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181 Cards in this Set

  • Front
  • Back
Hypothalamus
One of the primary interfaces between the nervous system and the endocrine system.

Made up of nuclei at the base of the brain.

Primary Plexus

Contains neurosecretory cells that function primarily as endocrine glands. Their neurohormones are released from neural axon terminals in response to neuronal impulses in a manner analogous to neurotarnsmitters but are released into blood vessels in the pituitary gland.
Pituitary Gland
Made up of two parts--anterior and posterior.

Derived from the soft tissues of the upper palate.
Posterior Pituitary Gland
Vasopressin and Oxytocin
Anterior Pituitary Gland
Secondary Plexus
Autocrine
pertaining to a system secreted by a cell into the environment that affects the transmitting cell
Intracrine
peptide hormones or growth factors that bind and act inside cells either after internalization by the cells or retention in their cells of synthesis
Paracrine
chemical mediators released by once cell that induce a biological response in an adjacent cell (neurons)
Ectocrine
A parahormonal chemical substance that is secreted (usually by an invertebrate organism) into its immediate environment (air or water) which alters physiology or behavior of the recipient individual

(substances released to the outside of an individual and induce ab iological response in another animal) EX. PHEROMONES
chemical messenger
any substance that is produced by a cell that affects the function of another cell
cytokine
a chemical messenger that evokes the proliferation of other cells, especially in the immune system.
Hormone
A chemical messenger that is released into the bloodstream or tissue fluid system taht affects the function of target cells some distance from the source
Neurohormone
A hormone produced by a neuron
Neuropeptide
A peptide hormone produced by a neuron
Neurosteroid
A steroid hormone produced by a neuron
Neuromodulator
A hormone that changes (modulates) the response of an euron to some other factor
Neurotransmitter
A chemical messenger that acts across the neural synapse
The endocrine system has several general features:
1) Endocrine glands are ductless

2) Endocrine glands have a rich blood supply

3) Hormones, the products of endocrine glands, are secreted into the bloodstream

4) Hormones can travel in the blood to virtually every cell in the body, and can thus potentially interact with any cell that has appropriate receptors.

5) Hormone receptors are specific binding sites, embedded in the cell membrane or located elsewhere in the cell, that interact with a particular hormone or class of hormones.
Endocrine glands
secreted directly into the blood

ex. Pineal, hypothalamus, pituitary, thyroid and parathyroid, adrenal, pancreas, gonads
exocrine glands
have ducts, or tubes, into which their products are released.

ex. salivary, mammary, and sweat glands
Types of Hormones
1) Peptides or proteins
2) Steroids
3) monoamines
4) lipid-based hormones
Thyroid Gland
-Consists of many sphere-shaped, colloid-filled structures called follicles which produce thyroid hormones in response to an anterior pituitary tropic hormone.

Also embedded are endocrine cells called C-cells, which secrete a protein hormone called calcitonin that is involved in calcium metabolism.
Portal System
a special closed blood circuit in which two beds of capillaries, one in the hypothalamus (the primary plexus) and one in the anterior pituitary (the secondary plexus) are connected by a vein that extends down the infundibulum. The portal system ensures that blood flows primarily in one direction (from the hypothalamus to the anterior pituitary), and also ensures that hormonal signals from the hypothalamus will be read by the pituitary rather than diluted in the general blood circulation.
Parathyroid
-secreted in the thyroid

-has several parts; in humans, two lobes are present in the outer layer of each of the thyroid on each side.

-secretes a parathyroid hormone which is also important in calcium regulation.
Pancreas
-Both endocrine and exocrine glands.

-Most of pancreas consists of exocrine cells that produce and secrete digestive juices into the intestines

-throughout the exocrine tissue are islands of endocrine tissue called ISLETS OF LANGERHANS. Within these islands are 4 types of cells, Beta cells, alpha cells, delta cells, and a few polypeptide-secreting cells, each of which secretes a different protein hormone. (ex. Beta cells secrete insulin).
Gastrointestinal tract
three major GI hormones-gastrin, secretin, and cholecystokinin--all of which are protein hormones that control various aspects of digestion.
Adrenal glands
Located on top of the kidneys.

