A&P 16: The Endocrine System Flashcards
1
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Endocrine system
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2nd great control system of the body; interacts with the nervous system to coordinate and integrate the activity of body cells
2
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Endocrinology
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the scientific study of hormones and the endocrine organs
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Endocrine glands
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ductless glands; produce hormones, which are released into the surrounding tissue fluid; typically have a rich vascular and lymphatic drainage that receives their hormones
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Neuroendocrine organ
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the hypothalamus is considered this type of organ because, along with its neural functions, it produces and releases hormones
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Autocrines
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chemicals that exert their effects on the same cells that secrete them; short-distance signal
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Paracrines
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chemicals that act locally (within the same tissue) but affect cell types other than those releasing the chemicals
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Amino-acid based hormones
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most hormones are classified chemically on this basis
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Steroids
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hormones synthesized from cholesterol; of the hormones produced by the major endocrine organs, only gonadal and adrenocortical hormones fall into this category
9
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Eicosanoids
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some researchers add a third class of hormones, which includes leukotrienes and prostaglandins; nearly all cell membranes release these biologically active lipids (made from arachidonic acid)
10
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Target cells
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a hormone influences the activity of only those tissue cells that have receptors for it (a hormone alters the cellular activity of these)
11
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Second messengers
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with the exception of the thyroid hormone, amino acid-based hormones exert their signaling effects through these intracellular ___ ____ generated when a hormone binds to a receptor in the plasma membrane
12
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Cyclic AMP (cAMP)
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second messenger used by neurotransmitters and olfactory receptors
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First messenger
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the hormone, acting as this, binds to its receptor in the plasma membrane
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G protein
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hormone binding causes the receptor to change shape, allowing it to bind to a nearby inactive one of these proteins; acts like a light switch - off when GDP is bound to it and on when GTP is bound
15
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Adenylate cyclase
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the activated G protein (moving along the membrane) binds to this effector enzyme; some G proteins stimulate this, some inhibit it
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Protein kinases
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enzymes that phosphorylate (add a phosphate group to) various proteins, many of which are other enzymes
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Phosphodiesterase
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the action of cAMP persists only briefly because the molecule is rapidly degraded by this intracellular enzyme; the quick work of this means no extracellular controls are necessary to stop the activity
18
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Phospholipase C
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the PIP2-calcium signaling mechanism involves a G protein (Gq) and this membrane-bound effector; splits a plasma membrane phospholipid (PIP2)
19
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Phophatidyl Inositol Bisphosphate (PIP2)
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Phopholipase C splits this plasma membrane phospholipid into 2 second messengers (diacylglycerol DAG) & inositol triphosphate (IP3))
20
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Diacylglycerol (DAG)
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like cAMP, activates a protein kinase enzyme, which triggers responses within the target cell
21
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Inositol triphosphate (IP3)
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releases Ca2+ from intracellular storage sites
22
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Calmodulin
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the liberated Ca2+ takes on a 2nd messenger role, either by directly altering the activity of specific enzymes and channels or by binding to this intracellular regulatory protein; once Ca2+ binds to this, it activates enzymes that amplify the cellular response
23
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Up-regulation
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persistently low levels of a hormone can cause its target cells to form additional receptors for that hormone
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Down-regulation
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prolonged exposure to high hormone concentrations can decrease the number of receptors for that hormone; desensitizes target cells, so they respond less vigorously to hormonal stimulation, preventing them from overreacting to persistently high hormone levels
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Negative feedback mechanism
