Perceived Danger 1 Endocrinology 11 - Adrenal Medul The Adrenal System Hypothalamus corticotropin-releasing hormone (CRH) vasopressin - Perceived Danger Pituitary - Hypothalamus - Anterior Pituitary adrenocorticotropic hormone (ACTH) /gland - Adrenal Gland Adrenal Cortex - Stress Response glucocorticoids (primarily cortisol) epinephrine and norepinephrine It's a biological response to a non-biological stimulus 1 HPA Axis Stress Response - Brain gets a stimulus from stress/danger - Is transduced by the higher centres of the brain into action potential - That stimulus the hypothalamus - Releases releasing hormone - Travels through the hypothalamic-hypophysial portal to the pituitary gland (anterior) - Travels through the blood to the adrenal cortex where it stimulates cortisol release Adrenal Glands - On top of the kidneys - Two adrenal glands, one of top each kidney - The capsule is the outer membrane and that keeps the integrity of the structure - Outer layer - cortex o 3 layers: each layer releases different adrenal cortical hormones Have different cell types so different receptors · Zona Glomerulosa · Mineralocorticoids (e.g. aldosterone, causes you to reabsorb water in the kidneys) · Zona Fasciculata (largest) · Glucocorticoids (e.g. cortisol, influences nutrient metabolism and stress) · Zona Reticularis · Sex hormones - similar to those produced in the sex organs - Middle layer - medulla o Essentially a modified sympathetic ganglion " preganglionic nerve that stimulate the adrenal medulla, " causing the release of catecholamines and just gets released into the blood " post-ganglionic neurones lack axon and function as endocrine cells o secrete catacholamines · adrenaline and noradrenaline o actions of these hormones · activate adrenergic receptors family of different receptors on different tissues
" in different tissues, will have different effects Steroidogenic Pathway Series of enzymatic reactions that leads to the release of the hormones form the adrenal gland Starting with cholesterol Aldosterone - it's a mineralocorticoid (binds to the mineralocorticoids receptors) - secreted from the zona glomerulosa - has potent effects in the kidneys - what stimulates aldosterone directly: o decrease in ECF osmolarity o increase K+ conc o causes release in ACTH (aldosterone precursor) - indirectly; o decrease in ECF vol o decrease in BP o causes release in ACTH (aldosterone precursor) - angiotensin II stimulates aldosterone release, independent to the HPA axis - site of aldosterone action is on the distal and collecting tubules of the kidney o promotes Na+ retention o enhances of K+ elimination - because of increased Na+ retention, there is increases water retention, expanding ECF volume - Therefore, blood pressure That's why high potassium levels in the ECF will stimulate aldosterone release as it Cortisol - Released in the medulla - End product hormone of a classical axis - External stress and circadian rhythm stimulate hypothalamus to release corticotropin-releasing hormone - Travels down the hypothalamic-hypophysial portal into the anterior pituitary Diurnal rhythm + - Binds to the CRHR found on the corticotropes Hypothalamus 4 - Leads to the release of (adrenocorticotropic hormone) ACTH from the corticotropes Corticotropin-releasing hormone (CRH) - Circulates through the blood