Lecture 27 - Chapter 25 - Urinary System

Question 1

What is the function of tubular secretion?

Answer 1

• To move unwanted substances from the blood into the urine. (substances, drugs)
• Occurs mostly in the DCT
• K+ , H+, NH4+, creatinine
• It’s important to control blood pH by altering the amounts of H+ or HCO3

Question 2

What is another main function of the kidney, not previously discussed?

(Osmosis)

Answer 2

To make the adjustment needed to maintain body fluid osmotic concentration at around 300 mOsm.

Question 3

Defintion of osmolality:

Answer 3

number of solute particles in 1 kg of H2O

Question 4

1. Countercurrent BLANK forms gradient. (Uses the nephron loop)
2. Countercurrent BLANK preserves gradient (Uses the vasa recta)

Answer 4

1. multiplier
2. exchanger

Question 5

Countercurrent multiplier

The descending limb lets water out but keeps solutes in. Why does this happen?

Answer 5

Water is allowed to leave the loop of henle because it follows the solutes that are outside in the interstital fluid. There are a lot of solutes, mainly NaCl, in the interstital fluid. This makes the osmolality increase, because there are more solutes than water in the loop of henle.

Question 6

The ascending limb allows solutes out but keeps water in. Why does this happen?

Answer 6

Both of the limbs have an influence on each others actions. The solutes (NaCl) leaving the ascending limb makes the interstitial fluid salty. Since the interstitial fluid is so salty, the water will want to leave the descending limb and follow the salt through osmosis.

Question 7

What is the countercurrent mechanism?

Answer 7

• The more NaCl the ascending limb actively transports out into the interstitial fluid, the more water diffuses out of the descending limb.
• The more water that diffuses out of the descending limb, the saltier the filtrate becomes.

Question 8

Which two ions are actively reabsorbed in thick segment?

Answer 8

Na+ and Cl- are reabsorbed in the thick segment of the ascending limb.

Question 9

Vasa Recta acts as a countercurrent exchanger so that blood can exchange NaCl and water with surrounding interstital fluid. What does this mean?

Answer 9

The vasa recta has the same mechanics as the nephron loop, meaning that it will maintain a difference of 300 OsM. This means that the vasa recta is able to reabsorb water and solutes while maintaining the osmotic gradient.

Question 10

What are the two ways the countercurrent exchanger preserves medullary gradient?

Answer 10

1. Preventing rapid removal of salt from interstitial fluid space
2. Removing reabsorbed water

Question 11

Why does some urea leave the collecting duct and go back into the thin ascending limb?

Answer 11

Urea contributes to high osmoality in the medulla. This means that urea helps form the medullary gradient.