the synthesis and release of most hormones are regulated by some type of this mechanism, in which some internal or external stimulus triggers hormonal secretion; as levels of a hormone rise, it causes target organ effects, when then feed back to inhibit further hormone release; as a result, blood levels of many hormones vary only within a narrow range
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Humoral stimuli
some endocrine glands secrete their hormones in direct response to changing blood levels of certain critical ions and nutrients; simplest endocrine controls; PTH, insulin, and aldosterone are released in response to this type of stimuli
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Neural stimuli
in a few cases, nerve fibers stimulate hormone release; classic example = response to stress, in which the sympathetic nervous system stimulates the adrenal medulla to release norepi and epi
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Hormonal stimuli
many endocrine glands release their hormones in response to hormones produced by other endocrine organs
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Half-life
the length of time for a hormone's blood level to decrease by half; varies from a fraction of a minute to a week; water-soluble hormones have the shortest ones
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Permissiveness
situation in which one hormone cannot exert its full effects without another hormone being present
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Synergism
occurs when more than 1 hormone produces the same effects as the target cell and their combined effects are amplified; ex. glucagon and epi cause the liver to release glucose to the blood; when acting together, the amount of glucose released is 150% of what is released when each hormone acts alone
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Antagonism
occurs when 1 hormone opposes the action of another hormone; ex. insulin (lowers blood glucose levels) is antagonized by glucagon (raises blood glucose levels)
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Pituitary gland (hypophysis)
tiny; seated in the sella turcica of the sphenoid bone; secretes at least 8 hormones; "pea on a stalk"
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Infundibulum
the funnel-shaped stalk of the pituitary; connects the pituitary to the hypothalamus superiorly
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Posterior pituitary (lobe)
composed largely of neural tissue such as pituicytes (glia-like supporting cells) and nerve fibers
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Neurohormones
posterior pituitary releases these hormones secreted by neurons received ready-made from the hypothalamus; = hormone storage area; not a true endocrine gland that manufacturers hormones
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Neurohypophysis
posterior lobe plus the infundibulum
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Anterior pituitary (lobe)
adenohypophysis; composed of glandular tissue; manufactures and releases a number of hormones
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Hypothalmic-hypophyseal tract
nerve bundle running through the infundibulum that maintains the neural connection with the hypothalamus and the posterior lobe of the pituitary, which is actually part of the brain
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Paraventricular & supraoptic nuclei
the hypothalamic-hypophyseal tract arises from neurons in these nuclei of the hypothalamus; neurosecretory cells that synthesize 1 of 2 neurohormones and transport them along their axons to the posterior pituitary; ___ neurons primarily make oxytocin; the ___ neurons mainly produce antidiuretic hormone
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Primary capillary plexus
in the infundibulum; communicates inferiorly with the small hypophyseal portal veins with a secondary capillary plexus in the anterior lobe
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Hypophyseal portal veins
with the primary and secondary capillary plexuses, make up the hypophyseal portal system
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Portal system
unusual arrangement of blood vessels in which a capillary bed feeds into veins, which in turn feeds into a 2nd capillary bed
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Releasing and inhibiting hormones
via the hypophyseal portal system, these hormones, secreted by neurons in the ventral hypothalamus circulate to the anterior pituitary, regulate secretion of its hormones
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Oxytocin
a strong stimulant of uterine contractions; released in significantly higher amounts during childbirth and in nursing women
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Antidiuretic hormone (ADH)
prevents wide swings in water balance, helping the body avoid dehydration and water overload
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Vasopressin
under certain conditions, such as severe blood loss, exceptionally large amounts of ADH are released; at such high blood concentrations, ADH causes vasoconstriction, primarily of visceral blood vessels, raising blood pressure; this response targets different ADH receptors found on vascular smooth muscle; for this reason, ADH is also called this
48
Diabetes insipidus
one result of ADH deficiency; syndrome marked by intense thirst and huge urine output; "tasteless overflow"; distinguished from diabetes mellitus ("honey") in which insulin deficiency cause large amounts of blood glucose to be lost in the urine
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Tropic hormones (tropins)
4 of the 6 anterior pituitary hormones - TSH, ADH, FSH, LH; regulate the secretory action of other endocrine glands
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Somatotropic cells
these cells of the anterior lobe of the pituitary produce growth hormone (GH), AKA somatotropin
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Growth hormone (GH)
anabolic (tissue building) hormone that has both metabolic and growth-promoting actions
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Insulin-like growth factors (IGFs)
GH mediates most of its growth enhancing effects indirectly via a family of these growth-promoting proteins; the liver, skeletal muscle, bone, and other tissues produce these in response to GH; if produced by the liver, act as hormones; if made in other tissues, act locally as paracrines
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Growth hormone-releasing hormone (GHRH)
