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Endocrine System
The document provides an overview of the endocrine system, including: - The endocrine system uses hormones to regulate bodily functions through slower chemical signaling compared to the nervous system. - Major endocrine glands include the pituitary, thyroid, parathyroid, adrenal, pancreas, ovaries/testes, thymus, placenta, and pineal glands. - Hormone secretion is regulated by negative and positive feedback loops to maintain homeostasis. Endocrine disorders can result from too much or too little hormone production.
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Endocrine System
- 1. Chapter 11 TheEndocrine System
- 2. Objectives Distinguish betweenendocrine and exocrine glands and define the terms hormone and prostaglandin Identify and locate the primary endocrine glands and list the major hormones produced by each gland Describe the mechanisms of steroid and non-steroid hormone action
- 3. Objectives Explain hownegative and positive feedback mechanisms regulate secretion of endocrine hormones Explain the primary mechanisms of endocrine disorders Identify the principal functions of each major endocrine hormone and describe the conditions that may result from hyposecretion or hypersecretion Define diabetes insipidus, diabetes mellitus, gigantism, goiter, cretinism, and glycosuria
- 4. Mechanisms of HormoneAction Endocrine glands secrete chemicals (hormones) into the blood Hormones perform general functions of communication and control, but a slower, longer-lasting type of control than that provided by nerve impulses Cells acted on by hormones are called target organ cells
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- 6. Mechanisms of HormoneAction Nonsteroid hormones (first messengers) bind to receptors on the target cell membrane, triggering second messengers to affect the cell’s activities Steroid hormones bind to receptors within the target cell nucleus and influence cell activity by acting on DNA
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- 9. Regulation of Hormone Secretion Hormone secretion is controlled by homeostatic feedback Negative feedback—mechanisms that reverse the direction of a change in a physiological system Positive feedback—(uncommon) mechanisms that amplify physiological changes
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- 11. Mechanisms of Endocrine Disease Hypersecretion—secretion of excess hormone Hyposecretion—insufficient hormone secretion Polyendocrine disorders—hyper- or hyposecretion of more than one hormone Target cell insensitivity produces results similar to hyposecretion Endocrinologists have developed many different strategies for treatment (e.g., surgery and hormone therapy)
- 12. Prostaglandins Prostaglandins (PGs)are powerful substances found in a wide variety of body tissues PGs are often produced in a tissue and diffuse only a short distance to act on cells in that tissue Several classes of PGs include prostaglandin A (PGA), prostaglandin E (PGE), and prostaglandin F (PGF) PGs influence many body functions, including respiration, blood pressure, gastrointestinal secretions, and reproduction
- 13. Pituitary Gland Anterior pituitary gland (adenohypophysis) Names of major hormones Thyroid-stimulating hormone (TSH) Adrenocorticotropic hormone (ACTH) Follicle-stimulating hormone (FSH) Luteinizing hormone (LH) Growth hormone (GH) Prolactin (lactogenic hormone)
- 14. Pituitary Gland Functionsof major hormones TSH—stimulates growth of the thyroid gland; also stimulates it to secrete thyroid hormone ACTH—stimulates growth of the adrenal cortex and stimulates it to secrete glucocorticoids (mainly cortisol) FSH—initiates growth of ovarian follicles each month in the ovary and stimulates one or more follicles to develop to the stage of maturity and ovulation; FSH also stimulates estrogen secretion by developing follicles; stimulates sperm production in the male
- 15. Pituitary Gland Functionsof major hormones LH—acts with FSH to stimulate estrogen secretion and follicle growth to maturity; causes ovulation; causes luteinization of the ruptured follicle and stimulates progesterone secretion by corpus luteum; causes interstitial cells in the testes to secrete testosterone in the male
- 16. Pituitary Gland GH—stimulatesgrowth by accelerating protein anabolism; also accelerates fat catabolism and slows glucose catabolism; by slowing glucose catabolism, tends to increase blood glucose to higher than normal level (hyperglycemia) Hypersecretion during childhood results in gigantism and during adulthood results in acromegaly Hyposecretion during childhood results in pituitary dwarfism Prolactin or lactogenic hormone—stimulates breast development during pregnancy and secretion of milk after the delivery of the baby
