Psy137HomeostaisThirst

When observed at low magnification left the capsule a

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When observed at low magnification (left) the capsule (A), cortex (B), and medulla (C) are visible. At higher magnifications (right) the divisions of the cortex are visible: Zona glomerulosa - zg -with cells in small clusters which secrete aldosterone , Zona fasciculata - zf - with cells arranged in columns or strips which secrete cortisol and Zona reticularis - zr - with cells that are somewhat unorganized which secretes sex steroids and may also secrete cortisol . The medulla is the site of epinephrine and norepinephrine production.
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Behavioral regulation of sodium balance Hamsters: No matter what concentration of sodium is offered, hamsters never prefer saline over water. After adx, hamsters do not change preference and most die. If you put saccharine in with the salt they drink plenty of the saccharine + NaCl and live. If given a choice: NaCl or saccharine? Then, the hamster drinks saccharine and dies. Why? Hamsters evolved in the desert Finding sodium not a physiological problem No sodium appetite has evolved!
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Satiation of Thirst Not as well defined as to what stops thirst Not as rigid a system Stomach receptors Water Liver receptors Water and salt Information sent via vagus nerve Suppression of drinking is from parainfundibular hypothalamic area
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Volume homeostasis Thirst is  triggered  by increased plasma  osmolality  (OVLT receptors) I.e  salt load  (hepatic Na + decrease in blood volume/pressure  hypovolemia  (angiotensin II in SFO  triggers response). Thirst is  inhibited   by decreased  plasma  osmolality   (OVLT receptors)  i.e. take in water  and by increased  blood pressure  (result of  AngioII)
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Volume homeostasis Hypovolemia  triggers not only  thirst , but also  salt appetite Blood volume is corrected only  by replacing  both water and  salt Drinking water  alleviates  thirst  (by reducing plasma  osmolality), but  triggers salt  appetite , whereas consuming  salt triggers subsequent thirst  (by increasing plasma  osmolality)
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When observed at low magnification left the capsule A...

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