endocrine

Nitric oxide

Gas. Lipid soluble. Produced in endothelial cells lining blood vessels.

Prostaglandins and leukotrienes

water soluble. Eicosanoids. All cells except red blood cells secrete.

Insulin, glucagon, somatostatin, pancreatic polypeptide

water soluble. Pancreas. Peptides and proteins.

Pancreatic islet cells

. Alpha or A cells constitute about 17% of pancreatic islet cells and secrete glucagon (GLOO-ka-gon). 2. Beta or B cells constitute about 70% of pancreatic islet cells and secrete insulin (IN-soo-lin). 3. Delta or D cells constitute about 7% of pancreatic islet cells and secrete somatostatin (sō′-ma-tō-STAT-in). 4. F cells constitute the remainder of pancreatic islet cells and secrete pancreatic polypeptide.

cont

3 Quickly, the hypothalamic hormones are transported by the blood through the hypophyseal portal veins and into the secondary plexus. This direct route permits hypothalamic hormones to act immediately on anterior pituitary cells, before the hormones are diluted or destroyed in the general circulation. Within the secondary plexus the hypothalamic hormones diff use out of the bloodstream and interact with anterior pituitary cells. When stimulated by the appropriate hypothalamic-releasing hormones, the anterior pituitary cells secrete hormones into the secondary plexus capillaries. 4 From the secondary plexus capillaries, the anterior pituitary hormones drain into the hypophyseal veins and out into the general circulation. Anterior pituitary hormones then travel to target tissues throughout the body. Those anterior pituitary hormones that act on other endocrine glands are called tropic hormones (TRO- -pik) or tropins.

Histamine

Amine. Water soluble. Mast cells.

Testosterone, estrogen, progesterone

Lipid soluble. Steroid hormones. Secreted by testes/ovaries. Testosterone = In women, testosterone is produced in various locations. One quarter of the hormone is produced in the ovary, a quarter is produced in the adrenal gland, and one half is produced in the peripheral tissues from the various precursors produced in the ovaries and adrenal gland

Aldosterone, cortisol, androgens

Lipid soluble. steroid hormones secreted by adrenal cortex

somatostatin

Somatostatin acts in a paracrine manner to inhibit both insulin and glucagon release from neighboring beta and alpha cells. It may also act as a circulating hormone to slow absorption of nutrients from the gastrointestinal tract. In addition, somatostatin inhibits the secretion of growth hormone. Pancreatic polypeptide inhibits somatostatin secretion, gallbladder contraction, and secretion of digestive enzymes by the pancreas.

Water soluble

amine, peptide, protein, and eicosanoid hormones

Paracrine communication

chemical signals transfer information from cell to cell within a single tissue

The two major hormones synthesized by the adrenal medulla are

epinephrine and norepinephrine (NE), also called adrenaline and noradrenaline, respectively. The chromaff in cells of the adrenal medulla secrete an unequal amount of these hormones—about 80% epinephrine and 20% norepinephrine.

Direct communication

exchange of ions and molecules between adjacent cells across gap junctions. Occurs between two cells of the same type. Highly specialized and relatively rare

Congenital adrenal hyperplasia

is a genetic disorder in which one or more enzymes needed for synthesis of cortisol are absent. Because the cortisol level is low, secretion of ACTH by the anterior pituitary is high due to lack of negative feedback inhibition. ACTH in turn stimulates growth and secretory activity of the adrenal cortex

Control of Secretion of Glucagon and Insulin

1 Low blood glucose level (hypoglycemia) stimulates secretion of glucagon from alpha cells of the pancreatic islets. 2 Glucagon acts on hepatocytes (liver cells) to accelerate the conversion of glycogen into glucose (glycogenolysis) and to promote formation of glucose from lactic acid and certain amino acids (gluconeogenesis). 3 As a result, hepatocytes release glucose into the blood more rapidly, and blood glucose level rises. 4 If blood glucose continues to rise, high blood glucose level (hyperglycemia) inhibits release of glucagon (negative feedback). 5 High blood glucose (hyperglycemia) stimulates secretion of insulin by beta cells of the pancreatic islets. 6 Insulin acts on various cells in the body to accelerate facilitated diff usion of glucose into cells; to speed conversion of glucose into glycogen (glycogenesis); to increase uptake of amino acids by cells and to increase protein synthesis; to speed synthesis of fatty acids (lipogenesis); to slow the conversion of glycogen to glucose (glycogenolysis); and to slow the formation of glucose from lactic acid and amino acids (gluconeogenesis). 7 As a result, blood glucose level falls. 8 If blood glucose level drops below normal, low blood glucose inhibits release of insulin (negative feedback) and stimulates release of glucagon.

