Counter current pattern of blood flow is not observed in vasa recta.

The vasa recta, U-shaped blood vessels in the kidney, exhibit a counter-current pattern of flow. Running parallel to the loop of Henle, this arrangement allows for efficient exchange of ions and solutes between the blood and filtrate. The counter-current exchange in the vasa recta is crucial for maintaining the concentration gradient in the renal medulla, aiding in the kidney's ability to concentrate urine and regulate water and electrolyte balance.