A mediator molecule that is released in one part of the body but regulates the activity of cells in other parts of the body.
One example of a mediator that acts as both a hormone and a neurotransmitter is _______, which is released as a neurotransmitter by sympathetic postganglionic neurons and as a hormone by chromaffin cells of the adrenal medullae.
Glands that secrete their products into ducts that carry the secretions into body cavities, into the lumen of an organ, or to the outer surface of the body. Includes sudoriferous (sweat), sebaceous (oil), mucous, and digestive glands.
Glands that secrete their products (hormones) into the interstitial fluid surrounding the secretory cells rather than into ducts. Includes the pituitary, thyroid, parathyroid, adrenal, and pineal glands, as well as some organs and tissues that are not exclusively classified as glands but contain cells that secrete hormones; these organs work together to create the endocrine system.
The system composed of all the endocrine glands and hormone-secreting cells in organs like the pancreas and kidneys.
The science of the structure and function of the endocrine glands and the diagnosis and treatment of disorders of the endocrine system.
Hormones, like neurotransmitters, influence their target cells by chemically binding to specific protein _______.
The resulting depletion of target-cell receptors due to an excess amount of hormone; this makes a target cell less sensitive to a hormone.
The resulting increase of target-cell receptors due to hormone deficiency; this makes a target cell more sensitive to a hormone.
Hormones that pass form the secretory cells that make them into interstitial fluid and then into the blood.
Hormones that act locally on neighboring cells or on the same cell that secreted them without first entering the bloodstream.
Local hormones that act on neighboring cells.
Local hormones that act on the same cell that secreted them.
Steroid hormones, thyroid hormones, and nitric oxide are _______ hormones.
Lipid-soluble hormones derived from cholesterol that have a large diversity of functions.
Lipid-soluble hormones that are synthesized by attaching iodine to the amino acid tyrosine.
Lipid-soluble hormone/neurotransmitter that is synthesized by the enzyme nitric oxide synthase.
Amine hormones, peptide and protein hormones, and eicosanoid hormones are _______ hormones.
Water-soluble hormones that are synthesized by decarboxylating (removing a molecule of CO₂) and otherwise modifying certain amino acids.
peptide and protein hormones
Water-soluble hormones that are amino acid polymers.
Protein hormones, such as thyroid-stimulating hormone, with attached carbohydrate groups.
Water-soluble hormones that are derived from arachidonic acid, a 20-carbon fatty acid. The two major types of this hormone are prostaglandins and leukotrienes. They are important local hormones, and they may act as circulating hormones as well.
prostaglandins and leukotrienes
The two major types of eicosanoid hormones.
Proteins that bind to most lipid-soluble hormone molecules making them temporarily water-soluble, slowing the rate of hormone loss in the urine, and providing a ready reserve or hormone, already present in the bloodstream.
The percentage of lipid-soluble hormone molecules that are not bound to a transport protein; they diffuse out of capillaries, bind to receptors, and trigger responses.
Alters gene expression by turning specific genes of nuclear DNA on or off.
When a water-soluble hormone binds to its receptor at the outer surface of the plasma membrane, it acts as the _______ during water-soluble hormone action.
During water-soluble hormone action, the first messenger stimulates the production of the _______ inside the cell, where specific hormone-stimulated responses take place. One common example is cyclic AMP or cAMP.
A common second messenger broken down by adenylate cyclase during water-soluble hormone action.
Activated by the hormone-receptor complex, this in turn then activates adenylate cyclase during water-soluble hormone action.
The enzyme that converts ATP into cAMP during water-soluble hormone action.
An enzyme that phosphorylates other cellular proteins (such as enzymes).
The enzyme that inactivates cAMP for a brief period.
The actions of some hormones on target cells require a simultaneous or recent exposrue to a second hormone. In such cases, the second hormone is said to have a _______ effect.
When the effect of two hormones acting together is greater or more extensive than the effect of each hormone acting alone, the two hormones are said to have a _______ effect.
