BIOL 244: Endocrine System
67 Cards in this Set
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Endocrine system
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glands, tissues, and cells that secret hormones
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Endocrinology
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study of the endocrine system and the diagnosis & treatment of its disorders
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Endocrine glands
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organs that are traditional sources of hormones
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Hormones
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-chemical messengers that are transported by the bloodstream
-stimulate physiological responses in cells of another tissues or organ (often a considerable distance away)
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Major organs of the endocrine system
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-pineal gland
-hypothalamus
-pituitary gland
-thyroid gland
-parathyroid gland(s)
-thymus
-adrenal gland
-pancreas
-ovary & testes
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Exocrine glands
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-have ducts that carry secretions to an epithelial surface or the mucosa of the digestive tract (external secretions)
-extracellular effects (i.e.; food digestion)
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Endocrine glands
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-no ducts
-contain dense, fenestrated capillary networks which allow easy uptake of hormones into bloodstream
-intracellular effects (i.e.; altering target cell metabolism)
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Nervous System vs Endocrine System: Both serve for internal communication
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Nervous: both electrical and chemical
Endocrine: only chemical
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Nervous System vs Endocrine System: Speed & persistence of response
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Nervous: reacts quickly (1-10msec), stops quickly
Endocrine: reacts slowly (hormone release in seconds or days), effect may continue for weeks
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Nervous System vs Endocrine System: Area of effect
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Nervous: targeted and specific (one organ)
Endocrine: general, widespread effects (many organs)
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Communication by nervous system
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neurons
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Communication by Endocrine System
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-capillary networks/bloodstream
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Nervous & Endocrine Systems: similarities
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-several chemicals function as both hormones and neurotransmitters (norepinephrine, dopamine, antidiuretic hormone…)
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Nervous & Endocrine Systems: similarities
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-some hormones secreted by neuroendocrine cells/neurons that release their secretions into the bloodstream (oxytocin and catecholamines)
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Nervous and Endocrine Systems: similarities
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both systems with overlapping effects on same target cells
-norepinephrine and glucagon cause glycogen hydrolysis in liver
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Nervous & Endocrine systems: similarities
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systems regulate each other
-neurons trigger hormone secretion
-hormones stimulate or inhibit neurons
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Nervous and Endocrine systems: similarities
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-target organs/cells (organs or cells that have receptors for a hormone and can respond to it)
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Hypothalamus
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-forms floor and walls of third ventricle of the brain (part of diencephalon)
-regulates a number of different functions (water balance and thermoregulation; sex drive and childbirth)
-many of its functions are carried out by pituitary gland
-*hypothalamus releasing and inhibiting horm…
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*Thyrotropin-releasing hormone (TRH)
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-promotes secretion of thyroid-stimulating hormone (TSH) and prolactin (PRL)
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*Corticotropin-releasing hormone (CRH)
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-promotes secretion of adrenocorticotropic hormone (ACTH)
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*Gonadotropin-releasing hormone (GnRH)
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-promotes secretion of follicle-stimulating horone (FSH) and luteinizing hormone (LH)
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*Growth hormone-releasing hormone (GHRH)
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-promotes secretion of growth hormone (GH)
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*Prolactin-inhibiting hormone (PIH)
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-inhibits secretion of prolactin (PRL)
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*Somatostatin
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-inhibits secretion of growth hormone (GH) and thyroid-stimulating hormone (TSH)
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Pituitary gland (hypophysis)
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-aka "Master Gland:
-suspended from hypothalamus by a stalk (infundibulum)
-composed of two structures with independent origins and separate functions
1)adenohypophysis (**anterior pituitary)
2)neurohypophysis (**posterior pituitary_
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**(A.P.): Follicle-stimulating hormone (FSH)
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target: ovaries, testes
-female: growth of ovarian follicles and secretion of estrogen
-male: sperm production
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**(A.P.): Luteinizing hormone (LH)
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target: ovaries, testes
-female: ovulation, maintenance of corpus luteum
-male: testosterone secretion
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**(A.P.): Thyroid-stimulating hormone (TSH)
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target: thyroid gland
-growth of thyroid gland
-secretion of thyroid hormone
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**(A.P.): adrenocorticotropic hormone (ACTH)
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target: adrenal cortex
-growth of adrenal cortex
-secretion of glucocorticoids
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**(A.P.): Prolactin (PRL)
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target: mammary glands, testes
-female: milk synthesis
-male: increase LH sensitivity & testosterone secretion
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**(A.P.): Growth hormone (GH)
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target: liver, bones, cartilage, muscle, fat
-widespread tissue growth (esp. in the stated tissues^)
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**(P.P.): Antidiuretic hormone (ADH)
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target: kidneys
-water retention
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**(P.P.): Oxytocin (OT)
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target: uterus, mammary glands
-labor contraction
-milk release
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Control of pituitary: Negative feedback from target hormones
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-increased target organ hormone levels inhibits release of hormones
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Control of pituitary: positive feedback
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-stretching of uterus increases OT release, causes contractions, causing more stretching of uterus, etc. until delivery
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Pineal gland
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-may synchronize physiological function with 24-hr circadian rhythms of daylight and darkness (sleep-wake cycle)
-may regulate timing of puberty in humans
-after age 7, it undergoes involution (shrinkage)
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Thymus
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-plays a role in 3 systems: endocrine, lymphatic, and immune
-site of maturation of T cells (important in immune defense)
