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Lecture 7

Lecture 7 Adrenal gland.docx

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Department
Physiology
Course
PSL300H1
Professor
Michelle French
Semester
Fall

Description
Lecture 7: Adrenal gland October-25-12 6:54 PM Adrenla medulla = modified sympathetic ganglia • Secretes catecholamines (e.g. epinephrine) Adrenal cortex = steroid factory • Secretes o Sex steroids eg testosterone o Mineralocorticoids eg aldosterone o Glucocorticoids eg cortisol Regulation of catecholamine release from the adrenal medulla • Main hormone is epinephrine because it is secreted in sufficient quantity to exert effects • Stimulus for release = activation of the sympathetic nervous system • Spinal chord -> preganglionic sympathetic neuron -> adrenal medulla, in presence of acetylcholine o The chromaffin cell is a modified post ganglionic sympathetic neuron o Catecholamines released into blood (epinephrine, norepinephrine, dopamine) Role of epinephrine: mediates the rapid stress response • Liver: glucose release (via enhanced glycogenesis) • Fat: fatty acid release • Heart: increases force of contraction • Intestine: muscle relation • Intestine, skin, kidney: arteriole constriction • Muscle: arteriole contraction (a-receptors); arteriole relaxation (b2 receptors) • Brain (increases alterness) • Triggers both vasoconstriction and vasodilation o Alpha -receptor response: • Intestinal Blood vessels contract • Reduced blood flow in the GI • Intestinal blood vessels: a- receptors only leads to vasoconstiction • Different tissues can respond differently • Local vasodilation caused by metabolites (CO2 etc) o Beta- 2 receptor response • Skeletal muscle blood vessel dilates • Muscle blood vessels: both a and b2 • Therefore, have less vasoconstriction in these vessels • Metabolite accumulation in these vessels during muscle contraction causes vasodilation Adrenal cortex: specific steroids synthesized in specific zones • Each layer makes more of one specific type of hormone • Each cell type has expressed the right combination of enzymes in the zone • Region and synthesis o Medulla: catecholamines o Zona reticularis: sex hormones o Zona fasciculata: glucocorticoids o Zona glomerulosa: aldosterone o Capsule • Main hormones produced by the adrenal cortex o DHEA o Androstendione o Corticosterone o Cortisol o Aldosterone Physiological roles of DHEA and Androstenedione • Weak androgens, less than 20% activity of testosterone, but converted to more potent androgens and estrogens in peripheral tissues like testoseterone, DHT, estrone and estradiol • Men: no physiological role; males get their testosterone from the testes, not through this pathway • Women: maintain pubic and auxillary hair, source of estrogens after menopause o Before menopause, estrogen comes from ovaries • Children: contribute to andrenarche - pubic hair, body odor, skin oiliness and acne at onset of puberty Regulation of DHEA and adrostenedione synthesis • Stimulated by adrenocorticotrophic hormone (ACTH) - activates an enzyme at an early step in steriodogenesis • But intrinsic changes in enzyme activity occur during the lifespan o Eg. Fetal males have huge increase Recall aldosterone acts on the kidney • Prevents degradation of apical NA+ channel • Increases expression of Na+ and K+ channels and NA+/K+ ATPase • Reabs
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