-Like pituitary is two distinct organs

-Adrenal cortex
-Adrenal Medula
Adrenal Cortex
-outer gland that surrounds adrenal medulla.

-Composed of 3 distinct zones
-zona glomerulosa (outer region)
-zona fasciculata (middle zone)
-zona reticularis (innermost zone)
adrenal medulla
-made up of chromaffin cells, so called because they have a high affinity for colored stains.

-in response to neural signals, releases three monoamine hormones
1) epinephrine
2) norepinephrine
3) dopamine

also produces protein hormones--enkephalins
Pineal Gland
Individual pineal cells (pinealocytes) function exclusively as secretory structures.

-Primary endocrine product of the pineal gand is melatonin, which is formed from serotonin.
Gonads
The hormones produced by the gonads, primarilty steroid hormones, are required for gamete development of the secondary sex characters.

-These hormones also mediate the behaviors necessary to bring sperm and eggs together.

-The functions of the gonads are regulated by tropic hormones from the anterior pituitary, known as gonadotropins.

HAS TWO FUNCTIONS:
1) production of gametes (sperm or eggs)
2) production of hormones
Testes
bilateral glands, located in most in an external sac called the scrotum, and in others in the abdomen.
Leydig cells
primary hormone-producing cells in the testes and are interspersed among the tubules.

-PRODUCE STEROID HORMONES--PRIMARILY ANDROGENS--UNDER THE INFLUENCE OF GONADOTROPINS FROM THE ANTERIOR PITUITARY!
Ovaries
bilateral glands in the dorsal part of the abdominal cavity, normally below the kidney.

Has three functional subunits:
1) follicles (which contain a developing egg or OVUM)
2) Corpura Lutea (structures taht develop from follicles after the ovum is released;
3) Supporting tissue, or STROMA
Signal transduction
The sequence of events from the time a hormone binds to its receptor to the ultimate response in a target cell.
Steroid receptors
-Located inside cells, either in the cytosol or the nucleus.

-Once binded to a specific steroid or thyroid hormone, they migrate to the nucleus to regulate gene transcription.
Protein and Peptide Hormone Receptors
Found embedded in the cell membrane and ahve at least three domains (a domain is a region of the receptor that has a specific recognized function)

1) an extracellular domain that specifically binds to the hormone in question to form a hormone-receptor complex (in this context called a LIGAND-the name for any molecule that binds to a receptor)
2) a transmembrane domain
3) cytoplasmic domain.

-These receptors are dynamic, changing inf orm and position in the cell membrane, and they turn over rapidly.

-Can be divided into two functional classes:

1) those with intrinsic enzymatic activity
2) those that require an intracellular "second messenger" to exert their effects.
Enzyme Amplification
a processes where a single protein or peptide hormone molecule triggers synthesis of thousands of enzyme molecules
Intracellular "second" messenger
-Requires a second messenger- a molecular "middleman" such as an enzyme or another protein--to transduce the hormonal signal.

-these receptors are coupled to G-proteins, which can bind and hydrolyze GTP.
Protein and Peptide Hormones
-most vertebrate hormones are proteins.

-made up of individual amino acid building blocks.

-Protein hormones only a few acids in length are called peptide hormones where as larger ones are called protein or polypeptide hormones.

-can be stored in endocrine cells and are released into the circulatory system by means of exocytosis.

-Soluble in blood, therefore do not require carrier protein to travel to target cells like steroid hormones.
Examples of Protein and peptide hormones
The insulin, the glucagons, the neurohormones of the hypothalamus, the tropic hormones of the anterior pituitary, inhib, calcitonin, parathyroid hormone, the gastrointestinal hormone, gherlin, leptin, adiponectin, and the posterior pituitary hormones.
Hypothalamic Hormones
Five hypothalamic releasing hormones:

1) thyrotropin-releasing hormone (TRH) or growth hormone-releasing hormone (GHRH)

2) gonadotropin-releasing hormone (GnRH)

3) melanotropin-releasing hormone (MRH)

4) Corticotropin-releasing hormone (CRH)

5) growth-hormone inhibiting hormone aka Somatostatin. (only inhibiting hormone)

-Dopamine (DA), a neurotransmitter and monoamine, also serves as a neurohormone in the hypothalamus to inhibit the release of prolactin and melanotropin from the anterior pituitary; in this context it is known as:
Prolactin Inhibitory Hormone (PIH) and
Melanotropin Inhibitory Hormone (MIH).
hypocretin
aka OREXIN. recently discovered in cells in the hypothalamus and projects widely to the rest of the brain and spinal cord.

