NURS1108 Lecture 13 - Endocrine System PDF

NURS1108: Introduction to Anatomy & Physiology Dr. Jermaine H. Whyte FMS- UWI [email protected] Endocrine System Sense Organs Objectives • Identify the endocrine organs/glands and their location; • Describe the structure and function of each of the endocrine glands; • Distinguish be...

NURS1108: Introduction to Anatomy & Physiology Dr. Jermaine H. Whyte FMS- UWI [email protected] Endocrine System Sense Organs Objectives • Identify the endocrine organs/glands and their location; • Describe the structure and function of each of the endocrine glands; • Distinguish between endocrine and exocrine glands; • List the functions of hormones; • Classify hormones into their major chemical categories; • Discuss the effects of the major hormones on the body; • Explain the hypothalamus and prostaglandin regulations of the functions of the endocrine system; Content • Endocrine system o Developmental aspects • Glands: structure & functions o o Definition Types & functions of each • Endocrine • Exocrine • Major endocrine organs: location, structure, function, hormones o o o o o o o o o Pituitary Thyroid Parathyroid Adrenal Ovaries Testes Pineal Thymus Pancreas (islets of Langerhans) • Exocrine glands: location, structure, function, hormones o o o o Salivary Bile-producing glands of the liver Pancreas (pancreatic fluid) Gastric • Hormones o o o o o o Types Chemistry Mechanisms of hormone action Hormone target cell specificity Half-life, onset & duration of hormone activity Control of hormone release • Regulatory mechanisms o o Hypothalamus Prostaglandin Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Introduction A. The endocrine system is made up of the cells, tissues, and organs that secrete hormones into body fluids. B. Hormones diffuse into the bloodstream to act target cells some distance away. C. The body has two kinds of glands; o Exocrine (secretes products into ducts) o Endocrine (secrete products into body fluids to affect target cells). 5 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. General Characteristics of the Endocrine System A. The endocrine system’s function is to communicate with cells using chemicals called hormones. B. Endocrine glands and their hormones regulate a number of metabolic processes within cells, and the whole body. 6 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. C. Their actions are precise, they only affect specific target cells D. Endocrine glands include the o pituitary gland o thyroid gland o parathyroid glands o Adrenal glands o Pancreas o other hormone - secreting glands and tissues. 11 12 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hormone Action A. Hormones are o steroids, amines, peptides, proteins, or glycoproteins o they can influence target cells even if they are present only in minute concentrations. 13 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. B. Steroid Hormones 1. Steroid hormones are lipid-soluble and can pass through cell membranes. 2. Receptors for steroid hormones located in the target cell’s nucleus. are 3. The hormone-receptor complex binds with the DNA and activates specific genes that, in turn, direct the synthesis of specific proteins. 15 16 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. C. Nonsteroidal Hormones 1. Nonsteroidal hormones combine with receptors in target cell membranes; the receptors have a binding site and an activity site. 2. The hormone-receptor complex (as first messenger) triggers a cascade of biological activity. 18 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3. The hormone-receptor complex generally activates a G protein, which then activates the enzyme adenylate cyclase that is bound to the inner cell membrane. 4. This enzyme removes two phosphates from ATP to produce cyclic AMP (the second messenger), which in turn activates protein enzymes that activate proteins. 19 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 5. These activated proteins induce changes in the cell. 6. Not all nonsteroid hormones use cAMP; others use diacylglycerol (DAG) or inositol triphosphate. 20 21 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. D. Prostaglandins • Prostaglandins are locally-produced lipids that affect the organ in which they are produced. • Prostaglandins produce a variety of effects: some relax smooth muscle, others contract smooth muscle, some stimulate secretion of other hormones, and others influence blood pressure and inflammation. 23 • Both steroid hormones and thyroid hormones are effective when taken by mouth. They are not split apart during digesion and easily cross the intestinal lining because they are lipid-soluble. • By contrast, peptide and protein hormones, such as insulin, are not effective oral medications because digestive enzymes destroy them by breaking their peptide bonds. This is why people who need insulin must take it by injection. Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Control of Hormonal Secretions A. Hormone levels are very precisely regulated. B. Control Mechanisms 1. Release of tropic hormones from the hypothalamus controls secretions of the anterior pituitary. 2. The nervous system influences certain endocrine glands directly. 3. Other glands respond directly to changes in the internal fluid composition. 25 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. C. Negative Feedback Systems 1. Commonly, negative feedback mechanisms control hormonal releases. 2. In a negative feedback system, a gland is sensitive to the concentration of the substance it regulates or which regulates it. 3. When the concentration of the regulated substance reaches a certain level (high or low), it inhibits the gland from secreting more hormone until the concentration returns to normal. 