5. Control of reabsorption and secretion in the nephron

Question 1

What 2 substances are almost complete reabsorbed in the nephron?

Answer 1

Glucose

Amino acids

Question 2

What 3 substances are variably reabsorbed in the nephron?

Answer 2

Na
Cl
Bicarbonate

Question 3

Which 2 substances are poorly resorbed and hence excreted?

Answer 3

Urea

Creatine

Question 4

What is the mechanism of sodium transport in the kidney tubular cells?

Answer 4

Active transport via the Na-K pump.
Transport Na from the interior of the cell across the basolateral membrane creating a low intracellular Na conc and negative electrical potential. Results in Na diffusion from tubular lumen into the epithelial cells through the brush border.

Question 5

Which secondary active transport?

Answer 5

Two or more substances interact with a specific membrane protein (a carrier molecule) and are transport together across the membrane.

Question 6

What is primary active transport?

Answer 6

Active transport can move a solute against an electrochemical gradient and requires energy derived from metabolism. It needs a pump that uses ATP.

Question 7

Example of secondary active transport in the kidney?

Answer 7

The energy released when Na diffuses down its electrochemical gradient is used to drive glucose against it’s electrochemical gradient. Hence ATP isn’t needed
E.g. SGLT- Sodium glucose co-transporter on apical tubular surface.

Question 8

What is the NHE found on the apical tubular surface/

Answer 8

Na/H Exchanger
An example of secondary active transport found in the kidneys. Pumps Na+ into the interstitial cell via diffusion and `H+ out

Question 9

Where is 65% of the filtered Na and H20 reabsorbed in the nephron?

Answer 9

in the proximal tubulele

Question 10

Why does the proximal tubule have a high capacity for reabsorption?

Answer 10

Has high metabolically active cells driving by the sodium pump.

Question 11

Transport characteristics of Loop of Henle:
Water/ ions reabsorption?
TDL?
AL?
TAL?

Answer 11

20% of filtered water reabsorbed
25% of filtered Na, Cl- and K+ reabsorbed

Thin descending limb: Permeable ot water diffusion
Ascending limb: Impermeable to water.
Thick ascending limb: Active transporters and absorbs NaCl and K+

Question 12

Secretion in the proximal tubule?

Answer 12

Organic bases/acids
Metabolic products
Drugs and toxins

Question 13

Mechanisms of sodium, chloride and potassium transport in the thick ascending limb?

Answer 13

Secondary active transporters on apical surface:

1. Na+, 2Cl-, K+ into cell
2. Na+ in, H+ out of cell

Question 14

Which transporters are inhibited by furosemide and bumethanide?

Answer 14

Secondary active transporters on apical surface-

Na+, 2Cl-, K+ into cell inhibited

Question 15

Transport characteristics of the early and late distal tubule?

Answer 15

5% of filtered load of Na reabsorbed
Impermeable to water
Pumps Na/2Cl-/K into tubular cells. Via Na+/Cl- transporter and Na+K+ATPase.
Late section has 2 cell types:
1. Principal cells absorb H2O and Na ions
2. Intercalated cells absorb K and secrete H+ ions

Question 16

What proteins are inhibited by thiazide diuretics in the early distal tubule?

Answer 16

Na+/Cl- secondary active transporter on apice surface on the tubular cells.

Question 17

Mechanism of NaCl transport in the late distal and cortical collecting ducts?
Inhibiting agents?

Answer 17

Lumen surface:
Diffusion of Na+ into cell
Diffusion of K+ out of cell

Interstitial surface:
Diffusion of Cl- out of the cell
Na+K+ ATPase: Na+ out, K+ in

Na+ channel blockers: Amiloride, triamterene

Aldosterone antagonists:
-Spironolactone, eplerenone

Question 18

Transport characteristics of the medullary collecting ducts?

Answer 18

Absorbs less than 10% of filtered water and Na ions
Vital to producing dilute and concentrated urine
Impermeable to water unless ADH is present.
Permeable to urea, transporters present.
Can secrete H+ ions, so plays a role in acid/base balance

Question 19

Aldosterone:
Released from?
Regulator of?
Major site of action in nephron?
Effect?

Answer 19

Released from: Adrenal cortex
Regulator of: Na reabsorption and K excretion
Major site of action in nephron: Cortical collecting duct
Effect: Stimulate Na+/K+ ATPase pump on the basolateral side of the cortical collecting tubule membrane. increases Na permeability of the luminal side of the membrane

Question 20

Angiotensin II:

Stimulates?

Answer 20

Stimulates:

• Aldosterone release from adrenal cortex
• Constricts afferent and/or efferent arterioles in the kidney
• Directly stimulates Na reabsorption in the proximal convoluted tubule, the Loops of Henle, the distal convoluted tubules and the collecting ducts
• Stimulates the sodium pump on the basolateral side of the tubular epithelia and the sodium-hydrogen exchange on the luminal membrane especially in the proximal tubule.

MOST POWERFUL NA RETAINING HORMONE (hence acts during haemorrhage, increases body fluid and solute levels)

Question 21

Antidiuretic hormone (ADH):
Action/site?
Mechanism?

Answer 21

Action/site: Increases the water permeability of the distal convoluted tubule, collecting tubule and collecting duct

Mechanism: ADH binds to specific V2 receptors and through signal transduction mechanisms stimulate the movement aquaporin 2 to the apical (luminal) surface of the epithelial cells.
This is reversible to allow control of water permeability of these distal sections of the tubule.

Question 22

Action of atrial natriuretic peptides on nephron reabsorption?

Answer 22

Atrial natriuretic peptides are secreted by the cardiac atria when they are distended by increased blood volume.

Direct inhibits the reabsorption of sodium and water by the renal tubules especially the collecting ducts to increase solute and water loss so to decrease blood volume.

Question 23

How does the sympathetic NS act to decrease Na and H2O?

Answer 23

Sympathetic nervous system activity acts by constricting renal arterioles —> reduces glomerular filtration rate.

Increases angiotensin II formation –> Increase in tubular reabsorption and so decrease excretion of sodium and water.

Question 24

Effect of parathyroid hormone on reabsorption of Ca in nephron?

Answer 24

Parathyroid hormone increases the tubular reabsorption of calcium in the distal convoluted tubules.