Loop of Henle is a long U-shaped part of the tubule that leads urine in each nephron of the kidney of reptiles, mammals and also in birds. The main role of the loop of Henle in nephron is to collect sodium chloride and water from urine. This allows the urine production that is more concentrated than blood by reducing the amount of water which is necessary for living. Those species that are present in arid environments such as deserts have very effective Henle curls.
Anatomically, the loop of Henle can be divided into three main segments:
- the descending thin member,
- the ascending thin member,
- the thick ascending member (sometimes also referred to as the dilution segment).
Each nephron in the kidney contains blood vessels and a special tubule. As the filtrate flows through the tubule of the nephron, it becomes more and more concentrated in the urine. The wastes are transferred from the blood into the filtrate while the nutrients from the filtrate are absorbed into the blood.
The fluid entering the loop of Henle is the solution of salt, urea and other substances transmitted by the proximal convoluted tubule , from which most of the dissolved components needed by the body – especially glucose, amino acids, and sodium bicarbonate – have been reabsorbed into the blood. The first segment of the loop, the thin descending limb, is permeable to water, and the fluid reaching the elbow of the loop is much richer in salt and urea than blood plasma.
As the fluid returns through the thin ascending loop of henle, sodium chloride diffuses out of the proximal convoluted tubule into the surrounding tissue, where its concentration is less. In the third segment of the loop, the thick ascending member, the tubular wall can, if necessary, perform additional salt removal, even against the concentration gradient, in an active transport process requiring the expenditure of energy.
In a healthy person, reabsorption of salt from urine exactly maintains the body’s needs: during periods of low salt intake, hardly any are allowed to escape in the urine, but during periods of high salt intake, excess is excreted.