stimulates GH release
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Growth hormone-inhibiting hormone (GHIH)
AKA somatostatin; inhibits GH release
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Gigantism
hypersecretion of GH in children results in this because GH targets the still-active epiphyseal (growth) plates
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Acromegaly
if excessive GH is secreted after the epiphyseal plates have closed, this condition results; "enlarged extremities"; characterized by overgrowth of bony areas still responsive to GH (bones of the hands, feet, and face)
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Pituitary dwarfism
hyposecretion of GH in children; slows long bone growth; max height 1.2 m (4ft) with fairly normal body proportions; often accompanied by deficiencies of other anterior pituitary hormones; if diagnosed before puberty, GH replacement therapy can promote nearly normal growth
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Thyroid-stimulating hormone (TSH)
AKA thyrotropin; tropic hormone that stimulates normal development and secretory activity of the thyroid gland; its release follows the hypothalamic-pituitary-target endocrine organ feedback loop
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Thyrotropin-releasing hormone (TRH)
hypothalamic peptide that triggers the release of TSH from thyrotropic cells of the anterior pituitary
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Thyrotropic cells
cells of the anterior pituitary that release TSH, triggered by thyrotropin-releasing hormone (TRH)
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Adrenocorticotropic hormone (ACTH)
AKA corticotropin; secreted by corticotropic cells of the anterior pituitary; split from a prohormone (large precursor molecule)
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Corticotropic cells
cells of the anterior pituitary that secrete ACTH
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Pro-opiomelanocortin (POMC)
prohormone from which ACTH is split
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Corticotropin-releasing hormone (CRH)
ACTH release is elicited by this hypothalamic hormone
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Follicle-stimulating hormone (FSH) & luteinizing hormone (LH)
gonadotropins; regulate the function of the gonad (ovaries/testes); ___ stimulates production of gametes (sperm/eggs); __ promotes production of gonadal hormones
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Gonadotropic cells
cells of the anterior pituitary that are activated during puberty causing gonadotropin levels to rise and the gonads to mature
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Gonadotropin-releasing hormone (GnRH)
in both sexes, this hormone produced by the hypothalamus prompts gonadotropin release
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Prolactin (PRL)
protein hormone structurally similar to GH; stimulates milk production by the breasts; role in male not well understood
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Prolactin cells
cells that produce prolactin
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Prolactin-inhibiting hormone (PIH)
AKA dopamine; prevents prolactin secretion; decreased secretion of this lead to a surge in PRL release
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Thyroid gland
butterfly-shaped gland located in the anterior neck, on the trachea, just inferior to the larynx; largest pure endocrine gland in the body
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Follicles
internally, the thyroid is composed of these hollow, spherical structures, the walls of which are formed largely by cuboidal or squamous epithelial cells which produce the glycoprotein thryoglobulin
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Thyroglobulin
glycoprotein produced by follicular cells of the thyroid
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Colloid
the central cavity (lumen) of the thyroid's follicle stores this amber-colored, sticky material consisting of thyroglobulin molecules with attached iodine atoms; thyroid hormone is derived from this iodinated thyroglobulin
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Thyroid hormone (TH)
the body's major metabolic hormone; actually 2 iodine-containing amine hormones - thyroxine (T4) and triiodothyronine (T3)
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Thyroxine
T4; major hormone secreted by the thyroid follicles; made of 2 linked tyrosine amino acids (with 4 bound iodine atoms)
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Trioodothyronine
T3; most is formed at the target tissues by conversion of T4 to T3; made of 2 linked tyrosine amino acids (with 3 bound iodine atoms)
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Calorigenic effect
increasing basal metabolic rate and body heat production turns on transcription of genes concerned with glucose oxidation; this has a heat-producing effect
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Monoiodotyrosine (MIT)
attachment of 1 iodine to a tyrosine produces this substance
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Diiodotyrosine (DIT)
attachment of 2 iodines to a tyrosine produces this substance
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Myxedema
in adults, full-blown hypothyroid syndrome; symptoms include a low metabolic rate; feeling chilled, constipation; thick, dry skin; puffy eyes; edema; lethargy; and mental sluggishness
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Goiter
enlarged, protruding thyroid gland; occurs if myxedema results from lack of iodine
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Cretinism
severe hypothyroidism in infants; the child is mentally retarded and has a short, disproportionately sized body and a thick tongue and neck; may reflect a genetic deficiency of the fetal thyroid gland or maternal factors, such as lack of dietary iodine
84
Graves' disease
most common hyperthyroid pathology; an autoimmune condition in which a person makes abnormal antibodies directed against thyroid follicular cells; rather than marking these cells for destructions as antibodies normally do, these antibodies paradoxically mimic TSH and continuously stimulate TH release; typical symptoms include elevated metabolic rate; sweating; rapid, irregular heartbeat; nervousness; weight loss despite adequate food; eyeballs made protrude if the tissue behind the eyes becomes edematous and fibrous
