Which of the following is the salt level-monitoring part of the nephron?

• A. Proximal convoluted tubule
• B. Macula densa
• C. Loop of Henle
• D. Bowman's capsule

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the role of the nephron in the kidney. The nephron is the functional unit of the kidney responsible for filtering blood, reabsorbing essential substances, and excreting waste products. Different parts of the nephron have specialized functions.
2. Step 2: Review the function of the macula densa. The macula densa is a group of specialized cells located in the distal convoluted tubule near the glomerulus. These cells monitor the concentration of sodium chloride (NaCl) in the filtrate and play a role in regulating blood pressure and filtration rate.
3. Step 3: Compare the macula densa to other parts of the nephron. The proximal convoluted tubule is primarily involved in reabsorbing nutrients, water, and ions. The Loop of Henle concentrates urine by reabsorbing water and salts. Bowman's capsule is the site of filtration where blood plasma enters the nephron.
4. Step 4: Identify the part of the nephron specifically responsible for salt level monitoring. Based on the specialized function of the macula densa in detecting NaCl concentration, it is the correct answer.
5. Step 5: Conclude that the macula densa is the salt level-monitoring part of the nephron, as it directly senses changes in sodium chloride concentration and signals adjustments to maintain homeostasis.