Physiology of Water Reabsorption in Collecting Duct

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Questions and Answers

What type of aquaporin is primarily responsible for water reabsorption in the collecting duct?

Aquaporin-II (correct)

Aquaporin-III

Aquaporin-IV

Aquaporin-I

Which of the following is NOT directly involved in regulating the reabsorption of water in the collecting duct?

Aldosterone

ADH

Calcium (correct)

Aquaporin-II

Which of the following cell types in the collecting duct is responsible for maintaining mineral and water balance?

Both Intercalated-A and Principal cells

Principal cells (correct)

Intercalated-A cells

Neither Intercalated-A nor Principal cells

The presence of ADH primarily increases the expression of which aquaporin in the collecting duct, thereby enhancing water reabsorption?

Aquaporin-II Signup and view all the answers

Intercalated-A cells in the collecting duct mainly respond to which physiological condition?

Acidosis Signup and view all the answers

During acidosis, what is the primary role of the H-K-ATPase pump in intercalated A-cells?

To move hydrogen ions (H+) out of the cell and potassium ions (K+) into the cell. Signup and view all the answers

What is the significance of the enzyme carbonic anhydrase in the context of acid-base balance within intercalated cells?

It catalyzes the formation of carbonic acid (H2CO3) from carbon dioxide (CO2) and water (H2O). Signup and view all the answers

What is the primary function of principal cells within the collecting duct?

Maintaining mineral and water balance. Signup and view all the answers

In response to alkalosis, what is the primary function of the HCO3–/Cl– transporter in intercalated B-cells?

To move bicarbonate ions (HCO3–) out of the cell and chloride ions (Cl-) into the cell. Signup and view all the answers

Which hormone directly influences the expression of aquaporin-II in the collecting duct?

Antidiuretic hormone (ADH) Signup and view all the answers

If there is elevated carbon dioxide (CO2) levels in the blood, what effect does this have on pH, and what type of cell is primarily involved in counteracting this?

It results in a decreased pH, and intercalated A-cells respond. Signup and view all the answers

What is the effect of aldosterone on sodium and potassium levels within the collecting duct?

Increases sodium reabsorption and potassium secretion. Signup and view all the answers

How does the body eliminate excess protons (H+) during acidosis?

By converting them into ammonium (NH4+) in the kidneys which is then excreted in the urine. Signup and view all the answers

In which part of the nephron does NaCl reabsorption occur through symporters?

Early Distal Convoluted Tubule (DCT) Signup and view all the answers

What is the general function of intercalated A and B cells in the collecting duct?

Maintaining acid-base balance. Signup and view all the answers

Which change is associated with the presence of ADH in the collecting duct?

Increased water reabsorption and decreased potassium levels. Signup and view all the answers

Under what condition are Intercalated A-cells most active?

Acidic condition Signup and view all the answers

Besides principal and intercalated cells, what other substances can be secreted by cells in the collecting duct?

Drugs, toxins, and creatinine Signup and view all the answers

What is the primary role of the H-K-ATPase in the collecting duct?

To move hydrogen ions out of the cell into the blood and potassium into the cell. Signup and view all the answers

Which of the following best describes the effect of antidiuretic hormone (ADH) on the collecting duct?

It increases water reabsorption by inserting aquaporin-II channels into the apical membrane. Signup and view all the answers

What happens to plasma osmolality when ADH is released in response to a hypertonic state?

Plasma osmolality decreases towards isotonic levels due to increased water reabsorption. Signup and view all the answers

What is the role of carbonic anhydrase in the renal cells?

It catalyzes the conversion of carbon dioxide and water into carbonic acid ($H_2CO_3$). Signup and view all the answers

Which change in ion concentrations would you expect in the collecting duct cells when the kidney is trying to excrete acid?

Increase in protons, decrease in bicarbonate. Signup and view all the answers

What does activation of adenylate cyclase in the principal cells of the collecting duct lead to?

Increased production of cAMP and subsequent activation of Protein Kinase A. Signup and view all the answers

In which conditions would you expect higher levels of ADH to be released?

Hypertonic plasma and low blood volume. Signup and view all the answers

After ADH binds to its receptor, what is the immediate effect of the G-stimulatory protein?

It activates adenylate cyclase to produce cAMP. Signup and view all the answers

Which of the following is NOT a cellular process associated with the action of ADH in the collecting duct?

Direct secretion of sodium into the urine. Signup and view all the answers

What mechanisms are used to excrete acid from the body?

