The vasa recta is a specialized capillary that branches from the efferent arteriole; The blood flow in the vasa recta runs parallel, but in the opposite direction to the flow of tubular filtrate within the nephron loop
The vasa recta capillaries are long, hairpin-shaped blood vessels that run parallel to the loops of Henle
The hairpin turns slow the rate of blood flow, which helps maintain the osmotic gradient required for water reabsorption
Absorbed water is returned to the circulatory system via the vasa recta, which surrounds the tips of the loops of Henle
Because the blood flow through these capillaries is very slow, any solutes that are reabsorbed into the bloodstream have time to diffuse back into the interstitial fluid, which maintains the solute concentration gradient in the medulla; this passive process is known as counter-current exchange
