An example of filtration occurs in the kidney and:
A Red blood cells filter from the capillary into the kidney tubule.
B Plasma proteins filter from the capillary into the kidney tubule.
C This filtration across the capillary is an active process.
D White blood cells filter from the kidney tubule into the capillary.
E lons and glucose filter from the capillary into the kidney tubule.
The correct answer and explanation is :
The correct answer is E: Ions and glucose filter from the capillary into the kidney tubule.
Explanation:
Filtration in the kidney is a key process in the formation of urine. It occurs primarily in the glomerulus, a network of capillaries in the nephron, the functional unit of the kidney. The process of filtration involves the movement of substances from the blood (in the capillaries) into the renal tubule, which is the beginning of urine formation.
Here’s how it works:
- Filtration Process: Blood enters the kidney through the renal artery, which branches into smaller arterioles that eventually form the glomerulus. The glomerulus is a bundle of capillaries with semi-permeable walls. The blood pressure in these capillaries forces water and small solutes (like glucose, ions, urea, and waste products) through the capillary walls into the Bowman’s capsule (the beginning of the kidney tubule). This is the filtrate that enters the renal tubule for further processing.
- What filters into the tubule: The filtrate that moves into the kidney tubule primarily contains:
- Water: The largest component of the filtrate.
- Ions: Including sodium, potassium, chloride, bicarbonate, and others.
- Glucose: A key energy source.
- Amino acids: The building blocks of proteins.
- Urea and other waste products: To be excreted later.
- What does not filter: Larger molecules like red blood cells and plasma proteins (like albumin) do not pass through the filtration barrier due to their size. Their retention in the bloodstream ensures proper circulation and function. The filtration process is passive, driven by blood pressure, not an active process.
Incorrect Options:
- A: Red blood cells do not filter into the kidney tubule because they are too large.
- B: Plasma proteins do not filter into the kidney tubule for the same reason.
- C: Filtration is a passive process driven by blood pressure, not an active one.
- D: White blood cells are not filtered into the kidney tubule under normal conditions. Their presence in the urine could indicate infection or inflammation.
Thus, E correctly describes the filtration of ions and glucose into the kidney tubule.