- 17. Pituitary Gland Posteriorpituitary gland (neurohypophysis) Names of hormones Antidiuretic hormone (ADH) Hyposecretion causes diabetes insipidus, characterized by excessive volume of urine Oxytocin (OT)
- 18. Pituitary Gland Functionsof hormones ADH—accelerates water reabsorption from urine in the kidney tubules into the blood, thereby decreasing urine secretion Oxytocin—stimulates the pregnant uterus to contract; may initiate labor; causes glandular cells of the breast to release milk into ducts
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- 20. Hypothalamus Actual productionof ADH and oxytocin occurs in the hypothalamus After production in the hypothalamus, hormones pass along axons into the pituitary gland The secretion and release of posterior pituitary hormones is controlled by nervous stimulation The hypothalamus controls many body functions related to homeostasis (temperature, appetite, and thirst)
- 21. Thyroid Gland Names of hormones Thyroid hormone—thyroxine (T 4 ) and triiodothyronine (T 3 ) Calcitonin (CT) Functions of hormones Thyroid hormones—accelerate catabolism (increase the body’s metabolic rate) Calcitonin—decreases the blood calcium concentration by inhibiting breakdown of bone, which would release calcium into the blood
- 22. Thyroid Gland Hyperthyroidism(hypersecretion of thyroid hormones) increases metabolic rate Characterized by restlessness and exophthalmos (protruding eyes) Graves disease is an inherited form of hyperthyroidism
- 23. Thyroid Gland Hypothyroidism(hyposecretion of thyroid hormones) May result from different conditions Simple goiter—painless enlargement of thyroid caused by dietary deficiency of iodine Hyposecretion during early development may result in cretinism (retardation) and during adulthood in myxedema (characterized by edema and sluggishness)
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- 25. Parathyroid Glands Name of hormone—parathyroid hormone (PTH) Function of hormone—increases blood calcium concentration by increasing the breakdown of bone with the release of calcium into the blood
- 26. Adrenal Glands Adrenal cortex Names of hormones (corticoids) Glucocorticoids (GCs)—chiefly cortisol (hydrocortisone) Mineralocorticoids (MCs)—chiefly aldosterone Sex hormones—small amounts of male hormones (androgens) secreted by adrenal cortex of both sexes
- 27. Adrenal Glands Threecell layers (zones) Outer layer—secretes mineralocorticoids Middle layer—secretes glucocorticoids Inner layer—secretes sex hormones Mineralocorticoids—increase blood sodium and decrease body potassium concentrations by accelerating kidney tubule reabsorption of sodium and excretion of potassium
- 28. Adrenal Glands Functionsof glucocorticoids Help maintain normal blood glucose concentration by increasing gluconeogenesis—the formation of “new” glucose from amino acids produced by the breakdown of proteins, mainly those in muscle tissue cells; also the conversion to glucose of fatty acids produced by the breakdown of fats stored in adipose tissue cells Play an essential part in maintaining normal blood pressure—make it possible for epinephrine and norepinephrine to maintain a normal degree of vasoconstriction, a condition necessary for maintaining normal blood pressure
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- 30. Adrenal Glands Actwith epinephrine and norepinephrine to produce an antiinflammatory effect, to bring about normal recovery from inflammations of various kinds Produce anti-immunity, antiallergy effect; bring about a decrease in the number of lymphocytes and plasma cells and therefore a decrease in the amount of antibodies formed Secretion of glucocorticoid quickly increases when the body is thrown into a condition of stress; high blood concentration of glucocorticoids, in turn, brings about many other stress responses
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- 32. Adrenal Glands Adrenalmedulla Names of hormones—epinephrine (Epi), or adrenaline, and norepinephrine (NR) Functions of hormones—help the body resist stress by intensifying and prolonging the effects of sympathetic stimulation; increased epinephrine secretion is the first endocrine response to stress
- 33. Adrenal Glands Adrenalabnormalities Hypersecretion of glucocorticoids causes Cushing syndrome: moon face, hump on back, elevated blood sugar levels, frequent infections Hypersecretion of adrenal androgens may result from a virilizing tumor and cause masculinization of affected women
