CSB325 Lecture 5 Review Notes

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University of Toronto St. George
Cell and Systems Biology
David Lovejoy

CSB325 Lecture 5 – Osmoregulation Physiology of osmoregulation - Osmoregulation involves two main processes o Maintenance of a constant volume of internal fluids during changing ion concentrations o Maintenance of a constant ratio of ions during changing body fluid levels - Osmoregulation at the cellular level involves o Permeability of membranes o Active transport across membranes o Passive movement of materials across membranes o Diameter of blood vessels and filtration rate in kidneys - Cellular dehydration = Extracellular osmolality > Intracellular osmolality o Osmolality is the amount of dissolved ions o E.g., fluid leaves cell = triggers cellular dehydration - Decreased extracellular volume = Volume changes without osmolality changes o E.g., loss of blood volume = drop in blood pressure Renin-angiotensin-aldosterone system  Activated by  Low blood pressure  Low blood volume  Low plasma Na+  low Na+ in distal tubules  macula densa  juxtaglomerular cells  renin  Low plasma H2O  Angiotensin-II  Angiotensin-II receptors  AT1 receptor, which is inhibited by ARBs  AT2 receptor  Vasoconstriction  Vasodilation  Sympathetic activation  Apoptosis  Sodium and fluid retention  Inhibition of cell growth  Stimulation of cell growth  ADRENAL CORTEX  Angiotensin-II regulates StAR protein, which is the rate limiting enzyme in steroid hormone synthesis  Secretes aldosterone (steroid hormone)  Released from adrenal cortex, which contain AT1 receptors o Zona glomerulosa  Aldosterone o Zona fasciculate  Cortisol, DHEA o Zona reticularis  DHEA, Androstenedione  Functions of aldosterone  ↑ Na+ excretion from large intestine and mammary gland ducts  ↓ Na+ excretion from kidney, sweat glands and saliva glands  ↓ Na+/K+ ratio in secreted fluids o ↑ Na+ resorption in distal tubules = ↑ Na+ o ↑ K+ excretion = ↓ K+  ↓ renin production  Maintain vasopressin responsiveness by regulating adenylyl cyclase  BRAIN  SO, AV3V, Amygdala  Angiotensin-II stimulates SO, AV3V, and amygdala  ↑ thirst and drinking behavior o Increase plasma volume o Increase blood pressure  Hypothalamus  posterior pituitary  Angiotensin-II stimulates paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the hypothalamus  pars nervosa (posterior pituitary; neurohypophysis)  ↑ AVP (and oxytocin)  Vasopressin (AVP) o ↑ vasoconstriction of smooth muscle of blood vessels (V1a)  ↑ plasma volume  ↑ BP o ↑ aquaporin-2  ↑ water reabsorption in the collecting tubules of kidneys (V2)  ↑ plasma volume  ↑ BP  V
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