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Calcitonin
polypeptide hormone released by the parafollicular (C) cells of the thyroid gland in response to a rise in blood Ca2+ levels; does not have a known physiological role in humans
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Parafollicular cells
AKA C cells; cells of the thyroid that produce calcitonin in response to a rise in blood Ca2+ levels
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Parathyroid glands
tiny, yellow-brown glands nearly hidden from view in the posterior aspect of the thyroid gland; usually 4 of these, but the number varies by individual
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Parathyroid cells
secrete parathyroid hormone
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Parathyroid hormone (PTH) or parathormone
protein hormone of the parathyroid gland; single most important hormone controlling calcium balance in the blood
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Adrenal glands
paired glands; pyramid-shaped organs perched atop the kidneys, where they are enclosed in a fibrous capsule and a cushion of fat; AKA suprarenal glands
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Adrenal medulla
inner part of an adrenal gland; more like a knot of nervous tissue than a gland; part of the sympathetic nervous system
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Adrenal cortex
outer part of the adrenal gland; encapsulates the medulla and forms the bulk of the gland; = glandular tissue derived from embryonic mesoderm
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Corticosteroids
the adrenal cortex synthesizes well over 2 dozen steroid hormones, collectively called these
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Zona glomerulosa
outside layer of the adrenal cortex; the cell clusters forming this superficial layer produce mineralocorticoids (hormones that help control the balance of minerals and water in the blood)
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Zona fasciculata
middle layer of the adrenal cortex; arranged in linear cords; mainly produce the metabolic hormones called glucocorticoids (and a little bit of gonadocorticoids)
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Zona reticularis
innermost layer of the adrenal cortex; abuts the adrenal medulla; have a netlike arrangement; mainly produce small amounts of adrenal sex hormones (gonadocorticoids) & a little bit of glucocorticoids
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Mineralocorticoids
essential function of this substances is to regulate electrolyte (mineral salt) concentrations in extracellular fluids, particularly Na+ (single most abundant extracellular fluid) and K+ (sets the resting membrane potential of all cells, determines how easily action potentials are generated in nerve and muscle)
98
Aldosterone
regulation of Na+ and K+ is the primary job of this most potent mineralocorticoid; accounts for more than 95% of the mineralocorticoids produced; reduces excretion of Na+ from the body (primary target = distal parts of the kidney tubules, where it stimulates Na+ reabsorption and water retention accompanied by elimination of K+); regulatory effects are brief
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Renin
when specialized cells of the juxtaglomerular complex in the kidneys are excited, they release this into the blood; it cleaves off part of the plasma protein angiotensinogen, triggering an enzymatic cascade that forms angiotensin II, which stimulates the glomerulosa cells to release aldosterone
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Angiotensinogen
plasma protein cleaved by renin; triggers enzymatic cascade that forms angiotensin II
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Angiotensin II
stimulates the glomerulosa cells to release aldosterone
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Glucocorticoids
essential to life, these substances influence the energy metabolism of most body cells and help us resist stressors; include cortisol (hydrocortisone), cortisone, and cortiocosterone; act on target cells by modifying gene activity
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Cushing's Syndrome
pathology of glucocorticoid excess; may be caused by an ACTH-releasing pituitary tumor; by an ACTH-releasing malignancy of the lungs, pancreas, or kidneys; or by a tumor of the adrenal cortex; syndrome is characterized by persistent elevated blood glucose levels (steroid diabetes), dramatic losses in muscle/bone protein, & water/salt retention, leading to hypertension and edema
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Cushing's Disease
when a glucocorticoid excess is caused by an ACTH-releasing pituitary tumor
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Addison's Disease
major hyposecretory disorder of the adrenal cortex; usually involves deficits in both glucocorticoids and mineralocorticoids; its victims tend to lose weight; plasma glucose/sodium levels drop, and potassium levels rise; severe dehydration/hypotension are common; corticosteroid replacement therapy is the usual treatment
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Gonadocorticoids
most of these secreted by the adrenal cortex are weak androgens; contribute to axillary and pubic hair development; in women, thought to contribute to sex drive; largely account for estrogens produced after menopause when ovarian estrogens are no longer produced
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Androgens
male sex hormones (eg. androstenedione and dehydroepiandrosterone = DHEA); most are converted in tissue cells to more potent male hormones such as testosterone; some are converted to estrogens
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Medullary chromaffin cells
spherical cells of the adrenal medulla which crowd around blood-filled capillaries and sinusoids and are modified postganglionic sympathetic neurons that synthesize the catecholamines epi and norepi
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Epinephrine & norepinephrine
catecholamines synthesized by the medullary chromaffin cells of the adrenal medulla via a molecular sequence from tyrosine to dopamine to ____ to ___
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Hyperglycemia
elevated blood glucose
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Pineal gland
