem. Often pyramidal in shape. B. A metabolic process that requires oxygen in order for it to proceed. C. The processes by which nitrogen circulates between the atmosphere and the biosphere. D. The cycle describing the movement of oxygen through the ecosystem. E. A sequence of steps describing how an organism derives energy from those before it. F. Organism that is capable of making its own food, e.g. green plants. G. A complex series of interactions showing the feeding relationships between organisms in an ecosystem. H. The catabolic process in which the chemical energy in complex organic molecules is coupled to ATP production. I. The cycling of water through the environment, from lakes, seas and oceans to clouds, rain, through organisms, to ground water and rivers and back. J. Biogeochemical cycle by which carbon is exchanged among the biotic and abiotic components of the Earth. K. Any of the feeding levels that energy passes through in an ecosystem. L. Process in which carbon dioxide, water and sunlight are used to produce glucose and oxygen. M. A metabolic process that does not require oxygen to proceed. N. An organism that obtains its carbon and energy from other organisms. a. anaerobic b. aerobic c. carbon cycle d. cellular respiration e. consumer f. ecological pyramid g. food chain h. food web i. hydrologic cycle j. nitrogen cycle k. oxygen cycle l. photosynthesis m. producer n. trophic level
Which parts of Oparin's hypothesis were tested by the Miller-Urey experiment? Which parts were not tested?