Endocrine System PDF

ENDOCRINE SYSTEM HYPOTHALAMUS and PITUITARY GLAND OVERVIEW 1. PITUITARY GLAND/hypophysis - was called the “master”...

ENDOCRINE SYSTEM HYPOTHALAMUS and PITUITARY GLAND OVERVIEW 1. PITUITARY GLAND/hypophysis - was called the “master” endocrine gland because it secretes several hormones that control The hormones of the endocrine system contribute to homeostasis other endocrine glands. (secretes seven) by regulating the activity and growth of target cells in your body. Hormones also regulate your metabolism. 2. HYPOTHALAMUS – master of pituitary gland, a small region of In girls, ESTROGEN promote accumulation of adipose tissue the brain below the thalamus is the major link between the nervous in the breasts and hips, sculpting a feminine shape. and endocrine systems. (synthesize at least nine different hormones) At the same time or a little later, increasing levels of o Together, these hormones play important roles in the TESTOSTERONE in boys begin to help build muscle mass regulation of virtually all aspects of growth, and enlarge the vocal cords, producing a lower-pitched development metabolism, and homeostasis. voice. NERVOUS SYSTEM - acts through nerve impulses PITUITARY GLAND conducted along axons of neurons. At synapses, nerve impulses trigger the release of mediator (messenger) 1. PITUITARY GLAND - is a pea-shaped structure that measures 1– molecules called neurotransmitters 1.5 cm (0.5 in.) in diameter and lies in the hypophysial fossa of the ENDOCRINE SYSTEM - controls body activities by sella turcica of the sphenoid bone. releasing mediators, called hormones. HORMONE - is a molecule that is released in one part of 2. INFUNDIBULAR STALK - attaches PG to the hypothalamus, the body but regulates the activity of cells in other parts of has two anatomically and functionally separate portions: the body. A. ANTERIOR PITUITARY (anterior o Most hormones enter interstitial fluid and then the lobe)/adenohypophysis) - accounts for about 75% of the bloodstream. total weight of the gland and is composed of epithelial o The circulating blood delivers hormones to cells tissue. throughout the body. o Responses of the endocrine system often are slower a. PARS DISTALIS - is the larger portion than responses of the nervous system b. PARS TUBERALIS - forms a sheath around the Nervous System – acts on specific muscles and glands infundibular stalk Endocrine System – regulates virtually in all types of body cells. B. POSTERIOR PITUITARY (posterior lobe)/ (much broader in influence) neurohypophysis - is composed of neural tissue. NS & ES function together as an interlocking a. PARS NERVOSA - the larger bulbar portion, “supersystem.” and the infundibular stalk. b. PARS INTERMEDIA - third region of the pituitary gland that atrophies during human fetal development and ceases to exist as a separate lobe in adults. 3. ANTERIOR PITUITARY - secretes hormones that regulate a wide range of bodily activities, from growth to reproduction. 1. SOMATOTROPHIC CELLS - secrete GROWTH HORMONE (GH)/somatotropin. Growth hormone EXOCRINE GLANDS - secrete their products into ducts that carry stimulates general body growth and regulates aspects of the secretions into body cavities, into the lumen of an organ, or to the metabolism. outer surface of the body. 2. THYROTROPHIC CELLS - secrete THYROID o sudoriferous, sebaceous, mucous, and digestive glands STIMULATING HORMONE (tSH)/thyrotropin. TSH ENDOCRINE GLANDS - secrete their products (hormones) into controls the secretions and other activities of the thyroid the interstitial fluid surrounding the secretory cells rather than into gland. ducts. 3. GONADOTROPHIC CELLS - secrete two o pituitary, thyroid, parathyroid, suprarenal, and pineal glands gonadotropins: FOLLICLE STIMULATING HORMONE (FSH) and LUTEINIZING HORMONE HORMONE-SECRETING CELLS - are not exclusively classified (LH). FSH and LH both act on the gonads (testes and as endocrine glands but contain cells that secrete hormones. ovaries). + hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, In men, they stimulate the testes to produce liver, small intestine, skin, heart, adipose tissue, and placenta. sperm and to secrete testosterone. In women, they stimulate the ovaries to mature oocytes (eggs) +Taken together, all endocrine glands and hormone-secreting cells and to secrete estrogens and progesterone. constitute the constitute the ENDOCRINE SYSTEM  4. PROLACTIN CELLS - secrete PROLACTIN (pRL), 2 hormones released by neuronal cell bodies of both the which initiates milk production in the mammary glands. paraventricular and the supraoptic nuclei: 5. CORTICOTROPHIC CELLS – secrete OXYTOCIN (OT) – contraction of the uterus, milk ejection ADRENOCORTICOTROPHIC HORMONE (aCtH)/corticotropin, which stimulates the suprarenal ANTIDIURETIC HORMONE (aDH)/vasopressin – decreases cortex to secrete glucocorticoids such as CORTISOL. urine production Some corticotrophs, remnants of the pars 1. OXYTOCIN (OT) intermedia, also secrete MELANOCYTE- FEMALE: During and after delivery of a baby, it affects two target STIMULATING HORMONE (MSH). tissues: the mother’s uterus and breasts. During delivery, stretching of the cervix of the uterus stimulates the release of oxytocin which, in turn, enhances contraction of smooth muscle fibers in the wall of the uterus After delivery, it stimulates milk ejection from the mammary glands in response to the mechanical stimulus provided by a suckling infant. MALE and NON-PREGNANT FEMALE: unknown function It may also be responsible, in part, for the feelings of sexual pleasure during and after intercourse. 