Cortical nephrons are the nephron which lies on the cortex region or most of the parts lies in the cortical region. Therefore, in cortical nephrons, vasa recta is absent or reduced in medulla part.

Vasa Recta in Cortical Nephrons

The vasa recta is a specialized network of blood vessels that plays a crucial role in the functioning of the kidney. It is responsible for maintaining the concentration gradient in the medulla, which is essential for the production of concentrated urine. The vasa recta follows a hairpin loop pattern and runs parallel to the loop of Henle in the juxtamedullary nephrons.

Presence of Vasa Recta

In cortical nephrons, the vasa recta is either absent or reduced. Cortical nephrons are located in the outer region of the kidney cortex and constitute the majority of nephrons in the kidney. They have a shorter loop of Henle which does not extend deep into the medulla. Consequently, the vasa recta in cortical nephrons is not as elaborate as in juxtamedullary nephrons.

Functions of Vasa Recta

The vasa recta serves several important functions in the kidney, including:

1. Maintaining the concentration gradient: The vasa recta helps to maintain the concentration gradient in the medulla by preventing the rapid washout of solutes. As blood flows through the vasa recta, it exchanges solutes with the surrounding interstitial fluid, helping to maintain the high osmolarity of the medulla.

2. Reabsorption of water and solutes: The vasa recta allows for the reabsorption of water and solutes from the medullary interstitial fluid. This helps to conserve water and maintain the osmolarity of the medulla.

3. Removal of waste products: The vasa recta helps to remove waste products, such as urea, from the medulla and transport them to the renal vein for excretion.

Importance of Vasa Recta

The presence of a well-developed vasa recta in juxtamedullary nephrons allows for the establishment and maintenance of a strong concentration gradient in the medulla. This gradient is essential for the kidney's ability to produce concentrated urine and regulate water balance in the body.

In contrast, the absence or reduction of the vasa recta in cortical nephrons limits their ability to establish and maintain a strong concentration gradient in the medulla. As a result, cortical nephrons are less efficient in producing concentrated urine compared to juxtamedullary nephrons.

Therefore, the correct answer to the question is option 'C' - Cortical nephrons.