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Chapter 9 - Endocrine System Overview coordinate and directs the activity of the body's cells more slowly acting than nervous system uses chemical messengers (hormones) released into the blood hormones transported leisurely throughout the body controls: reproduction growth and development mobilization of body defenses against stressors maintenance of electrolyte, water, and nutrient balance of the blood regulation of cellular metabolism and energy balance organs are small, unimpressive, lack the structural or anatomical continuity typical of most organs bits and pieces of endocrine tissue are tucked away in widely separated regions of the body The Chemistry of Hormones chemical substances secreted by cells into the extracellular fluids regulate the metabolic activity of other body cells amino acid- based molecules (including proteins, peptides, and amines) steroid hormones made from cholesterol include sex hormones made by the gonads (ovaries and testes) also hormones produced by the adrenal cortex prostaglandins made from highly active lipids found in plasma membranes increases blood pressure by acting as vasoconstrictors cause constriction of respiratory passageways stimulates muscle of the uterus (promoting labor) enhance blood clotting increase inflammation and pain increase output of digestive secretions stomach causes fever Mechanisms of Hormone Action blood-borne hormones circulate to all the organs of the body a given hormone affects only certain tissue cells or organs (target cells/organs) specific protein receptors must be present on plasma membrane or in its interior hormone attaches affects body cells primarily by altering cellular activity (increasing or decreasing the rate of a normal/usual metabolic process) precise changes depend on the specific hormone and the target cell type but may include: changes in plasma membrane permeability or electrical state synthesis of proteins/regulatory molecules in the cell activation or inactivation of enzymes stimulation of mitosis steroidal hormones (lipid-soluble molecules) diffuse through the plasma membranes of target cells enters the nucleus and binds to a specific receptor protein hormone-receptor complex binds to specific genes in the cell's DNA mRNA transcribed and translated in the cytoplasm results in the synthesis of new proteins nonsteroidal hormones bind to receptors on plasma membrane sets off a series of reactions that activates an enzyme enzymes catalyzes a reaction that produces a second messenger molecule 2nd molecule oversees additional intracellular changes causes the typical response of the target cell to the hormone Control of Hormone Release negative feedback mechanisms regulate blood levels of nearly all hormones secretion triggered by internal or external stimulus rising hormone levels inhibit further hormone release stimuli fall into three major categories (hormonal, humoral, neural) hormonal endocrine organs are stimulated into action by other hormones hypothalamic hormones stimulate the anterior pituitary gland to secrete its hormones humoral changing blood levels of certain ions/nutrients/body fluids insulin produced by the pancreas neural nerve fibers stimulate hormone release sympathetic nervous system stimulating release of norepinephrine and epinephrine Endocrine Organs/Glands major glands include the pituitary, thyroid, parathyroid, adrenal, pineal, thymus, pancreas, and gonads also includes the hypothalamus (part of the nervous system) because it produces several hormones Know Table 9.1 Pituitary Gland size of a grape on the inferior surface of the hypothalamus surrounded by the sphenoid bone two functional lobes - anterior pituitary (glandular tissue) and posterior pituitary (nervous tissue) anterior pituitary growth hormone and prolactin (affects non-endocrine targets) thyrotropic hormone, adrenocorticotropic hormone, and two gonadotropic hormones (stimulate target organs to secrete hormones which affects other organs/tissues) all are proteins, have 2nd messenger systems, regulated by hormonal stimuli/negative feedback growth hormone (GH) general metabolic hormone growth of skeletal muscles and long bones amino acids built into proteins and stimulates growth/division of target cells causes fats to be broken down and used for energy hyposecretion in childhood leads to pituitary dwarfism hypersecretion during childhood results in gigantism hypersecretion after long bone growth has ended results in acromegaly prolactin (PRL) protein hormone structurally similar to growth hormone only known target in humans is the breast (stimulate/maintain milk production) adrenocorticotropic hormone (ACTH) adrenal gland thyroid-stimulating hormone (TSH) growth and activity of the thyroid gland gonadotropic hormone regulate the hormonal activity of the gonads (ovaries and testes) follicle-stimulating hormone (FSH) stimulates follicle development in the ovaries stimulates sperm development by the testes luteinizing hormone (LH) triggers ovulation of an egg from the female ovary causes ruptured follicle to be converted to a corpus luteum stimulates the corpus luteum to produce progesterone and some estrogen stimulates testosterone production by the interstitial cells of the testes **anterior pituitary gland controls several endocrine glands - called the master endocrine gland **release of its hormones is controlled by releasing/inhibiting hormones produced by the hypothalamus posterior pituitary not an endocrine gland (it does not make the peptide hormones it releases) acts as a storage area for hormones made by hypothalamic neurons oxytocin during childbirth and in nursing women