Kidney Function: Ultrafiltration and Reabsorption
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Questions and Answers

What percentage of filtrate is typically reabsorbed in the proximal convoluted tubule?

  • 90%
  • 95%
  • 70%
  • 85% (correct)
  • What characterizes the ascending limb of the loop of Henlé?

  • Wide and impermeable to water (correct)
  • Narrow and permeable to water
  • Thick walls and highly permeable to sodium
  • Thin walls and impermeable to ions
  • The counter-current multiplier refers to which process in the loop of Henlé?

  • Water potential gradient established by opposing flows (correct)
  • Filtration of liquid in opposite directions
  • Enhanced absorption through parallel flow of liquids
  • Exchange of oxygen and carbon dioxide
  • What is primarily responsible for the increased hydrostatic pressure within the glomerulus?

    <p>The presence of the efferent arteriole (B)</p> Signup and view all the answers

    Which structure is specifically adapted to increase reabsorption surface area in the proximal convoluted tubule?

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

    Which of the following is NOT a component that resists the movement of filtrate out of the glomerulus?

    <p>Peritubular capillaries (D)</p> Signup and view all the answers

    What type of cells line the walls of the glomerular capillaries?

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

    What is the main function of the distal convoluted tubule?

    <p>Final adjustments to water and salts reabsorption (A)</p> Signup and view all the answers

    What role do mitochondria play in cells of the proximal convoluted tubule?

    <p>Produce ATP for active transport (C)</p> Signup and view all the answers

    What substance is NOT typically filtered out during ultrafiltration in the nephron?

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

    What is the primary function of the renal (Bowman's) capsule in the nephron?

    <p>To collect glomerular filtrate (B)</p> Signup and view all the answers

    How much water is estimated to leave the body as urine from the daily intake?

    <p>1 dm³ (B)</p> Signup and view all the answers

    In the loop of Henlé, what is the significance of the hairpin shape?

    <p>Enhances the counter-current exchange mechanism (D)</p> Signup and view all the answers

    How do the kidneys maintain the body's calcium level?

    <p>By regulating mineral ions in urine (A)</p> Signup and view all the answers

    Which statement is correct about the glomerulus in mammals?

    <p>It is unique in having both afferent and efferent arterioles. (B)</p> Signup and view all the answers

    Which process describes the selective reabsorption in the nephron?

    <p>The movement of substances from filtrate back into the blood (D)</p> Signup and view all the answers

    What is the primary role of podocytes in the kidney?

    <p>To facilitate ultrafiltration in the glomerulus (A)</p> Signup and view all the answers

    Which structure increases the surface area for reabsorption in the proximal convoluted tubule?

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

    What is the function of the descending limb of the loop of Henlé?

    <p>To passively reabsorb water (C)</p> Signup and view all the answers

    Where does most reabsorption occur within the nephron?

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

    During ultrafiltration, what path does the filtrate take from the glomerulus?

    <p>Through the endothelial cells and into the renal capsule (A)</p> Signup and view all the answers

    What substance is primarily active in endocytosis within tubule cells?

    <p>Pinocytic vesicles (D)</p> Signup and view all the answers

    How does the concentration of sodium ions change as filtrate moves along the nephron?

    <p>It decreases in the proximal convoluted tubule and increases in the collecting duct (C)</p> Signup and view all the answers

    What feature differentiates the ascending limb from the descending limb of the loop of Henlé?

    <p>Active transport of sodium ions (B)</p> Signup and view all the answers

    Flashcards

    Ultrafiltration

    The process where blood is filtered in the kidneys, forcing fluids and small molecules out of the glomerulus and into Bowman's capsule. This is the first step in urine formation.

    Selective Reabsorption

    The process of reabsorbing useful substances - like water, glucose, and amino acids - back into the bloodstream from the nephron tubules, after ultrafiltration.

    Afferent Arteriole

    These are tiny blood vessels that bring blood into the glomerulus for filtration. They are wider than the efferent arterioles, which helps create pressure for ultrafiltration.

    Efferent Arteriole

    These are tiny blood vessels that carry blood away from the glomerulus after filtration. They are narrower than the afferent arterioles, which further increases pressure inside the glomerulus.

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    Glomerulus

    This is a network of tiny blood vessels within Bowman's capsule, where ultrafiltration takes place.

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    Bowman's Capsule

    This is a cup-like structure at the start of the nephron, where ultrafiltration occurs. The glomerulus sits inside this structure.

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    Glomerular Filtrate

    This is the fluid formed by ultrafiltration in the nephron, containing water, glucose, mineral ions, and other small molecules, but not blood cells or proteins.

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    Peritubular Capillaries

    These are specialized capillaries that surround the tubules of the nephron, playing a role in reabsorbing substances from the filtrate back into the blood.

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    Proximal Convoluted Tubule

    The proximal convoluted tubule is the first part of the nephron where most of the filtrate is reabsorbed back into the blood.

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    Loop of Henlé

    The loop of Henlé is a hairpin-shaped tubule that extends into the medulla of the kidney. It helps to concentrate urine by creating a gradient of salt concentration.