Glucocorticoids have the following effects:

1. Protein breakdown. Glucocorticoids increase the rate of protein breakdown, mainly in muscle fibers, and thus increase the liberation of amino acids into the bloodstream. The amino acids may be used by body cells for synthesis of new proteins or for ATP production. 2. Glucose formation. On stimulation by glucocorticoids, liver cells may convert certain amino acids or lactic acid to glucose, which neurons and other cells can use for ATP production. Such conversion of a substance other than glycogen or another monosaccharide into glucose is called gluconeogenesis. 3. Lipolysis. Glucocorticoids stimulate lipolysis (lī-POL-i-sis), the breakdown of triglycerides and release of fatty acids from adipose tissue into the blood. 4. Resistance to stress. Glucocorticoids work in many ways to provide resistance to stress. The additional glucose supplied by the liver cells provides tissues with a ready source of ATP to combat a range of stresses, including exercise, fasting, fright, temperature extremes, high altitude, bleeding, infection, surgery, trauma, and disease. Because glucocorticoids make blood vessels more sensitive to other hormones that cause vasoconstriction, they raise blood pressure. This effect would be an advantage in cases of severe blood loss, which causes blood pressure to drop. 5. Anti-inflammatory effects. Glucocorticoids inhibit white blood cells that participate in inflammatory responses. Unfortunately, glucocorticoids also retard tissue repair; as a result, they slow wound healing. Although high doses can cause severe mental disturbances, glucocorticoids are very useful in the treatment of chronic inflammatory disorders such as rheumatoid arthritis. 6. Depression of immune responses. High doses of glucocorticoids depress immune responses. For this reason, glucocorticoids are prescribed for organ transplant recipients to retard tissue rejection by the immune system.

Lipid soluble hormones

1. Steroid hormones are derived from cholesterol. Each steroid hormone is unique due to the presence of diff erent chemical groups attached at various sites on the four rings at the core of its structure (see Table 18.2). These small diff erences allow for a large diversity of functions. 2. Two thyroid hormones (T3 and T4) are synthesized by attaching iodine to the amino acid tyrosine. The presence of two benzene rings within a T3 or T4 molecule makes these molecules very lipid-soluble (see Table 18.2). 3. The gas nitric oxide (NO) is both a hormone and a neurotransmitter.

The transport proteins, which are synthesized by cells in the liver, have three functions

1. They make lipid-soluble hormones temporarily water-soluble, thus increasing their solubility in blood. 2. They retard passage of small hormone molecules through the filtering mechanism in the kidneys, thus slowing the rate of hormone loss in the urine. 3. They provide a ready reserve of hormone, already present in the bloodstream.

Control of anterior pituitary secretion

1.Above the optic chiasm are clusters of neurons called neurosecretory cells. They synthesize the hypothalamic releasing and inhibiting hormones in their cell bodies and package the hormones inside vesicles, which reach the axon terminals by fast axonal transport (see Section 12.2), where they are stored. 2 When the neurosecretory cells of the hypothalamus are excited, nerve impulses trigger exocytosis of the vesicles. The hypothalamic hormones then diff use into the blood of the primary plexus of the hypophyseal portal system.

MOA water-soluble hormones

1.Binding of hormone (first messenger) to its receptor activates G protein, which activates adenylyl cyclase 2. Activated adenylyl cyclase converts ATP to cAMP 3. cAMP serves as a second messenger to activate protein kinases 4. Activated protein kinases phosphorylate cellular proteins 5. Millions of phosphorylated proteins cause reactions that produce physiological responses

RAA

5. The level of renin in the blood increases. 6 Renin converts angiotensinogen, a plasma protein produced by the liver, into angiotensin I. 7 Blood containing increased levels of angiotensin I circulates in the body. 8 As blood flows through capillaries, particularly those of the lungs, the enzyme angiotensin-converting enzyme (ACE) converts angiotensin I into the hormone angiotensin II. 9 Blood level of angiotensin II increases. 10 Angiotensin II stimulates the adrenal cortex to secrete aldosterone. 11 Blood containing increased levels of aldosterone circulates to the kidneys. 12 In the kidneys, aldosterone increases reabsorption of Na+, which in turn causes reabsorption of water by osmosis. As a result, less water is lost in the urine. Aldosterone also stimulates the kidneys to increase secretion of K+ and H+ into the urine. 13 With increased water reabsorption by the kidneys, blood volume increases. 14 As blood volume increases, blood pressure increases to normal. 15 Angiotensin II also stimulates contraction of smooth muscle in the walls of arterioles. The resulting vasoconstriction of the arterioles increases blood pressure and thus helps raise blood pressure to normal.

pars intermedia

A third region of the pituitary gland called the pars intermedia atrophies during human fetal development and ceases to exist as a separate lobe in adults (see Figure 18.20b). However, some of its cells migrate into adjacent parts of the anterior pituitary, where they persist.

