Exam 3 Lecture: Tubular Reabsorption

Question 1

What does the ultrafiltrate contain?

Answer 1

contains stuff the kidney wants to expel in the urine but also important stuff that it needs to retain and to return to the blood stream

Question 2

What is reabsorption defined as?

Answer 2

the movement of desired solutes from the lumen of the nephron back to the blood

Question 3

How can a molecule move from the lumen fluid into the blood?

Answer 3

either through the epithelial cells or between the epithelial cells

Question 4

What is the key molecule for reabsorption?

Answer 4

NaKATPase

Question 5

Where is the Na K ATPase pump located?

Answer 5

in the basolateral membrane

Question 6

Why is NaKATPase important?

Answer 6

3 Na move out, 2 K moves in creating a low intracellular concentration that creates an electrochemical gradient that was not otherwise there

Question 7

What is reabsorbed in the proximal tubule?

Answer 7

67% of H2O, Na, and solutes
99% of glucose and AA
90% of Bicarb

Question 8

What mechanisms are involved in reabsorption of Na and other solutes in the 1st 1/2 of the proximal tubule?

Answer 8

NaH antiporter, and Na symporters all on the luminal membrane

Question 9

How does the NaH antiporter work in the proximal tubule?

Answer 9

The Na moves into the cell due to the Na electrochemical gradient and H moves into the tubular fluid

Question 10

How do Na symporters work in the proximal tubule?

Answer 10

Na, glucose, and AA move via facilitated diffusion into the cell from the tubular fluid

Question 11

How is water reabsorbed in the proximal tubule?

Answer 11

The Na, AA, and glucose that enters the cell creates an osmotic gradient that brings H2O into the cell

Question 12

What are the reabsorption mechanisms in the second 1/2 of the proximal tubule?

Answer 12

Na H antiporter, Cl- anion antiporter, paracellular movement all on the luminal membrane

Question 13

What is reabsorbed paracellularly in the second half of the proximal tubule?

Answer 13

Chlorine and sodium, because the gaps are leaky

Question 14

How is reabsorbed Cl removed?

Answer 14

a K Cl symporter at the basolateral membrane

Question 15

What allows the Na and Cl reabsorption mechanisms to work?

Answer 15

the constant circulating of H and anions in and out of the epithelium

Question 16

How are proteins reabsorbed in the proximal tubule?

Answer 16

proteins are partially degraded by enzymes in the luminal membrane and reabsorbed by endocytosis, then degraded further into amino acids and leave via the basolateral membrane

Question 17

What is reabsorbed in the descending limb of the loop of Henle?

Answer 17

15% of the filtered water

Question 18

What is reabsorbed in the ascending limb of the loop of henle?

Answer 18

25% of filtered NaCl

Question 19

What are the reabsorption methods of the initial part of the distal tubule?

Answer 19

NaH antiporter, NKCC2, paracellular reabsorption - all on the luminal membrane

Question 20

How does the Na H antiporter work in the early part of the distal tubule?

Answer 20

Na enters the cell via facilitated diffusion

Question 21

Why can water not enter the cell when ADH is not present in the early part of the distal tubule?

Answer 21

because the tight junctions are too tight and water cannot follow Na into the cell

Question 22

What enters the cell via the NKCC2 transporter in the early part of the distal tubule?

Answer 22

Na, K, and 2 Cl

Question 23

What is absorbed paracellularly in the early part of the distal tubule?

Answer 23

Na, K, Ca

Question 24

What are the reabsorptive methods in the later part of the distal tubule?

Answer 24

NaCl symporter on the luminal membrane; Na and Cl enters the cell

Question 25

What inhibits the NaCl symporter?

Answer 25

thiazide diuretics inhibit it

Question 26

What are the reabsorptive methods of the principle cells in the collecting duct?

Answer 26

Amiloride sensitive Na channels, paracellular

Question 27

How does K leave the collecting ducts?

Answer 27

via K channels on both the laminal and basolateral membrane

Question 28

What enters the cell paracellularly in the principle cells of the collecting ducts?

Answer 28

Cl

Question 29

How does Na enter into the principle cells of the collecting ducts?

Answer 29

Na enters via amiloride sensitive Na channels

Question 30

Where is Na K ATPase the principle molecule for reabsorption in the nephron?

Answer 30

Proximal and distal tubules and the collecting ducts