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
Location of the endocrine glands. Thymus gland is shown at maximum size at puberty.
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
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 .
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.
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
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.
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
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
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.
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.
What does the hyposecretion of ADH cause? Diabetes insipidus How are dehydration and electrolyte imbalances treated? With injections or nasal sprays containing ADH
Pituitary hormones. Principal anterior and posterior pituitary hormones and their target organs.
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
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.
Thyroid and parathyroid glands. Note their relationship to each other and to the larynx (voice box) and trachea.
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.
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.
Secretion of glucocorticoid quickly increases when the body is under stress.
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).
During periods of prolonged stress, glucocorticoids may have harmful side effects because they are anti-inflammatory and cause blood vessels to constrict.
Stress responses induced by high concentrations of glucocorticoids in blood.
How do endocrine glands differ from pancreatic islets? Endocrine glands are much larger than pancreatic islets.
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.
What happens if the pancreatic islets don’t secrete enough insulin? Blood glucose increases: hyperglycemia.
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.
Diabetes mellitus. The signs and symptoms of this disorder (highlighted in yellow) all result from decreased insulin effects.
The cells of the testes produce what? Sperm The interstitial cells in the testes secrete what male sex hormone directly into the blood? Testosterone
Where is the thymus located? In the mediastinum
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.
Why is this gland named “pineal”? Because it resembles a pine nut.
Nearly every organ and system has an endocrine function.
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