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118 Cards in this Set
- Front
- Back
What is the function of endocrine glands?
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Synthesize and secrete chemical substances called hormones directly into the circulatory system
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What is the function of exocrine glands?
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Secrete substances that are transported by ducts
EX: gall bladder |
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What is the function of hormones?
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Regulate the function of target organs or tissues
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What is the specificity of hormonal action depend on?
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It is determined by the presence of specific receptors on or in the target cells.
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What is the pituitary gland?
What is another name for it? |
The pituitary (hypophysis) is a small, tri-lobed gland lying at the base of the brain.
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What are the three lobes of the pituitary gland?
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1. Anterior
2. Posterior 3. Intermediate (no function) |
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What is the function of the anterior pituitary?
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Synthesizes both direct hormones, which directly stimulate their target organs, and tropic hormones, which stimulate other endocrine glands to release hormones.
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What regulates the hormonal secretions of the anterior pituitary?
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Hypothalamic secretions called releasing/inhibiting hormones or factors
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What are the three direct hormones of the anterior pituitary?
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1. Growth Hormone (GH, somatotropin)
2. Prolactin 3. Endorphins |
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What is the function of Growth Hormone (GH)?
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Promotes bone and muscle growth, inhibits the uptake of glucose by certain cells, and stimulates the breakdown of fatty acid, thus conserving glucose.
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How is GH secretion controlled?
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Stimulated by the hypothalamic releasing hormone (GHRH) and inhibited by somatostatin
Secretion is also under neural and metabolic control |
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1. In children, what does a GH deficiency result in?
2. In children, what does an overproduction of GH result in? |
1. Dwarfism
2. Gigantism |
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In adults, what does an overproduction of GH result in?
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Acromegaly, a disorder characterized by a disproportionate overgrowth of bone, localized especially in the skull, jaw, feet, and hands
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What is the function of prolactin?
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Stimulates milk production and secretion in female mammary glands
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What is the function of endorphins? What is another name ?
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Endorphins (enkephalins)inhibit the perception of pain.
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What are the four tropic hormones?
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1. Adrenocorticotropic hormone (ACTH)
2. Thyroid-stimulating hormone (TSH) 3. Luteinizing hormone (LH) 4. Follicle-stimulating hormone (FSH) |
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What is the function of adrenocorticotropic hormone (ACTH)?
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Stimulates the adrenal cortex to synthesize and secrete glucocorticoids; regulated by the releasing hormone corticotropin releasing factor (CRF)
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What is the function of the thyroid-stimulating hormone (TSH)?
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Stimulates the thyroid gland to absorb iodine and then synthesize and release thyroid hormone; regulated by the releasing hormone TRH
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What is the function of the luteinizing hormone?
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In females, LH stimulates ovulation and formation of the corpus luteum.
In males, LH stimulates the interstitial cells of the testes to synthesize testosterone. |
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What regulates LH?
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Estrogen, progesterone, and gonadotropin releasing hormone (GnRH)
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What is the function of the follicle-stimulating hormone (FSH)?
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In females, FSH causes maturation of ovarian follicles.
In males, FSH stimulates maturation of the seminiferous tubules and sperm production. |
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What regulates FSH?
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Estrogen and GnRH
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What is the function of the posterior pituitary?
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It does not synthesize hormones; it stores and releases the hormones oxytocin and ADH, which are produced by the neurosecretory cells of the hypothalamus.
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How is hormone secretion in the posterior pituitary regulated?
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Stimulated by action potentials descending from the hypothalamus.
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What are the two hormones secreted by the posterior pituitary?
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1. Oxytocin
2. Antidiuretic Hormone (ADH) |
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What is the function of oxytocin?
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Secreted during childbirth, oxytocin increases the strength and frequency of uterine muscle contractions.
Oxytocin stimulates milk secretion in the mammary glands since oxytocin secretion is also induced by suckling. |
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What is the function of ADH?
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Increases the permeability of the nephron's collecting duct to water, thereby promoting water reabsorption and increasing blood volume.
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When is ADH secreted?
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When plasma osmolarity increases, as sensed by osmoreceptors in the hypothalamus, OR when blood volume decreases, as sensed by baroreceptors in the circulatory system
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What is the hypothalamus?
