Kidneys And Homeostasis

Question 1

Maintaining [water]

Answer 1

• 65% of water into nephron reabsorbed at proximal tube and 20% at descending loop of henle (can’t be controlled)
• 15% is reabsorbed in distal tubule and collecting ducts which is under homeostatic control

Question 2

Maintaining [water] homeostatic control system

Answer 2

Sensor:

• osmoreceptors (OR) in cells of hypothalamus monitor [water] in blood
• when [water] drops, water leaves hypothalamus, triggering OR

Integrator:
-OR sends signal to pituitary gland

Effector:

• pituitary gland releases ADH (antidiuretic hormone)
• ADH increases reabsorption of water in distal tubules and collecting ducts by making membranes more permeable
• once [water] in blood rises, OR are no longer triggered, ADH release is inhibited and nephrons don’t reabsorb the 15%

Question 3

How do diuretics decrease water reabsorption in kidneys?

Answer 3

• alcohol inhibits production of ADH

- caffeine prevents ADH from attaching to the collecting ducts in the kidney.

Question 4

Reacting to low blood pressure

Answer 4

Sensor: decrease in bp recognized by baroreceptors in arteries near glomerulus
-baroreceptors release renin into blood and renin converts angiotensinogen into angiotensin (active Pr enzyme)

Integrator: angiotensin constricts blood vessels, triggering thirst, targets adrenal glands

Effector: adrenal glands release aldosterone

• 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