Hormone involved in sleep, metabolic balance, and possibly activation of sympathetic nervous system.
Anterior Pituitary Hormones secreted by basophils.
Luteinizing Hormone (LH)

Follicle-stimulating Hormone (FSH)

Thyroid-stimulating Hormone (TSH)

(collectively known as GLYCOPROTEINS)
Anterior Pituitary Hormones secreted by acidophils
Growth Hormone (GH) (released from the anterior pituitary in response to GNRH from the hypothalamus).

Prolactin
Adrenocorticotrophic hormone (ACTH)
A polypeptide hormone that is secreted by the anterior pituitary gland that stimulates the adrenal cortex to secrete corticosteroids, such as cortisol and corticosterone. ACTH is also known as corticotrophin.
Androgens
Any of the C19 class of steroid hormones, so named because of their andros- (male) generating effects. Androgens are the primary steroidal product secreted from the testes. Testosterone and dihydrotestosterone are biologically important androgens.
Antidiuretic hormone (ADH)
A hormone secreted from the anterior pituitary that regulates removal of water from the blood via the kidneys. Also called vasopressin.
Autoradiography
A technique used to detect a radiolabeled substance, such as a hormone, in a cell or organism, by placing a thin slice of the material in contact with a photographic emulsion, which displays darkened silver grains in response to the radioactive emissions.
Calcitonin (CT)
A polypeptide hormone that is secreted from the C cells associated with the thyroid gland which lowers blood calcium concentrations and affects blood phosphorus.
Cannulation
A technique in which hollow electrodes or fine tubes (cannulas) are inserted into specific brain regions or into specific blood vessels, so that substances can be introduced precisely into a particular place or a blood sample obtained from a specific location.
Carrier protein
Also called binding protein or transport protein; (1) one of several different plasma proteins that bind to hormones of low solubility (primarily thyroid and steroid hormones), providing a transport system for them. Some carrier proteins are specific for particular hormones, whereas others bind to many hormones. (2) One of several different types of trans-membrane proteins that function to transport small molecules across cell membranes.
C-cells
Thyroid cells found in the interstitial spaces between the thyroid follicle spheres that secrete calcitonin. C-cells are also called parafollicular cells.
Cholecystokinin (CCK)
A hormone released by the lining of the small intestine that may be involved in satiation of food intake.
Chromaffin cells
Cells that make and store epinephrine secretory vesicles. Because these cells have an affinity for chromic salts, they were named chromaffin. These types of cells are common in the adrenal medulla.
Corticoids
A class of C21 steroid hormones secreted primarily from the adrenal cortices. There are two main types of corticoids: glucocorticoids and mineralocorticoids.
Corticotropin releasing hormone (CRH)
A peptide hormone secreted by the hypothalamus that stimulates the release of ACTH (corticotrophin) by the anterior pituitary gland. CRH is also called corticotrophin releasing factor (CRF).
Cytokine
A protein chemical messenger that evokes the proliferation of other cells, especially in the immune system. Examples of cytokines are interleukins and interferons.
Dehydroepiandrosterone (DHEA)
A steroid hormone that is produced from cholesterol in the adrenal cortex, which is the primary precursor of natural estrogens, and is a weak androgen. DHEA is also called dehydroisoandrosterone or dehydroandrosterone.
Dihydrotestosterone (DHT)
A potent androgen that is derived from testosterone and binds more strongly to androgen receptors than testosterone. There are both 5-alpha and 5-beta forms of DHT.
Dopamine
A neurotransmitter produced primarily in the forebrain and diencephalon that acts in the basal ganglia, olfactory system, and some parts of the cerebral cortex.
Down-regulation
A process that is similar to negative feedback in which the overproduction of a hormone causes occupation of virtually all available receptors so that subsequent high levels of hormones cannot have a biological effect.
Endorphin
A hormone that acts as an endogenous opioid and binds the same receptors as morphine.
Enzymoimmunoassay (EIA)
An assay that uses the principle of competitive binding of an antibody to its antigen to determine the presence or quantity of a biological substance such as a hormone.