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Part of the forebrain; located directly above the pituitary gland; receives neural transmissions from other part of the brain and from peripheral nerves that trigger specific responses from its neurosecretory cells
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How does the hypothalamus interact with the anterior pituitary?
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Hypothalamic releasing hormones are hormones that stimulate/inhibit the secretions of the anterior pituitary
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Where are releasing hormones secreted?
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Into the hypothalamic-hypophyseal portal system
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What is the hypothalamic-hypophyseal portal system?
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A circulatory pathway in which blood from the capillary bed in the hypothalamus flows through a portal vein into the anterior pituitary, where it diverges into a second capillary network
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What is the purpose of the hypothalamic-hypophyseal portal system?
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Serves as a way for releasing hormones to immediately reach the anterior pituitary
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Since overproduction of hormones is potentially harmful to an organism, what is a preventative mechanism used?
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Negative feedback
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How does the hypothalamus interact with the posterior pituitary?
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Neurosecretory cells in the hypothalamus synthesize both oxytocin and ADH and transport them via their axons into the posterior pituitary for storage and secretion
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What is the thyroid gland?
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A bi-lobed structure located on the ventral surface of the trachea
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What is the function of the thyroid gland?
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Produces and secretes throxine, triiodothyronine, and calcitonin
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What are the two thyroid hormones? How are they produced?
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1. Thyroxine (T4)
2. Triiodothyronine (T3) Both are derived from the iodination of the amino acid tyrosine |
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Why are thyroid hormones necessary for growth and neurological development in children?
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They increase the rate of cellular respiration and the rate of protein and fatty acid synthesis and degradation in many tissues
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What is the cause of hypothyroidism?
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inflammation of the thyroid or iodine deficiency; thyroid hormones are undersecreted or not secreted at all
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What are common symptoms of hypothyroidism?
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Slowed heart rate and respiratory rate, fatigue, cold intolerance, and weight gain
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What is cretinism?
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Hypothyroidism in newborn infants; characterized by mental retardation and short stature
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What are the symptoms of hyperthyroidism?
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Increased metabolic rate, feelings of excessive warmth, profuse sweating, palpitations, weight loss, and protruding eyes
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What is the function of calcitonin?
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Decreases plasma Ca+2 concentration by inhibiting the release of Ca+2 from bones
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What are the parathyroid glands?
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4 small pea-shaped structures embedded in the posterior surface of the thyroid
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What is the function of the parathyroid glands?
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Synthesize and secrete parathyroid hormone (PTH), which, together with calcitonin and Vitamin D, regulates plasma Ca+2 concentration
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How does Parathyroid hormone (PTH) stimulate intestinal calcium absorption?
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Converting Vitamin D into its active form
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How does PTH raise Ca+2 concentration in the blood?
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By stimulating Ca+2 release from bone and decreasing Ca+2 excretion in the kidneys
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What are the adrenal glands?
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Situated on top of the kidneys and consist of the adrenal cortex and the adrenal medulla
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How is the adrenal cortex stimulated?
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In response to stress, ACTH stimulates the adrenal cortex to synthesize and secrete the steroid hormones, which are collectively known as corticosteroids
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What are the corticosteroids?
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Derived from cholesterol; include:
glucocorticoids, mineralocorticoids, and cortical sex hormones |
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What is the function of the glucocorticoids?
ex: cortisol, cortisone |
Involved in glucose regulation and protein metabolism: raise blood glucose levels by promoting gluconeogenesis and decrease protein synthesis; also reduce body's immunological and inflammatory responses
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What is the function of mineralocorticoids?
ex: aldosterone |
Regulate plasma levels of sodium and potassium, and consequently, the total extracellular water volume; stimulates the secretion of potassium ion and hydrogen ion into the nephron and their subsequent excretion in urine
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What is the function of aldosterone?
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Causes active reabsorption of sodium and passive reabsorption of water in the nephron
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How is aldosterone secretion regulated?
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The renin-angiotensin system
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What is the renin-angiotensin system?
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When blood volume falls, the juxtaglomerular cells of the kidney produce renin (enzyme that converts the plasma protein angiotensinogen to angiotensin I; Angtiotensin I is converted to angiotensin II, which stimulates the adrenal cortex to secrete aldosterone
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What is the function of the cortical sex hormones?
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Androgens (male sex hormones) secreted by adrenal cortex have small effect in men. Overproduction of the adrenal androgens may have masculinizing effects on women.
