Regulation of Body Water Flashcards
• If excess Na+ is sensed how does the body initiate natriuresis (loss of Na ions)?
Aldosterone, ADH (vasopressin), natriuretic peptides e.g. ANP
• How is Na+ and water regulated?
Osmolarity (primary controller), water channels, sodium transporters & hormones
• What happens if there is too little blood volume, irrelevant of osmolality?
Thirst stimulated, hormones go up, Na retained, water retained
• Where does bulk water resorption occur?
In the proximal tubule
• Where is ADH formed and released from?
ADH is formed in the hypothalamus, stored and released from the posterior pituitary gland
• Where does ADH act and by what receptor?
V2 receptors – increase water permeability in the collecting ducts
V1 receptors – increase arterial pressure by vasoconstriction
• What mechanisms will result in increased release of ADH?
Hypovolaemia, hypotension, dehydration, increasing angiotensin II, increased sympathetic activation
• In hypovolaemia, where do the atrial stretch receptors synapse?
Within the nucleus tractus solitarius of the medulla
• What aquaporins are found in the renal tubule and where?
PT – AQP 1 & 7, CD – AQP 2, 3 & 4
• Why do the ECF and ICF remain isotonic, under normal conditions?
Because the cell membrane is permeable to water
• Why might ECF volume decrease?
Dehydration, loss from GIT, loss from blood, loss from sweating, loss from kidneys
• What two major mechanisms respond to an increased osmolarity?
Increased ADH and an increased sense of thirst
• What three mechanisms will cause hypernatraemia?
Decreased TBW and Na with a relatively greater decrease in TBW
Decreased TBW with near normal total body Na
Increased Na with normal or increased TBW
• How does aldosterone exert its effects?
Stimulates sodium/hydrogen exchange, increases the synthesis of ENaCs