Epinephrine
A catecholamine produced in the adrenal medulla that increases cardiac tone and glucose levels.
Estradiol
The primary estrogenic steroid hormone produced by mammalian ovaries.
Estrogen
Any of the C18 class of steroid hormones, so named because of their estrus-generating properties in female mammals. Biologically important estrogens include estradiol, estrone, and estriol.
Exocytosis
The extrusion or secretion of substances from a cell by the fusion of a vesicle membrane with the cell membrane. The vesicle contains the material to be extruded from the cell. This process occurs during hormone secretion and neurotransmitter release.
Fallopian tubes
Tubes that connect the ovary to the uterus. Ova travel down the fallopian tubes after ovulation, and fertilization normally occurs in these tubes.
Follicle
An epithelial cell-lined sac or compartment of the thyroid gland, ovary, or other structure. Thyroid follicles are filled with colloidal material that contains thyroid hormones. In the ovary, each follicle contains an ovum. As the follicle and ovum mature, cells lining the follicle produce estrogens that regulate ovulation; after ovulation, the follicle develops into another endocrine structure called the corpus luteum.
Follicle-stimulating hormone (FSH)
A gonadotropic hormone from the anterior pituitary that stimulates follicle development in females and sperm production in males.
G proteins
A class of proteins located adjacent to the intracellular part of a hormone or neurotransmitter receptor that are activated when an appropriate ligand binds to the receptor.
Gastrin
A polypeptide hormone that is secreted by the mucous lining of the stomach; induces the secretion of gastric secretions.
Gametic Sex
The sex of an individual as determined by the production of ova by females and sperm by males.
Ghrelin
A peptide hormone produced by stomach cells; it is thought to increase feelings of hunger.
Glucagon
A protein hormone that is secreted by the alpha cells of the islets of Langerhans in response to low blood glucose levels (hypoglycemia). Glucagon elevates blood glucose.
Glucocorticoids
One of the two types of corticoids secreted from the adrenal cortices. Glucocorticoids are involved in carbohydrate metabolism and are often released in response to stressful stimuli.
Gluconeogenesis
The production of glucose from amino acids, a process that occurs in the liver in response to mild fasting.
Glycogenolysis
The breakdown of stored glycogen in the liver or muscles to provide a steady supply of glucose for energy.
Glycoprotein
An organic compound composed of both a protein and a carbohydrate joined together in a covalent chemical bond.
Gonadotropin
A hormone from the anterior pituitary (luteinizing hormone and follicle-stimulating hormone) or placenta (human chorionic hormone) that stimulates steroid production and gamete maturation in the gonads.
Gonadotropin-releasing hormone (GnRH)
A decapeptide hormone from the hypothalamus that regulates FSH and LH release from the anterior pituitary.
Granulosa cells
The monolayer of flattened epithelial cells that surrounds the immature ova.
Growth hormone (GH)
A protein hormone that stimulates somatic (body) growth. GH, however, does not directly induce skeletal growth; it stimulates the production of growth-regulating substances called somatomedins by the liver, kidneys, and other tissues. Somatomedins cause bone to take up sulfates, leading to growth. GH and somatomedins also stimulate protein synthesis.
Growth hormone-inhibiting hormone (GHIH)
A peptide hormone secreted from the hypothalamus that reduces the secretion of growth hormone by the anterior pituitary gland.
Growth hormone-releasing hormone (GHRH)
A polypeptide hormone that is released from the arcuate nucleus of hypothalamus that provokes the secretion of growth hormone from the anterior pituitary gland.
Hypocretin
A polypeptide hormone found in cells located in the hypothalamus that project widely to the rest of the brain and spinal cord. This hormone is involved in sleep, metabolic balance, and possibly activation of the sympathetic nervous system (also called orexin).
Hypothalamus
A part of the diencephalon located just below the thalamus that is important in the regulation of autonomic and endocrine functions. The hypothalamus consists of several collections of nerve cell bodies, called nuclei, and regulates endocrine function by releasing neurohormones into the hypothalamicÐpituitary portal system and by releasing hormones into the circulation of the posterior pituitary gland.