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What is the function of the adrenal medulla?
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The secretory cells of the adrenal medulla can be viewed as specialized sympathetic nerve cells that secrete hormones into the circulatory system; produces epinephrine and norepinephrine
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Epinephrine and norepinephrine both belong to which class of amino acid-derived compounds?
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Catecholamines
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What is the function of epinephrine?
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Increases the conversion of glycogen to glucose in liver and muscle tissue, causing a rise in blood glucose levels and increase in the basal metabolic rate
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What is the "fight or flight response"?
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Effects elicited by the sympathetic nervous stimulation in response to stress
ex: increase the rate and strength of heartbeat, dilate and constrict blood vessels in such a way as to increase the blood supply to skeletal muscle, the heart, and brain, while decreasing the blood supply to kidneys, skin, and digestive tract |
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How is the endocrine function of the pancreas performed?
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Performed by small glandular structures called islets of Langerhans, which are composed of alpha, beta, and delta cells
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How is the exocrine function of the pancreas performed?
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Performed by cells that secrete digestive enzymes into the small intestine via a series of ducts
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What do alpha cells produce and secrete?
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Glucagon
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What is the function of glucagon?
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Stimulates protein and fat degradation, the conversion of glycogen to glucose, and gluconeogenesis - all of which serve to increase blood glucose levels
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How is glucagon secretion regulated?
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Stimulated by a decrease in blood glucose and by gastrointestinal hormones; inhibited by high plasma glucose levels; works antagonistically to insulin
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What is insulin?
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Protein hormone secreted in response to high blood glucose concentration; stimulates the update of glucose by muscle and adipose cells and the storage of glucose as glycogen, thus lowering blood glucose levels; stimulates the synthesis of fats from glucose and the uptake of amino acids
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What is the result of an overproduction of insulin?
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Hypoglycemia (low blood glucose levels)
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What is the result of an underproduction of insulin?
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Hyperglycemia (high blood glucose levels); insensitivity to insulin leads to diabetes mellitus
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What is the result of high blood glucose levels?
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Excretion of glucose and water loss
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What is ketoacidosis?
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Dangerous lowering of blood pH due to excess keto acids and fatty acids in the plasma; characteristic of diabetes
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What do beta cells produce and secrete?
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Insulin
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What do delta cells produce and secrete?
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Somatostatin
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What is somatostatin secretion regulated by?
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Increased by high blood glucose levels or high amino acid levels, leading to both decreased insulin and glucagon secretion; also regulated by CCK and GH levels
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What is the function of somatostatin?
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Inhibition...regardless of where it acts
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What is testosterone?
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Induces embryonic sexual differentiation and male sexual development at puberty; maintains secondary sex characteristics
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What is the function of the testes?
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Interstitial cells of testes produce and secrete androgens like testosterone
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How is the secretion of testosterone regulated?
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Negative feedback mechanism involving FSH and LH
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What is testicular feminization?
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Insensitivity to testosterone; genetic male (XY) has female secondary sexual characteristics
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What is the function of the ovaries?
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Synthesize and secrete estrogens and progesterone
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What is estrogen?
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Steroid hormones necessary for normal female maturation; stimulate development of female reproductive tract, contribute to development of secondary sexual characteristics, and responsible for thickening of endometrium
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How is estrogen secreted?
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Ovarian follicles and corpus luteum
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What is progesterone?
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Steroid hormone secreted by the corpus luteum during the luteal phase of the menstrual cycle; stimulates the development and maintenance of the endometrial walls in preparation for implantation
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What is the menstrual cycle?
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From puberty through menopause, the interactions between hormones secreted by ovaries, hypothalamus, and pituitary gland result in a monthly cyclical pattern
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What are the 4 phases of the menstrual cycle?
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1. Follicular phase
2. Ovulation 3. Luteal phase 4. Menstruation |
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What is the Follicular Phase?
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Follicles mature as FSH and LH act together
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What is Ovulation?
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A surge in LH at midcycle triggers ovulation; mature ovarian follicle bursts and releases an ovum
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What is the Luteal Phase?
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Ruptured follicle becomes corpus luteum and secretes estrogen and progesterone to build up uterine lining in preparation for implantation; progesterone + estrogen inhibit FSH and LH
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What occurs during menstruation?
