Ren 3 - Nephron Physiology

Question 1

What is absorbed in the proximal tubule?

Answer 1

• Glucose.
• Amino Acids.
• 2/3 of the fluids and electrolytes (isotonically).

Question 2

In which part of the kidney are glucose and AAs are reabsorbed?

Answer 2

Proximal convoluted tubule.

Question 3

How is bicarbonate recycled in the first part of the proximal tubules?

Answer 3

• CO2 and H2O from the lumen of the proximal tubule is reabsorbed by the proximal tubule.
• The enzyme carbonic anhydrase inside the proximal tubule combines the CO2 and H2O into H+ and HCO3- (bicarbonate).
• The H+ is pushed back into the lumen, while the bicarbonate is pushed into the interstitium by the sodium/potasium ATPase: uses ATP to do this.

Question 4

What is recycled and how in the second part of the proximal tubule?

Answer 4

Chloride and sodium reabsorption using the sodium potassium ATPase.

Question 5

What substances are actively secreted in the proximal tubule?

Answer 5

Anions and cations.

Question 6

How are anions excreted in the proximal convoluted tubules?

Answer 6

To secrete an anion: alpha-ketoglutarate is absorbed from the interstitium to the proximal tubule cell with one sodium by the sodium gradient established by the sodium potassium ATPase. Then, with this gradient an alpha-ketoglutarate is expelled into the interstitium in exchage for an organic anion coming inside the cell, which is later expelled into the lumen.

Question 7

How are cations excreted in the proximal tubule?

Answer 7

There is a net excretion of cations because we are excreting 3 sodium particles from the cell into the interstitium for 2 potassium entering from the interstitium into the cell. This sets an electrical gradient that allows cations to enter the cell. Then the cation is excreted into the lumen in exchange for hydrogen from the lumen into the cell.

Question 8

What does the thin descending limb do and how?

Answer 8

-H2O reabsorption: It is impermeable to Na+ but the interstitium in that place is hypertonic: water is going to follow that gradient, causing the luminal fluid to be more concentrated.

Question 9

What is being reabsorbed in the Thick ascending limb and how?

Answer 9

One sodium, one potassium and 2 chloride are being reabsorbed actively. Calcium and Magnesium are being reabsorbed, but they are sneaking into the interstittium through the crevices between tubular cells; induced reabsorption.

Question 10

What class of drugs inhibit the Na+/2Cl-/K+ symporter in the think ascending limb?

Answer 10

Loop diuretic.

Question 11

What is the thick ascending limb impermeable to?

Answer 11

Water.

Question 12

What does the thick ascending limb do to the urine and why?

Answer 12

It is diluting the urine because it is reabsorbing sodium, chloride, potassium, calcium and magnesium from the urine.

Question 13

What is reabsorbed in the early part of the distal convoluted tubule?

Answer 13

Sodium and chloride.

• Not always permeable to water.
• Calcium reabsorption is under the control of PTH.

Question 14

How does Parathyroid levels raise calcium levels in the body?

Answer 14

1. Stimulates bone resorption. 2. Stimulates the kidneys to activate vitamin D. 3. Stimulates the kidneys to reabsorb more Ca2+.

Question 15

What two types of cells compose the collecting duct and the last segment of the distal tubule? What do they do?

Answer 15

1. Principal cells: They reabsorb water and Na+ and they secrete K+.
2. Intercalated cells: Secrete either H+ or HCO3-, and reabsorb K+.

Question 16

What are the two types of intercalated cells?

Answer 16

1. Alpha cells (A cells): Secrete H+ ions.

2. Beta cells (B cells): Secrete HCO3-.

Question 17

What determines how much water is reabsorbed in the distal tubules and the collecting ducts?

Answer 17

-ADH (anti-diuretic hormone)(vasopressin).

Question 18

Where in the kidneys does the ADH work on and what does it do there?

Answer 18

On the V2 cells in the Principal cells in the collecting tubules: it makes the principal cells to insert aquaporins inside the lumen side of the cells, allowing water to be aquaporin.

Question 19

What drug blocks the function of aquaporins?

Answer 19

Lithium.

Question 20

What is the function of the principal cells?

Answer 20

To absorb Na from the lumen and excrete potassium into it.

Question 21

What class of diuretic directly affects principal cells?

Answer 21

Potassium-sparing diuretics.

Question 22

Which potassium-sparing diuretics are also aldosterone antagonists?

Answer 22

Spirolactone and Eplerenone.

Question 23

Which potassium-sparing diuretics are inhibited epithelial Na+ channels?

Answer 23

Triamterene and Amiloride.

Question 24

What effect does aldosterone have on the principal cells and intercalated cells of the collecting duct?

Answer 24

1. Principal cells: Reabsorption of Na+ and secretion of K+.

2. Intercalated cells: Stimulates secretion of H+ ions.

Question 25

What part of the kidney reabsorbs 67% of the fluid and electrolytes filtered by the glomerulus?

Answer 25

Proximal tubule.

Question 26

What part of the kidney is site of secretion of organic anions and cations?

Answer 26

Proximal tubules.

Question 27

What part of the kiney is always impermeable to water?

Answer 27

Thick ascending limb.

Question 28

What part of the kidney is permeable to water only in the presence of ADH?

Answer 28

Late distal tubule (also the collecting duct).

Question 29

What part of the kidney is site of the NA+/2Cl-/K+ co-transporter?

Answer 29

Thick ascending limb.

Question 30

What part of the kidney is site of isotonic fluid reabsorption?

Answer 30

Proximal tubule.

Question 31

What part of the kidney is site responsible for diluting urine?

Answer 31

Thick ascending limb.

Question 32

What part of the kidney is the only site where glucose and amino acids are reabsorbed?

Answer 32

Proximal tubule.

Question 33

Where in the loop of Henle is water reabsorption?

Answer 33

Descending limb.