B. Loop of Henle - Descending limb is a monolayer of squamous cells that descends and then ascends. The length of the loop varies with the location of the nephrons in the kidney. In many animals loops that are connected to glomeruli in the outer portions of the cortex have shorter loops than juxtamedullary glomeruli. The thin segment of the Loop of Henle connects to the thick ascending Loop of Henle. These cells are renin secreting and form the macula densa.
Some fluid reabsorption occurs in the ascending limb.
Urine concentration is established by bringing tubular fluid down though the increasing osmotic gradient established by the Loop of Henle. ADH controls water permeability of the tubule. The blood supply to the nephron. Blood flow through the kidney is not homogeneously distributed. The composition of the glomerular fluid vs. plasma.