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    Descending Limb

    The descending limb of the loop of Henlé is permeable to water but not to salts, allowing water to move out of the filtrate and into the interstitial fluid.

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    Ascending Limb

    The ascending limb of the loop of Henlé is impermeable to water but permeable to salts, allowing salts to move out of the filtrate and into the interstitial fluid.

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    Distal Convoluted Tubule

    The distal convoluted tubule is the second part of the nephron where fine adjustments to the composition of the filtrate are made. It controls pH and adjusts the levels of water and salts.

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    Counter-current Multiplier

    The counter-current multiplier system is a mechanism used by the loop of Henlé to create a concentration gradient in the medulla of the kidney. This gradient allows for the reabsorption of water from the collecting duct.

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    Microvilli

    Microvilli are tiny finger-like projections that increase the surface area of cells, allowing for more efficient absorption of substances from the filtrate.

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    Mitochondria

    Mitochondria are organelles within cells that produce energy (ATP) for cellular processes, such as active transport.

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    Podocytes

    Special cells in the glomerulus that have foot-like processes, creating gaps for filtration. They play a crucial role in preventing large molecules from entering the filtrate.

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    Basement Membrane (in the kidney)

    The membrane that separates the blood in the glomerulus from the space inside the renal capsule. It acts as a barrier, allowing small molecules like water and waste products to pass through.

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    Foot-like processes of podocytes

    The tiny projections of the podocyte cells that interlock, forming slits that regulate the passage of substances during filtration.

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    Proximal Convoluted Tubule (PCT)

    The first part of the renal tubule where most reabsorption occurs. It features microvilli, which increase its surface area for efficient reabsorption.

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    Microvilli (in the PCT)

    Tiny finger-like projections on the epithelial cells of the PCT that increase surface area for reabsorption. They enhance the efficiency of reabsorbing important substances from the filtrate.

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    Ultrafiltration in the kidney

    The process that occurs in the glomerulus where blood is filtered, separating waste products and small molecules from the blood.

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    Study Notes

    Kidney Function - Ultrafiltration and Selective Reabsorption

    • Kidneys regulate blood composition, maintaining a constant water potential, removing wastes (e.g., urea), regulating minerals, and blood pressure. Red blood cell production is also regulated.
    • Blood enters the kidney through the renal artery, branching into millions of arterioles. Each arteriole leads to a renal (Bowman's) capsule, forming a glomerulus (capillary network).
    • The glomerulus's afferent arteriole (incoming) is wider than the efferent arteriole (outgoing), creating hydrostatic pressure. This forces water, glucose, mineral ions, and other small molecules (up to 68000 relative molecular mass) into the renal capsule. This filtration under pressure is ultrafiltration.
    • Filtrate is prevented from fully leaving by capillary endothelium, basement membrane, epithelial cells of renal capsule, intracapsular pressure, and glomerulus' low water potential.
    • Specialized podocytes in the renal capsule have "feet" (podocyte) allowing fluid to pass between, not through them. The glomerular capillaries have large spaces (100 nm) between their cells.
    • Filtrate is similar to blood plasma except for plasma proteins.

    The Glomerulus - a Unique Capillary Bed

    • The glomerulus is unique. This is an arteriole supplying blood, and another draining it (efferent arteriole), unlike other capillary beds.
    • This structure is important for creating the hydrostatic pressure necessary for ultrafiltration to occur.
    • The efferent arteriole further divides into peritubular capillaries, draining into a venule, away from the glomerulus.
    • The efferent arteriole merging into further capillaries increases hydrostatic pressure within the glomerulus.

    Selective Reabsorption

    • Nearly 85% of filtrate is reabsorbed into the blood in the proximal convoluted tubule, because molecules smaller or below 68000 relative molecular mass are filtered out and many are essential to the body's functions.
    • About 180 dm³ of water enter the nephrons daily, with only 1 dm³ exiting as urine.
    • Reabsorption of water in the proximal convoluted tubule is 85%.

    The Loop of Henle

    • The loop of Henle, a hairpin-shaped structure in the medulla, is crucial for concentrating urine. It creates conditions (i.e high ion concentration, low water potential) for water reabsorption in the distal convoluted tubule.
    • The descending limb is thin-walled, highly permeable to water.
    • The ascending limb is thick-walled, impermeable to water.
    • Sodium ions are actively pumped out of the ascending limb into the interstitial region. This creates a concentration gradient.
    • Water passively moves out of the descending limb, lowering filtrate water potential.
    • The loop acts as a counter-current multiplier, establishing a gradient in the interstitial fluid of the kidney, necessary for the further reabsorption of water in the collecting duct.

    Distal Convoluted Tubule

    • The distal convoluted tubule, controls water and salt balance, and adjusts pH by selectively reabsorbing ions.
    • This reabsorption is hormone-regulated.
    • Microvilli and mitochondria allow rapid reabsorption in the distal tubule.

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    Description

    This quiz explores the critical processes of ultrafiltration and selective reabsorption in kidney function. Learn how kidneys regulate blood composition and maintain water potential while removing waste products. Discover the role of the glomerulus, afferent and efferent arterioles, and specialized structures involved in kidney filtration.

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