The major androgen secreted by the adrenal gland is dehydroepiandrosterone (DHEA

Aft er puberty in males, the androgen testosterone is also released in much greater quantity by the testes. Thus, the amount of androgens secreted by the adrenal gland in males is usually so low that their eff ects are insignificant. In females, however, adrenal androgens play important roles. They promote libido (sex drive) and are converted into estrogens (feminizing sex steroids) by other body tissues. Aft er menopause, when ovarian secretion of estrogens ceases, all female estrogens come from conversion of adrenal androgens.

interesting

Although blood glucose level is the most important regulator of insulin and glucagon, several hormones and neurotransmitters also regulate the release of these two hormones. In addition to the responses to blood glucose level just described, glucagon stimulates insulin release directly; insulin has the opposite eff ect, suppressing glucagon secretion. As blood glucose level declines and less insulin is secreted, the alpha cells of the pancreas are released from the inhibitory eff ect of insulin so they can secrete more glucagon. Indirectly, growth hormone (GH) and adrenocorticotropic hormone (ACTH) stimulate secretion of insulin because they act to elevate blood glucose.

Melatonin

Amine. Water soluble. Pineal gland.

Epinephrine, norepinephrine

Amine. Water soluble. Produced in adrenal medulla.

endocrine vs exocrine

An important distinction exists between exocrine and endocrine glands. Whereas exocrine glands secrete substances into a ductal system to an epithelial surface, endocrine glands secrete products directly into the bloodstream. The pancreas is both an endocrine gland and an exocrine gland. Roughly 99% of the exocrine cells of the pancreas are arranged in clusters called acini.

eppy & noreppy

By increasing heart rate and force of contraction, epinephrine and norepinephrine increase the output of the heart, which increases blood pressure. They also increase blood flow to the heart, liver, skeletal muscles, and adipose tissue; dilate airways to the lungs; and increase blood levels of glucose and fatty acids.

Estrogen

Estrogen is produced in sizable quantities in the testis, as well as the brain

Androgens

In both males and females, the adrenal cortex secretes small amounts of weak androgens.

inhibin

Inhibits secretion of FSH from anterior pituitary

Various target cells respond differently to the same hormone.

Insulin, for example, stimulates synthesis of glycogen in liver cells and synthesis of triglycerides in adipose cells.

Calcitriol

Lipid soluble. Steroid hormone. Active form of vitamin D. Secreted by kidneys.

Hormone Transport in the Blood

Most water-soluble hormone molecules circulate in the watery blood plasma in a "free" form (not attached to other molecules), but most lipid-soluble hormone molecules are bound to transport proteins.

pars distalis

The anterior pituitary consists of two parts in an adult: The pars distalis is the larger portion, and the pars tuberalis (PARS too-be′-RAL-is) forms a sheath around the infundibulum.

Glucocorticoids

The glucocorticoids, which regulate metabolism and resistance to stress, include cortisol , corticosterone, and cortisone. Of these three hormones secreted by the zona fasciculata, cortisol is the most abundant, accounting for about 95% of glucocorticoid activity

Adrenal medulla

The inner region of the adrenal gland, = the adrenal medulla, is a modified sympathetic ganglion of the autonomic nervous system (ANS). It develops from the same embryonic tissue as all other sympathetic ganglia, but its cells, which lack axons, form clusters around large blood vessels. Rather than releasing a neurotransmitter, the cells of the adrenal medulla secrete hormones. The hormone-producing cells, called chromaff in cells, are innervated by sympathetic preganglionic neurons of the ANS. Because the ANS exerts direct control over the chromaff in cells, hormone release can occur very quickly