tiny, cone-shaped gland hanging from the roof of the 3rd ventricle in the diencephalon; handy landmark of determining brain orientation in x-rays due to its calcium salts being radiopaque
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Pinealocytes
secretory cells of the pineal gland; arranged in compact cords/clusters
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Melatonin
only major secretory product of the pineal gland; an amine hormone derived from serotonin
114
Pancreas
soft, tadpole-shaped organ partially behind the stomach; mixed gland composed of both endocrine and exocrine gland cells; mostly acinar cells, which produce an enzyme-rich juice that is carried by ducts to the small intestine during digestion
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Pancreatic islets
islets of Langerhans; scattered among the acinar cells in the pancreas are a million of these tiny cell clusters that produce pancreatic hormones
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Alpha cells
1 of 2 major populations of hormone-producing cells; synthesizes glucagon; stains bright pink
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Beta cells
1 of 2 major populations of hormone-producing cells; synthesizes insulin; more numerous than other type; stains pale pink
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Glucagon
29-amino-acid polypeptide; extremely potent hyperglycemic agent (1 molecule can cause the release of 100 million glucose molecules into the blood); major target = liver, where it promotes breakdown of glycogen to glucose (glycogenolysis), synthesis of glucose from lactic acid and from noncarbs (gluconeogenesis), and release of glucose to the blood by liver cells, causing blood glucose levels to rise
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Insulin
small (51-amino acid) protein consisting of 2 amino acid chains linked by disulfide bonds; synthesized as part of a larger polypeptide chain (proinsulin)
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Proinsulin
larger polypeptide chain that synthesizes insulin (enzymes excise the middle portion of the chain, releasing functional insulin); the "clipping" process occurs in the secretory vesicles just before the beta cell releases insulin
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Diabetes mellitus (DM)
results from either hyposecretion or hypoactivity of insulin; when insulin is absent = type I; if insulin present, but its effects are deficient = type II
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Ketones (ketone bodies)
fatty acid metabolites
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Ketoacidosis
when ketones accumulate in the blood, the blood pH drops, resulting in this condition
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Polyuria
huge urine output that decreases blood volume and causes dehydration; 1st cardinal sign of DM
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Polydipsia
excessive thirst; 2nd cardinal sign of DM
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Polyphagia
excessive hunger and food consumption; 3rd cardinal sign of DM; plenty of glucose available, but body cannot use it and consumes its fat and protein stores for energy metabolism instead ("starving in the land of plenty")
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Hypoglycemia
excessive insulin secretion (hyperinsulinism); triggers the release of hyperglycemic hormones, which cause anxiety, nervousness, tremors, and weakness; commonly caused by an overdose of insulin; easily treated by ingesting sugar
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Gonads
male and female ___ produce steroid sex hormones, identical to those produced by adrenal cortical cells; major distinction is the source and relative amounts produced
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Estrogens and progesterones
hormones produced by the ovaries; ___ responsible for maturation of the reproductive organs and the appearance of secondary sex characteristics of females at puberty; both promote breast development and cyclic changes in the uterine mucosa (menstrual cycle)
130
Testosterone
male sex hormone; during puberty, initiates the maturation of the male reproductive organs and the appearance of the secondary sex characteristics and sex drive; necessary for normal sperm production and maintains the reproductive organs in their mature functional state in adult males
131
Leptin
adipose cells release this substance, which serves to tell your body how much stored energy (as fat) you have; the more fat you have, the more of this there will be in your blood; binds with CNS neurons concerned with appetite control, producing a sensation of satiety; also appears to stimulate increased energy expenditure
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Atrial natriuretic peptide (ANP)
the atria in the heart contain specialized cardiac muscle cells that secrete this, which decreases the amount of sodium in the extracellular fluid, thereby reducing blood volume and blood pressure
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Erythropoietin (EPO)
"red-maker"; a glycoprotein hormone that signals the bone marrow to increase production of red blood cells
134
Renin
kidneys release this, which acts as an enzyme to initiate the renin-angiotensin-aldosterone mechanism of aldosterone release
135
Cholecaciferol
inactive form of vitamin D3, which is produced by the skin when modified cholesterol molecules in epidermal cells are exposed to UV radiation
136
Calcitriol
active form of D3; essential regulator of the carrier system intestinal cells used to absorb Ca2+ from food; bones become soft and weak without this vitamin
137
Thymus
located deep to the sternum in the thorax is this lobulated organ; large and conspicuous in children, it shrinks throughout adulthood; by old age, it is composed largely of adipose and fibrous connective tissues
138
Peptide hormones secreted by the thymus
thymulin, thymopoietins, thymosins; thought to be involved in the normal development of T lymphocytes and the immune response; mainly act locally as paracrines
139
Type 1 Diabetes Mellitus
formerly insulin-dependent diabetes mellitus (IDDM)
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Type 2 Diabetes Mellitus
formerly non-insulin-dependent diabetes mellitus (NIDDM)
141
Insulin resistance
a condition in which type 2 diabetics produce insulin, but their insulin receptors are unable to respond to it
