Regulation of Sodium (Na+) Balance

1. Sodium (Na+) - 90% of solutes in the ECF; most important and prevalent of all electrolytes
2. Aldosterone - released by adrenal cortex (renin-angiotensin)
1. released in response to:
• a. decrease in blood pressure
• b. decreased osmolality of filtrate
• c. sympathetic stimulation of juxtoglomerular cells
2. function - increase Na+ reabsorption at distal tubule
• a. water will follow if ADH makes the distal tubule permeable to water
3. Baroreceptors
1. located in carotid arteries and aorta
2. respond to changes in stretch due to blood pressure
• blood pressure increases ------> hypothalamic stimulation ------> sympathetics to kidneys decrease ------> increased GFR (water removed)
• blood pressure decreases (same path as above) ----> ----> ----> lower GFR (water retained)
4. Antidiuretic Hormone (ADH)
1. released from the posterior pituitary
2. responds to osmoreceptors in the hypothalamus
• decrease in osmo of ECF ------> decreased release of ADH ------> less permeability of distal tubule to water ------> more water released into urine
• increase in osmo of ECF ------> increased release of ADH ------> more permeability of distal tubule to water ------> less water released into urine

5. Atrial Natriuretic Factor (ANF)
1. released by cell of heart atria under high B.P.
2. reduces blood pressure and blood volume by INHIBITING nearly all events that promote vasoconstriction and Na+/water retention."
6. Steroid Hormones
1. estrogen - increases resorption of Na+ in distal convoluted tubule
2. glucocorticoids (cortisol) - increases resorption of Na+ in the distal tubules

Category: Physiology Notes