stimulates powerful contractions of the uterine muscle during labor, causes milk ejection antidiuretic hormone inhibits/prevents urine production causes kidneys to reabsorb more water from forming urine as a urine volume decreases - blood volume increases Thyroid Gland base of the throat inferior to the Adam's apple thyroid hormone major metabolic hormone controls rate at which glucose is burned/oxidized and converted to body heat/chemical energy important for normal tissue growth and development calcitonin decreases blood calcium levels by causing calcium to be deposited in the bones released directly to the blood in response to increasing levels of blood calcium Parathyroid Glands tiny masses of glandular tissue on the posterior surface of the thyroid gland parathyroid hormone (PTH) most important regulator of calcium ion homeostasis of the blood released when calcium levels drop below a certain level stimulates osteoclasts to break down bone matrix and release calcium into the blood **PTH is a hypercalcemic hormone (acts to increase blood levels of calcium) **calcitonin is a hypocalcemic hormone (acts to decrease blood levels of calcium) Adrenal Gland top of the kidneys structurally and functionally two endocrine organs in one - glandular (cortex) and neural tissue (medulla) adrenal cortex produces three major groups of steroid hormones collectively called corticosteroids mineralocorticoids regulates mineral (or salt) content of the blood (particularly sodium and potassium ions) target is kidney tubules that reabsorb minerals or allow them to be flushed out in urine help regulate both water and electrolyte balance in body fluids glucocorticoids promote normal cell metabolism help the body to resist long-term stresses increases blood glucose levels, decreases edema, inhibits some pain-causing molecules sex hormones produced by throughout life in relatively small amounts adrenal medulla develops from a knot of nervous tissue stimulated by sympathetic nervous system neurons release two similar hormones - epinephrine (adrenaline) and norepinephrine as (noradrenaline) fight-or-flight response stimulates the adrenal medulla hormones pumped into the bloodstream heart rate, blood pressure, blood glucose levels increase body is better able to deal with a short-term stressor **glucocorticoids operate during resistance stage of the stress response **prolonged/continuing stressors (death of a family member/having a major operation) Pancreatic Islets little masses of hormone-producing tissue scattered among enzyme-producing tissue of the pancreas more than a million insulin and glucagon regulate the amount of glucose in the blood insulin acts on just about all body cells increases ability to transport glucose across their plasma membranes glucose oxidized for energy or converted to glycogen or fat for storage as blood glucose levels fall, the stimulus for insulin release ends (negative feedback) absolutely necessary for the use of glucose by body cells glucagon antagonist of insulin primary target is the liver breaks down stored glycogen to glucose to be released into the blood Pineal Gland roof of the third ventricle of the brain somewhat of a mystery melatonin secreted in substantial amounts important role in establishing the body's day-night cycle helps regulate mating behavior and rhythms coordinates the hormones of fertility inhibits reproductive system (sexual maturation is prevented from occurring during childhood) Thymus upper thorax, posterior to the sternum large in infants and children but decreases in size throughout adulthood incubator for the maturation of T lymphocytes (important in the immune response) Gonads, Ovaries paired, almond-sized organs located in the pelvic cavity produces female sex cells and two groups of steroid hormones (estrogens and progesterone) begin to function at puberty (stimulated by anterior pituitary gonadotropic hormones) corpus luteum produces both estrogen and progesterone estrogens stimulate development of secondary sex characteristics in females prepare the uterus to receive a fertilized egg causes cyclic changes in the uterine lining (menstrual cycle) helps maintain pregnancy prepares the breasts to produce milk progesterone acts with estrogen to bring about the menstrual cycle quiets the muscles of the uterus so that an implanted embryo will not be aborted helps prepare breast tissue for lactation Gonads, Testes suspended in the scrotum outside the pelvic cavity produce male sex hormones (androgens) testosterone most important androgen causes development of adult male sex characteristics responsible for growth and maturation of the reproductive system necessary for continuous production of sperm Other Hormone Producing Tissues and Organs hormone-producing cells are found in the walls of the small intestine, stomach, kidneys, and heart also in the placenta and certain tumor cells (lung and pancreatic cancers) placenta formed temporarily in the uterus of pregnant women acts as the respiratory, excretory, and nutrition-delivery systems for the fetus also produces hormones to help maintain the pregnancy and deliver the baby - human chorionic gonadotropin stimulates the corpus luteum of the ovary to continue producing estrogen/progesterone so the uterine lining is not sloughed off in menses - human placental lactogen works cooperatively with estrogen/progesterone to prepare breasts for lactation - relaxin causes pelvic ligaments/pubic symphysis to relax and become more flexible Developmental Aspects most endocrine organs seem to operate smoothly until old age efficiency of the endocrine system as a whole gradually declines with age target organs also become less productive