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50 Cards in this Set

  • Front
  • Back
Definition of hormone
bloodborne substance that regulates physiological process
Functions of hormones
1) digestion, utilization, storage of nutrients
2)growth and development
3)ion and water balance
4)reproductive function
Autocrine signaling
acts on adjacent cells of same type or as negative feedback on same cell
Paracrine signalling
acts on adjacent target cells
Endocrine signalling
hormone secreted into blood and carried to target cells
Neurocrine signalling
released from neuron and diffuses into blood to target cells
Amino acid derived and polypeptide/protein hormones
-synthesized in advance and stored in vesicles
-may be cleaved from preprohormones or prohormones
-transported dissolved in plasma
Steroid hormones
-cholesterol derivatives - hydrophobic
-produced on demand
-transported bound to plasma proteins
Hormone release characteristics
-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
Hormone transport
Hydrophilic - dissolve easily in plasma - peptide hormones
Hydrophobic - bind to plasma proteins - steroid and thyroid, only free hormone binds receptor
Bound hormone is
free hormone
2 types of hormone receptors
-extracellular - peptide hormones that activate 2nd messenger systems
-intracellular - in cytoplasm, and hormone -receptor complex binds to DNA (steroid, thyroid, vitamin D, retinoic acid)
Down regulation occurs when
there is chronically elevated hormone levels
Up regulation occurs when
chronically low hormone levels
Describe hormone action pattern
Follows dose-response curve
-basal activity intrinsic to cells
-threshold hormone concenration increases cellular response
-maximal response - no greater response can be elicited
ED 50
Halfway between threshold and max response
Hormone degradation mechanisms
-by liver and kidney
-by target cells
-excreted in bile or urine
Half life of hormone
time required to clear 50 % of hormone from blood
75 % in 2 half lifes, 87.5 in 3
Feedback loops
endocrine processes usually regulated by negative and rarely by positive feedback
This ensures maintenance of homeostasis
Hypothalamic derived hormones
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
Posterior pituitary
Axons from hypothalamus terminate on posterior pituitary
AP received at hypothalamus stimulates release into circulation
ADH action
-stimulated by increased blood osmolality and decreased blood volume
-increases water reabsorption in collecting duct
Oxytocin action
stimulated by breastfeeding and child birth
-increases milc secretion and uterine contractions
How oxytocin stimulates uterus
-lowers threshold for smooth muscle depolarization
-causes rhythmic contractions
Anterior pituitary
Hypothalamic hormones released into hypophyseal portal system
travel to pituitary and stimulate release of anterior pituitary hormones
DA inhibits which hormone
Prolactin releasing hormone
Anterior pituitary hormones
ACTH - adrenocorticotropic - adrenals
TSH - thyroid stimulating - thyroid
GH - growth hormone - liver
FSH - ovaries and testes
LH - ovaries and testes
PRL - prolactin - breast
Adrenal cortex
-Zona fasciculata + zona reticularis -stimulated by ACTH, secretes glucocorticoid and androgens
-Zona glomerulosa - secretes aldosterone
-stimulated by ACTH
-renin-angiotensin system primary stimulator
secreted by adrenal cortex in very low levels
Thyroid gland
-composed of follicular cells - filled with coloid, contain thyroglobulin, partially form T3 and T4 (iodines + tyrosine)
-parafollicular cells produce calcitonin, decreases Ca in blood
Thyroid hormone synthesis
3 steps :
-throglobulin synthesis
-iodide uptake
-iodothyronine formation
Thyroglobulin synthesis and secretion
-synthesized by ribosomes on rough ER
-undergoes dimerization and glycoylation in smooth ER
-packaged into vesicles by Golgi
-extruded into colloid
Iodide uptake
-follicular iodide transporters carry iodide into cell (ATP driven, iodide trapping)
-iodide diffuses into colloid for iodination
Formation of iodothyronine
-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
Thyroid hormone formation
Colloid droplets are exocytosed
-lysosomes migrate towards droplets, fuse with them, and hydrolyze thyroglobulin - T3 and T4 released in cytosol and diffuse to blood
Thyroid hormone action at target
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
Hypersecretion of thyroid hormone
-Excessive sweating
-Weight loss but increased food intake
-fatigue but inability to sleep
-muscle weakness
-protruding eyes
Hyposecretion of thyroid hormone
-obesity but reduced appetite
-excessive sleeping
-mental sluggishness
-lower body temperature
Growth hormone actions
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
Pituitary dwarfism
-may be due to lack of GH only or GH and other pituitary hormones
-may be due to dysfunctional receptor
GH excess leads to what
-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
Insulin dependent glucose transport
-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
DM general symptoms
-frequent urination
-increased thirst
-increased food consumption
-weight loss
Type I diabetes
-inadequate insulin production - mutation in insulin gene, autoimmune disorder and some environmental factors
-Insulin injections REQUIRED
Type II diabetes
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
Treatments for type II diabetes
-milder forms - diet and exercise
-sulfonylurea drugs - increase insulin action and production
-some cases insulin treatment necessary
Parathyroid hormone
-main action on renal tubule and bone
-increased Ca reabsorption and decreased phosphate reabsorption
-increased bone resorption
Vitamin D
main action on intestine and bone
-increases intestinal Ca and P absorption
-increase bone formation and resorption
-small increase in renal Ca reabsorption
Main action on bone
Deactivates osteoclasts to decrease bone resorption