Tubular Reabsorption

Question 1

Trans-epithelial transport

Answer 1

1. Substance leaves the tubular fluid by crossing the liminal membrane
2. Must pass through the cytosol
3. Cross the basolateral membrane of the tubular cell to the interstitial fluid
4. Diffuse through the interstitial fluid
5. Penetrate the capillary wall to enter the blood plasma

Question 2

Where is sodium reabsorbed?

Answer 2

65% proximal tubule
25% loop of henle
4-8% distal and collecting tubule

Question 3

What is the role of sodium reabsorption in the proximal tubule?

Answer 3

Reabsorbing glucose, amino acids, H2O, Cl and urea

Question 4

What is the role of sodium reabsorption in the ascending limb of the loop of henle?

Answer 4

Kidney’s ability to produce urine of varying concentrations and volumes
Depends on the body’s need to conserve or eliminate H2O
Also Cl reabsorption

Question 5

What is the role of sodium reabsorption in the distal and collecting tubules?

Answer 5

Variable and subject to hormonal control
Regulates ECF volume- important in long-term control of arterial blood pressure

Question 6

What is essential for Na reabsorption in the basolateral membrane?

Answer 6

An active Na-K ATPase pump

Question 7

_____ of the total energy spent by the kidney is spent on running the _______

Answer 7

80%
Na/K ATPase pump

Question 8

Steps in Na-K pump

Answer 8

1. Na passively moves from the lumen (high concentration) into the cell across lumina border
2. Extrudes Na from cell and builds up the concentration of Na in the lateral space
3. Na diffuses down concentration gradient into the lateral space into the interstitial fluid
4. From the fluid into the capillary

Question 9

What is Na followed by?

Answer 9

Water
It’s passively reabsorbed throughout the length of the proximal tubule, it follows osmotically

Question 10

How much water is passively reabsorbed?

Answer 10

65% is passively reabsorbed by the end of the proximal tubule
117 L a day

Question 11

How does H2O pass?

Answer 11

Primarily through Aquaporin 1 water channel

Question 12

How is the return of filtered H2O to the plasma enhanced?

Answer 12

By the fact that the plasma colloid osmotic pressure is greater in the peritubular capillaries

Question 13

What else is active reabsorption responsible for?

Answer 13

The passive reabsorption of urea and chloride

Question 14

How much urea passively reaborbed?

Answer 14

50%

Question 15

How are chloride ions reabsorbed down the electrical gradient?

Answer 15

By active reabsorption of the sodium ions

Question 16

Substances with a molecular weight of ____ are freely filtered at the glomerulus

Answer 16

10 kDa

Question 17

What does the proximal tubule absorb?

Answer 17

Filtered peptides and low-molecular weight proteins

Question 18

How are filtered proteins degraded?

Answer 18

Degraded to amino acids by peptidases in the proximal tubule brush border
Reabsorbed by co-transport with Na+ across the apical plasma membrane

Question 19

What are the low molecular weight proteins?

Answer 19

Insulin
Glucagon
Parathyroid hormone
Microglobulinuria

Question 20

How are the low molecular weight proteins taken up?

Answer 20

At the apical plasma membrane by receptor-mediated endocytosis

Question 21

Steps to receptor mediated endocytosis

Answer 21

1. Low molecular weight proteins taken up at apical plasma membrane by receptor-mediated endocytosis
2. Proteins bind with meaglin and cubilin in plasma membrane and undergo endocytosis
3. Endocytosed proteins are delivered to lysosomes and degraded
4. Released amino acids are transported to the capillaries

Question 22

Glomerular proteinuria

Answer 22

Glomerulus not working properly
Albumin is going through glomerulus not being filtered
Albumin in the urine

Question 23

Proximal Tubule proteinuria

Answer 23

Normal proteins being filtred through glomerulus
Proteins can’t be absorbed because of blockage
They’re not reabsorbed, in the urine