L4 Renal tubular reabsorption and secretion (P1 Mid)
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Questions and Answers

Where does the active reabsorption of phosphate primarily occur?

  • Collecting ducts
  • Distal convoluted tubules
  • Proximal convoluted tubules (correct)
  • Loop of Henle

What role does parathyroid hormone (PTH) have in phosphate reabsorption?

  • Inhibits reabsorption by proximal convoluted tubules (correct)
  • Has no effect on phosphate levels
  • Enhances excretion of phosphate
  • Stimulates reabsorption by DCT

Calcium reabsorption occurs through which mechanisms?

  • Exclusively through osmosis
  • Either 2nd active transport or passive reabsorption (correct)
  • Only passive transport
  • Only active transport

Which segment of the nephron reabsorbs both calcium and phosphate?

<p>Both proximal and distal convoluted tubules (C)</p> Signup and view all the answers

What limits the reabsorption of phosphate in the kidneys?

<p>The concentration of phosphate in the plasma (A)</p> Signup and view all the answers

What is the primary mode of glucose reabsorption in the early portion of the PCT?

<p>Secondary active transport (A)</p> Signup and view all the answers

At what plasma glucose level does glucose begin to appear in urine?

<p>180 mg% (D)</p> Signup and view all the answers

Which transporter is responsible for glucose translocation across the basolateral border of the epithelial cell?

<p>GLUT-2 (C)</p> Signup and view all the answers

Which part of the nephron is primarily responsible for the obligatory reabsorption of 65% of sodium?

<p>Proximal convoluted tubule (A)</p> Signup and view all the answers

Which mechanism is NOT involved in potassium transport in the kidneys?

<p>Endocytosis (C)</p> Signup and view all the answers

What does the sodium-potassium ATPase pump do in the context of sodium reabsorption?

<p>Moves sodium out of the tubular cell into interstitial fluid (B)</p> Signup and view all the answers

What percentage of sodium is reabsorbed in the Loop of Henle?

<p>25-30% (A)</p> Signup and view all the answers

What is the role of tight junctions in the epithelial cell lining of the tubule?

<p>Prevent passive transport of molecules (A)</p> Signup and view all the answers

What is the primary function of tubular reabsorption in the kidneys?

<p>To selectively reclaim substances needed by the body (D)</p> Signup and view all the answers

Which of the following processes occurs primarily through the transepithelial route during tubular reabsorption?

<p>Reabsorption of ions like Na and Ca (A)</p> Signup and view all the answers

What is meant by the term 'paracellular' in the context of renal tubular reabsorption?

<p>Transport occurring between adjacent cells (D)</p> Signup and view all the answers

Which mechanism of tubular reabsorption does not require energy?

<p>Passive diffusion of water (D)</p> Signup and view all the answers

Which barrier does a substance NOT need to cross during transepithelial reabsorption?

<p>Epithelial tight junctions (D)</p> Signup and view all the answers

Which of the following substances is primarily reabsorbed through active transport mechanisms in the renal tubules?

<p>Chloride ions (D)</p> Signup and view all the answers

What is the significance of maintaining the concentration of various substances in glomerular filtrate?

<p>To prevent the loss of electrolytes and nutrients (C)</p> Signup and view all the answers

What is NOT a characteristic of passive diffusion during renal tubular reabsorption?

<p>It involves energy expenditure (A)</p> Signup and view all the answers

What mechanism primarily drives the passive reabsorption of Cl- in the proximal convoluted tubule (PCT)?

<p>Concentration gradient due to Na+ reabsorption (B)</p> Signup and view all the answers

Which statement accurately describes the reabsorption of H2O in the proximal tubule?

<p>H2O reabsorption occurs only in the presence of active Na+ transport. (B)</p> Signup and view all the answers

What percentage of filtered urea is reabsorbed in the proximal convoluted tubule?

<p>50% (C)</p> Signup and view all the answers

How does a decline in kidney function affect blood urea levels?

<p>Blood urea levels increase. (B)</p> Signup and view all the answers

What percent of water reabsorption in the nephron is obligatory?

<p>80% (B)</p> Signup and view all the answers

The primary mechanism for H+ secretion in the proximal convoluted tubule involves what process?

<p>Secondary active transport with sodium (A)</p> Signup and view all the answers

What hormone primarily regulates K+ secretion in the distal tubule and collecting duct?

<p>Aldosterone (B)</p> Signup and view all the answers

Which is true regarding the transport of K+ in the nephron?

<p>Secretion occurs mainly through distal and collecting tubules. (D)</p> Signup and view all the answers

What is the relationship between plasma [H+] and H+ secretion in the renal tubules?

<p>Directly proportional (D)</p> Signup and view all the answers

Which of the following substances is primarily secreted by the proximal convoluted tubule?

<p>Hydrogen ions (A)</p> Signup and view all the answers

Which mechanism is primarily responsible for Na+ reabsorption in the distal tubule?

