Please Help! 1. What is the effect of countercurrent multiplier in the loop of H
ID: 173932 • Letter: P
Question
Please Help!
1. What is the effect of countercurrent multiplier in the loop of Henle?
2. Where does the reabsorption of ions occur in the nephron to produce a hyposmotic solution in the tubules?
3. Hyponatremia _____ the secretion of ADH/vasopressin and _____ the secretion of aldosterone.
4. ________ interstitial osmolarity allows urine to be concentrated.
A. Solutes (ions) are most concentrated as filtrate leaves the loop of Henle. B. The filtrate is least concentrated at the deepest part of the loop of Henle. C. Water is reabsorbed in the descending loop of Henle. D. The filtrate becomes progressively more hyposmotic as it descends the loop.Explanation / Answer
Answer:
The correct answer is Option- C.
During the operation of the countercurrent mechanism taking place in the Loop of Henle of the kidney, the descending loop of Henle remains very permeable to water. It is permeable and leaky as compared to the ascending loop due to the presence of aquaporins. The water present in the tubular fluid diffuses out of the tube into the medullary interstitium. therefore the tubular fluid osmolarity gradually rises as it flows toward the tip of the loop of Henle. As a result, the tubular fluid osmolarity quickly becomes equal to the renal medullary osmolarity. Thus it can be easily understood that reabsorption of water into the interstitium takes place in the descending loop forming hyperosmotic filtrate at the deepest part of the Henle's loop.
2) The correct answer is Option-D.
Reabsorption of ions principally occurs in the ascending limb of the loop of Henle. The ascending limb possesses thick epithelial cells in the thick segment of the ascending limb specialized for this purpose. About 25 per cent of the filtered loads of sodium, chloride, and potassium are reabsorbed in the loop of Henle, mostly in the thick ascending limb. Considerable amounts of other ions, such as calcium, bicarbonate, and magnesium, are also reabsorbed in the thick ascending loop of Henle. The sodium-potassium ATPase pump in the basolateral cell membrane maintains a low intracellular sodium concentration in these cells. The low intracellular sodium concentration in turn provides a favorable gradient for movement of sodium from the tubular fluid into the cell. In the process, chloride and potassium ions are also brought into the cells by 1-sodium, 2-chloride, 1-potassium co-transporter facilitating reabsorption. There is also significant paracellular reabsorption of cations, such as Mg++, Ca++, Na+, and K+, in the thick ascending limb owing to the slight positive charge of the tubular lumen relative to the interstitial fluid. The thick segment of the ascending loop of Henle is virtually impermeable to water. Thus despite loss of ions, the amount of water supplied to this segment remains the same producing hypoosmotic tubular filtrate.
3) The correct answer is Option-A.
Hyponatremia is the condition in which there is low sodium conc. in the extracellular fluid. Decreased plasma sodium concentration can result from loss of sodium chloride from the extracellular fluid or addition of excess water to the extracellular fluid. A primary loss of sodium chloride usually results in hypo-osmotic dehydration and is associated with decreased extracellular fluid volume. ADH or antidiuretic hormone causes retention of water in the body thereby eliminating concentrated urine. Release of excess ADH results in greater reabsorption of water which lowers the sodium conc. in extracellular fluid. in case of Addison's disease aldosterone levels are diminished due to its lower secretion. Aldosterone is responsible for sodium retention in the body. Decreased secretion of the hormone aldosterone, impairs the ability of the kidneys to reabsorb sodium and can cause hyponatremia.
4) The correct option is option-D.
There are two prerequisites for generation of concentrated urine- (1) a high level of ADH, which increases the permeability of the distal tubules and collecting ducts to water, thereby allowing these tubular segments to reabsorb water, and (2) a high osmolarity of the renal medullary interstitial fluid, which provides the osmotic gradient necessary for water reabsorption to occur in the presence of high levels of ADH. The renal medullary interstitium surrounding the collecting ducts normally is very hyperosmotic, so that when ADH levels are high, water permeability also increases & moves through the tubular membrane by osmosis into the renal interstitium. The renal interstitium remains highly concentrated due to the presence of different ions and maintains a gradient that favors water reabsorption.
Reference- Guyton's book of Medical Physiology