Which hormone helps control ovulation?
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Hormone Ovulation
A hormone (from the Greek participle “”) is any member of a class of signaling molecules produced by glands in multicellular organisms that are transported by the circulatory system to target distant organs to regulate physiology and behaviour.  Hormones have diverse chemical structures, mainly of 3 classes: eicosanoids, steroids, and amino acid derivatives (amines, peptides, and proteins). The glands that secrete hormones comprise the endocrine signaling system. The term hormone is sometimes extended to include chemicals produced by cells that affect the same cell (autocrine or intracrine signalling) or nearby cells (paracrine signalling).

Hormones are used to communicate between organs and tissues for physiological regulation and behavioral activities, such as digestion, metabolism, respiration, tissue function, sensory perception, sleep, excretion, lactation, stress, growth and development, movement, reproduction, and mood.    Hormones affect distant cells by binding to specific receptor proteins in the target cell resulting in a change in cell function. When a hormone binds to the receptor, it results in the activation of a signal transduction pathway. This may lead to cell type-specific responses that include rapid non-genomic effects or slower genomic responses where the hormones acting through their receptors activate gene transcription resulting in increased expression of target proteins. Amino acid–based hormones (amines and peptide or protein hormones) are water-soluble and act on the surface of target cells via second messengers; steroid hormones, being lipid-soluble, move through the plasma membranes of target cells (both cytoplasmic and nuclear) to act within their nuclei.

Hormone secretion may occur in many tissues. Endocrine glands are the cardinal example, but specialized cells in various other organs also secrete hormones. Hormone secretion occurs in response to specific biochemical signals from a wide range of regulatory systems. For instance, serum calcium concentration affects parathyroid hormone synthesis; blood sugar (serum glucose concentration) affects insulin synthesis; and because the outputs of the stomach and exocrine pancreas (the amounts of gastric juice and pancreatic juice) become the input of the small intestine, the small intestine secretes hormones to stimulate or inhibit the stomach and pancreas based on how busy it is. Regulation of hormone synthesis of gonadal hormones, adrenocortical hormones, and thyroid hormones is often dependent on complex sets of direct influence and feedback interactions involving the hypothalamic-pituitary-adrenal (HPA), -gonadal (HPG), and -thyroid (HPT) axes.

Upon secretion, certain hormones, including protein hormones and catecholamines, are water-soluble and are thus readily transported through the circulatory system. Other hormones, including steroid and thyroid hormones, are lipid-soluble; to allow for their widespread distribution, these hormones must bond to carrier plasma glycoproteins (e.g., thyroxine-binding globulin (TBG)) to form ligand-protein complexes. Some hormones are completely active when released into the bloodstream (as is the case for insulin and growth hormones), while others are prohormones that must be activated in specific cells through a series of activation steps that are commonly highly regulated. The endocrine system secretes hormones directly into the bloodstream typically into fenestrated capillaries, whereas the exocrine system secretes its hormones indirectly using ducts. Hormones with paracrine function diffuse through the interstitial spaces to nearby target tissue.

Overview 

Hormonal signaling involves the following steps:
# Biosynthesis of a particular hormone in a particular tissue
# Storage and secretion of the hormone
# Transport of the hormone to the target cell(s)
# Recognition of the hormone by an associated cell membrane or intracellular receptor protein
# Relay and amplification of the received hormonal signal via a signal transduction process: This then leads to a cellular response. The reaction of the target cells may then be recognized by the original hormone-producing cells, leading to a down-regulation in hormone production. This is an example of a homeostatic negative feedback loop.
# Breakdown of the hormone.

Hormone cells are typically of a specialized cell type, residing within a particular endocrine gland, such as the thyroid gland, ovaries, and testes. Hormones exit their cell of origin via exocytosis or another means of membrane transport. The hierarchical model is an oversimplification of the hormonal signaling process. Cellular recipients of a particular hormonal signal may be one of several cell types that reside within a number of different tissues, as is the case for insulin, which triggers a diverse range of systemic physiological effects. Different tissue types may also respond differently to the same hormonal signal.

Regulation 

The rate of hormone biosynthesis and secretion is often regulated by a homeostatic negative feedback control mechanism. Such a mechanism depends on factors that influence the metabolism and excretion of hormones. Thus, higher hormone concentration alone cannot trigger the negative feedback mechanism. Negative feedback must be triggered by overproduction of an "effect" of the hormone.

Hormone secretion can be stimulated and inhibited by:
* Other hormones (stimulating- or releasing -hormones)
* Plasma concentrations of ions or nutrients, as well as binding globulins
* Neurons and mental activity
* Environmental changes, e.g., of light or temperature

One special group of hormones is the tropic hormones that stimulate the hormone production of other endocrine glands.  For example, thyroid-stimulating hormone (TSH) causes growth and increased activity of another endocrine gland, the thyroid, which increases output of thyroid hormones.

