Problem 5 - Biology of Humans: Concepts, Applications, and Issues

Question

Microvilli dramatically increase surface area for reabsorption. In the nephron, microvilli characterize the a. proximal convoluted tubule. b. collecting duct. c. distal convoluted tubule. d. glomerulus.

Step-by-Step Solution

Answer

a. proximal convoluted tubule.

Step 1: Understand Microvilli Function

Microvilli are small projections that increase the surface area of cells and are often involved in absorption or secretion functions.

Step 2: Identify Nephron Components

The nephron consists of various parts: the glomerulus, proximal convoluted tubule, distal convoluted tubule, and collecting duct.

Step 3: Match Microvilli with Nephron Part

Microvilli are most commonly associated with the parts of the nephron where reabsorption is critical. The proximal convoluted tubule is the primary site for reabsorption in the nephron.

Step 4: Analyze Options

a. Proximal convoluted tubule (high reabsorption activity and presence of microvilli)b. Collecting duct (not primarily involved in reabsorption)c. Distal convoluted tubule (some reabsorption but fewer microvilli)d. Glomerulus (functions mainly in filtration, not reabsorption)

Step 5: Conclusion

Based on the functions and structure of the nephron components, the proximal convoluted tubule is the part characterized by microvilli for increased reabsorption.

Key Concepts

microvilli function

Microvilli are tiny, finger-like projections on the surface of certain cells. These structures dramatically increase the surface area available for absorption and secretion. This is especially important in environments where a lot of material needs to be moved across cell membranes quickly.

By increasing surface area, microvilli help cells to absorb more nutrients and substances efficiently. For example, in the intestines, microvilli help to absorb nutrients from digested food. Similarly, in the nephron of the kidney, microvivi play a crucial role in reabsorbing essential substances back into the blood.

It's important to highlight that the presence of microvilli is often a marker of cells with high absorptive or secretory functions. This makes them crucial in organs and tissues where rapid and efficient transport is needed.

proximal convoluted tubule

The proximal convoluted tubule (PCT) is a vital part of the nephron in the kidney. It is located immediately after the glomerulus, the structure that initially filters the blood.

The PCT is lined with epithelial cells that have a high concentration of microvilli on their surface. These microvilli form what is known as the

reabsorption in nephron

Reabsorption in the nephron is a critical process that ensures essential substances are not lost from the body. This process occurs predominantly in the proximal convoluted tubule (PCT).

In the PCT, approximately 70% of the filtered water and a large percentage of filtered ions, glucose, and amino acids are reabsorbed. Microvilli increase the surface area of the PCT cells, allowing for more efficient reabsorption.

Reabsorption involves both passive and active transport mechanisms. For instance:

• Water reabsorption is primarily a passive process driven by osmotic gradients.
• Ions like sodium (Na+) are actively transported back into the bloodstream, which helps in water reabsorption.
• Glucose and amino acids are reabsorbed through co-transport mechanisms linked to sodium ions.

Without effective reabsorption, many crucial substances would be lost in the urine, leading to severe consequences for body function and homeostasis.