Question

Select the incorrect statement from the following: (a) The DCTs of many nephrons opens into a straight tube called collecting duct. (b) In cortical nephrons (majority), the loop of Henle is too short and extended only very little in medulla. (c) In juxta medullary nephrons (minority), the loop of Henle is very long and runs deeply into medulla. (d) Vasa recta is not a part of peritubular network.

Short answer

The incorrect statement is (d): 'Vasa recta is not a part of peritubular network'. The Vasa Recta is indeed part of the peritubular capillary network and it plays a crucial role in the functioning of the nephron

Step-by-step solution

Understanding the Terms

A nephron is the basic structural and functional unit of the kidney. Each kidney contains millions of nephrons, and each nephron consists of distinct parts such as the Distal Convoluted Tubule (DCT), the Loop of Henle, and the Collecting Duct. Cortical nephrons and juxta medullary nephrons are two types of nephrons characterized by the length of their Loop of Henle and their position in the kidney. The Vasa Recta, a network of blood vessels, runs parallel to the Loop of Henle and plays a role in the concentration of urine.

Analyzing Statement (a)

Statement (a) says that 'The DCTs of many nephrons opens into a straight tube called collecting duct' which is a correct statement. After filtrate has passed through the DCT, it enters the collecting duct system. This system is responsible for the final modification of the filtrate (which becomes urine).

Analyzing Statement (b)

Statement (b) says that 'In cortical nephrons (majority), the loop of Henle is too short and extended only very little in medulla'. This is also correct as cortical nephrons are largely in the cortex of the kidney, as their name suggests, and they possess a relatively short loop of Henle.

Analyzing Statement (c)

Statement (c) states 'In juxtamedullary nephrons (minority), the loop of Henle is very long and runs deeply into medulla'. This is also a correct statement because juxtamedullary nephrons have a long loop of Henle that extends deep into the medulla, allowing for the production of highly concentrated urine.

Analyzing Statement (d)

Statement (d) claims that 'Vasa recta is not a part of peritubular network'. This is incorrect as the vasa recta is actually part of the peritubular capillary network. It surrounds the Loop of Henle and is essential in maintaining the osmotic gradient in the medulla of the kidney. Therefore, the statement is false.

Key concepts

Cortical nephrons

Cortical nephrons are one of the two main types of nephrons found in the kidneys. They make up about 85% of the nephron population, which highlights their prevalence. These nephrons are primarily located in the renal cortex, which is the outer portion of the kidney, close to its surface.

The distinguishing feature of cortical nephrons is their relatively short Loop of Henle. This loop extends only a modest distance into the medulla, in contrast to juxta medullary nephrons. Since the loop is short, these nephrons are not significantly involved in the concentration of urine. Instead, they mainly serve the function of filtering blood and reabsorbing nutrients.

Cortical nephrons are characterized by the following points:

• Short Loop of Henle
• Primarily located in the renal cortex
• Involved in blood filtration and nutrient reabsorption

Juxta medullary nephrons

Juxta medullary nephrons, though fewer in number compared to cortical nephrons, play a vital role in the kidney's ability to produce highly concentrated urine. These specialized nephrons constitute about 15% of the total nephron count and are located close to the boundary between the renal cortex and the medulla.

They possess a long Loop of Henle that penetrates deeply into the medulla. The length of the loop is crucial because it enhances the kidney's capability to conserve water by producing more concentrated urine. This feature is particularly important for maintaining the body's fluid and electrolyte balance, especially in conditions where water conservation becomes necessary.

The main features of juxta medullary nephrons include:

• Long Loop of Henle
• Critical for concentrating urine
• Found at the border closer to the medulla

Loop of Henle

The Loop of Henle is a critical component of the nephron that plays a central role in the kidney’s ability to concentrate urine. It acts as a countercurrent multiplier system that establishes a concentration gradient in the medulla.

Water and salt reabsorption occurs during the passage of filtrate through the loop. As the filtrate moves down the descending limb of the loop, it becomes more concentrated due to water being reabsorbed into the surrounding tissue. Conversely, in the ascending limb, sodium and chloride ions are pumped out, making the filtrate more dilute.

Features of the Loop of Henle include:

• Maintains osmotic gradient important for water reabsorption
• Comprises descending and ascending limbs
• Works synergistically with the Vasa Recta for urine concentration

Vasa Recta

The Vasa Recta is a series of straight, capillary-like blood vessels that run parallel to the Loop of Henle in the medulla. These vascular structures are essential for the kidney's function, as they play a key role in conserving the medullary osmotic gradient crucial for water reabsorption.

The Vasa Recta operate as part of the peritubular capillary network. They maintain an equilibrium between the fluid in the Loop of Henle and the surrounding interstitium by allowing for the exchange of water and solutes. This action helps prevent the dissipation of the gradient while providing oxygen and nutrients to the renal medulla.

Key points about the Vasa Recta are:

• Part of the peritubular network
• Helps maintain osmotic gradients
• Facilitates nutrient supply to the medulla