To release active hormones quickly into the circulation, hormone biosynthetic cells may produce and store biologically inactive hormones in the form of pre- or prohormones. These can then be quickly converted into their active hormone form in response to a particular stimulus.

Eicosanoids are considered to act as local hormones.

Receptors 

 Most hormones initiate a cellular response by initially binding to either cell membrane associated or intracellular receptors. A cell may have several different receptor types that recognize the same hormone but activate different signal transduction pathways, or a cell may have several different receptors that recognize different hormones and activate the same biochemical pathway.

Receptors for most peptide as well as many eicosanoid hormones are embedded in the plasma membrane at the surface of the cell and the majority of these receptors belong to the G protein-coupled receptor (GPCR) class of seven alpha helix transmembrane proteins.  The interaction of hormone and receptor typically triggers a cascade of secondary effects within the cytoplasm of the cell, often involving phosphorylation or dephosphorylation of various other cytoplasmic proteins, changes in ion channel permeability, or increased concentrations of intracellular molecules that may act as secondary messengers (e.g., cyclic AMP). Some protein hormones also interact with intracellular receptors located in the cytoplasm or nucleus by an intracrine mechanism.

For steroid or thyroid hormones, their receptors are located inside the cell within the cytoplasm of the target cell. These receptors belong to the  nuclear receptor family of ligand-activated transcription factors. To bind their receptors, these hormones must first cross the cell membrane. They can do so because they are lipid-soluble. The combined hormone-receptor complex then moves across the nuclear membrane into the nucleus of the cell, where it binds to specific DNA sequences, regulating the expression of certain genes, and thereby increasing the levels of the proteins encoded by these genes. However, it has been shown that not all steroid receptors are located inside the cell. Some are associated with the plasma membrane.

Effects 

Hormones have the following effects on the body:

* stimulation or inhibition of growth
* wake-sleep cycle and other circadian rhythms
* mood swings
* induction or suppression of apoptosis (programmed cell death)
* activation or inhibition of the immune system
* regulation of metabolism
* preparation of the body for mating, fighting, fleeing, and other activity
* preparation of the body for a new phase of life, such as puberty, parenting,  and menopause
* control of the reproductive cycle
* hunger cravings
* sexual arousal

A hormone may also regulate the production and release of other hormones. Hormone signals control the internal environment of the body through homeostasis.

Chemical classes 

As hormones are defined functionally, not structurally, they may have diverse chemical structures. Hormones occur in multicellular organisms (plants, animals, fungi, brown algae and red algae). These compounds occur also in unicellular organisms, and may act as signaling molecules,   but there is no consensus if, in this case, they can be called hormones.

Animal 

Vertebrate hormones fall into four main chemical classes:

* Amino acid derived – Examples include melatonin and thyroxine.
* Peptides, polypeptides and proteins. – Small peptide hormones include TRH and vasopressin. Peptides composed of scores or hundreds of amino acids are referred to as proteins. Examples of protein hormones include insulin and growth hormone. More complex protein hormones bear carbohydrate side-chains and are called glycoprotein hormones. Luteinizing hormone, follicle-stimulating hormone and thyroid-stimulating hormone are examples of glycoprotein hormones.
* Eicosanoids – hormones derive from lipids such as arachidonic acid, lipoxins and prostaglandins.
* Steroid – Examples of steroid hormones include the sex hormones estradiol and testosterone as well as the stress hormone cortisol.

Compared with vertebrate, insects and crustaceans possess a number of structurally unusual hormones such as the juvenile hormone, a sesquiterpenoid. 

Plant 

Plant hormones include abscisic acid, auxin, cytokinin, ethylene, and gibberellin.

Therapeutic use 

Many hormones and their structural and functional analogs are used as medication. The most commonly prescribed hormones are estrogens and progestogens (as methods of hormonal contraception and as HRT),  thyroxine (as levothyroxine, for hypothyroidism) and steroids (for autoimmune diseases and several respiratory disorders). Insulin is used by many diabetics. Local preparations for use in otolaryngology often contain pharmacologic equivalents of adrenaline, while steroid and vitamin D creams are used extensively in dermatological practice.

A "pharmacologic dose" or "supraphysiological dose" of a hormone is a medical usage referring to an amount of a hormone far greater than naturally occurs in a healthy body. The effects of pharmacologic doses of hormones may be different from responses to naturally occurring amounts and may be therapeutically useful, though not without potentially adverse side effects. An example is the ability of pharmacologic doses of glucocorticoids to suppress inflammation.

Hormone-behavior interactions 

At the neurological level, behavior can be inferred based on: hormone concentrations; hormone-release patterns; the numbers and locations of hormone receptors; and the efficiency of hormone receptors for those involved in gene transcription. Not only do hormones influence behavior, but also behavior and the environment influence hormones. Thus, a feedback loop is formed. For example, behavior can affect hormones, which in turn can affect behavior, which in turn can affect hormones, and so on.