When one hormone opposes the actions of another hormone, the two hormones are said to have _______ effects.
A small endocrine gland occupying the hypophyseal fossa of the sphenoid bone and attached to the hypothalamus by the infundibulum. Also called the hypophysis.
The small region of the brain below the thalamus that is the major link between the nervous and endocrine systems.
The stalk that attaches the pituitary gland to the hypothalamus; part of the posterior pituitary.
anterior pituitary (anterior lobe) or adenohypophysis
The portion of the pituitary gland that is composed of epithelial tissue and secretes hormones that regulate a wide range of bodily activities from growth to reproduction. Release of these hormones is stimulated by releasing hormones and suppressed by inhibiting hormones from the hypothalamus.
The larger portion of the anterior lobe of the pituitary gland.
The sheath formed around the infundibulum; part of the anterior pituitary.
posterior pituitary (posterior lobe) or neurohypophysis
The portion of the pituitary gland that is composed of neural tissue and does not synthesize hormones, but stores and releases two hormones. It consists of axons and axon terminals of more than 10,000 hypothalamic neurosecretory cells.
The larger bulbar portion of the posterior pituitary.
A third region of the pituitary gland that atrophies during human fetal development and ceases to exist as a separate lobe in adults. However, some of its cells migrate into adjacent parts of the anterior pituitary, where they persist.
Release of anterior pituitary hormones is stimulated by _______ hormones and suppressed by _______ hormones from the hypothalamus.
hypophyseal portal system
In the _______, blood flows from capillaries in the hypothalamus into portal veins that carry blood to capillaries of the anterior pituitary.
superior hypophyseal arteries
Branches of the internal cartoid arteries that bring blood into the hypothalamus. They divide into the primary plexus of the hypophyseal portal system at the junction of the median eminence of the hypothalamus and the infundibulum.
At the junction of the median eminence of the hypothalamus and the infundibulum, the superior hypophyseal arteries divide into a capillary network called the _______ of the hypophyseal portal system.
hypophyseal portal veins
From th eprimary plexus, blood drains into the _______ that pass down the outside of the infundibulum.
In the anterior pituitary, the hypophyseal portal veins divide again and form another capillary network called the _______ of the hypophyseal portal system.
Clusters of specialized neurons above the optic chiasm that synthesize the hypothalamic releasing and inhibiting hormones in their cell bodies and package the hormones inside vesicles, which reach the axon terminals by axonal transport.
Anterior pituitary hormones that act on other endocrine glands.
Anterior pituitary cells that secrete human growth hormone (hGH), also known as somatotropin. Human growth hormone in turn stimulates several tissues to secrete insulinlike growth factors (somatomedins), hormones that stimulate general body growth and regulate aspects of metabolism.
Anterior pituitary cells that secrete thyroid-stimulating hormone (TSH), also known as thyrotropin.
human growth hormone (hGH)
This hormone, released from somatotrophs in the anterior pituitary, stimulates several tissues to secrete insulinlike growth factors, hormones that stimulate general body growth and regulate aspects of metabolism.
thyroid-stimulating hormone (TSH)
This hormone, released by thyrotrophs in the anterior pituitary, controls the secretions and other activities of the thyroid gland.
Anterior pituitary cells that secrete two gonadotropins: follicle-stimulating hormone (FSH) and lutenizing hormone (LH).
follicle-stimulating hormone (FSH); luteinizing hormone (LH)
Two gonadotropins, _______ and _______, released from gonadotrophs in the anterior pituitary, act on the gonads. They stimulate secretion of estrogens and progesterone and the maturation of oocytes in the ovaries, and they stimulate sperm production and secretion of testosterone in the testes.
Anterior pituitary cells that secrete prolactin (PRL).
Hormone released by lactotrophs in the anterior pituitary that initiates milk production int he mammary glands.
