The glomerular filtrate contains the following substances EXCEPT

1. Analyze the question We need the one substance that is NOT found in the glomerular filtrate, the fluid that is filtered out of the blood in the kidney.

2. Explain the concept Each nephron starts with a Bowman's capsule containing a knot of capillaries called the glomerulus. Blood enters the glomerulus under high pressure (ultrafiltration), and this pressure forces small molecules out of the blood into the capsule.

• Small molecules pass through: water, glucose, amino acids, mineral salts (such as Na⁺, Cl⁻), urea, vitamins.
• Large particles stay in the blood: blood cells (red cells, white cells, platelets) and large plasma proteins (such as albumin and fibrinogen).

The filtration membrane is made of the capillary wall, the basement membrane, and the podocytes of the Bowman's capsule. Its pores are too small for blood cells and big proteins.

3. Go through the options

• A. Blood cells: too large to pass through the filter, so they are not in the filtrate.
• B. Glucose: small, so it is filtered (and later reabsorbed in the proximal convoluted tubule).
• C. Mineral salts: small, so they are filtered.
• D. Water: filtered.
• E. Urea: a small waste molecule, so it is filtered.

4. Answer The substance that does not appear in the glomerular filtrate is A. blood cells.

5. Exam tip Remember: "Filtrate = plasma minus proteins and cells." If blood cells or large proteins appear in urine, it signals kidney damage, because the filter should block them.