Question

Which is true about the difference between cortical and juxtamedullary nephrons?
a) Majority of nephrons are juxtamedullary
b) Glomeruli and loops of Henle and cortical nephrons lie completely in the cortex
c) The afferent arterioles of the juxtamedullary nephrons give rise to most of vasa recta
d) Cortical nephrons lack vasa recta

Answer 1

Hint:-Kidneys are organs of excretion in vertebrates. Kidneys have a cortex on the outside and a medulla inside. Nephrons are the structural and functional units of the kidneys. They are composed of glomerulus and tubules. Based on the location of the glomerulus and the Loop of Henle (a part of tubules), nephrons can be cortical or juxtamedullary.

Complete Answer:-
Nephrons are defined as the functional and structural unit of the kidneys. The microanatomy of the nephrons is described below:
Nephrons receive blood through afferent arterioles. The blood from afferent arterioles enter a bed of capillaries called the Glomerulus. The glomerulus is surrounded by the Bowman’s Capsule which is connected to the Proximal Convoluted Tubule or PCT. The PCT remains connected to the Loop of Henle which in turns connects to the Distal Convoluted Tubule or DCT. The DCT is connected to the collecting tubule which is common to all nephrons of a kidney.
The glomerulus of each nephron is located in the cortex of the kidney. The nephrons whose Loop of Henle does not extend far beyond the cortex is known as Cortical nephrons. On the other hand, nephrons whose Loop of Henle extend into the medulla of the kidneys are termed Juxtamedullary nephrons.
Option (a) is incorrect. Majority of the nephrons are cortical, while few are juxtamedullary.
Option (b) is incorrect. Glomeruli of the cortical and juxtamedullary nephron lie exclusively in the kidney cortex. However, the loop of Henle of cortical nephrons extend to the outer portion of the kidney medulla while that of the juxtamedullary nephrons extend deep into the medullary region.
Option (c) is incorrect. The vasa recta are a network of blood vessels that are the extensions of the efferent arterioles. They are present exclusively in the kidney medulla and run parallel to the Loop of Henle of juxtamedullary nephrons. The vasa recta helps to reabsorb water and solutes from the Loop of Henle.
Option (d) is correct. The cortical nephrons lack vasa recta. Vasa recta is a network of blood vessels that surround the Loop of Henle in the medulla of the kidney. They are present in the juxtamedullary nephrons only. The function of vasa recta is to maintain the osmotic gradient in the Loop of Henle for efficient reabsorption of water.
Thus, the right option is D.

Note:- Kidneys function as the organ of excretion in vertebrates. There are two kidneys in the body. Each is composed of units called nephrons. The nephrons filter blood and form urine. It is through the formation of urine that these structures excrete substances that are toxic to the body. Nephrons can be cortical or juxtamedullary.