The are an important part of the kidney's urine-concentrating mechanism found surrounding the nephron loops (loops of henle) of juxtamedullary nephrons.

Vasa recta

Explanation:

Concentration of urine occurs by counter current mechanism. It is a mechanism to retain water in the body and it occurs by vasa recta and loop of Henle. Vasa rectae are the peritubular capillaries found near the loop of Henle (LOH). The blood flow in opposite directions in the two limbs of vasa rectae and also in the two limbs of LOH. The flow of fluid in the descending limb of LOH is in opposite direction to the flow of blood in ascending limb of vasa retae and vice versa. These counter current systems significantly contribute to the concentration of urine in the kidneys.

It is the cyclic movement of Na+, Cl- from the ascending limb of loop of Henle to the descending limb of vasa rectae via the medullary interstitial fluid. This is responsible for 5 % absorption of water in the descending limb of LOH, making the filtrate hypertonic. Due to this the concentration of Na+ and Cl- is more in the renal medulla. The osmolarity increases from 300 to 1200 mOsml/l from cortex to inner medulla, concentrating the urine.

yay can i have brainliest

cells use diffusion to get substances in and out of themselves. that diffusion will occur across the cell membrane or the outer covering of the cell. because we are talking about the surface of the cell, surface area and volume are  important factors here. as a cell increases in size, its surface area and volume increase as well.  we call that the surface area to volume ratio (sa: vol).  but the catch is that  volume increases at a greater rate than surface  area. in other words, as a cell gets bigger, the sa: vol gets smaller. so a really small cell like bacteria is mostly cell membrane (surface) with very little contents (volume). a really big cell like an egg, is mostly insides with a super thin membrane. so what ends up happening is that the cell cannot efficiently diffuse all of the stuff it needs in/out to survive. therefore cell size is limited to about 100mm. so how do we make organisms bigger than 100mm? cells divide! by dividing and becoming multicellular, organisms are able to grow!   check out the diagrams i attached to see the effect of sa: vol. i hope this ! good luck!