Anterior pituitary cells that secrete adrenocorticotropic hormone (ACTH), also known as corticotropin. Some corticotrophs, remnants of the pars intermedia, also secrete melanocyte-stimulating hormone (MSH).
adrenocorticotropic hormone (ACTH)
Hormone released by corticotrophs in the anterior pituitary that stimulate the adrenal cortex to secrete glucocorticoids such as cortisol; also called corticotropin.
The most numerous cells in the anterior pituitary.
human growth hormone (hGH)
The most plentiful anterior pituitary hormone.
An abnormally low blood glucose concentration.
An abnormally high blood glucose concentration.
thyroid-stimulating hormone (TSH)
This anterior pituitary hormone stimulates the synthesis and secretion of the two thyroid hormones, triiodothyronine (T₃) and thyroxine (T₄), both produced by the thyroid gland.
follicle-stimulating hormone (FSH)
This anterior pituitary hormone initiates the development of several ovarian follicles, saclike arrangements of secretory cells that surround a developing oocyte. It also stimulates follicular cells to secrete estrogens. In males, it stimulates sperm production in the testes.
luteinizing hormone (LH)
This anterior pituitary hormone triggers ovulation, the release of a secondary oocyte (future ovum) by an ovary. It stimulates formation of the corpus luteum (structure formed after ovulation ) in the ovary and the secretion of progesterone (another female sex hormone) by the corpus luteum. Together with FSH, it also stimulates secretion of estrogens by ovarian cells. In males, it stimluates cells in the testes to secrete testosterone.
This anterior pituitary hormone, together with other hormones, initiates and maintains milk production by the mammary glands.
adrenocorticotropic hormone (ACTH)
This anterior pituitary hormone controls the production and secretion of cortisol and other glucocorticoids by the cortex (outer portion) of the adrenal glands.
melanocyte-stimulating hormone (MSH)
This anterior pituitary hormone increases skin pigmentation in amphibians by stimulating hte dispersion of melanin granules in melanocytes. Its exact role in humans is unknown, but the presence of MSH receptors in the brain suggests it may influence brain activity.
The cell bodies of the neurosecretory cells are in the paraventricular and supraoptic nuclei of the hypothalamus; their axons form the _______ tract; this tract begins in the hypothalamus and ends near blood capillaries in the posterior pituitary.
oxytocin (OT); antidiuretic hormone (ADH)
The neuron cell bodies in the paraventricular nucleus synthesize the hormone _______ and the neuronal cell bodies in the supraoptic nucleus produce _______, also called vasopressin.
The axon terminals in the posterior pituitary are associated with specialized neuroglia called _______. These cells have a supporting role similar to that of astrocytes.
inferior hypophyseal arteries
Blood is supplied to the posterior pituitary by the _______, which branch from the internal cartoid arteries.
In the posterior pituitary, the inferior hypophyseal arteries drain into the _______ of the infundibular process, a capillary network that receives secreted oxytocin and antidiuretic hormone.
posterior hypophyseal veins
From the capillary plexus of the posterior pituitary, hormones pass into the _______ for distribution to target cells in other tissues.
This posterior pituitary hormone affects a mother's uterus and breasts during and after pregnancy. Stretching of the cervix during delivery stimulates its release, and it enhances contraction of smooth muscle cells in the walls of the uterus (creating a positive feedback loop). After delivery, it stimulates milk ejection ("letdown") from the mammary glands in response to the mechanical stimulus provided by a suckling infant. Its function in males and unpregnant females is undetermined, but experiments on animals suggests that it supplies us with the protective instinct over our children. It may also be responsible, in part, for the feelings of sexual pleasure during and after intercourse.
antidiuretic hormone (ADH)
This posterior pituitary hormone is a substance that decreases urine production. It also decreases water lost through sweating and causes constriction of arterioles, which increases blood pressure, hence its other name, vasopressin.
Neurons in the hypothalamus that monitor blood osmotic pressure.
The butterfly-shaped gland that is located just inferior to the larynx (voice box). It is composed of right and left lateral lobes, one on either side of the trachea, that are connected by an isthmus anterior to the trachea.
lateral lobes; isthmus
The thyroid gland is composed of right and left _______, one on either side of the trachea, that are connected by an _______ anterior to the trachea.