Reabsorption of bicarbonate with secretion of protons. Signup and view all the answers

What percentage of sodium is reabsorbed in the early distal convoluted tubule (DCT)?

5-6% Signup and view all the answers

Which of the following is NOT a function of the vasa recta?

Rapidly remove sodium chloride from the medulla Signup and view all the answers

What is the primary mechanism driving water reabsorption in the descending limb of the Loop of Henle?

Osmosis, due to increased solute concentration in the medullary interstitium Signup and view all the answers

What is the role of PTH in relation to calcium reabsorption in the kidneys?

PTH is essential for calcium reabsorption in the nephron. Signup and view all the answers

If ADH levels increase, what is the direct effect on water reabsorption in the collecting duct?

Water reabsorption will increase because aquaporin-II expression increases Signup and view all the answers

How does the vasa recta contribute to creating concentrated urine?

By maintaining the high solute concentration in the medullary interstitium via the counter-current exchange mechanism Signup and view all the answers

What process describes the movement of NaCl into the vasa recta as it descends into the medulla?

Simple diffusion driven by the counter-current multiplier mechanism Signup and view all the answers

What is the significance of urea recycling in the kidney?

To contribute to the medullary osmotic gradient Signup and view all the answers

Where in the nephron does the majority of water reabsorption occur?

The proximal convoluted tubule (PCT) Signup and view all the answers

Which of the following events occurs in the ascending limb of the Loop of Henle?

Reabsorption of 25% of sodium via active transport Signup and view all the answers

Study Notes

Collecting Duct Review

The collecting duct plays a vital role in maintaining mineral and water balance in the body.
It helps maintain the body's acid-base balance and homeostasis.
It is found in the late distal tubule and collecting duct. Intercalated A cells maintain an acidic internal environment, and intercalated B cells maintain a basic internal environment. Other substances (drugs, toxins, creatinine, ammonia, etc.) may also impact the collecting duct,
NaCl reabsorption occurs in the early distal tubule (DCT), utilizing sodium symporters. Calcium reabsorption depends on parathyroid hormone (PTH).
Aldosterone influences sodium reabsorption and potassium secretion.
Antidiuretic hormone (ADH) increases aquaporin-II expression, allowing water to move into the bloodstream. This decreases potassium levels and increases sodium levels, increasing blood volume and pressure.

Intercalated A-Cells

Respond to acidosis (low pH), such as respiratory or metabolic acidosis.
They actively move CO2 into the cell, which reacts with water to form carbonic acid (H2CO3).
Carbonic acid dissociates into a proton (H+) and bicarbonate (HCO3-).
The released H+ is pumped out of the cell using an H+-K+ ATPase.
Simultaneously, bicarbonate is transported out of the cell.
Ammonia (NH3) is secreted into the urine, where it combines with protons to form ammonium (NH4+), which is excreted.

Intercalated B-Cells

Respond to alkalosis (high pH), including respiratory or metabolic alkalosis.
Bicarbonate (HCO3-) is actively pumped out of the cell into the urine or back into the bloodstream, removing excess base from the body.
Protons (H+) are actively taken up into the cell using an H+-K+ ATPase, and transported back into the bloodstream.

Principal Cells

Maintain mineral and water balance.
They respond to changes in serum osmolality.
Vasopressin receptors (on principal cells) trigger the insertion of aquaporin-II channels in the cell membrane.
Water is transported out of the collecting duct, increasing blood volume and pressure.
Principal cells are also involved in sodium reabsorption and potassium secretion.

Reabsorption

Calcium, water, and sodium reabsorption occurs in different sections of the nephron (i.e. proximal convoluted tubule (PCT), loop of Henle, distal convoluted tubule (DCT)).
Water reabsorption is dependent on ADH and aquaporin-II.
Different percentages of these substances are reabsorbed in different nephron segments.

Vasa Recta

The peritubular capillary network within the medulla, known as the counter-current exchanger.
It helps to maintain the medullary osmotic gradient.

Urea Recycling

Urea is reabsorbed in the collecting duct
Urea's reabsorption assists in concentrating urine.
Urea contributes to the medullary osmotic gradient.

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Description

This quiz focuses on the physiological mechanisms of water reabsorption in the collecting duct, including the roles of various aquaporins and cell types. Explore how hormones like ADH influence water balance and how intercalated cells respond to physiological changes. Test your knowledge on the renal system's intricate functions.