- 34. Adrenal Glands Hyposecretionof cortical hormones may result in Addison disease: muscle weakness, reduced blood sugar, nausea, loss of appetite, and weight loss
- 35. Pancreatic Islets Names of hormones Glucagon—secreted by alpha cells Insulin—secreted by beta cells Functions of hormones Glucagon increases the blood glucose level by accelerating liver glycogenolysis (conversion of glycogen to glucose)
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- 37. Pancreatic Islets Functions of hormones Insulin decreases the blood glucose by accelerating the movement of glucose out of the blood into cells, which increases glucose metabolism by cells
- 38. Pancreatic Islets Diabetesmellitus Type 1 results from hyposecretion of insulin Type 2 results from target cell insensitivity to insulin Glucose cannot enter cells and thus blood glucose levels rise, producing glycosuria (glucose in the urine)
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- 40. Female Sex GlandsThe ovaries contain two structures that secrete hormones—the ovarian follicles and the corpus luteum; see Chapter 22 Effects of estrogen (feminizing hormone) Development and maturation of breasts and external genitals Development of adult female body contours Initiation of menstrual cycle
- 41. Male Sex GlandsThe interstitial cells of testes secrete the male hormone testosterone; see Chapter 22 Effects of testosterone (masculinizing hormone) Maturation of external genitals Beard growth
- 42. Male Sex GlandsEffects of testosterone Voice changes at puberty Development of musculature and body contours typical of the male
- 43. Thymus Name ofhormone—thymosin Function of hormone—plays an important role in the development and function of the body’s immune system
- 44. Placenta Name ofhormones—chorionic gonadotropins, estrogens, and progesterone Functions of hormones—maintain the corpus luteum during pregnancy
- 45. Pineal Gland Asmall gland near the roof of the third ventricle of the brain Glandular tissue predominates in children and young adults Becomes fibrous and calcified with age Called third eye because its influence on secretory activity is related to the amount of light entering the eyes
- 46. Pineal Gland Secretesmelatonin, which: Inhibits ovarian activity Regulates the body’s internal clock Abnormal secretion of (or sensitivity to) melatonin may produce seasonal affective disorder (SAD) or winter depression, a form of depression that occurs when exposure to sunlight is low and melatonin levels are high
- 47. Other Endocrine StructuresMany organs (e.g., the stomach, intestines, and kidney) produce endocrine hormones The atrial wall of the heart secretes atrial natriuretic hormone (ANH), which stimulates sodium loss from the kidneys Fat-storing cells secrete leptin, which controls how full or hungry we feel
Editor's Notes
- #5 What are endocrine glands? Ductless glands that secrete hormones into intracellular spaces What is a target organ cell? A cell that has receptors for a specific hormone
- #6 Location of the endocrine glands. Thymus gland is shown at maximum size at puberty.
- #7 What are the two major classes of hormones? Nonsteroid and steroid hormones What is a second messenger mechanism? Chemical that provides communication within a hormone’s target cell What are steroid hormones? Hormones that can pass through the target cell’s membrane to the nucleus where they bind with a receptor to form a hormone-receptor complex Give an example of a steroid hormone. Estrogen
- #8 Mechanism of protein hormone action. The hormone acts as “first messenger,” delivering its message via the bloodstream to a membrane receptor in the target organ cell much like a key fits into a lock. The “second messenger” causes the cell to respond and perform its specialized function .
- #9 Mechanism of steroid hormone action. Steroid hormones pass through the plasma membrane and enter the nucleus to form a hormone receptor complex that acts on DNA. As a result, a new protein is formed in the cytoplasm that produces specific effects in the target cell.
- #10 Give an example of positive feedback. During labor, muscle contractions become stronger by means of a positive feedback mechanism that regulates the secretion of oxytocin. Give an example of negative feedback. Insulin
- #11 Negative feedback. The secretion of most hormones is regulated by negative feedback mechanisms that tend to reverse any deviations from normal. In this example, an increase in blood glucose triggers secretion of insulin. Because insulin promotes glucose uptake by cells, the blood glucose level is restored to its lower, normal level.