2. ANTIDIURETIC HORMONE (aDH)/vasopressin causes the kidneys to return more water to the blood, thus decreasing urine volume/production. In the absence of ADH, urine output increases more than tenfold, from the normal 1 to 2 liters to about 20 liters a day Drinking alcohol often causes frequent and copious urination because alcohol inhibits the secretion of ADH. (This dehydrating effect of alcohol may cause both the thirst and the headache typical of a hangover.) ADH also decreases the water lost through sweating and causes constriction of arterioles, which increases blood pressure. POSTERIOR PITUITARY THYROID GLAND 4. POSTERIOR PITUITARY - does not synthesize hormones, but it does store and release two hormones THYROID GLAND - butterfly- shaped gland located just inferior to the larynx (voice box). o It consists of axons and axon terminals of more than 10,000 hypothalamic neurosecretory cells. o It is composed of RIGHT and LEFT LOBES, one on either side of the trachea, that are connected by an PARAVENTRICULAR and SUPRAOPTIC NUCLEI of the ISTHMUS anterior to the trachea hypothalamus, their axons form the HYPOTHALAMIC– HYPOPHYSEAL TRACT (begins in the hypothalamus and ends near About 50% of thyroid glands have a small third lobe, called the blood capillaries in the posterior pituitary) PYRAMIDAL LOBE. It extends superiorly from the isthmus. The normal mass of the thyroid is about 30 g (1 oz). THYROID FOLLICLES - microscopic spherical sacs that make up osteoclasts and by accelerating uptake of calcium and most of the thyroid gland. phosphates into bone extracellular matrix. o The wall of each follicle consists primarily of cells called T THYROCYTES (follicular cells), most of which extend to the lumen (internal space) of the follicle. BASEMENT MEMBRANE - surrounds each follicle. o + When the T thyrocytes are inactive, their shape is low cuboidal to squamous, but under the influence of TSH they become active in secretion and range from cuboidal to low columnar in shape. +The T THYROCYTES/follicular cells produce two hormones: 1. THYROXINE/tetraiodothyronine (T4) - because it contains four atoms of iodine 2. TRIIODOTHYRONINE (T3) - which contains three atoms of iodine. T3 and T4 together are also known as THYROID HORMONES T thyrocytes also produce THYROGLOBULIN C THYROCYTES /(parafollicular cells) - lie between follicles, produces hormone CALCITONIN (Ct) ACTIONS OF THYROID HORMONES (T3/T4) 1. Increase basal metabolic rate. Thyroid hormones raise the basal metabolic rate (BMR), the rate of energy expenditure under standard or basal conditions (awake, at rest, and fasting). PARATHYROID GLANDS/HORMONE 2. Enhance actions of catecholamines. (epinephrine and norepinephrine) The “fight or flight” response of the PARATHYROID GLANDS - small, round masses of tissue partially sympathetic nervous system. Therefore, symptoms of embedded in the posterior surface of the lobes of the thyroid gland excess levels of thyroid hormone include increased heart o Each has a mass of about 40 mg (0.04 g). Usually, one rate, more forceful heartbeats, and increased blood superior and one inferior parathyroid gland are attached to pressure. each thyroid lobe for a total of four. 3. Regulate development and growth of nervous tissue and PARATHYROID HORMONE (PTH) - bones. o The specific action of PTH is to increase the number and Nervous system: promote synapse formation, myelin production, and activity of osteoclasts. growth of dendrites. o The result is elevated bone resorption, which releases ionic Growth of the skeletal system: They promote formation of calcium (Ca2+) and phosphates (HPO4 2−) into the blood. ossification centers in developing bones, synthesis of many bone CALCITRIOL – active form of vitamin D, PTH on kidneys proteins, and secretion of growth hormone (GH) and insulin-like promote formation of this hormone, it increases the rate of Ca2+, Growth factors (IGFs). HPO4 2−, and Mg2+ absorption from the digestive canal into the Deficiency of thyroid hormones during fetal development, blood. infancy, or childhood causes severe mental retardation and stunted SUPRARENAL (ADRENAL) GLAND bone growth. SUPRARENAL GLAND/adrenal glands (paired) - one of which lies CALCITONIN superior to each kidney in the retroperitoneal