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If the ovum isn't fertilized, corpus luteum atrophies, progesterone and estrogen levels decrease, menses occurs, and LH and FSH levels begin to rise again
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What occurs during the first trimester of pregnancy?
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Corpus luteum is preserved by human chorionic gonadotropin (HCG)--> hormone produced by the blastocyst and the developing placenta; progesterone and estrogen secretion by corpus luteum is maintained
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What occurs during the second trimester of pregnancy?
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HCG levels decline, progesterone + estrogen levels increase which in turn inhibit GnRH secretion, preventing FSH and LH secretion and the onset of a new menstrual cycle
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What do urine pregnancy tests look for?
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Presence of HCG in the urine; can be detected in the urine 1-2 weeks after conception
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What is menopause?
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Result of a progressive decline in functioning of ovaries with advancing age
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What is the pineal gland?
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Tiny structure at the base of the brain that secretes the hormone melatonin
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What is the role of melatonin?
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Not clear, but believed to play a role in regulation of circadian rhythms
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What is renin?
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Enzyme secreted by kidney; involved in regulation of aldosterone secretion
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What is erythropoietin?
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Secreted by the kidney in response to decreased renal oxygen levels; stimulates bone marrow to produce red blood cells
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What is atrial natriuretic hormone?
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Heart is an endocrine organ; releases this hormone which is involved in the regulation of salt and water balance
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What is thymosin?
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Secreted by thymus; stimulates T lymphocyte development and differentiation
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What are the three classifications of hormones?
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1. Peptides
2. Steroids 3. Amino acid derivatives |
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What are the 2 ways in which hormones affect the activities of their target cells?
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1. Extracellular receptors
2. Intracellular responses |
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Peptide hormones act as:
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First messengers: their binding to specific receptors on the surface of their target cells triggers a series of enzymatic reactions within each cell --> cascade effect = with each step, the hormone's effects are amplified
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What are the enzymes responsible for the production and destruction of cyclic AMP?
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Synthesized by adenylate cyclase (plasma membrane enzyme)
Destroyed/hydrolyzed by phosphodiesterase = cytoplasmic enzyme |
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How are steroid hormones synthesized?
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Precursors already present in the cell undergo enzymatic reactions that convert them into active hormones; steroid hormones are not stored, but secreted at a rate determined by rate of synthesis
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What is th mechanism of steroid hormones?
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Enter their target cells directly and bind to specific receptor proteins in the cytoplasm; receptor-hormone complex enters the nucleus and directly activates the expression of specific genes by binding to receptors on the chromatin; this induces a change in mRNA transcription and protein synthesis
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What are amino acid derivatives?
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Hormones composed of one or two modified amino acids; synthesized in the cytoplasm of glandular cells
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What is the mechanism of amino acid derivatives?
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Activate target cells via secondary messengers (in most cases)
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What is the function of the hormone secretin?
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Secreted by duodenum when acidic chyme enters the small intestine; secretin stimulates the secretion of pancreatic juice, which contains a high concentration of bicarbonate ion and is therefore alkaline enough to neutralize the chyme
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Steroid hormones bind to receptors in the nucleus and directly regulate:
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the transcription of mRNA
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T/F: Hormones must be present in large quantities to have an effect.
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FALSE; hormones are capable of being effective at picomolar concentrations
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T/F: K+ is reabsorbed from the glomerular filtrate.
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FALSE: K+ is considered a waste product and is secreted into the distal convoluted tubule
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Where is glucose reabsorbed?
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Proximal convoluted tubule
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What is acetycholine?
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Primary neurotransmitter in a parasympathetic nervous response
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At which end is hydrostatic pressure greater?
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Arteriolar end - forcing fluids out of vessels
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At which end is osmotic pressure greater?
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Venule end - drives fluids back into the vessels
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T/F: ACh diffuses through the presynaptic membrane after its synthesis.
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FALSE: AChE degrades ACh very quickly after release in order to prevent constant stimulation of the synapse
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What is the pathway of estrogen?
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Since estrogen is derived from cholesterol, it is lipid soluble. Thus, it crosses membranes via simple diffusion - does not require channels
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T/F: Insulin would require a second messenger to relay its signal.
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TRUE: Insulin is a peptide hormone. Peptide hormones are unable to cross the plasma membrane and a second messenger is activated to relay the signal to the interior of the cell.
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