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NEPHRON PHYSIOLOGY

NEPHRON PHYSIOLOGY

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Refer to the diagram above for Questions 1-15

1. What is function of Early Proximal Convoluted Tubule

The proximal convoluted tubule is involved in reabsorbing most of the

filtered bicarbonate, glucose, and amino acids, as well as 40% or more of the

filtered sodium, fluids, chlorides, and phosphates.

2. Describe the passage of different substances through the thin descending

limb of loop of Henle.

The permeability of various substances across the thin descending limb of

loop of Henle is as follows:

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➢ Ions have Low permeability, sodium and chloride ions do not readily

pass through.

➢ Urea has moderate permeability

➢ Water is highly permeable and readily reabsorbed from the

descending limb through osmosis.

Because of these, the concentration of the urine increases in the descending

limb.

3. How is Chloride transported in Early Distal Convoluted Tubule?

In the early Distil Convoluted Tubule, chloride is transported in a

trans-cellular fashion from the tubular lumen with sodium through NCC.

Sodium and chloride transport through this co transporter is interdependent.

4. What is the role of Thick Ascending loop of Henle?

The thick ascending limb is impermeable to water. In this limb, sodium (Na+),

potassium (K+) and chloride (Cl−) ions are reabsorbed through active

transport. K+ is passively transported along its concentration gradient via K+

leak channels in the apical aspect of the cells, back into the lumen of the

ascending limb. This K+ leak creates a positive potential difference in the

lumen. This drives more paracellular reabsorption of Na+, as well as other

cations such as magnesium (Mg2+) and importantly calcium Ca2+ as a result

of their charge repulsion.

5. What is the function of collecting tubule?

The collecting duct system consisting of the collecting tubules is the final

passage of the kidneys to control the body's fluid electrolyte balance. In

humans, it caters for 4–5% of the kidney's reabsorption of sodium and 5% of

the kidney's reabsorption of water. At times of severe dehydration, over 24%

of the filtered water can be reabsorbed by the collecting tubules.

The significant variations in water reabsorption by the collecting tubules are

due to their dependence on hormonal stimuli. The ducts, particularly, the outer

medullary and cortical collecting ducts, are mostly impermeable to water

without the presence of antidiuretic hormone (vasopressin). When ADH is

present, aquaporins allow for the reabsorption of water.

The collecting duct system participates in the regulation of other electrolytes,

including chloride, potassium, hydrogen ions, and bicarbonate.

Collecting tubules reabsorb Na+ in exchange for secreting K+ and H+ and the

same is regulated by aldosterone which acts on the mineralocorticoid

receptors.

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Refer to the diagram above for Questions 1-15 1. What is function of Early Proximal Convoluted Tubule The proximal convoluted tubule is involved in reabsorbing most of the filtered bicarbonate, glucose, and amino acids, as well as 40% or more of the filtered sodium, fluids, chlorides, and phosphates. 2. Describe the passage of different substances through the thin descending limb of loop of Henle. The permeability of various substances across the thin descending limb of loop of Henle is as follows: ➢ Ions have Low permeability, sodium and chloride ions do not readily pass through. ➢ Urea has moderate permeability ➢ Water is highly permeable and readily reabsorbed from the descending limb through osmosis. Because of these, the concentration of the urine increases in the descending limb. 3. How is Chloride transported in Early Distal Convoluted Tubule? In the early Distil Convoluted Tubule, chloride is transported in a trans-cellular fashion from the tubular lumen with sodium through NCC. Sodium and chloride transport through this co transporter is interdependent. 4. What is the role of Thick Ascending loop of Henle? The thick ascending limb is impermeable to water. In this limb, sodium (Na+), potassium (K+) and chloride (Cl−) ions are reabsorbed through active transport. K+ is passively transported along its concentration gradient via K+ leak channels in the apical aspect of the cells, back into the lumen of the ascending limb. This K+ leak creates a positive ...
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