Renal Physiology: Tubular Reabsorption G28- 2

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Questions and Answers

Which of the following cells increase in number during chronic metabolic acidosis?

Principal cells

Type A intercalated cells (correct)

Type B intercalated cells

Macula densa cells

What is the primary function of the pinion transporter?

Secretion of potassium in the collecting ducts

Excretion of bicarbonate in the collecting ducts (correct)

Reabsorption of sodium in the late distal tubule

Excretion of chloride in the cortical collecting tubule

Which of the following statements about the late distal tubule and cortical collecting tubule is FALSE?

Their permeability to water is controlled by aldosterone (correct)

They secrete potassium

They are impermeable to urea

They reabsorb primarily sodium under control of aldosterone

Which of the following mechanisms directly contributes to the maintenance of a high intracellular potassium concentration in the tubular cells?

Activity of sodium-potassium pumps (C) Signup and view all the answers

Which of the following statements accurately describes the function of type B intercalated cells?

They reabsorb bicarbonate ions from the tubular lumen. (D) Signup and view all the answers

Which of the following is directly inhibited by sodium channel blockers?

The entry of sodium into tubular cells (D) Signup and view all the answers

Which of the following accurately describes the permeability of the collecting ducts to water?

Their permeability to water is increased in the presence of vasopressin. (D) Signup and view all the answers

How do the cells of the medullary collecting ducts differ from those in the cortical collecting ducts?

They are responsible for reabsorbing a larger percentage of filtered water. (D) Signup and view all the answers

Which of the following statements accurately describes the role of the thin descending limb of the loop of Henle?

It is highly permeable to water and moderately permeable to most solutes, facilitating simple diffusion. (E) Signup and view all the answers

Which of the following substances is NOT primarily reabsorbed in the proximal tubule?

Creatinine (B) Signup and view all the answers

What is the primary mechanism responsible for the reabsorption of sodium chloride and water in the proximal tubule?

Active transport facilitated by the sodium-potassium pump (D) Signup and view all the answers

Which of the following cellular structures is NOT a characteristic of the proximal tubule?

Thin epithelial membrane with no brush border (E) Signup and view all the answers

What is the significance of the impermeability of the ascending limb of the loop of Henle to water?

It enables the generation of a high osmotic gradient in the medullary interstitium. (A) Signup and view all the answers

Which of the following statements accurately describes the role of para-aminohippuric acid (PAH) in renal physiology?

It is used as a marker to estimate renal plasma flow due to its rapid clearance. (D) Signup and view all the answers

What is the primary function of the thick ascending limb of the loop of Henle?

Active reabsorption of sodium chloride and potassium (E) Signup and view all the answers

Which of the following is NOT a factor contributing to the high rate of sodium reabsorption in the proximal tubule?

High permeability of the thin descending limb to sodium (B) Signup and view all the answers

Which hormone significantly increases water permeability in the distal and collecting tubules?

Antidiuretic hormone (C) Signup and view all the answers

What is the permeability of the ascending loop of Henle to water?

Always low (B) Signup and view all the answers

How are chloride ions primarily reabsorbed in the nephron?

Active transport linked to sodium reabsorption (A) Signup and view all the answers

What percentage of filtered urea is reabsorbed by the tubules?

50% (C) Signup and view all the answers

Which of the following statements about creatinine reabsorption is correct?

Creatinine is practically not reabsorbed (D) Signup and view all the answers

What factor leads to passive diffusion of chloride ions during sodium reabsorption?

Electrical potential created by sodium reabsorption (D) Signup and view all the answers

What is the primary role of aquaporins in the nephron?

Allowing water to move through cell membranes (A) Signup and view all the answers

What is primarily responsible for the reabsorption of sodium in the proximal tubule?

Active transport mechanisms (D) Signup and view all the answers

What does an increase in the kidney's ability to form concentrated urine indicate?

An increase in water reabsorption. (D) Signup and view all the answers

Which substance is primarily used to measure GFR due to its properties of not being reabsorbed or secreted?

Inulin. (C) Signup and view all the answers

If the proximal tubular reabsorption increases due to an increase in GFR, what happens to the percentage of reabsorption?

It remains constant. (D) Signup and view all the answers

Which of the following statements best describes the relationship between water and solute reabsorption?

More water reabsorption leads to lower solute concentration. (B) Signup and view all the answers

What defines the phenomenon of tubular balance?

Increased reabsorption rate in response to increased tubular load. (A) Signup and view all the answers

Which of the following substances is typically minimally reabsorbed by the kidneys?

Creatinine. (B) Signup and view all the answers

What primarily regulates the independent reabsorption of certain solutes in the kidneys?