Three broad stages of reasoning may be used when determining hormone-behavior interactions:
* The frequency of occurrence of a hormonally dependent behavior should correspond to that of its hormonal source
* A hormonally dependent behavior is not expected if the hormonal source (or its types of action) is non-existent
* The reintroduction of a missing behaviorally dependent hormonal source (or its types of action) is expected to bring back the absent behavior

Comparison with neurotransmitters 

There are various clear distinctions between hormones and neurotransmitters:
* A hormone can perform functions over a larger spatial and temporal scale than can a neurotransmitter.
* Hormonal signals can travel virtually anywhere in the circulatory system, whereas neural signals are restricted to pre-existing nerve tracts
* Assuming the travel distance is equivalent, neural signals can be transmitted much more quickly (in the range of milliseconds) than can hormonal signals (in the range of seconds, minutes, or hours). Neural signals can be sent at speeds up to 100 meters per second.
* Neural signalling is an all-or-nothing (digital) action, whereas hormonal signalling is an action that can be continuously variable as dependent upon hormone concentration

Discovery

The discovery of hormones and endocrine signaling occurred during studies of how the digestive system regulates its activities, as explained at Secretin § Discovery. Ovulation is the release of egg from the ovaries. In humans, this event occurs when the de Graaf's follicles rupture and release the secondary oocyte ovarian cells.  After ovulation, during the luteal phase, the egg will be available to be fertilized by sperm. In addition, the uterine lining (endometrium) is thickened to be able to receive a fertilized egg. If no conception occurs, the uterine lining as well as blood will be shed during menstruation. 

Ovulation in humans 

In humans, ovulation occurs about midway through the menstrual cycle, after the follicular phase. The few days surrounding ovulation (from approximately days 10 to 18 of a 28-day cycle), constitute the most fertile phase.     The time from the beginning of the last menstrual period (LMP) until ovulation is, on average, 14.6 [http://onlinelibrary.wiley.com/doi/10.1046/j.1469-0705.1991.01030212.x/pdf] days, but with substantial variation between females and between cycles in any single female, with an overall 95% prediction interval of 8.2 to 20.5 days.

The process of ovulation is controlled by the hypothalamus of the brain and through the release of hormones secreted in the anterior lobe of the pituitary gland, luteinizing hormone (LH) and follicle-stimulating hormone (FSH).       In the pre-ovulatory phase of the menstrual cycle, the ovarian follicle will undergo a series of transformations called  cumulus expansion, which is stimulated by FSH. After this is done, a hole called the stigma will form in the follicle, and the secondary oocyte will leave the  follicle through this hole. Ovulation is triggered by a spike in the  amount of FSH and LH released from the pituitary gland. During the luteal (post-ovulatory) phase, the secondary oocyte will travel through the fallopian tubes toward the uterus. If fertilized by a sperm, the fertilized secondary oocyte or ovum may implant there 6–12 days  later. 

Follicular phase 

The follicular phase (or proliferative phase) is the phase of the menstrual cycle during which the ovarian follicles mature. The follicular phase lasts from the beginning of menstruation to the start of ovulation.  

For ovulation to be successful, the ovum must be supported by the corona radiata and cumulus oophorous granulosa cells. The latter undergo a period of proliferation and mucification known as cumulus expansion. Mucification is the secretion of a hyaluronic acid-rich cocktail that disperses and gathers the cumulus cell network in a sticky matrix around the ovum. This network stays with the ovum after ovulation and has been shown to be necessary for fertilization.

An increase in cumulus cell number causes a concomitant increase in antrum fluid volume that can swell the follicle to over 20 mm in diameter. It forms a pronounced bulge at the surface of the ovary called the blister.

Ovulation 

Estrogen levels peak towards the end of the follicular phase. This causes a surge in levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). This lasts from 24 to 36 hours, and results in the rupture of the ovarian follicles, causing the oocyte to be released from the ovary via the oviduct. 

Through a signal transduction cascade initiated by LH, proteolytic enzymes are secreted by the follicle that degrade the follicular tissue at the site of the blister, forming a hole called the stigma. The secondary oocyte leaves the ruptured  follicle and moves out into the peritoneal cavity through the stigma, where it is caught by the fimbriae at the end of the fallopian tube (also called the oviduct). After entering the oviduct, the oocyte is pushed along by cilia, beginning its journey toward the uterus.