space, have a flattened o produced by the C thyrocytes of the thyroid gland pyramidal shape. (highly vascularized) o CT can decrease the level of calcium in the blood by o In an adult, each suprarenal gland is 3–5 cm in height, 2–3 inhibiting the action of cm in width, and a little less than 1 cm thick, with a mass of o OSTEOCLASTS (the cells that break down bone 3.5–5g, only half its size at birth extracellular matrix) o When its blood level is high, calcitonin lowers the amount of blood calcium and phosphates by inhibiting bone resorption (breakdown of bone extracellular matrix) by  1. SUPRARENAL CORTEX - large, peripherally located, 2. Beta or B cells constitute about 70% of pancreatic islet cells and comprising 80–90% of the gland secrete INSULIN 1. ZONA GLOMERULOSA – outer zone, secretes hormone called 3. Delta or D cells constitute about 7% of pancreatic islet cells and MINERALOCORTICOIDS – ALDOSTERONE (affect mineral secrete SOMATOSTATIN homeostasis) 4. Pancreatic polypeptide cells constitute the remainder of 2. ZONA FASCICULATA – middle zone, widest, secretes pancreatic islet cells and secrete PANCREATIC POLYPEPTIDE GLUCOCORTICOIDS – Cortisol (Glucose homeostasis) 3. ZONA RETICULARIS – inner zone, synthesize small amounts of weak ANDROGENS (steroid hormones that have masculinizing effects) 2. SUPRARENAL MEDULLA – small, inner region of the suprarenal gland, is a modified sympathetic ganglion of the autonomic nervous system (ANS). – the hormones released intensify sympathetic responses that occur in other parts of the body. CHROMAFFIN CELLS –hormone-producing cells, are innervated by sympathetic preganglionic neurons of the ANS. NOREPINEPHRINE/adrenaline/noradrenaline – 80%; EPINEPHRINE – 20% OVARIES and TESTES GONADS - organs that produce gametes— sperm in males and oocytes in females. In addition to their reproductive function, the gonads secrete hormones. 1. OVARIES- paired oval bodies located in the female pelvic cavity, produce several steroid hormones, including two ESTROGEN (estradiol and estrone) and PROGESTERONE. o These 2 hormones together with FSH and LH (anterior PANCREAS pituitary) - regulate the menstrual cycle, maintain PANCREAS - is both an endocrine gland and an exocrine gland. pregnancy, and prepare the mammary glands for lactation. o A flattened organ that measures about 12.5–15 cm (5–6 in.) o They also promote enlargement of the breasts and in length, the pancreas is in the curve of the duodenum, the widening of the hips at puberty and help maintain these first part of the small intestine, and consists of a head, a female secondary sex characteristics. body, and a tail INHIBIN - a protein hormone that inhibits secretion of FSH. PANCREATIC ACINI – cluster of exocrine cells that makes up roughly 99% of the cells of the pancreas o During pregnancy, the ovaries and placenta produce a peptide hormone called RELAXIN (RLX), which o The pancreatic acini produce DIGESTIVE ENZYMES, increases the flexibility of the pubic symphysis during which flow into the digestive canal through a network of pregnancy and helps dilate the uterine cervix during ducts. labor and delivery. These actions help ease the baby’s passage by enlarging the birth canal. PANCREATIC ISLETS/Islets of Langerhans - 1–2 million tiny clusters of endocrine cells scattered among the pancreatic acini. 2. TESTES- are oval glands that lie in the scrotum. o Each pancreatic islet includes four types of hormone- o TESTOSTERONE – androgen or male sex hormone secreting cells: o Testosterone stimulates descent of the testes before birth, regulates production of sperm, and stimulates the 1. Alpha or A cells constitute about 17% of pancreatic islet cells and development and maintenance of male secondary sex secrete GLUCAGON characteristics, such as beard growth and deepening of the voice. INHIBIN - which inhibits secretion of FSH. PINEAL GLAND and THYMUS PINEAL GLAND- is a small endocrine gland attached to the roof of the third ventricle of the brain at the midline o Part of the epithalamus, it is positioned between the two superior colliculi, has a mass of 0.1–0.2 g, and is covered by a capsule formed by the pia mater. PINEALOCYTES - masses of neuroglia and secretory cells MELATONIN - an amine hormone derived from serotonin. o Melatonin appears to contribute to the setting of the body’s biological clock, which is controlled by the suprachiasmatic nucleus of the hypothalamus. o As more melatonin is liberated during darkness than in light, this hormone is thought to promote sleepiness. THYMUS - located behind the sternum between the lungs. o The hormones produced by the thymus—thymosin, thymic humoral factor (THF), thymic factor (TF), and thymopoietin promote the maturation of T cells (a type of white blood cell that destroys microbes and foreign substances) and may retard/slow down the aging process. ENDOCRINE GLAND PITUARY GLAND  SUPRARENAL GLAND PARATHYROID GLANDS/HORMONE