describe the events that occur in countercurrent multiplication in the Loop of H
ID: 91800 • Letter: D
Question
describe the events that occur in countercurrent multiplication in the Loop of Henle. Describe what happens in each limb of the loop and what histological features of each portion contribute to their respective functions. Why is it called countercurrent multiplication? Besides water and ion reabsorption, what other critical function does the loop of Henle serve in juxtameduallary nephrons? What properties does the blood in the vasa recta have that are different from blood elsewhere in the body and why is this important? Finally, explain how the diuretics called “loop diuretics” work. Why are they such powerful diuretics? For what conditions (that we have discussed) might they be prescribed? What acid/base balance problem can result from their use and why?
Explanation / Answer
(1) Describe the events that occur in countercurrent multiplication in the Loop of Henle.
The kidneys reabsorb water from the tubular fluid by a process namely countercurrent multiplication. In this process, the kidney uses energy to generate an osmotic gradient that enables reabsorbing water from the tubular fluid and produces concentrated urine. This mechanism is useful for preventing the production of voluminous urine daily which is the reason why we need not drink water in order to stay hydrated.
(2) Describe what happens in each limb of the loop and what histological features of each portion contribute to their respective functions.
The fluid leaving the ascending limb of the loop of Henle enters the distal convoluted tubule. The composition of the fluid is adjusted here before draining into collecting tubules. These tubules empty the fluid into the collecting ducts that descend back through the medulla, and connects to the ureter, which transports urine to the bladder.
The thin descending limb is passively permeable to water and small solutes such as sodium, potassium, chloride and urea. As the reabsorption of solutes from the ascending limb of the loop of Henle increases the concentration of solutes within the interstitial space, the water and the solutes move down their concentration gradients until their concentrations within the descending tubule and the interstitial space are adjusted. Then the water moves out of the tubular fluid and solutes to move in. So, the tubular fluid becomes hyperosmotic as it travels down the thin descending limb of the tubule.
(3) Why is it called countercurrent multiplication?
Because this mechanism expends energy to create a concenration gradient. The blood flow through the capillaries is very slow. So, any solutes that are reabsorbed into the bloodstream have time to diffuse back into the interstitial fluid, which maintains the solute concentration gradient in the medulla.
(4) Besides water and ion reabsorption, what other critical function does the loop of Henle serve in juxtameduallary nephrons?
The juxtameduallary nephrons are longer. This creates an increased osmotic gradient and so there is more water reabsorption.
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