In the kidney of mammals, the site of ultrafiltration is the

Step 1: Analyze the question The question asks where ultrafiltration happens in the mammalian kidney. Ultrafiltration is the first stage of urine formation, where blood plasma is filtered under high pressure.

Step 2: Explain the concept Each nephron has two main parts:

• Renal corpuscle: the glomerulus (a knot of capillaries) enclosed by the Bowman's capsule.
• Renal tubule: the proximal convoluted tubule, loop of Henle, and distal convoluted tubule.

Urine formation happens in three stages:

1. Ultrafiltration in the glomerulus and Bowman's capsule
2. Selective reabsorption in the proximal tubule, loop of Henle, and distal tubule
3. Secretion and concentration in the distal tubule and collecting duct

Step 3: Work through the solution

• The afferent arteriole is wider than the efferent arteriole, so blood pressure builds up in the glomerulus.
• This pressure forces water, glucose, amino acids, salts, and urea through the capillary walls into the Bowman's capsule.
• Blood cells and large proteins are too big to pass through, so they stay in the blood.
• The fluid collected in the capsule is called the glomerular filtrate.

Step 4: Check the options

• A. Uriniferous tubule: another name for the whole nephron, so it is too general. Reabsorption happens along its tubular part.
• B. Bowman's capsule: the cup-shaped structure that receives the filtrate from the glomerulus. This is the site of ultrafiltration.
• C. Loop of Henle: concentrates urine by water and salt reabsorption. It does not filter.
• D. Renal tubule: handles reabsorption and secretion, not filtration.

Answer: B. Bowman's capsule

Tip: Remember the order F-R-S: Filtration in the Bowman's capsule/glomerulus, Reabsorption in the tubules, Secretion in the distal tubule. If an exam question says "ultrafiltration" or "filtration", think glomerulus and Bowman's capsule.