Biology Chapter: Kidney Function and Filtration

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Questions and Answers

What structure allows plasma to pass into the tubule during glomerular filtration?

  • Efferent arteriole
  • Podocytes
  • Basement membrane
  • Capillary wall (correct)

Which of the following substances is reabsorbed in the Proximal Convoluted Tubule (PCT)?

  • Creatinine
  • Glucose (correct)
  • Hydrogen ions
  • Urea

What type of transport primarily facilitates the reabsorption of Na+ in the PCT?

  • Facilitated diffusion
  • Osmosis
  • Active transport (correct)
  • Simple diffusion

What is the sequence that materials must follow to be reabsorbed from the PCT into the capillaries?

<p>Luminal membrane, Cytosol, Basolateral membrane (D)</p> Signup and view all the answers

What characteristic of the basement membrane aids in glomerular filtration?

<p>Negatively charged to repel proteins (D)</p> Signup and view all the answers

What triggers the release of ADH from the posterior pituitary?

<p>Increase in osmolarity of blood (B)</p> Signup and view all the answers

Which receptors does ADH act upon in the distal convoluted tubule and collecting duct?

<p>V2 receptors (A)</p> Signup and view all the answers

What effect does ADH have on urine concentration?

<p>Concentrates the urine when present (B)</p> Signup and view all the answers

How do AQP-2 channels function in relation to ADH?

<p>They are inserted into the luminal membrane in response to ADH (A)</p> Signup and view all the answers

What is the primary role of the loop of Henle in the process of water reabsorption?

<p>To create an osmotic gradient (A)</p> Signup and view all the answers

What is the primary function of the Na+/K+ pump in relation to sodium transport?

<p>It creates a concentration gradient for sodium transport. (D)</p> Signup and view all the answers

Which type of nephron has a longer loop of Henle?

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

How does the vertical osmotic gradient in the kidney aid in water reabsorption?

<p>It allows passive water transport through the collecting ducts. (A)</p> Signup and view all the answers

What is the main role of the countercurrent multiplication system?

<p>It sets up a concentration gradient for efficient water reabsorption. (A)</p> Signup and view all the answers

What characterizes the vasa recta in relation to juxtamedullary nephrons?

<p>They are involved in the countercurrent exchange process. (B)</p> Signup and view all the answers

What is the primary function of the glomerulus in the nephron?

<p>Filtration of blood plasma (D)</p> Signup and view all the answers

Which component of the urinary system is responsible for storing urine?

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

How many nephrons are approximately found in each kidney?

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

Which part of the nephron is primarily involved in the reabsorption of water?

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

What role does the vasa recta play in kidney function?

<p>It maintains the concentration gradient (D)</p> Signup and view all the answers

Why might a low nephron count be associated with chronic kidney disease (CKD)?

<p>It reduces the body's ability to filter blood effectively (C)</p> Signup and view all the answers

What percentage of plasma is filtered by the nephron each day?

<p>20% (C)</p> Signup and view all the answers

Which section of the nephron creates a concentration gradient for water reabsorption?

<p>Ascending limb of the Loop of Henle (B)</p> Signup and view all the answers

What is the primary role of the descending limb of the Loop of Henle?

<p>Reabsorbs water (D)</p> Signup and view all the answers

Which mechanism is responsible for creating the osmotic gradient in the Loop of Henle?

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

What happens to the blood in the vasa recta as it descends?

<p>It becomes more concentrated (B)</p> Signup and view all the answers

What percentage of water reabsorption occurs before reaching the distal convoluted tubule?

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

Which hormone regulates the final 20% of water reabsorption in the nephron?

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

Which structure in the nephron is impermeable to water?

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

What is the function of AQP-1 channels in the nephron?

<p>Facilitate water reabsorption (D)</p> Signup and view all the answers

How does vasopressin affect the collecting duct?

<p>Increases permeability to water (D)</p> Signup and view all the answers

What occurs if blood does not become 'salty' in the vasa recta?

<p>Excess salt will wash away (B)</p> Signup and view all the answers

What is the role of NKCC2 in the nephron?

<p>Transports Na+, Cl-, and K+ (A)</p> Signup and view all the answers

Flashcards

Nephron

The functional unit of the kidney, responsible for filtering blood and producing urine.

Glomerulus

A network of capillaries within Bowman's capsule that filters blood.