About 50% of thyroid glands have a small third lobe, called the _______. It extends superiorly from the isthmus.
Microscopic spherical sacs called _______ make up most of the thyroid gland.
The wall of each thyroid follicle consists of cells called _______, most of which extend to the lumen of the follicle. A basement membrane surrounds each follicle.
thyroxine; triiodothyronine; thyroid hormones
The follicicular cells of the thyroid gland produce two hormones: _______, which is also called tetraiodothyronine or T₄, because it contains four atoms of iodine, and _______, or T₃, which contains three atoms of iodine. T₃ and T₄ together are also known as _______.
A few cells called _______ or C cells lie between thyroid follicles. They produce the hormone calcitonin.
This hormone, produced by C cells in the thyroid gland, helps regulate calcium homeostasis.
A large glycoprotein that is produced in the rough endoplasmic reticulum, modified in the Golgi complex, and packaged into secretory vesicles of the follicular cells of the thyroid gland.
thyroxine-binding globulin (TBG)
More than 99% of both the T₃ and the T₄ combine with transport proteins in the blood, mainly _______.
basal metabolic rate (BMR)
Thyroid hormones increase _______, the rate of oxygen consumption under standard or basal conditions (awake, at rest, and fasting), by stimulating the use of cellular oxygen to produce ATP. When this increases, cellular metabolism of carbohydrates, lipids, and proteins increases.
As cells produce and use more ATP, more heat is given off, and body temperature rises. This phenomenon is called the _______ effect.
The actions of _______ are as follows: 1) They increase basal metabolic rate (BMR), 2) They play an important role in maintaining normal body temperature, 3) They stimulate protein synthesis and increase the use of glucose and fatty acids for ATP production, and also increase lipolysis and enhance cholesterol excretion, thus reducing blood cholesterol level, 4) They enhance some actions of the catecholamines (norepinephrenine and epinephrine) by up-regulating beta receptors, and 5) They accelerate body growth with the help of human growth hormone and insulin.
This thyroid gland hormone can decrease the level of calcium in the blood by inhibiting the action of oseoclasts, the cells that break down bone extracellular matrix.
Partially embedded in the posterior surface of the lateral lobes of the thyroid gland are several small, round masses of tissue called the _______.
The more numerous cells in the parathyroid glands that produce parathyroid hormone (PTH) or parathormone are called _______ (principal) cells.
The other type of cell found in the parathyroid gland; its function is unknown in a normal parathyroid gland, but its presence clearly helps to identify the parathyroid gland histologically due to its unique staining characteristics. Furthermore, in a cancer of the parathyroid glands, these cells secrete excess PTH.
parathyroid hormone (PTH)
This parathyroid hormone is the major regulator of the levels of calcium (Ca²⁺), magnesium (Mg²⁺), and phosphate (HPO₄²⁻) ions in the blood. Its specific action is to increase the number and activity of osteoclasts. the result is elevated bone resorption, which releases ionic calcium (Ca²⁺) and phosphates (HPO₄²⁻) into the blood. It also acts on the kidneys, increasing Ca²⁺ and Mg²⁺ levels and decreasing HPO₄²⁻ levels, and also promoting the formation of calcitrol, the active form of vitamin D.
The paired _______ (suprarenal) glands, one of which lies superior to each kidney in the retroperitoneal space, have a flattened pyramidal shape.
adrenal cortex; adrenal medulla
During embryonic development, the adrenal glands differentiate into two structurally and functionally distinct regions: a large, peripherally located _______, comprimising 80-90% of the gland, and a small, centrally located _______.
The part of the adrenal glands that produces steroid hormones that are essential for life.
The _______ produces three catecholamine hormones -- norepinephrine, epinephrine, and a small amount of dopamine.
The outer zone of of the adrenal cortex, just deep to the connective tissue capsule. Its cells, which are closely packed and arranged in spherical and arched columns, secrete hormones called mineralocorticoids because they affect mineral homeostasis.
