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50 Cards in this Set
- Front
- Back
Definition of hormone
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bloodborne substance that regulates physiological process
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Functions of hormones
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1) digestion, utilization, storage of nutrients
2)growth and development 3)ion and water balance 4)reproductive function |
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Autocrine signaling
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acts on adjacent cells of same type or as negative feedback on same cell
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Paracrine signalling
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acts on adjacent target cells
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Endocrine signalling
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hormone secreted into blood and carried to target cells
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Neurocrine signalling
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released from neuron and diffuses into blood to target cells
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Amino acid derived and polypeptide/protein hormones
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-synthesized in advance and stored in vesicles
-may be cleaved from preprohormones or prohormones -transported dissolved in plasma |
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Steroid hormones
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-cholesterol derivatives - hydrophobic
-produced on demand -transported bound to plasma proteins |
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Hormone release characteristics
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-may be stimulated by NT --> higher brain areas stimulate hormone release in response to sensory input
-may be stimulated by another hormone --> hormone released into blood by one organ stimulates another to release a different hormone -may be pulsatile --> pulse generator or circadian cycle stimulates hormone release in pulses in absense of external stimulation |
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Hormone transport
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Hydrophilic - dissolve easily in plasma - peptide hormones
Hydrophobic - bind to plasma proteins - steroid and thyroid, only free hormone binds receptor |
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Bound hormone is
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free hormone
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2 types of hormone receptors
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-extracellular - peptide hormones that activate 2nd messenger systems
-intracellular - in cytoplasm, and hormone -receptor complex binds to DNA (steroid, thyroid, vitamin D, retinoic acid) |
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Down regulation occurs when
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there is chronically elevated hormone levels
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Up regulation occurs when
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chronically low hormone levels
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Describe hormone action pattern
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Follows dose-response curve
-basal activity intrinsic to cells -threshold hormone concenration increases cellular response -maximal response - no greater response can be elicited |
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ED 50
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Halfway between threshold and max response
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Hormone degradation mechanisms
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-by liver and kidney
-by target cells -excreted in bile or urine |
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Half life of hormone
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time required to clear 50 % of hormone from blood
75 % in 2 half lifes, 87.5 in 3 |
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Feedback loops
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endocrine processes usually regulated by negative and rarely by positive feedback
This ensures maintenance of homeostasis |
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Hypothalamic derived hormones
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CRH - corticotropin releasing hormone
TRH - thyrotropin releasing hormone GHRH - growth hormone releasing hormone DA - dopamine PRH - prolactin releasing hormone Somatostatin - inhibits growth hormone and thyroid stimulating hormone secretion from pituitary LHRH - lutenizing hormone releasing hormone |
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Posterior pituitary
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Axons from hypothalamus terminate on posterior pituitary
AP received at hypothalamus stimulates release into circulation |
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ADH action
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-stimulated by increased blood osmolality and decreased blood volume
-increases water reabsorption in collecting duct |
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Oxytocin action
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stimulated by breastfeeding and child birth
-increases milc secretion and uterine contractions |
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How oxytocin stimulates uterus
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-lowers threshold for smooth muscle depolarization
-causes rhythmic contractions |
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Anterior pituitary
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Hypothalamic hormones released into hypophyseal portal system
travel to pituitary and stimulate release of anterior pituitary hormones |
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DA inhibits which hormone
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Prolactin releasing hormone
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Anterior pituitary hormones
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ACTH - adrenocorticotropic - adrenals
TSH - thyroid stimulating - thyroid GH - growth hormone - liver FSH - ovaries and testes LH - ovaries and testes PRL - prolactin - breast |
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Adrenal cortex
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-Zona fasciculata + zona reticularis -stimulated by ACTH, secretes glucocorticoid and androgens
-Zona glomerulosa - secretes aldosterone |
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Aldosterone
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-stimulated by ACTH
-renin-angiotensin system primary stimulator |
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Androgens
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secreted by adrenal cortex in very low levels
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Thyroid gland
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-composed of follicular cells - filled with coloid, contain thyroglobulin, partially form T3 and T4 (iodines + tyrosine)
-parafollicular cells produce calcitonin, decreases Ca in blood |
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Thyroid hormone synthesis
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3 steps :
-throglobulin synthesis -iodide uptake -iodothyronine formation |
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Thyroglobulin synthesis and secretion
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-synthesized by ribosomes on rough ER
-undergoes dimerization and glycoylation in smooth ER -packaged into vesicles by Golgi -extruded into colloid |
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Iodide uptake
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-follicular iodide transporters carry iodide into cell (ATP driven, iodide trapping)
-iodide diffuses into colloid for iodination |
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Formation of iodothyronine
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-thyroid peroxidase catalyzes iodination
-binds iodide ion and tyrosine in thyroglobulin -undergoes oxidation -produces monoiodotyrosine (MIT) -MIT undergoes iodination to DIT -MIT and DIT remain connected to thyroglobulin |
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Thyroid hormone formation
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Colloid droplets are exocytosed
-lysosomes migrate towards droplets, fuse with them, and hydrolyze thyroglobulin - T3 and T4 released in cytosol and diffuse to blood |
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Thyroid hormone action at target
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T4 and T3 diffuse into cell, T4 converted to T3
-intracellular receptors similar to steroid receptors -gene expression altered -influences CNS development, growth and metabolism |
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Hypersecretion of thyroid hormone
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-Excitability
-Excessive sweating -Weight loss but increased food intake -diarrhea -fatigue but inability to sleep -muscle weakness -tremor -protruding eyes |
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Hyposecretion of thyroid hormone
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-obesity but reduced appetite
-excessive sleeping -mental sluggishness -constipation -lower body temperature |
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Growth hormone actions
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One of counter regulatory hormones, limit actions of insulin on liver, adipose and muscle
-inhibits glucose use by muscle and adipose -increases gluconeogenesis -makes muscle and adipose resistant to insulin |
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Pituitary dwarfism
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-may be due to lack of GH only or GH and other pituitary hormones
-may be due to dysfunctional receptor |
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GH excess leads to what
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-gigantism - can grow to 7-8 ft tall
-excess occuring in adulthood causes bones of hands, feet, face to thicken and organ hypertrophy - acromegaly -metabolic disturbances - insulin resistance, hyperglycemia |
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Insulin dependent glucose transport
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-tissues requiing insulin for efficient glucose transport are adipose and resting skeletal muscle
-insulin facilitaties glucose uptake in liver - enhances glucose metabolism, does not insert glucose transporters here |
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DM general symptoms
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-frequent urination
-increased thirst -increased food consumption -weight loss |
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Type I diabetes
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-inadequate insulin production - mutation in insulin gene, autoimmune disorder and some environmental factors
-Insulin injections REQUIRED |
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Type II diabetes
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Causes :
-insulin resistance at target tissues normal to high insulin levels in blood may be receptor or post receptor defect -Strong genetic component -diet plays big role -being overweight increases risk |
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Treatments for type II diabetes
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-milder forms - diet and exercise
-sulfonylurea drugs - increase insulin action and production -some cases insulin treatment necessary |
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Parathyroid hormone
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-main action on renal tubule and bone
-increased Ca reabsorption and decreased phosphate reabsorption -increased bone resorption |
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Vitamin D
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main action on intestine and bone
-increases intestinal Ca and P absorption -increase bone formation and resorption -small increase in renal Ca reabsorption |
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Calcitonin
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Main action on bone
Deactivates osteoclasts to decrease bone resorption |