- #12 What is the name of a physician who specializes in endocrine disorders? Endocrinologist What are some diseases caused by hypersecretion of a hormone? Hypoglycemia, Graves disease, gigantism, water retention, Cushing syndrome What are some diseases caused by hyposecretion of a hormone? Goiter, cretinism, dwarfism, diabetes insipidus, Addison disease, myxedema
- #13 Do prostaglandins meet the definition of a typical hormone? No How do prostaglandins differ from most hormones? Prostaglandins only influence the activities of neighboring cells. What research is being conducted with prostaglandins? The role of prostaglandins in the treatment of high blood pressure, asthma, and ulcers
- #14 Why is the anterior pituitary gland sometimes called the master gland? It controls the thyroid gland, the adrenal cortex, the ovarian follicles, and the corpus luteum. What do the major hormones do? ACTH stimulates the adrenal cortex, causing it to increase in size and secrete larger amounts of its hormones. See Table 11-1.
- #17 How do growth hormones promote normal growth? They speed up the movement of amino acids out of the blood and into the cells, which accelerates the cells’ anabolism of amino acids to form tissue proteins.
- #18 What does the hyposecretion of ADH cause? Diabetes insipidus How are dehydration and electrolyte imbalances treated? With injections or nasal sprays containing ADH
- #20 Pituitary hormones. Principal anterior and posterior pituitary hormones and their target organs.
- #21 In addition to oxytocin and ADH, what substances does the hypothalamus produce? Releasing and inhibiting hormones that travel to the anterior pituitary gland The hypothalamus regulates many body functions related to homeostasis. Give some examples. Body temperature, appetite, and thirst
- #22 How do T 3 and T 4 influence body cells? They speed up their release of energy from foods. How does calcitonin help maintain homeostasis of blood calcium? It decreases blood calcium concentrations. Where is the thyroid located? In the neck just below the larynx Place thumb and forefinger on each side of the trachea and swallow. The part you feel that goes up and down is the thyroid.
- #25 Thyroid and parathyroid glands. Note their relationship to each other and to the larynx (voice box) and trachea.
- #26 How does PTH increase calcium? It stimulates bone-resorbing cells to increase their breakdown of bone’s hard matrix, which frees the calcium stored there.
- #28 Where is the adrenal gland? It curves over the top of each kidney. What are hormones secreted by the adrenal cortex called? Corticoids What are the adrenal cortex and the adrenal medulla? The adrenal cortex is the outer part of an adrenal gland; the medulla is its inner part. What is the chief mineralocorticoid? Aldosterone What does aldosterone do? Increases the amount of sodium and decreases potassium in the blood.
- #29 Secretion of glucocorticoid quickly increases when the body is under stress.
- #30 The adrenal gland. The three cell layers of the adrenal cortex are easily seen here. The outer zone cells secrete mineralocorticoids (aldosterone). The middle zone cells secrete glucocorticoids (hydrocortisone). The inner zone cells secrete sex hormones (androgens).
- #31 During periods of prolonged stress, glucocorticoids may have harmful side effects because they are anti-inflammatory and cause blood vessels to constrict.
- #32 Stress responses induced by high concentrations of glucocorticoids in blood.
- #36 How do endocrine glands differ from pancreatic islets? Endocrine glands are much larger than pancreatic islets.
- #37 Pancreas . Location and structure of the pancreas (cut open). Inset shows a pancreatic islet (of Langerhans) in cross section, showing the glucagon-producing alpha cells and insulin-producing beta cells. Notice the many exocrine cells surrounding the endocrine pancreatic islet.
- #38 What happens if the pancreatic islets don’t secrete enough insulin? Blood glucose increases: hyperglycemia.
- #39 How are most screening tests for diabetes mellitus done? With a drop of blood Testing for sugar in the urine is another common screening procedure.
- #40 Diabetes mellitus. The signs and symptoms of this disorder (highlighted in yellow) all result from decreased insulin effects.
- #43 The cells of the testes produce what? Sperm The interstitial cells in the testes secrete what male sex hormone directly into the blood? Testosterone
- #44 Where is the thymus located? In the mediastinum
- #45 These hormones maintain the corpus luteum during pregnancy. What fact led to the development of the early pregnancy test? During the earliest weeks of pregnancy the kidneys excrete chorionic gonadotropins into the urine.
- #46 Why is this gland named “pineal”? Because it resembles a pine nut.
- #48 Nearly every organ and system has an endocrine function.