By this time, the oocyte has completed meiosis I, yielding two cells: the larger secondary oocyte that contains all of the cytoplasmic material and a smaller, inactive first polar body. Meiosis II follows at once but will be arrested in the metaphase and will so remain until fertilization. The spindle apparatus of the second meiotic division appears at the time of ovulation. If no fertilization occurs, the oocyte will degenerate between 12 and 24 hours after ovulation.[http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1340563/ Ovarian ultrasonography highlights precision of symptoms of ovulation as markers of ovulation] Approximately 1-2% of ovulations release more than one oocyte. This tendency increases with maternal age. Fertilization of two different oocytes by two different spermatozoa results in fraternal twins.

The mucous membrane  of the uterus, termed the functionalis, has reached its maximum size, and so have the endometrial glands, although they are still non-secretory.

Luteal  phase 

The follicle proper has met  the end of its lifespan. Without the oocyte, the follicle folds inward on  itself, transforming into the corpus luteum (pl. corpora lutea), a  steroidogenic cluster of cells that produces estrogen and progesterone. These hormones induce the  endometrial glands to begin production of the proliferative endometrium and later  into secretory endometrium, the site of embryonic growth if  implantation occurs. The action of progesterone increases basal body temperature by one-quarter to one-half degree  Celsius (one-half  to one degree Fahrenheit).  The corpus luteum continues this paracrine  action for the remainder of the menstrual cycle, maintaining the  endometrium, before disintegrating into scar tissue during menses. 

Clinical  presentation

The start of ovulation can be detected by signs. Because the signs are not readily discernible by people other than the female, humans are said to have a concealed ovulation. In many animal species there are distinctive signals indicating the period when the female is fertile. Several explanations have been proposed to explain concealed ovulation in humans.

Females near ovulation  experience changes in the cervix,  in mucus produced by the cervix, and in their basal body temperature. Furthermore, many females experience secondary fertility signs  including Mittelschmerz (pain associated with ovulation) and a heightened sense of smell, and can sense the precise moment of ovulation.  

Many females experience heightened sexual desire in the several days immediately before ovulation.   One study concluded that females subtly improve their facial  attractiveness during ovulation. 

Symptoms related to the onset of ovulation, the moment of ovulation and the body's process of beginning and ending the menstrual cycle vary in intensity with each female but are fundamentally the same. The charting of such symptoms — primarily basal body temperature, Mittelschmerz and cervical position — is referred to as the sympto-thermal method of fertility awareness, which allow auto-diagnosis by a female of her state of ovulation. Once training has been given by a suitable authority, [http://download-fertility-charts.com/download-fertility-charts fertility charts] can be completed on a cycle-by-cycle basis to show ovulation. This gives the possibility of using the data to predict fertility for natural contraception and pregnancy planning.

The moment of ovulation has been photographed. 

Disorders 

Disorders of ovulation are classified as menstrual disorders and include oligoovulation and anovulation:

* Oligoovulation is infrequent or irregular ovulation (usually defined as cycles of greater than 36 days or fewer than 8 cycles a year)
* Anovulation is absence of ovulation when it would be normally expected (in a post-menarchal, premenopausal female).  Anovulation usually manifests itself as irregularity of menstrual periods, that is, unpredictable variability of intervals, duration, or bleeding. Anovulation can also cause cessation of periods (secondary amenorrhea) or excessive bleeding (dysfunctional uterine bleeding).

The World Health Organization (WHO) has developed the following classification of ovulatory disorders: 

* WHO group I: Hypothalamic–pituitary-gonadal axis failure
* WHO group II: Hypothalamic–pituitary-gonadal axis dysfunction. WHO group II is the most common cause of ovulatory disorders, and the most common causative member is polycystic ovary syndrome (PCOS). 
* WHO group III: Ovarian failure
* WHO group IV: Hyperprolactinemia

Induction and  suppression

Induced ovulation

Ovulation  induction is a promising assisted reproductive technology for patients with conditions such as polycystic ovary syndrome (PCOS)  and oligomenorrhea. It is also used in in vitro fertilization to make the follicles mature before egg retrieval. Usually, ovarian stimulation is used in conjunction with ovulation induction to stimulate the formation of multiple oocytes. Some sources include ovulation induction in the definition of ovarian stimulation.

A low dose of human chorionic gonadotropin (HCG) may be injected after completed ovarian stimulation. Ovulation will occur between 24–36 hours after the HCG injection.[http://www.ivf.com/ovind.html IVF.com > Ovulation Induction] Retrieved on Mars 7, 2010

Suppressed ovulation

Contraception can be achieved by suppressing the ovulation.

The majority of hormonal contraceptives and conception boosters focus on the ovulatory phase of the menstrual cycle because it is the most important determinant of fertility. Hormone therapy can positively or negatively interfere with ovulation and can give a sense of cycle control to the female.

Estradiol and  progesterone, taken in various forms including combined oral contraceptive pills, mimics the hormonal levels of  the menstrual cycle and engage in negative feedback of folliculogenesis  and ovulation.
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 What hormone helps control ovulation? 

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