Countercurrent Mechanism Flashcards
What is the countercurrent mechanism in the kidney?
A system in the kidney that generates a concentration gradient to concentrate urine and conserve water.
What are the main components of the countercurrent mechanism?
The loop of Henle, vasa recta, and collecting ducts.
How does the loop of Henle contribute to the countercurrent mechanism?
It establishes an osmotic gradient in the medulla, essential for water reabsorption.
What is the role of the descending limb of the loop of Henle in the countercurrent mechanism?
The descending limb is permeable to water but not to solutes, leading to an increase in filtrate osmolarity.
How does the ascending limb of the loop of Henle function in the countercurrent mechanism?
The ascending limb actively transports solutes out but is impermeable to water, decreasing filtrate osmolarity.
What is the significance of the thick ascending limb of the loop of Henle?
It actively transports sodium, potassium, and chloride out of the filtrate, creating a hyperosmotic medullary interstitium.
How is the osmolarity of the filtrate affected as it moves down the descending limb of the loop of Henle?
It increases as water is reabsorbed and solutes remain.
What happens to the osmolarity of the filtrate as it moves up the ascending limb of the loop of Henle?
It decreases as solutes are actively transported out.
What is the role of the countercurrent multiplier system in urine concentration?
It amplifies the osmotic gradient created by active transport of solutes in the ascending limb.
How does the countercurrent multiplier establish a concentration gradient in the medulla?
By continuously moving solutes from the filtrate into the medullary interstitium.
What is the role of urea recycling in the countercurrent mechanism?
It contributes to the high osmolarity of the medullary interstitium, enhancing water reabsorption.
How does the medullary interstitial osmolarity affect water reabsorption?
High medullary interstitial osmolarity draws water out of the collecting ducts.
What is the function of the vasa recta in the countercurrent mechanism?
It maintains the concentration gradient by countercurrent exchange, preventing washout.
How does the countercurrent exchange mechanism in the vasa recta preserve the medullary concentration gradient?
It allows for exchange of solutes and water between the blood and medullary interstitium without dissipating the gradient.
What is the significance of the slow blood flow in the vasa recta?
It prevents the washout of the medullary concentration gradient.
How does the structure of the vasa recta facilitate its function in the countercurrent mechanism?
Its hairpin structure allows for countercurrent exchange of solutes and water.
What role does the collecting duct play in the countercurrent mechanism?
It reabsorbs water and concentrates urine as it passes through the medulla.
How does antidiuretic hormone (ADH) influence the countercurrent mechanism?
ADH increases the permeability of the collecting ducts to water.
What is the effect of ADH on the collecting ducts in the kidney?
It makes the collecting ducts more permeable to water, allowing more water reabsorption.
How does the permeability of the collecting duct change in the presence of ADH?
The presence of ADH increases the number of aquaporins in the collecting duct membrane.
What is the maximum osmolarity that the human kidney can achieve in the medullary interstitium?
About 1200 mOsm/kg.
How is the osmolarity of urine regulated?
By adjusting water and solute reabsorption in the collecting ducts.
How does the length of the loop of Henle affect the concentration gradient?
Longer loops create a steeper concentration gradient.
What is the role of the juxtamedullary nephrons in the countercurrent mechanism?
They have longer loops of Henle that extend deep into the medulla, crucial for generating a high osmotic gradient.