27 29 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pituitary Gland A. The pituitary gland is attached to the base of the brain and has an anterior lobe (anterior pituitary) and a posterior lobe (posterior pituitary). 30 31 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. B. The brain controls the activity of the pituitary gland. 1. Releasing hormones from the hypothalamus control the secretions of the anterior pituitary. a. The releasing hormones are carried in the bloodstream directly to the anterior pituitary by hypophyseal portal veins. 2. The posterior pituitary releases hormones into the bloodstream in response to nerve impulses from the hypothalamus. 32 34 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. C. Anterior Pituitary Hormones 1. The anterior pituitary consists mostly of epithelial tissue arranged around blood vessels and enclosed in a capsule of collagenous connective tissue. 35 Anterior Pituitary Gland Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 2. Growth hormone (GH) stimulates body cells to grow and reproduce; it also speeds the rate at which cells use carbohydrates and fats. a. Growth hormone-releasing hormone from the hypothalamus increases the amount of GH released, GH release-inhibiting hormone inhibits its release. b. Nutritional status affects the release of GH; more is released when nutrients are insufficient. 38 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3. Prolactin (PRL) promotes milk production following the birth of an infant. a. The effect of PRL in males is less-well understood, although it may cause a deficiency of male sex hormones. 39 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 4. Thyroid-stimulating hormone (TSH) controls the secretion of hormones from the thyroid gland. a. Thyrotropin-releasing hormone (TRH) from the hypothalamus regulates the release of TSH. b. As blood concentrations of thyroid hormones increases, secretions of TRH and TSH decrease. 40 41 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 5. Adrenocorticotropic hormone (ACTH) controls the secretion of hormones from the adrenal cortex. a. It is regulated by corticotropin-releasing hormone from the hypothalamus, and stress can also increase its release. 6. Follicle-stimulating hormone (FSH) andluteinizing hormone (LH) are gonadotropins affecting the male and female sex organs 42 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. D. Posterior Pituitary Hormones 1. The posterior lobe consists of nerve fibers and neuroglial cells that support nerve fibers arising in the hypothalamus. 2. Neurons in the hypothalamus produce antidiuretic hormone and oxytocin, which are stored in the posterior pituitary. 44 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3. Antidiuretic hormone (ADH) produces its effect by causing the kidneys to conserve water. a. The hypothalamus regulates the secretion of ADH based on the amount of water in body fluids. 46 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 4. Oxytocin plays a role in childbirth by contracting muscles in the uterine wall, and in milk-letdown by forcing milk into ducts from the milk glands. a. Stretching of the uterus in the latter stages of pregnancy stimulates release of oxytocin. b. Suckling of an infant at the breast stimulates release of oxytocin after childbirth. 47 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Thyroid Gland A. The thyroid gland is located below the larynx and consists of two broad lobes connected by an isthmus. B. Structure of the Gland 1. The thyroid consists of secretory parts called follicles filled with hormone-storing colloid. 50 52 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. C. Thyroid Hormones 1. The follicular cells produce two iodinecontaining hormones, thyroxine (T4 ) (tetraiodothyronine) and triiodothyronine (T3), that together regulate energy metabolism. a. These two hormones increase the rate at which cells release energy from carbohydrates, enhance protein synthesis, and stimulate the breakdown and mobilization of lipids. 54 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. b. These hormones are essential for normal growth and development. c. The hypothalamus and pituitary gland control release of thyroid hormones. 55 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 2. Extrafollicular cells of the thyroid secrete calcitonin, which lowers blood levels of calcium and phosphate ions when they are too high. a. Calcitonin increases the rate at which calcium is stored in bones and excreted in the urine. b. Calcitonin secretion is regulated by negative feedback involving blood concentrations of calcium. 56 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Parathyroid Glands A. The four, tiny parathyroids are located on the posterior of the thyroid. B. Structure of the Glands 1. Parathyroid glands consist of tightly packed secretory cells covered by a thin capsule of connective tissue. 58 60 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Parathyroid Glands 1. Parathyroid hormone (PTH) increases blood calcium ion concentration and decreases phosphate ion concentration. 2. PTH stimulates bone resorption by osteoclasts, which releases calcium into the blood. 3. PTH also influences the kidneys to conserve calcium and causes increased absorption of calcium in the intestines. 61 64 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 4. A negative feedback mechanism involving blood calcium levels regulates release of PTH. D. Calcitonin and PTH exert opposite effects in regulating calcium ion levels in the blood. 65 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Adrenal Glands A. The adrenal glands sit atop the kidneys enclosed in a layer of fat. B. Structure of the Glands 1. The pyramid-shaped glands consist of an inner adrenal medulla and an outer adrenal cortex. 