Nervous and hormonal control mechanisms. (A) Signup and view all the answers

In the proximal tubule, if the concentration of inulin is three times greater at the end of the tubule than when it was filtered, what does this indicate?

One third of the filtered water remains. (D) Signup and view all the answers

What is the primary mechanism by which the sodium potassium pump contributes to the reabsorption of solutes in the thick ascending limb?

It creates a concentration gradient that drives passive sodium reabsorption, leading to the secondary active transport of other solutes. (C) Signup and view all the answers

Which of the following transporters is directly inhibited by loop diuretics?

One sodium two chloride one potassium transporter (A) Signup and view all the answers

How does the thick ascending limb contribute to the diluting and concentrating properties of the kidney?

By actively reabsorbing solutes while remaining impermeable to water, resulting in a dilute urine. (B) Signup and view all the answers

Which of the following statements correctly describes the functional characteristic of the distal tubule?

It is a relatively impermeable segment to water, contributing to the dilution of urine. (D) Signup and view all the answers

What is the primary function of the principal cells in the second half of the distal tubule and cortical collecting ducts?

Reabsorption of sodium and water and secretion of potassium into the tubular lumen. (A) Signup and view all the answers

Which of the following statements accurately describes the role of the macula densa in the regulation of GFR and blood flow?

It monitors the concentration of sodium in the tubular fluid and feeds back to the afferent arteriole to regulate GFR. (C) Signup and view all the answers

Which of the following is NOT a key feature of the thick ascending limb of the loop of Henle?

The reabsorption of solutes in this segment is driven primarily by the sodium-hydrogen counter transporter. (D) Signup and view all the answers

How does the sodium-potassium pump contribute to potassium secretion by principal cells in the distal tubule and cortical collecting ducts?

It creates a low intracellular potassium concentration, causing potassium to move from the cell into the tubular lumen. (A) Signup and view all the answers

Study Notes

Tubular Reabsorption

Tubular membranes facilitate water reabsorption, predominantly through aquaporins and tight junctions in the nephron.
Water permeability in distal parts of nephron (loop of Henle) is influenced by antidiuretic hormone (ADH), increasing permeability.
Proximal tubule exhibits high water permeability, while the descending loop of Henle has high water permeability driven by aquaporins.
Ascending loop of Henle shows low water permeability.
Distal tubules, collecting tubules, and ducts exhibit ADH-dependent water permeability.

Sodium Reabsorption

Sodium reabsorption is coupled with chloride reabsorption, due to electrical potentials drawing chloride ions into the cell.
Active sodium reabsorption creates electrochemical gradient, driving passive chloride reabsorption.
Chloride is reabsorbed via secondary active transport.
Urea passively reabsorbed at lower rate compared to chloride.
Urea reabsorption driven by the concentration gradient.

Waste Product Reabsorption

Creatinine is impermeable to the tubular membrane and virtually all is excreted in the urine.
Roughly 65% of filtered sodium and water are reabsorbed in the proximal tubule.
This high capacity is due to extensive mitochondria, a brush border, and extensive channels, facilitating high transport rates.
Sodium transport coupled with other molecules like glucose, amino acids, through co-transport mechanisms.

Other Important Processes

Glucose, amino acids, and bicarbonate are avidly reabsorbed in the proximal tubule, decreasing concentration in the filtrate.
Organic acids and bases (bile salts, oxalate, urate, catecholamines) are also excreted in the proximal tubules, waste products, harmful drugs, and toxins are also excreted.
Loop of Henle segments (thin descending, thin ascending, thick ascending) have distinctive permeability characteristics impacting urine concentration.

Distal Tubule Processes

Distal tubule regions (macula densa) part of the juxtaglomerular apparatus impacting GFR and blood flow regulation.
Distal tubule and collecting ducts primarily reabsorb sodium and water, with principal cells handling sodium transport, and intercalated cells involved in potassium regulation.
Principal cells participate in sodium reabsorption/potassium secretion, driven by sodium potassium pumps.
Intercalated cells regulate acid-base balance, secreting hydrogen ions or bicarbonate.

Collecting Duct

Collecting ducts reabsorb less than 5% of filtered sodium and water.
Crucial role in urine concentration due to water reabsorption mechanisms and urea transporters.
Active hydrogen ion secretion against concentration gradient in collecting ducts.
Water permeability tightly regulated by ADH, key factor in maintaining urine concentration.

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Description

This quiz covers the essential concepts of tubular reabsorption in the nephron, detailing mechanisms of water and sodium reabsorption. It highlights the roles of aquaporins, tight junctions, and the influence of antidiuretic hormone (ADH) on water permeability. Test your understanding of these critical physiological processes.