<p>Primary active transport (D)</p> Signup and view all the answers

What is the role of hydrostatic pressure in tubular reabsorption?

<p>It drives filtration at the glomerulus. (B)</p> Signup and view all the answers

Which of the following correctly describes urea reabsorption?

<p>Urea reabsorption increases as H2O is reabsorbed. (B)</p> Signup and view all the answers

Where in the nephron does most of the obligatory water reabsorption occur?

<p>Proximal convoluted tubule (B)</p> Signup and view all the answers

Flashcards

Tubular Reabsorption

The process by which substances are moved from the tubular fluid back into the bloodstream.

Transepithelial Reabsorption

The movement of substances across the epithelial cells of the renal tubules.

Paracellular Reabsorption

The movement of substances between the cells of the renal tubules.

Active Transport

The type of transport that requires energy to move substances against their concentration gradient.

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Secondary Active Transport

The type of transport that uses the energy from the movement of one substance to move another substance.

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Passive Diffusion

The movement of substances down their concentration gradient, requiring no energy.

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Tubular Reabsorption Regulation

The precise control of the concentration of different substances in the tubular fluid to maintain the proper composition and volume of the body's internal environment.

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Tubular Secretion

The process by which substances are moved from the bloodstream into the tubular fluid.

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Phosphate Reabsorption

The process of moving phosphate from the tubular fluid back into the bloodstream.

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How is Phosphate Reabsorbed?

Reabsorbing phosphate happens actively using co-transport with sodium in the proximal tubules.

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Phosphate Reabsorption Limit

The body can only reabsorb phosphate up to normal plasma levels.

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How does PTH affect Phosphate Reabsorption?

Parathyroid hormone (PTH) inhibits phosphate reabsorption in the proximal convoluted tubules.

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Calcium Reabsorption

The process by which calcium moves from the tubular fluid back into the blood.

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Sodium Reabsorption

Sodium reabsorption in the kidney occurs as a result of active transport by the Na+–K+ ATPase pump located on the basolateral membrane of tubular cells. Sodium moves from the tubular fluid into the interstitial fluid, creating a concentration gradient that drives passive diffusion of sodium across the luminal membrane.

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Glucose Reabsorption

Glucose reabsorption in the kidneys is a two-step process involving sodium-dependent secondary active transport and facilitated diffusion. Glucose and sodium are co-transported across the luminal membrane through a carrier protein called SGLT. This uses energy from the sodium gradient created by the Na+–K+ ATPase pump. Glucose then moves down its concentration gradient across the basolateral membrane via GLUT-2 carrier proteins, back into the bloodstream.

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K+ Transport

Potassium (K+) reabsorption occurs in the proximal convoluted tubule (PCT) and the loop of Henle. PCT reabsorbs 65% of filtered K+ (obligatory), while the loop of Henle reabsorbs 25-30%.

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How K+ moves

Potassium (K+) can be actively reabsorbed or secreted in the tubules, depending on the body's needs. Reabsorption occurs in the PCT via primary active transport, while secretion occurs in the collecting duct, where its movement is influenced by aldosterone.

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Phosphate & Calcium Reabsorption

Phosphate and calcium reabsorption is regulated by the kidneys, maintaining their plasma levels within a typical range. Their threshold is equal to their normal plasma concentration which means that they are normally reabsorbed.

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Renal Threshold

The renal threshold for a substance is the plasma concentration at which that substance starts appearing in urine. For example, the renal threshold for glucose is 180 mg%. This means that when blood glucose levels exceed 180 mg%, excess glucose is not reabsorbed and spills over into urine.

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Glucose in Urine

The plasma glucose level at which glucose starts to appear in urine is called the renal threshold for glucose. This is usually around 180 mg%. Normally, all filtered glucose is reabsorbed by the kidneys.

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Passive Reabsorption

The passive movement of substances from the tubular fluid back into the bloodstream.

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Hydrogen Ion Secretion

The process of moving hydrogen ions from the bloodstream into the tubular fluid.

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Potassium Ion Secretion

The process of moving potassium ions from the bloodstream into the tubular fluid.

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Study Notes

Renal Module Information

  • Course code: IMP-07-20318
  • Phase: I
  • Year/semester: 2nd year / Semester 3
  • Credit hours: Not specified
  • Course duration: 5 weeks

Lecture 4: Renal Tubular Reabsorption and Secretion

  • Intended Learning Outcomes (ILOs):
    • Describe the function of various parts of renal tubules (tubular reabsorption and secretion)
    • Identify tubular reabsorption and secretion and its significance

Tubular Functions

  • Tubular functions are divided into reabsorption and secretion

Tubular Reabsorption

  • Each material is reabsorbed to maintain the proper composition and volume of the internal fluid environment and its concentration in plasma
  • Reabsorption occurs via two main pathways:
    • Paracellular (in between cells), primarily for water (H₂O)
    • Transcellular (through cells), for most substances
  • Transepithelial reabsorption: substances cross five barriers (luminal, cytosol, basolateral membrane, interstitial fluid, and capillary wall)

