Tubular reabsorption a. of glucose and many other substances is a Tₘ -limited active transport process, b. of chloride is always linked to the passive transport of Na⁺ , c. is the movement of substances from the blood into the nephron, d. of sodium occurs only in the proximal tubule.

Verified step by step guidance

1. Step 1: Understand the concept of tubular reabsorption, which is the process by which the nephron removes water and solutes from the tubular fluid (pre-urine) and returns them to the circulating blood.
2. Step 2: Analyze option (a): Tubular reabsorption of glucose and many other substances is a Tₘ-limited active transport process. Tₘ refers to the transport maximum, which is the maximum rate at which a substance can be reabsorbed.
3. Step 3: Evaluate option (b): Tubular reabsorption of chloride is always linked to the passive transport of Na⁺. This involves the electrochemical gradient created by sodium reabsorption, which facilitates chloride reabsorption.
4. Step 4: Consider option (c): Tubular reabsorption is the movement of substances from the nephron back into the blood, not from the blood into the nephron. This option describes secretion, not reabsorption.
5. Step 5: Review option (d): Tubular reabsorption of sodium occurs primarily in the proximal tubule, but it also occurs in other parts of the nephron, such as the loop of Henle, distal tubule, and collecting duct.

Key Concepts

Tubular Reabsorption

Tubular reabsorption is the process by which substances are reabsorbed from the renal tubules back into the bloodstream. This process is crucial for maintaining homeostasis, as it allows the body to reclaim essential nutrients, electrolytes, and water that would otherwise be lost in urine. It occurs primarily in the proximal convoluted tubule, but also in other parts of the nephron.

Active Transport and Tₘ

Active transport is a mechanism that moves substances against their concentration gradient, requiring energy, typically in the form of ATP. The term Tₘ (transport maximum) refers to the maximum rate at which a substance can be reabsorbed, which is particularly relevant for glucose and other solutes. When the concentration of a substance exceeds Tₘ, it will not be fully reabsorbed, leading to its excretion in urine.

Link between Sodium and Chloride Transport

The reabsorption of chloride ions (Cl⁻) in the nephron is often coupled with the passive transport of sodium ions (Na⁺). This process is driven by the electrochemical gradient created by sodium reabsorption, which facilitates the movement of chloride ions through various transport mechanisms. This coupling is essential for maintaining electrolyte balance and osmotic pressure in the body.