#4: Kidneys & Homeostasis Flashcards
Maintaining [water] in the body
- 65% of the water that enters the nephron is reabsorbed in the proximal tubule (cannot be controlled)
- 20% of the water that enters the nephron is reabsorbed at the descending loop of Henle (cannot be controlled)
- 15% of the water that enters the nephron can be reabsorbed in the distal tubule and collecting ducts
(under homeostatic control)
Osmoreceptors (OR)
in the cells of the hypothalamus
monitor the [water] in the blood (sensor)
When the [water] in the blood decreases…
water leaves the cells of the hypothalamus – triggering the OR
the OR send a signal to the pituitary gland (integrator)
the pituitary gland releases ADH (antidiuretic hormone) (effector)
ADH increases the reabsorption of water in the distal tubules and collecting ducts of the nephrons by making the membranes more permeable to water
When the [water] in the blood increases…
the OR are not triggered
the release of ADH will be inhibited and the nephrons will not reabsorb a portion of the remaining 15% of water
Diuretics
decrease water reabsorption in the kidney
(increase urine production, can lead to dehydration)
alcohol inhibits the production of ADH
caffeine prevents ADH from attaching to the collecting ducts in the kidney
Reacting to low blood pressure
decrease in blood pressure is recognized by baroreceptors in the arteries near the glomerulus (sensor)
the baroreceptors release renin into the blood
renin converts angiotensinogen (an inactive pr- enzyme produced by the liver) into angiotensin (active)
angiotensin constricts the blood vessels, triggers thirst, and targets the adrenal glands (integrator)
the adrenal glands release aldosterone (effector)
aldosterone increases Na+ reabsorption in the distal tubule and collecting duct
water moves out of the nephron and into the peritubular capillaries due to the change in osmotic pressure
