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The loop of Henle is always a U-shaped tubule, with a descending limb and an ascending limb, however its length varies among different vertebrates. This is associated with the fact that it has two functions; whilst the first is to clean wastes, the second is to maintain a balance between ions and H 2 O.
The thick descending limb is less important than the thin descending limb, so often the terms "descending limb" and "thin descending limb" are used interchangeably. Some sources simply refer to a "thin limb". In this context, the thin ascending limb of loop of Henle would be included.
AQP-1 is a widely expressed water channel, whose physiological function has been most thoroughly characterized in the kidney. It is found in the basolateral and apical plasma membranes of the proximal tubules, the descending limb of the loop of Henle, and in the descending portion of the vasa recta.
The descending limb of the loop of Henle is permeable to water but impermeable to solutes, due to the presence of aquaporin 1 in its tubular wall. Thus, water moves across the tubular wall into the medullary space, making the filtrate hypertonic (with a lower water potential). This is the filtrate that continues to the ascending limb. [2]
This stops the loop of Henle from concentrating urine, which usually uses the high osmotic and solute gradient to transport solutes and water. These agents can also act at other parts of the body. For example, they can be used to reduce intracranial [4] and intra-ocular pressure. Osmotic diuretics increase plasma volume, but because they do not ...
In the kidney, the macula densa is an area of closely packed specialized cells lining the wall of the distal tubule where it touches the glomerulus.Specifically, the macula densa is found in the terminal portion of the distal straight tubule (thick ascending limb of the loop of Henle), after which the distal convoluted tubule begins.
Both limbs of the loop of Henle are lined with the simple squamous epithelium. [2] Their main function is to regulate the levels of water and solutes in the primary urine . The basement membrane of the thin limb in humans has very uniform nodular thickenings that form a network that surrounds the tubule and acts as a support structure that is ...
Descending limb of loop of Henle: one segment of equal thickness; Ascending limb of loop of Henle: two segments of differing thickness (proximal portion lined by simple squamous epithelium is called the thin ascending limb of loop of Henle, distal portion lined by simple cuboidal epithelium is called the thick ascending limb of loop of Henle).