Bowman's Capsule

A cup-shaped structure surrounding the glomerulus, collecting the filtered fluid from blood.

Filtration

The process of removing waste products and excess fluids from the blood and into the nephron.

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Reabsorption

The process of returning essential nutrients, water and electrolytes from the nephron back into the bloodstream.

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Secretion

The process of removing waste products and excess fluids from the nephron into the collecting duct.

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Collecting Duct

A tube that collects urine from the nephron and transports it to the renal pelvis

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Renal Pelvis

A funnel-shaped structure that collects urine from the collecting ducts and transports it to the ureter.

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Efferent arteriole

The efferent arteriole is the blood vessel that carries blood away from the glomerulus, the filtering unit of the kidney.

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Glomerular filtration

Glomerular filtration is the first step in urine formation, where blood plasma is filtered from the glomerulus into Bowman's capsule.

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Proximal convoluted tubule

The proximal convoluted tubule (PCT) is the first part of the renal tubule, where most of the filtered substances are reabsorbed back into the bloodstream.

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Transepithelial transport

Transepithelial transport is the movement of substances across the epithelial cells that line the renal tubule, allowing for reabsorption and secretion.

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Active transport

Active transport is the movement of substances across the cell membrane against their concentration gradient, requiring energy.

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Sodium Transport in the Proximal Tubule

Sodium (Na+) is transported into the luminal cells against its concentration gradient using the Na+/K+ pump.

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Symport of Glucose and Amino Acids

Glucose and amino acids are co-transported into luminal cells alongside sodium, using the energy of the sodium gradient created by the Na+/K+ pump.

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Water Reabsorption (Passive)

The passive movement of water follows the osmotic gradient created by reabsorbed solutes, such as sodium, in the proximal tubule.

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Water Reabsorption (Active)

The active transport of ions, particularly sodium, creates the osmotic gradient that drives water reabsorption.

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Vertical Osmotic Gradient

The loop of Henle, particularly in juxtamedullary nephrons, establishes a vertical osmotic gradient in the interstitial fluid, with higher concentration in the medulla. This gradient allows for regulated water reabsorption in the proximal convoluted tubule and collecting ducts.

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What triggers ADH release?

Osmoreceptors in the hypothalamus detect an increase in blood osmolarity, signaling dehydration.

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Where does ADH act in the nephron?

ADH (antidiuretic hormone) binds to V2 receptors on the distal convoluted tubule (DCT) and collecting duct (CD).

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How does ADH increase water reabsorption?

ADH stimulates the insertion of aquaporin-2 (AQP-2) water channels into the luminal membrane of the DCT and CD.

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How does water move through AQP-2?

Water diffuses into the cells of the DCT and CD via AQP-2 and then exiting into the bloodstream through AQP-3 or AQP-4.

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How does ADH control urine concentration?

The amount of ADH released determines the extent of AQP-2 insertion, controlling how much water is reabsorbed and the concentration of urine.

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Descending Limb of the Loop of Henle: Water Permeability

The descending limb of the loop of Henle is highly permeable to water due to the presence of aquaporin-1 channels, allowing water to move out of the tubule and into the surrounding interstitial fluid, increasing the concentration of solutes in the tubule.

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Ascending Limb of the Loop of Henle: Salt Reabsorption

The ascending limb of the loop of Henle is impermeable to water. However, it actively reabsorbs sodium, potassium, and chloride ions using the Na+/K+ ATPase pump and the NKCC2 transporter, creating a concentration gradient.

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Countercurrent Multiplication

The countercurrent multiplication system is created by the opposing flow of fluid in the descending and ascending limbs of the loop of Henle. This flow pattern establishes a concentration gradient, allowing for efficient reabsorption of water and solutes.

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Vasa Recta: Countercurrent Exchange

The vasa recta, a network of blood vessels surrounding the loop of Henle, maintains the osmotic gradient by acting as a countercurrent exchanger. The blood in the vasa recta flows in the same direction as the fluid in the loop of Henle, allowing for selective reabsorption and preventing diffusion of solutes out of the medulla.

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Distal Convoluted Tubule and Collecting Duct

The distal convoluted tubule and collecting duct are the final segments of the nephron, where fine-tuning of urine concentration takes place under hormonal control. They reabsorb water and solutes according to hormonal regulation.

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Fluid Reabsorption

About 80% of filtered water is reabsorbed before reaching the distal convoluted tubule and collecting duct. The remaining 20% is regulated by hormones.

