A

hormone

A is a regulating substance secreted by an endocrine gland.

target cell

is any cell with one or more receptors for a particular hormone.

 All steroid hormones have a cholesterol molecule at their core. The molecule consists of three six-sided rings and one five-sided ring joined together.

 The major categories of nonsteroid hormones are protein hormones, glycoprotein hormones, peptide hormones, and amino acid derivative hormones.

 The following is the second messenger mechanism most completely explained in the text. The hormone joins a receptor on the cell membrane. This hormone receptor complex causes a membrane protein called the

G protein

to bind to a nucleotide called

guanosine triphosphate

. This activates a second membrane protein called

adenyl cyclase

. This is an enzyme that promotes the removal of two phosphate groups from an ATP molecule in the cytosol. The product of this is cyclic adenosine monophosphate (cAMP). The cAMP acts as a second messenger within the cell. The cAMP activates protein kinases, which are a set of enzymes that activate other types of enzymes. It is this final set of specific, activated enzymes that catalyze the reaction that is characteristic of the cell's response to the hormone.

 Calmodulin is an intercellular molecule that can bind to calcium ions. The calcium calmodulin complex that forms can act as a second messenger, producing the target cell's response.

 There are nine structural classes of prostaglandins classified as A through I. The text discusses the following three classes: 

Prostaglandins A

result in an immediate fall in blood pressure accompanied by an increase in regional blood flow to several areas, including the coronary and renal systems. These effects are apparently caused by the relaxation of smooth muscle fibers in the walls of certain arteries.



Prostaglandins E

have an important role in various vascular, metabolic, and gastrointestinal functions. Vascular effects include regulation of red blood cell deformability and platelet aggregation. PGEs also have a role in systemic inflammations such as fever. PGEs also regulate hydrochloric acid secretions in the stomach, helping to prevent gastric ulcers.



Prostaglandins F

play an important role in the reproductive system. They cause uterine muscle contraction. PGFs also affect intestinal motility and are required for normal peristalsis.

 The two subdivisions of the adenohypophysis are the pars anterior and the pars intermedia.

 There are three types of cells in the anterior pituitary gland that are identified by their staining tendency: (1)

chromophobes,

which literally means "afraid of color"; (2)

acidophils

, which have an attraction to acid stains; and (3)

basophils

, which have an attraction to basic stains (no percentages are given in the text).

 Growth hormone promotes bodily growth indirectly by stimulating the liver to produce certain growth factors that accelerate amino acid transport into the cell. This allows protein anabolism at an increased rate, which allows an increased rate of growth. Growth hormone promotes growth in bone, muscle, and other tissue. Growth hormone also stimulates fat metabolism, accelerates mobilization of lipids from storage and speeds up catabolism of those lipids. It also causes blood glucose levels to rise.

 Growth hormone increases blood glucose levels, promotes fat mobilization and catabolism and promotes protein anabolism.

 The four tropic hormones secreted by the basophils of the anterior pituitary gland are thyroid-stimulating hormone, adrenocorticotropic hormone, follicle stimulating hormone, and luteinizing hormone. Follicle-stimulating hormone and luteinizing hormone are also called gonadotropins.

 Antidiuretic hormone acts to reduce the volume of urine. It does this by causing water to be reabsorbed from the tubules of the kidney and returned to the blood. This increases the water content of the blood and reduces the volume of urine.

 Oxytocin has two positive feedback mechanisms associated with it. The first is the release of milk. The mechanical and psychological stimulation of the baby's suckling triggers the release of oxytocin. This provides more milk, which allows the baby to continue to suckle, which in turn stimulates the release of more oxytocin. The other feedback mechanism is the stimulation of uterine contractions. Once uterine contractions begin, they push down on receptors in the pelvis, which triggers the release of more oxytocin, which causes more uterine contractions.

 Thyroxine and triiodothyronine synthesis occurs in tiny structural units called follicles. The colloid produced by the cuboidal cells of the follicle wall contains the protein-iodine complexes known as thyro- globulins, the precursors of thyroid hormones. The thyroid hormones are stored as thyroglobulins in the follicles until they are released into the blood. They are transported in the blood attached to plasma proteins, principally a globulin called thyroxine-binding globulin and albumin. They circulate in the blood as a hormone-globulin complex.

 The parathyroid hormone helps maintain calcium homeostasis. It acts on bone, kidney, and intestinal cells to increase the release of calcium into the blood.

 There are three zones in the adrenal cortex that are involved in hormone production: (1) The

zona glomerulosa

produces aldosterone, which stimulates the kidney tubules to conserve sodium, which triggers the release of antidiuretic hormone, which in turn results in the conservation of water

 (2) The

zona fasciculata

produces cortisol, which influences the metabolism of food molecules and has an antiinflammatory effect in large amounts. (3) The

zona reticularis

produces androgens and estrogens, which may have a role in supporting sexual function.

 The adrenal medulla secretes two important hormones, epinephrine and norepinephrine. Both of these hormones can bind to the receptors of sympathetic effectors to prolong and enhance the effects of the sympathetic nervous system.

 Alpha cells in the pancreatic islets produce glucagon. Beta cells produce insulin. Delta cells produce somatostatin, and pancreatic polypeptide cells produce pancreatic polypeptide.

 The pregnancy-promoting hormone is progesterone.

 Human chorionic gonadotropin is produced by the placenta. It serves as a signal to the mother's gonads to maintain the uterine lining rather than allow it to degenerate and fall away in menstruation.

 Atrial natriuretic hormone is secreted by cells in the atrium in response to increased stretch due to abnormally high blood volume or blood pressure. The principal effect of this hormone is to promote the loss of sodium in the urine. The increased concentration of sodium in the urine draws water from the body into the urine, which acts to decrease blood volume.

 The condition resulting from hypersecretion of growth hormone during the growth years is giantism. The condition resulting from hyposecretion of growth hormone during the growth years is pituitary dwarfism.

 Cushing syndrome causes a fatty "moon face" with thin, reddened skin.

 Exercise along with other lifestyle changes can control type 2 maturity onset diabetes mellitus, often without the need for insulin.