Which of the following structures is NOT a portion of a nephron?
a. vasa recta
b. nephron loop (loop of Henle)
c. distal convoluted tubule
d. proximal convoluted tubule
The correct answer and explanation is:
The correct answer is a. vasa recta.
The nephron is the functional unit of the kidney responsible for filtering blood and forming urine. It consists of several key structures: the proximal convoluted tubule (PCT), the nephron loop (loop of Henle), and the distal convoluted tubule (DCT). These parts play a direct role in the filtration and reabsorption processes essential for maintaining the body’s fluid and electrolyte balance.
- Proximal Convoluted Tubule (PCT): The PCT is the first segment of the nephron after the glomerulus. It is responsible for the reabsorption of nutrients, ions, and water from the filtrate into the blood. About 65% of the filtrate’s water and sodium are reabsorbed here.
- Nephron Loop (Loop of Henle): The loop of Henle is a U-shaped structure that extends from the proximal convoluted tubule into the medulla of the kidney. It has two limbs: the descending limb, which is permeable to water but not salts, and the ascending limb, which is impermeable to water but actively transports sodium, chloride, and potassium ions out into the surrounding interstitial fluid.
- Distal Convoluted Tubule (DCT): The DCT is the segment that follows the nephron loop and is involved in further reabsorption of sodium and calcium ions, as well as secretion of potassium and hydrogen ions into the filtrate. It plays a role in regulating blood pressure by responding to hormones like aldosterone and antidiuretic hormone (ADH).
- Vasa Recta: The vasa recta, though closely associated with the nephron, is NOT a part of the nephron itself. It is a network of capillaries that surrounds the loop of Henle and helps maintain the concentration gradient in the renal medulla, which is essential for the kidney’s ability to concentrate urine. While the vasa recta is critical for the kidney’s function, it is not technically a part of the nephron structure.
In summary, the vasa recta is essential for kidney function but is not a component of the nephron. The nephron consists only of the PCT, nephron loop, and DCT.