Inhibin
A peptide hormone that is secreted by the ovarian follicular cells and the testicular Sertoli cells that acts to inhibit secretion of FSH from the anterior pituitary gland.
Insulin
A protein hormone that regulates glucose uptake by all cells in the body (except the brain).
Islets of Langerhans
Islands of endocrine tissue nested throughout the exocrine tissue of the pancreas. There are four different cell types among the islets of Langerhans, each of which secretes a different type of protein hormone.
Leptin
A protein hormone secreted by fat cells that may communicate information to the brain about body fat content.
Leydig cells
The interstitial cells between the seminiferous tubules in the testes that produce androgens in response to luteinizing hormone from the anterior pituitary.
Ligand
A substance that binds to a receptor molecule.
Lipid-based hormone
A hormone derived from a fatty acid. Many lipid-based hormones are called eicosanoids, which are a class of oxygenated hydrophobic hormones that largely function as paracrine factors. All eicosanoids, including prostaglandins, leukotrienes, and thromboxanes, derive from arachidonic acid, which is a fatty acid derivative.
Luteinizing hormone (LH)
A gonadotropin from the anterior pituitary that promotes formation of the corpora lutea in females and testosterone production in males.
Melanocyte-stimulating hormone (MSH)
A peptide hormone secreted by the pituitary gland that regulates skin color in some vertebrates by stimulating melanin synthesis in melanocytes and melanin granule dispersal in melanophores. MSH is also called intermedin and melanotropin.
Melanotropin-inhibiting hormone (MIH)
A peptide hormone that inhibits MSH secretion.
Melanotropin-releasing hormone (MRH)
A hexapeptide that stimulates the secretion of melanotropin.
Melatonin
An indole amine hormone released by the pineal gland.
Mineralocorticoids
One of the two types of corticoids secreted from the adrenal cortices. Aldosterone is the most important mineralocorticoid secreted by terrestrial vertebrates, and is important in ion exchange and water metabolism.
Monoamine
A hormone or neurotransmitter that contains one amine group.
Müllerian ducts
A duct system present in both sexes during embryonic development that connects the gonads to the exterior. During normal development, the MŸllerian duct system develops into the accessory sex organs in females and regresses in males.
Müllerian inhibitory hormone (MIH)
A peptide hormone produced in the Sertoli cells in the developing testis that suppresses development of the MŸllerian duct system, which prevents development of the uterus and cervix. Also called MŸllerian inhibitory factor (MIF).
Neurohormone
A hormone that is released into the blood from a neuron rather than from an endocrine gland.
Neurosteroid
Steroids that are synthesized in the central nervous system (CNS) and the peripheral nervous systems (PNS), independently of the steroidogenic activity of the endocrine glands (e.g., gonads and adrenals).
Norepinephrine
A substance that can act as either a hormone or neurotransmitter, which is secreted by the adrenal medulla and the nerve endings of the sympathetic nervous system. It is also called noradrenalin, and is chemically similar to epinephrine (adrenalin).
Ovary
The female gonad, which produces estrogens, progestins, and ova.
Ovulation
The release of a mature egg (ovum) from the ovary. Ovulation may occur spontaneously in response to a specific hormonal milieu or as a direct result of stimuli associated with copulation.
Ovum
A haploid female gamete.
Oxytocin
A peptide hormone secreted by the posterior pituitary that triggers milk letdown in lactating females and may be involved in other reproductive behaviors.
Pancreas
A composite vertebrate gland with both endocrine and exocrine functions. In humans, the pancreas is located within the curve of the duodenum behind the stomach and liver, and secretes digestive enzymes (exocrine function), insulin, glucagon, and somatostatin (endocrine function), as well as bicarbonate.
Parathyroid gland
In humans and most other eutherian mammals, four to eight islands of separate endocrine tissue associated with the thyroid gland. The parathyroid gland secretes parathyroid hormone, which increases blood calcium levels and decreases blood phosphate levels.
Parathyroid hormone (PTH)