The middle zone of the adrenal cortex that is the widest of the three zones and consists of cells arranged in long, straight columns. Its cells secrete mainly glucocorticoids, primarily cortisol, so named because they affect glucose homeostasis.
The innermost zone of the adrenal cortex, whose cells are arranged in branching cords. They syntheize small amounts of weak androgens, steroid hormones that have masculinizing effects.
The major mineralocorticoid; regulates homeostasis of two mineral ions -- namely, sodium ions (Na⁺) and potassium ions (K⁺)-- and helps adjust blood pressure and blood volume. It also promotes excretion of H⁺ in the urine; this removal of acids from the body can help prevent acidosis.
renin-angiotensin-aldosterone (RAA) pathway
The name of the pathway that controls secretion of aldosterone.
The enzyme whose release is triggered in the juxtaglomerular cells of the kidneys in response to lowered blood pressure. When it reaches the blood, it converts angiotensinogen, a plasma protein produced by the liver, into angiotensin I.
angiotensin-converting enzyme (ACE)
As blood flows through capillaries, particularly those of the lungs, the enzyme _______ converts angiotensin I into the hormone angiotensin II.
The _______, which regulate metabolism and resistance to stress, include cortisol (also called hydrocortisone), corticosterone, and cortisone. Of these, cortisol is the most abundant.
corticotropin-releasing hormone (CRH)
Low blood levels of glucocorticoids, m ainly cortisol, stimulate neurosecretory cells in the hypothalamus to secrete _______. This hormone (together with a low level of cortisol) promotes the release of ACTH from the anterior pituitary.
Conversion of a substance other than glycogen or another monosaccharide into glucose.
The major androgen secreted by the adrenal gland.
Hormone-producing cells in the adrenal medullae that are innervated by sympathetic preganglionic neurons of the ANS.
epinephrine and norepinephrine (NE)
The two major hormones synthesized by the adrenal medulla are _______ and _______, also called adrenaline and noradrenaline, respectively.
This organ is both an endocrine gland and an exocrine gland; it is a flattened organ located in the curve of the duodenum, and consists of a head, a body, and a tail.
Roughly 99% of the exocrine cells of the pancreas are arranged in clusters called _______. They produce digestive enzymes, which flow into the gastrointestinal tract through a network of ducts.
Scattered among the exocrine acini of the pancreas are 1-2 million tiny clusters of endocrine tissue called _______ or islets of Langerhans.
alpha (A) cells
These cells constitute about 17% of pancreatic islet cells and secrete glucagon.
beta (B) cells
These cells constitute about 70% of pancreatic islet cells and secrete insulin.
delta (D) cells
These cells constitute about 7% of pancreatic islet cells and secret somatostatin.
These cells constitute the small remainder of pancreatic islet cells and secrete pancreatic polypeptide.
glucagon; insulin; somatostatin; pancreatic polypeptide
Although the interactions of the four pancreatic hormones are complex and not completely understood, we do know that _______ raises blood glucose level, and _______ lowers it. _______ acts in a paracrine manner to inhibit both insulin and glucagon release from neighboring beta and alpha cells. In addition, it inhibits the secretion of growth hormone. _______ inhibits somatostatin secretion, gallbladder contraction, and secretion of digestive enzymes by the pancreas.
The organs that produce gametes-- sperm in males and oocytes in females. They also secrete hormones.
Paired oval bodies located in the female pelvic cavity that produce several steroid hormones, including two estrogens and progesterone. They also produce inhibin.
estrogens and progesterone
These female sex hormones, along with FSH and LH from the anterior pituitary, regulate the menstrual cycle, maintain pregnancy, and prepare the mammary glands for lactation. They also promote enlargement of the breasts and widening of the hips at puberty, and help maintain these female secondary sex characteristics.
A protein hormone that inhibits secretion of follicle-stimulating hormone (FSH); produced by the ovaries.
