Problem 90 - Objective Biology for NEET

Question

Which of these will be completely reabsorbed from glomerular filtrate under normal conditions in the nephrons? (a) Urea (b) Salts (c) Uric acid (d) Glucose

Step-by-Step Solution

Answer

Under normal conditions in the nephrons, glucose is the substance that will be completely reabsorbed from the glomerular filtrate.

Step 1: Understanding Kidney Function

Nephrons are the microscopic functional units of the kidney, responsible for filtering blood, removing wastes, and reabsorbing necessary substances. The glomerulus, part of the nephron, filters blood creating a filtrate of waste and other substances.

Step 2: Identifying Substance Reabsorption

During the process of reabsorption, the useful substances are reabsorbed from the glomerular filtrate back into the bloodstream. These can include salts, glucose, amino acids and water.

Step 3: Determining Complete Reabsorption

Among the options, glucose is a crucial source of energy, and under normal circumstances, it is completely reabsorbed from the glomerular filtrate so as not to be lost in urine.

Key Concepts

Glomerular Filtration

The journey of waste removal in the kidneys begins with glomerular filtration. This process takes place in the nephrons, the basic structural and functional units of the kidneys.
In each nephron, there is a small network of capillaries known as the glomerulus. Blood flows into the glomerulus under pressure, and filtration occurs, causing a separation of substances in the blood.
Substances like water, salts, small molecules, and waste products pass through the glomerular filter to form the glomerular filtrate. Not everything gets filtered; larger molecules, like proteins, and blood cells typically remain in the blood.

• This process is vital because it helps to remove toxins and waste products from the bloodstream.
• It ensures that the blood remains free from harmful substances.
• It also allows for further processing and reabsorption of valuable substances later on.

This initial filtration is the first step in the kidney's complex waste management system, setting the stage for further refining and reabsorption.

Substance Reabsorption

After the glomerular filtrate is created, not all substances are destined for excretion. Many essential components need to be reabsorbed back into the bloodstream.
This is where substance reabsorption comes into play, occurring mainly in the proximal tubule of the nephron.
As the filtrate passes through the nephron, cells lining the nephron walls will selectively reabsorb substances, such as glucose, salts, and amino acids. This happens through various mechanisms, including active transport, which requires energy, and passive transport, which does not.

• Glucose is typically 100% reabsorbed because it's critical for providing energy to the body.
• Salts are reabsorbed to help maintain the body's electrolyte balance.
• Other important molecules, such as amino acids, are also mostly reabsorbed for reuse.

Reabsorption helps the body conserve needed nutrients and maintain homeostasis while allowing waste products to be passed out of the body.

Kidney Function

The kidney is a remarkable organ with multiple critical functions necessary for maintaining the body's overall health.
Primarily, kidneys filter blood, removing waste products and excess substances, which is primarily done through the nephrons.
The kidneys maintain the body's internal environment through several processes:

• They regulate fluid balance by adjusting the volume of urine excreted.
• Help regulate blood pressure by balancing the concentration of ions like sodium and potassium.
• Maintain acid-base balance by reabsorbing bicarbonate and secreting hydrogen ions.
• Produce important hormones, like erythropoietin, which stimulates red blood cell production.

In essence, the kidneys act as the body's natural filtration and regulation system, helping ensure the body can function optimally under various conditions. Without them, maintaining the delicate balance needed for health would be virtually impossible.