A protein hormone that is secreted by the parathyroid glands that regulates calcium and phosphate metabolism. PTH raises the extracellular calcium and blood plasma calcium concentrations.
Paraventricular nucleus
A collection of cell bodies in the hypothalamus that produce vasopressin and oxytocin. These hormones are transported down the cells’ axons for release from the posterior pituitary.
Peptide hormone
A class of hormones. Each consists of a relatively short chain of amino acids residues.
Pheromone
A chemical signal produced in one individual (the sender) that can alter the physiology and/or the behavior of another individual (the receiver).
Pineal gland
An endocrine gland (also called the epiphysis), located in mammals between the telencephalon and diencephalon, that secretes melatonin, a hormone important in the regulation of daily and seasonal cycles.
Pinealocytes
The primary cells of the pineal gland. They produce and secrete melatonin. Pinealocytes have a unique organelle called a synaptic ribbon, which serves as a specific marker for pinealocytes. Enzymes of the pinealocytes include 5-HT, N-acetyltransferase, and 5-hydroxyindole-O-methyltransferase which are used to convert serotonin to melatonin.
Pituitary gland
An endocrine gland that has two distinct anatomical components in humans, the anterior pituitary and the posterior pituitary, which have different embryological origins and different functional roles in the endocrine system. The pituitary gland (also called the hypophysis) is connected to the median eminence of the hypothalamus by the pituitary stalk, or infundibulum.
Placenta
A specialized organ produced by the mammalian embryo that is attached to the uterine wall and serves to provide nutrients, hormones, and energy to the fetus.
Polypeptide
An unbranched string of amino acids linked together by peptide bonds.
Portal system
A special closed blood circuit in which two beds of capillaries are connected by a vein; thus, the flow of blood is in one direction only. The hypothalamus–pituitary portal system comprises the hypothalamic capillary bed and the anterior pituitary capillary bed, connected by a vein. The majority of blood flow, and hence endocrine information, is from the hypothalamus to the anterior pituitary.
Posterior pituitary
The rear part of the endocrine gland that extends from the base of the brain and stores and releases oxytocin and vasopressin (or some variant of these two nanapeptide hormones) which are produced in the hypothalamus.
Preoptic medial nucleus (POM)
A collection of cell bodies in the songbird preoptic area that stains positively for estrogen receptors as well as for aromatase, and is thought to be critical in male avian copulatory behavior.
Preprohormone
A sequence of amino acids that contains three different elements: (1) a signal sequence, (2) one or more copies of a peptide hormone, and (3) other peptide sequences that may or may not possess biological activity. Peptide hormones are first synthesized as preprohormones in the rough endoplasmic reticulum of endocrine cells.
Proceptivity
The extent to which females initiate copulation.
Progestins
A class of C21 steroid hormones, so named for their “progestational,” or pregnancy-maintaining, effects in mammals. Progesterone is a common progestin.
Prohormone
A molecule that can act as a hormone itself or can be converted into another hormone with different properties.
Prolactin
A protein hormone that is highly conserved throughout vertebrate evolution and has many physiological functions, which can be broken down into five basic classes: (1) reproduction, (2) growth and development, (3) water and electrolyte balance, (4) maintenance of integumentary structures, and (5) actions on steroid-dependent target tissues or synergisms with steroid hormones to affect target tissues.
Prolactin inhibitory hormone (PIH)
Dopamine inhibits prolactin secretion from the anterior pituitary.
Pro-opiomelanocortin (POMC)
A precursor protein that consists of 241 amino acid residues. It is synthesized in the anterior and intermedate pituitary gland. Depending on the stimulus and site of production, POMC can be cleaved into a number of peptide hormones including ACTH, b-LPH, and met-enkephalin (in the anterior pituitary in response to CRH), or CLIP, g-LPH, a-MSH, and b-endorphin (in the intermediate pituitary in response to dopamine).
Protein hormone
A class of hormones. Each consists of a large chain of amino acids residues; also called a polypeptide.