Water soluble hormones

Water soluble hormones= 1. Amine hormones (a-MEN) are synthesized by decarboxylating (removing a molecule of CO2) and otherwise modifying certain amino acids. They are called amines because they retain an amino group (NH3 +). The catecholamines—epinephrine, norepinephrine, and dopamine—are synthesized by modifying the amino acid tyrosine. Histamine is synthesized from the amino acid histidine by mast cells and platelets. Serotonin and melatonin are derived from tryptophan. 2. Peptide hormones and protein hormones are amino acid polymers. The smaller peptide hormones consist of chains of 3 to 49 amino acids. the larger protein hormones include 50 to 200 amino acids. Examples of peptide hormones are antidiuretic hormone and oxytocin. protein hormones include growth hormone and insulin. Several of the protein hormones, such as thyroid-stimulating hormone, have attached carbohydrate groups and thus are glycoprotein hormones. 3. The eicosanoid hormones are derived from arachidonic acid, a 20-carbon fatty acid. The two major types of eicosanoids are prostaglandins (PGs) and leukotrienes (LTs). The eicosanoids are important local hormones, and they may act as circulating hormones as well.;

Zona fasciculata

Zona fasciculata is the layer situated between the glomerulosa and reticularis. This layer is responsible for producing glucocorticoids, such as 11-deoxycorticosterone, corticosterone, and cortisol in humans. Cortisol enhances the activity of other hormones including glucagon and catecholamines.

adrenocorticotropic hormone

a hormone from the anterior pituitary → stimulates the release of cortisol by the adrenal cortex.

The anterior pituitary (anterior lobe)

also called the adenohypophysis, accounts for about 75% of the total weight of the gland and is composed of epithelial tissue. The anterior pituitary consists of two parts in an adult: The pars distalis is the larger portion, and the pars tuberalis forms a sheath around the infundibulum.

The posterior pituitary (posterior lobe),

also called the neurohypophysis, is composed of neural tissue. It also consists of two parts: the pars nervosa, the larger bulbar portion, and the infundibulum.

The pineal gland secretes melatonin

an amine hormone derived from serotonin. Melatonin appears to contribute to the setting of the body's biological clock, which is controlled by the suprachiasmatic nucleus of the hypothalamus.

phosphodiesterase

inactivates cAMP. Thus, the cell's response is turned off unless new hormone molecules continue to bind to their receptors in the plasma membrane.

Parathyroid hormone

parathyroid glands

Receptors

receptors for lipid-soluble hormones are located inside target cells. The receptors for water-soluble hormones are part of the plasma membrane of target cells.

Somatotrophs

secrete growth hormone (GH), also known as human growth hormone (hGH) or somatotropin. Growth hormone stimulates general body growth and regulates aspects of metabolism.

Lactotrophs

secrete prolactin (PRL), which initiates milk production in the mammary glands.

Thyrotrophs

secrete thyroid-stimulating hormone (TSH), also known as thyrotropin. TSH controls the secretions and other activities of the thyroid gland.

Gonadotrophs

secrete two gonadotropins: follicle-stimulating hormone (FSH) and luteinizing hormone (LH). FSH and LH both act on the gonads (testes and ovaries). In men, they stimulate the testes to produce sperm and to secrete testosterone. In women, they stimulate the ovaries to mature oocytes (eggs) and to secrete estrogens and progesterone.

All hypothalamic releasing and inhibiting hormones

secreted by hypothalamus. Water soluble. Peptides and proteins. Oxytocin and antidiuretic hormone = water soluble. Posterior pituitary

Anterior pituitary cells

somatotrophs, thyrotrophs, gonadotrophs, lactotrophs and corticotrophs Corticotrophs = secrete adrenocorticotropic hormone (ACTH), also known as corticotropin, which stimulates the adrenal cortex to secrete glucocorticoids such as cortisol. Some corticotrophs, remnants of the pars intermedia, also secrete melanocyte stimulating hormone (MSH).

Thyroid hormones

t3 (triiodothyronine) and t4 (thyroxine). Lipid soluble. Produced in thyroid gland follicular cells

calcitonin

thyroid glands (parafollicular cells). Proteins and peptides. Water soluble.

Growth hormone, thyroid-stimulating hormone, adrenocorticotropic hormone, follicle-stimulating hormone, luteinizing hormone, prolactin, melanocytestimulating hormone

water soluble. Peptides and proteins. anterior pituitary

Insulin secretion is also stimulated by:

• Acetylcholine, the neurotransmitter liberated from axon terminals of parasympathetic vagus nerve fibers that innervate the pancreatic islets • The amino acids arginine and leucine, which would be present in the blood at higher levels aft er a protein-containing meal • Glucose-dependent insulinotropic peptide (GIP),* a hormone released by enteroendocrine cells of the small intestine in response to the presence of glucose in the gastrointestinal tract