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What is the basic principle of body water balance?
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Intake must be equal to output.
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Where is ADH released from?
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The posterior pituitary gland. it is stored in secretory granules in nerve endings in the posterior pituitary gland.
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Where are the cell bodies of the nerves that contain ADH located?
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In the hypothalamus.
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What causes the release of ADH?
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Depolarization of the nerve terminals, which causes an increase in Ca2+ influx into the terminal, which causes exocytosis of the granules that contain the ADH.
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What are the 2 main stimuli of ADH release?
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An increase in plasma osmolality (more important)Decrease in ECF volume
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Increased plasma osmolality causes what 2 events?
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1. ADH release2. Thirst
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Large loss of ECF leads to what 2 events?
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1. ADH release2. Thirst
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T/F. Large loss of ECF does NOT cause ADH release and thirst if the plasma osmolality is low.
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FALSE. Even if the plasma osmolality is low, a large loss of ECF will cause ADH release and thirst (this is because it will activate the baroreceptors in the aortic arch and carotid bodies, which will send signals to the hypothalamus to release ADH from the posterior pituitary nerve terminals).
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What is another name for ADH?
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Vasopressin, or arginine vasopressin
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Why is ADH also called vasopressin?
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Because when it is released in response to a large decrease in ECF volume, it also acts as a pressin to increase blood pressure.
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In what causes would ADH be released when the plasma osmolality is low?
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In functional hypovolemia. Even though there is not actually a decrease in ECF volume (there may even be an increase, like generalized edema), there is decreased venous return, so the body is responding to these signals as if there is a decrease in ECF. Therefore, the body will release more ADH and aldosterone to retain more Na and water, even though that is not needed.
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What is functional hypovolemia?
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A state in which ECF can be massively expanded, but the body is reacting as is ECF volume is significantly depleted. So ADH levels are high and the RAS system is activated, resulting in increased Na+ and water retention.
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Give 4 examples of functional hypovolemia?
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Congestive heart failureCirrhosisNephrotic syndromeAV shunting due to fistula or congenital defect
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Describe the feedback regulation of body water in response to water deficit.
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Water deficit causes increased plasma osmolality, which triggers 2 things- ADH release and thirst.Osmoreceptors in the supraoptic nucleus of the hypothalamus are activated --> send depolarizing action potentials to the posterior pituitary, which causes release of ADH --> Luminal membranes of the CNT and collecting duct become more H2O permeable --> excretion of hyperosmotic urine --> decreases the plasma osmolalityOsmoreceptors in the hypothalamic thirst centerActivation of behaviorl thirst drive --> increased water intake --> decrease the plasma osmolality
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What is the main determinant of ECF volume balance?
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Na+ balance in the bodyi.e. a constant amount of Na+ in the body
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