Endocrine System Notes PDF

ENDOCRINE SYSTEM The hormones of the endocrine system contribute to homeostasis by regulating the activity and growth of target cells in your body. Hormones also regulate your metabolism. In girls, ESTROGEN promote ENDOCRINE...

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