Chapter 28 - Guyton

Question 1

Explain the ADH-thirst osmoreceptor system.

Answer 1

increased extracellular osmolality (NaCl) stimulates ADH (vasopressin) release from the posterior pituitary, which increases water absorption and stimulates thirst (water intake)

Question 2

How is dilute urine formed?

Answer 2

electrolytes are reabsorbed while less water is reabsorbed through decreased ADH release and reduced water permeability in distal and collecting tubules

Question 3

How is concentrated urine formed?

Answer 3

continue electrolyte reabsorption and increase water reabsorption through increased ADH release which increases water permeability in distal and collecting tubules

Question 4

Two requirements for excreting concentrated urine?

Answer 4

high ADH and high osmolality of the renal medullary interstitial fluid (countercurrent flow of tubular fluid)

Question 5

If the body is unable to concentrate urine, how will the required amount of solute be excreted?

Answer 5

increased volume output (occurs during renal disease)

Question 6

How are ions transported into the medullary interstitium?

Answer 6

active transport

Question 7

Where is most water reabsorbed?

Answer 7

proximal tubule

Question 8

Obligatory Urine Volume

Answer 8

600 mOsm day / 1200 mOsm L = 0.5 L per day

Question 9

Water Clearance Equation

Answer 9

C = V - [(U x V) / P]; where V = urine flow rate, U = urine osmolarity, P = plasma osmolarity

Question 10

Stimuli for increased ADH secretion

Answer 10

increased osmolarity, decreased blood volume, decreased blood pressure, input from cerebral cortex (fear), angiotensin II, nausea, nicotine, morphine

Question 11

The most powerful feedback system in the body for controlling extracellular fluid osmolarity and sodium concentration.

Answer 11

ADH-thirst mechanism