During pregnancy, the ovaries and placenta produce a peptide hormone called _______, which increases the flexibility fo the pubic symphysis during pregnancy and helps dilate the uterine cervix during labor and delivery.
The male gonads that are oval glands that lie in the scrotum. They mainly produce and secrete testosterone, an androgen or male sex hormone. They also produce inhibin.
This male sex hormone stimulates descent of the testes before birth, regulates production of sperm, and stimulates the development and maintenance of male secondary sex characteristics, such as beard growth and deepening of the voice.
A small endocrine gland attatched to the roof of the third ventricle of the brain at the midline; part of the epithalamus and covered by the pia mater; consists of masses of neuroglia and secretory cells called pinealocytes.
The pineal gland secretes the hormone _______, and amine hormone derived from serotonin. This hormone appears to contriute to the setting of the body's biological clock, which is controlled by the suprachiasmic nucleus of the hypothalamus. It is also thought to promote sleepiness.
The organ located behind the sternum between the lungs; produces thymosin, thymic humoral factor (THF), thymic factor (TF), and thymopoietin.
The hormones produced by the thymus promote the maturation of _______ and may retard the aging process.
A modified prostaglandin (PG) that constricts blood vessels and promotes platelet activation.
Eicosanoids that alter smooth muscle contraction, glandular secretions, blood flow, reproductive processes, platelet function, respiration, nerve impulse transmission, lipid metabolism, and immune responses. They also have roles in promoting inflammation and fever, and in intensifying pain.
Eicosanoids that stimulate chemotaxis (attraction to a chemical stimulus) of white blood cells and mediate inflammation.
Recently discovered hormones that play important roles in tissue development, growth, and repair. They are mitogenic substances-- they cause growth by stimulating cell division.
Stress that prepares us to meet certain challenges and thus is helpful.
Stress that is harmful.
Any stimulus that produces a stress response is called a _______.
stress response or general adaptation syndrome (GAS)
Changes in the body elicited by a variety of stressful conditions of noxious agents. They are controlled mainly by the hypothalamus.
The first stage of stress response that is initiated by nerve impulses fromt he hypothalamus to the sympathetic division of the autonomic nervous sytem (ANS), including the adrenal medulla, quickly mobilizes the body's resources for immediate physical activity.
The second stage of stress response that is initiated in large part by hypothalamic releasing hormones and is a longer-lasting response than fight-or-flight.
The third stage of stress response that may occur if the body becomes so depleted that they cannot sustain the resistance stage.
About 3 weeks after fertilization, the _______ (hypophysis) begins to develop from two different regions of the ectoderm.
The posterior pituitary (neurohypophysis) is derived from an outgrowth of ectoderm called the _______, located on the floor of the hypothalamus.
hypophyseal (Rathke's) pouch
The anterior pituitary (adenohypophysis) is derived from an outgrowth of ectoderm from the roof of the mouth called the _______.
thyroid gland; thyroid diverticulum
The _______ develops during the fourth week as a midventral outgrowth of endoderm, called the _______, from the floor of the pharynx at the level of the second pair of pharyngeal pouches.
parathyroid glands; pharyngeal pouches
The _______ develop during the fourth week from endoderm as outgrowths from the third and fourth _______, which help to form the structures of the head and neck.
The _______ is derived fromt he same region of mesoderm that produces the gonads.
adrenal medulla; neural crest
The _______ is derived from ectoderm from the _______ cells that migrate to the superior pole of the kidney.
The _______ develops during the fifth through seventh weeks from two outgrowths of endoderm fromt the part of the _______ that later becomes the duodenum.
The _______ arises during the seventh week as an outgrowth between the thalamus and colliculi of the midbrain from ectoderm associated with the diencephalon.
The _______ arises during the fifth week from endoderm of the third pharyngeal pouches.
Of the three hormones secreted by the zona fasciculata [cortisol (also called hydrocortisone), corticosterone, and cortisone], _______ is the most abundant, accounting for about 95% of glucocorticoid activity.