-secretes hormones (thymosin, thymulin, thymopoietin) that stimulate development of other lymphatic organs and activity of T-lymphocytes
-undergoes involution after…
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Thyroid gland
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-largest endocrine gland
-secretes thyroxine (T4) and triiodothyronine (T3): increase metabolic rate, oxygen consumption, heat production, appetite, growth hormone secretion, alertness, and quicker reflexes
-parafollicular cells (C or clear cells): secrete calcitonin with rising blood c…
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Parathyroid gland
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-4 glands partially embedded in posterior surface of thyroid gland
-secrete parathyroid hormone (PTH): increases blood calcium levels (ALSO: promotes synthesis of calcitriol, increases absorption of calcium, decreases urinary excretion, increases bone resorption)
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Adrenal gland: adrenal medulla
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-inner core
-has dual nature acting as an endocrine gland and sympathetic ganglion of sympathetic nervous system
~when stimulated, releases catecholamines (epinephrine and norepinephrine) and a traces of dopamine into the bloodstream
-effects longer lasting than neurotransmitters
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Adrenal gland: adrenal medulla (cont'd)
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~increases blood pressure, heart rate, blood flow to muscles, pulmonary air flow, and metabolic rate
~decreases digestion and urine production
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Adrenal gland: adrenal cortex
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-surrounds adrenal medulla & produces corticosteroids/corticoids (steroid hormones)
-secretes fiver major steroids from 3 layers of glandular tissue
1) zona glomerulosa (thin, outer layer)
2) zona fasciculata (thick, middle layer)
3) zona reticularis (narrow, inner layer)
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Categories of corticosteroids:mineralocorticoids (zona glomerulosa)
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-regulate electrolyte balance
-aldosterone: stimulates sodium retention and potassium excretion; water is retained with sodium by osmosis, so blood volume and blood pressure are maintained
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Categories of corticosteroids: glucocorticoids (zona fasciculata)
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regulate metabolism of glucose and other fuels (esp. cortisol, which stimulates fat and protein catabolism, gluconeogenesis, and release of fatty acids + glucose into blood)
-helps body adapt to stress and repair tissues
-anti-inflammatory effect
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Categories of corticosteroids: sex steroids (zona reticularis)
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-androgens: sex libido throughout life; large role in prenatal male development
-estradiol: small quantity; important after menopause for sustaining adult bone mass
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Pancreas
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-exocrine digestive gland
-endocrine cell clusters (islets)
-1-2 million pancreatic islets (Islets of Langerhans) produce hormones
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Pancreatic hormones: Insulin
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-secreted by B or beta cells
-secreted during and after a meal (when glucose and amino acid blood levels are rising)
-stimulates cells to absorb these nutrients & store or metabolize them, lowering blood glucose levels
-insufficiency/inaction = cause of Diabetes mellitus
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Pancreatic hormones: glucagon
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secreted by A or alpha cells
-released between meals when blood glucose concentration is falling
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Pancreatic hormones: somatostatin
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-secreted by D or delta cells
-partially suppresses secretion of glucagon and insulin
-inhibits nutrient digestion and absorption, which prolongs absorption of nutrients
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Pancreatic hormones: Pancreatic polypeptide
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-secreted by PP or F cells
-inhibits gallbladder contraction and secretion of pancreatic digestive enzymes
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Pancreatic hormones: gastrin
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-secreted by G cells
-stimulates stomach acid secretion, motility, and emptying
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Pineal Gland
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-hormone: melatonin
-target: brain
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Thymus
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-hormones: thymopoietin, thymosin, thymulin
-target: immune cells (T lymphocytes)
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Thyroid gland
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-hormone: T4 & T3; target: most tissues
-hormone: calcitonin; target: bone
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Parathyroid gland
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-hormone: parathyroid hormone
-target: bone, kidneys, small intestine
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Adrenal medulla
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-hormones: epinephrine, norepinephrine, dopamine
-target: most tissues
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Adrenal cortex
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-hormone: aldosterone; target: kidney
-hormones: cortisol & corticosterone; target: most tissues
-hormone: dehydroepiandrosterone; target: bone, muscle, integument, brain, many other tissues
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Ovary: ovarian hormones
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-estradiol & progesterone
~development of female reproductive system and physique, including adolescent bone growth
~regulate menstrual cycle, sustain pregnancy
~prepare mammary glands for lactation
-inhibin
~suppresses FSH secretion from anterior pituitary
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Testes: testicular hormones
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-testosterone (&other hormones)
~stimulates development of male reproductive system in fetus and adolescent and sex drive
~sustains sperm production
-inhibin
~limits FSH secretion in order to regulate sperm production
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Endocrine functions of other organs (review)
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-skin
-liver
-kidneys
-heart
-stomach & small intestine
-placenta
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Hormone Chemistry
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-all hormones are made from either cholesterol or amino acids (w/ carbohydrates added to make glycoproteins)
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3 classes of hormones: steroids
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-derived from cholesterol
-secreted by gonads and adrenal glands
-Ex: estrogen, progesterone, testosterone, cortisol, corticosterone, aldosterone, DHEA, calcitriol
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3 classes of hormones: peptides & glycoproteins
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-created from chains of amino acids
-secreted by pituitary and hypothalamus
-ex: oxytocin, antidiuretic hormone, releasing and inhibiting hormones, and anterior pituitary hormones
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3 classes of hormones: monoamines
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-derived from amino acids
-secreted by adrenal, pineal, and thyroid glands
-ex: epinephrine, norepinephrine, melatonin, and thyroid hormone
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Hormone receptors
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-hormones stimulate only those cells that have receptors for them
-receptors are protein or glycoprotein molecules (on plasma membrane, in cytoplasm, or in the nucleus)
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Hormone mode of action: hydrophobic hormones
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-penetrate plasma membrane and enter the nucleus
-act directly on the genes, changing target cell physiology
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Hormone mode of action: hydrophilic hormones
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-cannot penetrate into target cell
-must stimulate physiology indirectly
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BIOL 244: Exam 1