Protein kinase
An enzyme that transfers a phosphate group from adenine triphosphate (ATP) to the protein substrate of the enzyme. The activation of specific protein kinases represents the mechanism by which most protein hormones initially exert their effects on cellular function.
Receptivity
The stimulus value of a female for eventually eliciting an intravaginal ejaculation from a male conspecific.
Receptor
A chemical structure on the cell surface or inside the cell that has an affinity for a specific chemical configuration of a hormone, neurotransmitter, or other chemical compound.
Releasing hormone
One of several polypeptides released from the hypothalamus that increase or decrease the release of hormones from the anterior pituitary gland.
Ribonucleic acid (RNA)
A nucleic acid that implements the information stored in DNA. Two forms of RNA are transfer RNA and messenger RNA.
Scrotum
An external pouch of skin that contains the testes.
Second messenger
A biological molecule released when a hormone binds to its receptor; the second messenger activates the cellular machinery of the target cell (the hormone is the first messenger).
Secretin
A polypeptide hormone produced in the duodenum, in response to gastric acid secretion, to stimulate production of pancreatic secretions.
Serotonin (5-HT)
A neurotransmitter formed from tryptophan (5-hydroxytryptamine); 5-HT is also a vasoconstrictor and the precursor to melatonin formation in the pineal gland.
Sertoli cells
Cells located along the basement membrane of the seminiferous tubules in which sperm cells are embedded while they mature.
Sex determination
The point at which an individual begins to develop as either a male or a female. In animals with sex chromosomes, sex determination occurs at fertilization; in animals that lack sex chromosomes, sex determination coincides with the presence of a specific environmental or social condition.
Sexual differentiation
The process by which individuals develop the characteristics associated with being male or female. Among vertebrates, differential exposure to gonadal steroid hormones after sex determination causes sexual dimorphism in several structures, including the brain.
Signal transduction
The intercellular or intracellular transfer of information (biological activation/inhibition) through a signal pathway which is mediated by a biologically active molecule (e.g., hormone, neurotransmitter) through the binding to a receptor/enzyme as part of a cascade of activation/inhibition of a second messenger system or an ion channel.
Single-unit recording
A technique that involves the placement of very small electrodes in or near one nerve cell to record changes in its neural activity before, during, and after some experimental treatment.
Somatocrinin
See growth hormone-releasing hormone.
Somatostatin
A polypeptide hormone that is mainly produced in the hypothalamus that inhibits the secretion of various other hormones, including somatotropin, glucagon, insulin, TSH, and gastrin.
Sperm
A haploid male gamete.
Steroid hormones
A class of structurally related fat-soluble chemicals that are derived from cholesterol and are characterized by three six-carbon rings plus one conjugated five-carbon ring.
SRY gene
Sex-determining region of the Y chromosome; the gene that is responsible for the transformation of the undifferentiated gonad into a testis.
Suprachiasmatic nuclei (SCN)
A collection of cell bodies in the hypothalamus, located above the optic chiasm, that contains one or more biological clocks responsible for the temporal organization of many physiological and behavioral parameters.
Supraoptic nuclei (SON)
A collection of cell bodies in the hypothalamus, located above the optic nerve, that produces vasopressin, which is transported to the axon terminals in the posterior pituitary gland for release into the general circulation.
Temperature-dependent sex determination
A process that occurs in animals without sex chromosomes in which sex is determined solely on the basis of the temperature at which the egg incubates.
Testicular feminization mutation (TFM)
A condition in males, also called androgen insensitivity syndrome, in which functional androgen receptors are absent. TFM is caused by a genetic mutation on the X chromosome; genetic females have an additional X chromosome to code for androgen receptors and are not affected, but males develop male internal sex organs and a female external morphology.