2. The adrenal medulla is made up of modified postganglionic neurons that are connected to the sympathetic nervous system. 67 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. B. Structure of the Glands 1. The pyramid-shaped glands consist of an inner adrenal medulla and an outer adrenal cortex. 2. The adrenal medulla is made up of modified postganglionic neurons that are connected to the sympathetic nervous system. 3. The adrenal cortex makes up most of the adrenal glands and consists of epithelial cells in three layers--an outer, middle, and an inner zone. 69 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. C. Hormones of the Adrenal Medulla 1. The adrenal medulla secretes epinephrine and norepinephrine into the blood stream. 2. The effects of these hormones resemble those of the sympathetic division neurotransmitters of the same name, except that they last up to 10 times longer when they are secreted as hormones. 72 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3. The are used in times of stress and for “fight or flight.” 4. Release of medullary hormones is regulated by nervous impulses from the central nervous system. 74 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. D. Hormones of the Adrenal Cortex 1. The cells of the adrenal cortex produce over 30 different steroids, some of which are vital to survival, the most important of which are aldosterone, cortisol, and the sex hormones. 75 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 2. Aldosterone a. Aldosterone, a mineralocorticoid, causes the kidneys to conserve sodium ions and thus water, and to excrete potassium ions. b. Aldosterone is secreted in response to decreasing blood volume and blood pressure as a result of changes in the kidney. 76 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3. Cortisol a. Cortisol, a glucocorticoid, influences the metabolism of glucose, protein, and fat in response to conditions that stress the body and require a greater supply of energy in the bloodstream. 78 79 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. b. A negative feedback mechanism involving CRH from the hypothalamus and ACTH from the anterior pituitary controls the release of cortisol. c. Stress, injury, or disease can also trigger increased release of cortisol. 80 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 4. Adrenal Sex Hormones a. Sex hormones, produced in the inner zone, are mostly of the male type, but can be converted to female hormones in the skin, liver, and adipose tissues. b. These hormones supplement those released by the gonads and may stimulate early development of reproductive organs. 81 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pancreas A. The pancreas secretes hormones as an endocrine gland, and digestive juices to the digestive tract as an exocrine gland. 82 83 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. B. Structure of the Gland 1. The pancreas is an elongated organ posterior to the stomach. 2. Its endocrine portions are the islets of Langerhans that include two cell types-alpha cells that secrete glucagon, and beta cells that secrete insulin. 86 87 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. C. Hormones of the Islets of Langerhans 1. Glucagon increases the blood levels of glucose by stimulating the breakdown of glycogen and the conversion of noncarbohydrates into glucose. a. The release of glucagon is controlled by a negative feedback system involving low blood glucose levels. 90 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 2. Insulin decreases the blood levels of glucose by stimulating the liver to form glycogen, increasing protein synthesis, and stimulating adipose cells to store fat. a. The release of insulin is controlled by a negative feedback system involving high blood glucose levels. • Insulin and glucagon coordinate to maintain a relatively stable blood glucose concentration. 91 93 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Other Endocrine Glands A. Pineal Gland 1. The pineal gland, near the upper portion of the thalamus, secretes melatonin, which is involved in the regulation of circadian rhythms of the body. B. Thymus Gland 1. The thymus gland, lying between the lungs under the sternum, secretes thymosins that affect production and differentiation of T lymphocytes that are important in immunity. 95 Effect of Light on Pineal Gland • Melatonin secretion producing sleepiness occurs during darkness due to lack of stimulation from 96 sympathetic ganglion Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. C. Reproductive Glands 1. The ovaries produce estrogen and progesterone. 2. The placenta produces estrogen, progesterone, and gonadotropin. 3. The testes produce testosterone. 97 Hormonal Control of Male Reproductive Functions • hypothalamus controls maturation of sperm cells and development of male secondary sex characteristics • negative feedback among the hypothalamus, the anterior lobe of the pituitary gland, and the testes controls the concentration of testosterone 98 Actions of Testosterone • increased growth of body hair • sometimes decreased growth of scalp hair • enlargement of larynx and thickening of vocal cords • thickening of skin • increased muscular growth • thickening and strengthening of the bones 99 Hormonal Control of Female Reproductive Functions • estrogens inhibit LH and FSH during most of the reproductive cycle 100 Effects of Estrogens • development of breasts and ductile system of the mammary glands • increased adipose tissue in breasts, thighs, and buttocks • increases vascularization of skin 101 Female Reproductive Cycle 102 Menopause • usually occurs in late 40s or early 50s • reproductive cycles stop • ovaries no longer produce as much estrogens and progesterone • some female secondary sex characteristics may disappear • may produce hot flashes and fatigue • hormone therapy may prevent effects on bone tissue 103 Mammary Glands • located in the subcutaneous tissue of the anterior thorax within the breasts • composed of lobes • estrogens stimulate breast development in females 104 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. D. Digestive Glands 1. The digestive glands secrete hormones associated with the processes of digestion. E. Other Hormone Producing Organs 1. The heart secretes atrial natriuretic peptide affecting sodium and the kidneys secrete erythropoietin for blood cell production. 