Problem 151 - Objective Biology for NEET

Question

Assertion: Filteration is a selective process performed by the glomerulus using the glomerular capillary blood pressure. Reason: Blood is filtered through fine pores present in PCT.

Step-by-Step Solution

Answer

The function of glomerulus mentioned in the assertion is correct, but the function of PCT in the reason is incorrect. Thus, the reason does not justify the assertion.

Step 1: Analyze Assertion

In the glomerulus, blood is indeed filtered through a process called 'glomerular filtration.' It is a selective process regulated by the blood pressure in glomerular capillaries, which allows water and solutes smaller than proteins to pass through while preventing larger molecules or cells from passing through.

Step 2: Analyze Reason

The PCT or Proximal Convoluted Tubule indeed contains fine pores, but here, reabsorption happens. Most of the solutes that got filtered in glomerulus like glucose, amino acids, and ions are reabsorbed back into the blood stream from the filtrate through the PCT. Hence, the function of PCT is not filtration but reabsorption.

Step 3: Conclusion

From step 1 and 2, it can be seen that, while the function of the glomerulus explained in the assertion is correct, the function of the PCT in the reason is incorrect. Thus, in this context, the reason does not correctly justify the assertion.

Key Concepts

Glomerulus

The glomerulus is a tiny network of capillaries located in the kidney, playing a critical role in the process of filtering blood. It's part of a larger structure known as the nephron, which is the basic unit of the kidney responsible for filtering out waste and maintaining fluid balance in the body.
The process the glomerulus is involved in is known as glomerular filtration. During this process, blood pressure forces water and small solutes out of the blood through the walls of the glomerular capillaries into the Bowman's capsule. This initial stage of urine formation is crucial because it helps to eliminate waste products and excess substances while retaining larger molecules and blood cells within the bloodstream.
One of the key aspects of the glomerular filtration is its selectivity. The fine meshwork formed by the glomerular capillary wall prevents large molecules like proteins and blood cells from passing, while allowing smaller molecules like water, glucose, and ions to pass through. This ensures that only excess or waste substances are removed from the blood, efficiently purifying the bloodstream.

Proximal Convoluted Tubule (PCT)

The first section of the nephron that receives the filtrate from the glomerulus is the proximal convoluted tubule (PCT). Its primary role is not filtration but reabsorption.
As the filtrate travels through the PCT, a significant amount of water, glucose, amino acids, and essential ions are reabsorbed back into the bloodstream. The cells lining the PCT have microvilli, which increase the surface area for reabsorption, making this process extremely efficient.
The fine pores in the PCT cells help transport these molecules actively and passively, ensuring that the body retains essential nutrients and maintains balance, while still processing and eventually excreting what is not needed. Thus, the PCT is perfectly designed to reclaim the majority of what is valuable from the initial filtrate formed in the glomerulus.

Blood Pressure

Blood pressure plays a crucial role in the glomerular filtration process within the kidneys. This is a key factor because the filtration of blood through the glomerulus is largely driven by the blood pressure within its capillaries.
When the heart pumps, it generates pressure that moves blood through the circulatory system. At the glomerulus, this pressure pushes liquid and small solutes through the capillary walls into the Bowman's capsule.
In essence, the level of blood pressure affects how efficiently the glomerulus can perform its filtration role. If blood pressure is too low, it might reduce the glomerular filtration rate (GFR), leading to inefficient clearance of waste from the blood. Conversely, overly high blood pressure can damage the delicate glomerular capillaries, which can impair kidney function over time.

• Therefore, maintaining appropriate blood pressure is crucial for effective kidney filtration and overall body homeostasis.