Mechanisms of Tubular Reabsorption

  • Passive diffusion:
    • Water (H₂O)
    • Chloride (Cl⁻)
    • Urea
  • Active transport:
    • Primary active (e.g., Na+, K+, Ca²+, H+)
    • Secondary active (e.g., glucose, amino acids)

Sodium Reabsorption

  • Sodium is reabsorbed actively, driving other substances through co-transport

Glucose Reabsorption

  • Requires sodium-dependent secondary active transport via sodium-glucose cotransporter in the proximal convoluted tubule (PCT) early part

  • All filtered glucose is reabsorbed

  • The plasma glucose level at which glucose starts to appear in urine is 180 mg/dL

K Transport

  • PCT reabsorbs 65% of potassium (obligatory)
  • Loop of Henle reabsorbs 25-30% of potassium (obligatory)
  • Reabsorption happens through active transport (both primary and secondary) in PCT and in Loop

Phosphate and Calcium Reabsorption

  • Kidneys regulate their plasma levels based on body needs
  • Renal threshold = normal plasma concentration.

Phosphate Reabsorption

  • Active, primarily via co-transport with sodium (Na⁺) in the proximal convoluted tubule (PCT).
  • Limited by the normal plasma concentration (usually more phosphate is ingested than needed).
  • Controlled by parathyroid hormone (PTH), which inhibits phosphate reabsorption by the PCT.

Calcium Reabsorption

  • Occurs via secondary active transport or passive diffusion.
  • Both the PCT and distal convoluted tubule (DCT) reabsorb calcium.
  • Reabsorption is limited by the normal plasma concentration
  • Controlled by parathyroid hormone (PTH), which stimulates calcium reabsorption in the PCT.

Other Substances Passively Reabsorbed

  • Chloride (Cl⁻), water (H₂O), and urea and depend on sodium (Na+) reabsorption.

Chloride Reabsorption

  • Passive, occurring due to electrical and concentration gradients in the PCT; influenced by water (H₂O) reabsorption

Water Reabsorption

  • Passive (osmosis), occurring due to the concentration gradient established by sodium (Na+) reabsorption.
  • Obligatory reabsorption (65% in the PCT and 15% in the Loop of Henle)
  • Facultative reabsorption (20%, variable)

Urea Reabsorption

  • Passive, linked to sodium (Na⁺) reabsorption and water (H₂O) removal in the PCT.
  • Approximately 50% of filtered urea is reabsorbed

Waste Product Loss in Urine

  • Waste products that are filtered by the kidneys are not reabsorbed and are lost in the urine.

Summary of Tubular Reabsorption (other than sodium)

Location Active Transport Passive Transport
Proximal tubule Glucose, amino acids, K⁺, phosphate, calcium Cl⁻, H₂O, urea
Loop of Henle Cl⁻, K⁺ H₂O
Distal and other

Tubular Secretion

  • Removal of substances from the blood into the tubular fluid.

Substances Secreted

  • Hydrogen ions (H⁺) (PCT, DCT, collecting duct)
  • Potassium ions (K⁺) (DCT, collecting duct)
  • Organic compounds (PCT) (e.g., creatinine, uric acid, drugs)

Hydrogen Ion (H⁺) Secretion

  • All excreted H⁺ is through secretion; filtered H⁺ is very little
  • Active, primarily via both primary and secondary transport in all tubules.
  • Directly proportional to plasma [H⁺].
  • PCT: Counter-transport with sodium (Na⁺).
  • DCT & Collecting ducts: Primary active transport (pump).

Potassium (K⁺) Secretion

  • Occurs mainly due to active transport in the DCT and collecting ducts.
  • Regulates the secretion is mostly by hormones.

Control of H+ secretion

  • Directly proportional to plasma [H⁺] or PCO₂

Mechanism of H⁺ Secretion

  • Counter-transport with sodium (Na⁺) in PCT (around 90%)
  • Primary active transport on the luminal membrane of DCT and collecting ducts (about 5%)

HCO₃⁻ Reabsorption"

  • Coupled with H⁺ secretion; the kidney effectively reabsorbs filtered bicarbonate even though it doesn't technically happen in a way where it is absorbed.

K⁺ Transport (Reabsorption and Secretion)

  • Both types of transport occur during reabsorption and secretion.

Potassium (K⁺) Secretion

  • Almost all K⁺ is secreted into the urine by active transport in the distal convoluted tubule (DCT) and collecting duct (CD).
  • (10-15% of filtered K⁺ is secreted)
  • Regulated hormonally (aldosterone stimulates K⁺ secretion).

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Renal Tubular Reabsorption and Secretion PDF

Description

Test your knowledge on kidney physiology, focusing on the processes of reabsorption for various substances such as phosphate, calcium, and sodium. This quiz delves into the mechanisms involved, including the roles of hormones and transporters within different segments of the nephron. Enhance your understanding of renal functions and their significance in overall physiology.

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