Testis determination factor (TDF)
A protein product arising from a gene on the Y chromosome that instructs the medulla of the germinal ridge to develop into a testis.
Testis
The male gonad, which produces steroid hormones and sperm.
Testosterone
The primary androgen secreted by most vertebrate animals.
Thyroid gland
A double-lobed endocrine gland located on or near the trachea or esophagus in vertebrates that secretes several hormones important in metabolism, including triiodothyronine and thyroxine.
Thyroid-stimulating hormone (TSH)
A glycoprotein hormone secreted by the anterior pituitary gland that stimulates and regulates activity of the thyroid gland. TSH is also called thyrotropin.
Thyrotropin
See thyroid-stimulating hormone.
Thryotropin-releasing hormone (TRH)
A tripeptide hormone secreted by the hypothalamus that stimulates the release of thyroid-stimulating hormone (TSH) (thyrotropin) from the anterior pituitary gland.
Thyroxine (T4)
The primary hormone secreted from the thyroid gland; it acts to increase oxidation rates in tissue. Also known as tetraiodothyronine.
Transgenic
Relating to an animal in which a gene has been inserted, altered, or deleted. Knockout mice are one type of transgenic mice.
Triiodothyronine (T3)
A tyrosine-based hormone that is produced by the thyroid gland and acts to increase the basal metabolic rate, affect protein synthesis, and increase sensitivity to catecholamines. T3 is less biologically active than thyroxin (T4).
Tropic hormones
Hormones from the anterior pituitary that stimulate various physiological processes, either by acting directly on target tissues or by causing other endocrine glands to release hormones.
Vagus nerve
The largest of the cranial nerves, the vagus nerve is made up of efferent fibers of the parasympathetic division of the autonomic nervous system that travel to the organs in the thorax and abdomen via specific branches. The vagus nerve also carries sensory fibers from these organs back to the brain.
Vasopressin
A nanopeptide released from the posterior pituitary gland that reduces blood pressure during serious blood loss. Also called antidiuretic hormone (ADH) because it also stimulates reabsorption of water in the kidney.
Ventromedial nucleus (VMH)
A collection of cell bodies in the hypothalamus, located near the walls of the third ventricle, that is important in the regulation of sexual behavior in female rodents.
Vesicle
A secretory granule or sac within a cell in which hormone or neurotransmitter molecules are stored.
Wolffian ducts
A duct system present in both sexes during embryonic development that connects the gonads to the exterior. During normal development, the Wolffian duct system develops into the accessory sex organs in males and regresses in females.
Zona fasciculata
The middle (and largest) zone of the adrenal cortex, consisting of orderly bands of epithelial cells. Glucocorticoid hormones are released from these cells in response to ACTH stimulation from the anterior pituitary.
Zona glomerulosa
The outermost zone of the adrenal cortex, consisting of whorls of epithelial cells. Aldosterone is released from these cells as an indirect response to low blood sodium levels.
Zona pellucida
The outer layer of cells surrounding the cell membranes of the maturing ovum.
Zona reticularis
The innermost zone of the adrenal cortex, consisting of a disorganized arrangement of epithelial cells. Sex steroid hormones are often released from this zone.
Zygote
A fertilized egg that contains both maternal and paternal DNA. A zygote develops into a blastocyst within days of conception.
Diabetes insipidus
A condition characterized by the failure of the kidneys to retain water because of a lack of antidiuretic hormone. Symptoms include excessive urination, thirst, and water intake.
Dihydrotestosterone (DHT)
A potent androgen that is derived from testosterone and binds more strongly to androgen receptors than testosterone. There are both 5-alpha and 5-beta forms of DHT.
Deoxyribonucleic acid (DNA)
A nucleic acid that codes hereditary information.
2-deoxyglucose (2-DG)
A molecular mimic of glucose that provides no nutritional value. Cells that are actively working accumulate more 2-DG than inactive cells. If 2-DG is marked with a radioactive or immunoreactive tag, active neurons can be visualized.
Up-regulation
A process similar to positive feedback in which a hormone causes an increase in the production of receptors for that hormone.