Which of the following represents the proper sequence of flow through the nephron?
a) Renal corpuscle, proximal convoluted tubule, loop of Henle, distal convoluted tubule, collecting duct
b) Proximal convoluted tubule, loop of Henle, renal corpuscle, distal convoluted tubule, collecting duct
c) Renal corpuscle, loop of Henle, proximal convoluted tubule, distal convoluted tubule, collecting duct
d) Proximal convoluted tubule, renal corpuscle, loop of Henle, distal convoluted tubule, collecting duct
The Correct Answer and Explanation is:
The correct answer is: a) Renal corpuscle, proximal convoluted tubule, loop of Henle, distal convoluted tubule, collecting duct.
Explanation:
The nephron is the functional unit of the kidney, responsible for filtering blood, removing waste, and balancing bodily fluids and electrolytes. The flow of filtrate through the nephron follows a specific sequence:
- Renal Corpuscle:
- The renal corpuscle consists of two parts: the glomerulus, a network of capillaries, and the Bowman’s capsule, which surrounds the glomerulus. This is where filtration begins. Blood enters the glomerulus under pressure, and water, salts, glucose, and small molecules are filtered into Bowman’s capsule, forming glomerular filtrate.
- Proximal Convoluted Tubule (PCT):
- The filtrate from the renal corpuscle enters the proximal convoluted tubule. The PCT is lined with microvilli that increase surface area for reabsorption. Here, about 65-70% of the filtered sodium, water, glucose, amino acids, and bicarbonate ions are reabsorbed into the bloodstream.
- Loop of Henle:
- The filtrate then passes into the loop of Henle, a U-shaped portion that consists of a descending and ascending limb. The descending limb is permeable to water, allowing water to be reabsorbed as the filtrate moves deeper into the medulla. The ascending limb is impermeable to water but actively transports sodium, chloride, and potassium out of the filtrate, contributing to the creation of an osmotic gradient that aids in water reabsorption.
- Distal Convoluted Tubule (DCT):
- The filtrate then moves into the distal convoluted tubule, where further regulation of sodium, potassium, and calcium occurs under the influence of hormones like aldosterone and parathyroid hormone. Some additional reabsorption of sodium and chloride takes place here, and hydrogen and potassium ions are secreted into the filtrate.
- Collecting Duct:
- Finally, the filtrate flows into the collecting duct. Here, water reabsorption is further regulated by the antidiuretic hormone (ADH), which makes the duct permeable to water. This is where urine is concentrated and sent toward the renal pelvis for excretion.
Thus, the correct sequence is: renal corpuscle → proximal convoluted tubule → loop of Henle → distal convoluted tubule → collecting duct.