1. Chapter 11
The Endocrine System

2. Mechanisms of Hormone Action
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
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

3. Mechanism of protein hormone action
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.

4. Mechanism of steroid hormone action
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.

5. 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)
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

6. 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
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

7. Pituitary Gland
GH—stimulates growth 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
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.

8. Pituitary Gland Functions of 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

9. Parathyroid Glands Name of hormone—parathyroid hormone (PTH)
Function of hormone—increases blood calcium by increasing the breakdown of bone to release calcium into blood
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.

10. 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

11. Adrenal Glands
Mineralocorticoids—increase blood sodium and decrease body potassium by accelerating kidney reabsorption of sodium and excretion of potassium
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.

12. Adrenal Glands Functions of glucocorticoids
Help maintain blood glucose conc by increasing gluconeogenesis— formation of “new” glucose from amino acids from breakdown of proteins; also the conversion to glucose by the breakdown of glycerol from fats stored in adipose tissue
Play an essential part in maintaining normal BP—make it possible to maintain a normal degree of vasoconstriction, necessary for maintaining normal BP
Secretion of glucocorticoid quickly increases when the body is under stress.

13. 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).

14. Adrenal Glands
Produce anti-immunity, anti-allergy effect; bring about a decrease in the number of lymphocytes and therefore a decrease in amount of antibodies
Secretion of glucocorticoid quickly increases when the body is thrown into a condition of stress; high blood conc of glucocorticoids, in turn, brings about many other stress responses
During periods of prolonged stress, glucocorticoids may have harmful side effects because they are anti-inflammatory and cause blood vessels to constrict.

15. Stress responses induced by high concentrations of glucocorticoids in blood.

16. Adrenal Glands Adrenal medulla
Names of hormones—epinephrine (Epi), or adrenaline, and norepinephrine (NR)
Function —help the body resist stress by intensifying and prolonging the effects of sympathetic stimulation; increased epinephrine secretion is the first endocrine response to stress

17. Adrenal Glands Adrenal abnormalities
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

18. Adrenal Glands
Hyposecretion of cortical hormones may result in Addison disease: muscle weakness, reduced blood sugar, nausea, loss of appetite, and weight loss

19. Pancreatic Islets Names of hormones Functions 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)
How do endocrine glands differ from pancreatic islets? Endocrine glands are much larger than pancreatic islets.

20. Pancreas. Location and structure of the pancreas (cut open)
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.

21. 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
What happens if the pancreatic islets don’t secrete enough insulin? Blood glucose increases: hyperglycemia.

22. Pancreatic Islets Diabetes mellitus
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)
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.

23. Diabetes mellitus. The signs and symptoms of this disorder (highlighted in yellow) all result from decreased insulin effects.

24. Female Sex Glands
The 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

25. Male Sex Glands
The interstitial cells of testes secrete the male hormone testosterone; see Chapter 22
Effects of testosterone (masculinizing hormone)
Maturation of external genitals
Beard growth

26. Male Sex Glands Effects of testosterone Voice changes at puberty
Development of musculature and body contours typical of the male
The cells of the testes produce what? Sperm
The interstitial cells in the testes secrete what male sex hormone directly into the blood? Testosterone

27. Thymus Name of hormone—thymosin
Function of hormone—plays an important role in the development and function of the body’s immune system
Where is the thymus located? In the mediastinum

28. Placenta
Name of hormones—chorionic gonadotropins, estrogens, and progesterone
Functions of hormones—maintain the corpus luteum during pregnancy
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.

29. Pineal Gland
A small 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
Why is this gland named “pineal”? Because it resembles a pine nut.

30. Pineal Gland Secretes melatonin, 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

31. Other Endocrine Structures
Many 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
Nearly every organ and system has an endocrine function.