Endocrine system: Maintains the blood levels of the cellular fuels by controlling and regulating their storage and their release from storage (e.g., insulin and glucagons).
Nervous system: Monitors oxygen levels and nutrient content in the blood and, in response, modulates the cardiovascular, pulmonary, and endocrine systems and induces feeding and drinking behaviors. In addition to energy metabolism, the cells of the body must maintain a relatively constant intracellular environment to survive. This includes the uptake of fuels needed to produce ATP, the export from the cell of cellular wastes, the maintenance of an appropriate intracellular ionic environment, the establishment of a resting membrane potential, and the maintenance of a constant cellular volume. All of these functions are carried out by specific membrane transport proteins.
The composition of the extracellular fluid (ECF) that bathes the cells must also be maintained relatively constant. In addition, the volume and temperature of the ECF must be regulated. Epithelial cells in the lungs, gastrointestinal tract, and kidneys are responsible for maintaining the volume and composition of the ECF, while the skin plays a major role in temperature regulation. On a daily basis, H2O and food are ingested, and essential components are absorbed across the epithelial cells of the gastrointestinal tract. This daily intake of solutes and water must be matched by excretion from the body, thus maintaining steady-state balance. The kidneys are critically involved in the maintenance of steady-state balance for water and many components of the ECF (e.g., Na+ , K+ , HCO3 − , pH, Ca++ , organic solutes). The lungs ensure an adequate supply of O2 to “burn” the cellular fuels for the production of ATP and excrete the major waste product of this process (i.e., CO2). Because CO2 can affect the pH of the ECF, the lungs work with the kidneys to maintain ECF pH.
Because humans inhabit many different environments and often move between environments, the body must be able to rapidly adapt to the challenges imposed by changes in ambient temperature and availability of food and water. Such adaptation requires coordination of the function of cells in different tissues and organs as well as their regulation. The nervous and endocrine systems coordinate and regulate cell, tissue, and organ function. The regulation of function can occur rapidly (seconds to minutes), as is the case for levels of cellular fuels in the blood, or over much longer periods of time (days to weeks), as is the case for acclimatization when an individual moves from a cool to a hot environment or changes from a high-salt to a low-salt diet.
The function of the human body represents complex processes at multiple levels. This book explains what is currently known about these processes. Although the emphasis is on the normal function of the human body, discussion of disease and abnormal function is also appropriate, as these often illustrate physiologic processes and principles at the extremes.
The authors for each section have presented what they believe to be the most likely mechanisms responsible for the phenomena under consideration. We have adopted this compromise to achieve brevity, clarity, and simplicity.
Bruce M. Koeppen, MD, PhD Bruce A. Stanton, PhD 29TheGastricPhaseoftheIntegratedResponsetoaMeal,529 30TheSmallIntestinalPhaseoftheIntegratedResponsetoaMeal,541 31TheColonicPhaseoftheIntegratedResponsetoaMeal,559 32TransportandMetabolicFunctionsoftheLiver,568
Section 7: The Renal System, 580 37RoleoftheKidneysintheRegulationofAcid-BaseBalance,670
Section 8: The Endocrine and Reproductive Systems, 685
SECTION 1Cellular Physiology BRUCE M. KOEPPEN AND BRUCE A. STANTON
Upon completion of this chapter, the student should be able to answer the following questions: 1.
What organelles are found in a typical eukaryotic cell, and what is their function?
2.
What is the composition of the plasma membrane?
3.