106 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Stress and Health A. Factors that serve as stressors to the body produce stress and threaten homeostasis. B. Types of Stress 1. Stress may be physical, psychological, or some combination of the two. 111 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 2. Physical stress threatens the survival of tissues, such as extreme cold, prolonged exercise, or infections. 3. Psychological stress results from real or perceived dangers, and includes feelings of anger, depression, fear, and grief; sometimes even pleasant stimuli cause stress. 112 Copyright©The McGraw-Hill Companies, Inc. Permission required for reproduction or display. C. Response to Stress 1. Responses to stress maintain homeostasis. are designed to 2. The hypothalamus controls the general adaptation syndrome, which involves increased sympathetic activity and increased secretion of cortisol, glucagon, growth hormone, and antidiuretic hormone. 113 115 Hypercortisolism Thyroid Hormone Disorders Growth Hormone Clinical Application Growth Hormone Ups and Downs • Gigantism - hypersecretion of GH in children • Acromegaly – hypersecretion of GH in adults • Dwarfism – hyposecretion of GH in children Figure shows oversecretion of GH in adulthood as changes occur in the same person at ages (a) nine, (b) sixteen, (c) thirty-three, and (4) fifty-two 120 Growth Hormone Disorders Life-Span Changes • endocrine glands decrease in size • muscular strength decreases as GH levels decrease • ADH levels increase due to slower break down in liver and kidneys • calcitonin levels decrease; increase risk of osteoporosis • PTH level changes contribute to risk of osteoporosis • insulin resistance may develop • changes in melatonin secretion affect the body clock • thymosin production declines increasing risk of infections 122 Adrenal Cortex - Review • • • Mineralocorticoids o Mineralocorticoids (e.g., aldosterone) increase sodium and water reabsorption and decrease potassium reabsorption, helping to regulate sodium and potassium levels in the body. o Secretion is controlled by the renin-angiotensin pathway (Figure 18.16) and the blood level of potassium. Glucocorticoids o Glucocorticoids (e.g., cortisol) promote breakdown of proteins, formation of glucose, lipolysis, resistance to stress, anti-inflammatory effects, and depression of the immune response. o Secretion is controlled by CRH (corticotropin releasing hormone) and ACTH (adrenocorticotropic hormone) from the anterior pituitary (Figure 18.17). Androgens o Androgens secreted by the adrenal cortex usually have minimal effects. 123 Adrenal Medulla Review • The adrenal medulla consists of hormone-producing cells, called chromaffin cells, which surround large blood-filled sinuses. • Medullary secretions are epinephrine and norepinephrine (NE), which produce effects similar to sympathetic responses. • They are released under stress by direct innervation from the autonomic nervous system. Like the glucocorticoids of the adrenal cortex, these hormones help the body resist stress. However, unlike the cortical hormones, the medullary hormones are not essential for life. • Table 18.8 summarizes the hormones produced by the adrenal glands, the principal actions, and control of secretion. 124 Review: Cell Types in the Pancreatic Islets • Alpha cells secrete the hormone glucagon which increases blood glucose levels. • Beta cells secrete the hormone insulin which decreases blood glucose levels. • Delta cells secrete growth hormone inhibiting hormone or somatostatin, which acts as a paracrine to inhibit the secretion of insulin and glucagon. • F-cells secrete pancreatic polypeptide, which regulates release of pancreatic digestive enzymes. 125 OVARIES AND TESTES Review • Ovaries are located in the pelvic cavity and produce sex hormones (estrogens and progesterone) related to development and maintenance of female sexual characteristics, reproductive cycle, pregnancy, lactation, and normal reproductive functions. The ovaries also produce inhibin and relaxin. • Testes lie inside the scrotum and produce sex hormones (primarily testosterone) related to the development and maintenance of male sexual characteristics and normal reproductive functions. The testes also produce inhibin. 126 PINEAL GLAND Review • The pineal gland (epiphysis cerebri) is attached to the roof of the third ventricle, inside the brain (Figure 18.1). • Histologically, it consists of secretory parenchymal cells called pinealocytes, neuroglia cells, and scattered postganglionic sympathetic fibers. The pineal secrets melatonin in a diurnal rhythm linked to the dark-light cycle. • Seasonal affective disorder (SAD), a type of depression that arises during the winter months when day length is short, is thought to be due, in part, to over-production of melatonin. Bright light therapy, repeated doses of several hours exposure to artificial light as bright as sunlight, may provide relief for this disorder and for jet lag. 127 THYMUS GLAND • The thymus gland secretes several hormones related to immunity . • Thymosin, thymic humoral-factor, thymic factor, and thymopoietin promote the proliferation and maturation of T cells, a type of white blood cell involved in immunity. 128