It runs parallel to the Henley loop and is U-shaped. Blood flows in opposite directions in the two legs of the vasa recta. As a result, blood entering the renal medulla in the descending limb is in near contact with the existing blood in the ascending limb.
The osmolarity of the inner medulla increases by the countercurrent mechanism. It helps to preserve the concentration gradient, which in effect helps to promote the flow of water from the collection of tubules. The gradient is the result of NaCl and urea movements.
Step 2: The thick ascending limb active ion pump on Henle 's loop reduces the concentration inside the tubule and increases the interstitial concentration. Step 3: Due to osmosis of water out of the descending limb, the tubular fluid in the lower limb and the interstitial fluid rapidly achieve osmotic equilibrium.
Step 4: Additional fluid flow from the proximal tubule into Henle 's loop, which allows the hyperosmotic fluid produced previously in the descending limb to flow into the ascending limb. Step 6: Again, the fluid in the descending limb comes into equilibrium with the hyperosmotic interstitial medullary fluid, and as the hyperosmotic tubular fluid from the descending limb flows into the ascending limb, the more solute is continually drained out of the tubules and deposited in the medullary interstitium.
The countercurrent multiplier, or counter-current mechanism, is used by the nephrons of the human excretory system to concentrate urine in the kidneys. The nephrons involved in concentrated urine formation stretch all the way from the kidney cortex to the medulla and are followed by vasa recta. The movement of filtrate is in opposite directions in the two limbs of the Henle 's circle, and so is the movement of blood cells in vasa recta.
In short, by this point, the cyclicality of this process becomes apparent to most people. In spite of that, usually tube diagrams of the countercurrent mechanism continue for another cycle, as if expecting that those who have not yet grasped the concept will surely grasp it if only somebody were to patiently repeat it to them again without adding any new explanatory material.
Without insulting the reader with any further diagrams, the gist of this is that a small difference in osmotic pressure generated by a single effect the effect of ion pumps in the thick ascending limb ends up being multiplied by the countercurrent flow which brings fluid of increasingly higher and higher osmolality to the aforementioned pumps, allowing their One Weird Trick to produce increasingly higher and higher interstitial osmolalities.
Moreover, even as the osmolality climbs higher and higher, the gradient between the tubular fluid and the intersititum remains relatively stable, which means the ion pumps never have to pump against a very high gradient, making this whole thing a lot more efficient.
On the basis of these italicised underlined elements, this process is generally referred to as the countercurrent multiplier effect. How much does this multiplier mechanism multiply the medullary interstitial solute concentration? What are the values in the tubules of the living human kidney? One might be tempted to retort tartly that surely this must depend on the individual kidney, and in any case the understanding of the mechanism is more important than memorising numbers.
Unfortunately, this is both true, and a terrible attitude to adopt for the CICM First Part Exam, which is built on the foundation of memorising pointless values.
What's a reputable resource for these sort of data? The college's need for quotable numbers does not diminish the fact that most of the values are measured in experimental animals, and not even from whole animals but often from tortured chunks of kidney.
Moreover, they all give different values, and have different starting conditions. To make matters worse, the osmolality of the renal medulla varies widely in the course of normal renal function.
As an example, in some hamster experiments by Schmidt-Nielsen et al , inner medulla osmolality was measured in states of minimal diuresis, maximal diuresis, and everything in between. In short, the deeper you go in search of the One True Osmolality, the closer you approach the point of no return, beyond which you go insane. One should really just pick a source and stick with it; ideally a resource which represents some sort of mean values with which people are unlikely to disagree.
One such resource is Kurbel et al , a review article which describes regional differences in medullary osmolality as "horizons". Apart from this poetic advantage, the authors list three textbooks as their references, suggesting that this diagram was compiled from reputable sources. The terms "countercurrent multiplication" and "countercurrent exchange" are not interchangeable. Countercurrent multiplication is something the tubule does to create the high interstitial osmolality, and a large osmolality gradient between the renal medulla and the renal cortex.
The countercurrent exchange mechanism is something the vasa recta do to maintain this gradient. In the fewest words possible, this exchange mechanism represents the endless recirculation of solutes in and out of vasa recta vessels. The microcirculation of the medulla is a system designed to trap salt and urea in the innermost renal medulla, and to carry away only the reabsorbed water. It achieves this goal by having relatively permeable walls.
In this fashion, blood which flows into the medulla ends up becoming highly concentrated because medullary interstitial salt and urea diffuse into it, and blood coming back out of the medulla does not carry any of this salt and urea away because they diffuse back out of the blood just as easily.
To borrow words from Wirz ,. In between it may adapt itself to the osmotic pressure of the surroundings by a passive uptake on its way down and release on its way up of osmotically active solutes. That's the solutes. Also one needs to remember that water is deposited in the medulla by diffusion out of the descending tubule.
There's no other way for it to leave there are no lymphatics down there , so the ascending vasa recta must be carrying it away. This is indeed what is observed experimentally. When micropuncture experiments Zimmerhackl et al, measured the protein content of blood in the descending and ascending vasa recta, they confirmed that descending blood became more concentrated lost water and gained solute , and ascending blood became more dilute.
Specifically, blood leaving the medulla was more dilute than blood entering the medulla, confirming that a net removal of water was taking place. It surrounds the opening of the bladder to the urethra and relaxes to allow urine to pass. The external sphincter is voluntary. It surrounds the urethra outside the bladder and must be relaxed for urination to occur.
The counter current mechanism takes place in Juxtamedullary nephron. The function of the countercurrent multiplier is to produce the hyperosmotic Medullary Interstitium.
The ADH promotes water reabsorption through the walls of the distal convoluted tubule and collecting duct. The structure of the loop of Henle and associated peritubular capillary create a countercurrent multiplier system Figure The countercurrent term comes from the fact that the descending and ascending loops are next to each other and their fluid flows in opposite directions countercurrent.
Many animals including humans have another way to conserve heat. Such a mechanism is called a countercurrent heat exchanger. When heat loss is no problem, most of the venous blood from the extremities returns through veins located near the surface. Not only do the vasa recta bring nutrients and oxygen to the medullary nephron segments but, more importantly, they also remove the water and solute that is continuously added to the medullary interstitium by these nephron segments.
Rather than using lungs, gaseous exchange takes place across the surface of highly vascularized gills. Gills use a countercurrent flow system that increases the efficiency of oxygen-uptake and waste gas loss. When oxygen-depleted afferent blood arrives at the membrane, it meets substantially deoxygenated medium. As blood and medium flow along the exchange surface in opposite directions, blood encounters higher and higher oxygen partial pressure in the medium.
Basically, what occurs in the countercurrent multiplier process? A higher sodium concentration is produced in the kidney medulla tissue that osmotically draws out water, reducing it within the tubules and the urine. The filtrate is produced within the proximal convoluted tubule. Unlike the other countercurrent systems, a countercurrent multiplier system expends energy in active transport. Before leaving your body, urine travels through the urinary tract.
The urinary tract is a pathway that includes the: kidneys: two bean-shaped organs that filter waste from the blood and produce urine. What is the correct order of urine flow from its source? Urine is formed in the kidneys through a filtration of blood. The urine is then passed through the ureters to the bladder, where it is stored.
During urination, the urine is passed from the bladder through the urethra to the outside of the body.
0コメント