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Vasopressin/Antidiuretic Hormone (ADH)

Vasopressin (Antidiuretic Hormone - ADH) is a hormone released by the posterior pituitary gland. It increases the permeability of the distal convoluted tubule and collecting duct to water, allowing for water reabsorption and concentrated urine.

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Mechanism of Action of Vasopressin/ADH

ADH acts on the kidneys by binding to receptors on the cells of the distal convoluted tubule and collecting duct. This binding triggers a series of events that increase water permeability and allow for water reabsorption.

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Urine Concentration in the Loop of Henle

The loop of Henle is crucial for concentrating urine, but the urine isn't actually concentrated within the loop itself. It's the overall process that leads to concentrated urine.

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Osmotic Gradient in Loop of Henle

Countercurrent flow in the loop of Henle creates the osmotic gradient, which is essential for water reabsorption and urine concentration.

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Study Notes

Renal System Overview

  • The urinary system's components include kidneys, ureters, bladder, and urethra.
  • Key learning objectives include describing urinary system components and their functions, identifying nephron areas and their role in water conservation, and discussing voluntary and reflex control of micturition (urination).

Kidney Anatomy

  • Kidneys filter blood, and urine drains into collecting ducts, connecting to the renal pelvis, and then to the ureter.
  • The nephron, the kidney's functional unit, filters blood and reabsorbs useful components, while excreting wastes. There are about 1 million nephrons per kidney. Low nephron counts can be linked to chronic kidney disease (CKD) and high blood pressure, or hypertension.
  • Blood is filtered by a network of capillaries in the glomerulus.

Glomerulus and Bowman's Capsule

  • Bowman's capsule is a cup-shaped structure that encloses the glomerulus.
  • The glomerulus and Bowman's capsule, together, act like a sieve, allowing certain substances to pass from blood into the tubule.
  • Roughly 20% of the plasma enters the nephron for filtration.
  • About 180 liters of plasma are filtered daily, approximately 65 times the body's plasma volume.

Proximal Convoluted Tubule (PCT)

  • The PCT is the site of reabsorption.
  • The PCT selectively reabsorbs nutrients (like glucose and amino acids), and electrolytes (like Na+, K+, and Cl-).
  • Most filtered water and electrolytes are reabsorbed here. Typically 124 mL/min is reabsorbed.

Transepithelial Transport

  • Substances move across the tubular cells, crossing several membranes before entering the interstitial fluid.
  • Movement across the cells can be active (using energy) or passive (following concentration gradients).
  • Crucial components like sodium and water are actively or passively transported across various membranes. A sodium-potassium pump helps create gradients. Glucose and amino acids often travel in with sodium.

Water Reabsorption

  • Water is reabsorbed through osmosis and primarily through aquaporin-1 (AQP-1) channels.
  • The process occurs with a concentration gradient.
  • Water reabsorption is controlled by hormonal signals, such as antidiuretic hormone (ADH, or vasopressin).

Loop of Henle and Vasa Recta

  • The loop of Henle, a hairpin-shaped structure in the nephron, helps create a concentration gradient.
  • Juxtamedullary nephrons in the medulla have longer loops and significantly contribute to concentration gradients.
  • The vasa recta capillaries alongside the loop of Henle help maintain the concentration gradient.

Common Misconceptions

  • Urine becomes more dilute, not concentrated, as it passes through the loop of Henle.
  • Countercurrent flow occurs, where fluid moves in opposite directions through adjacent tubules.

Distal Convoluted Tubule and Collecting Duct

  • These components adapt water reabsorption based on hormonal (vasopressin) control.
  • The distal tubule and collecting ducts fine-tune water and electrolyte balance, influencing urine concentration.

Micturition

  • Micturition, or urination, involves the process of bladder emptying. Blackboard materials cover this in detail.

Summary

  • The nephron is the functional unit.
  • Blood is filtered by the glomerulus, passing liquid through the tubules.
  • The tubules reabsorb nutrients and electrolytes.
  • Water balance is regulated by hormones like ADH.

Next Session Topics

  • Glomerular Filtration Rate (GFR)
  • Loop Diuretics
  • Plasma Clearance Rate
  • Renin-Angiotensin-Aldosterone System (RAAS).

Further Reading

  • Specific chapters and articles provide more detailed information on the topics covered.

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