Biology · Excretory Products and Their Elimination · NEET
It is called ultrafiltration because the blood is filtered so finely that almost all the small parts of plasma (water, glucose, amino acids, salts, urea) pass through, but the large plasma proteins are held back. A normal filter cannot separate things this finely, so NCERT calls it ultra (very fine) filtration. This word is a common one-word NEET answer.
Blood is filtered through 3 layers: (1) the endothelium of the glomerular blood capillaries, (2) the basement membrane in the middle, and (3) the epithelium of Bowman's capsule (made of podocytes). Remember the order from blood to capsule: endothelium then basement membrane then podocytes. NEET often asks the correct order of these layers.
Water, glucose, amino acids, sodium, urea and other small plasma solutes pass into Bowman's capsule. Plasma proteins (large molecules) and blood cells normally stay back in the blood. So the filtrate is almost like plasma but without proteins. If proteins appear in urine, it signals a filtration problem.
Podocytes are the special epithelial cells of Bowman's capsule. They wrap around the capillaries and their branches leave tiny gaps called filtration slits or slit pores. Blood is filtered through these slits. NEET frequently matches podocytes with filtration slits, so link these two words together.
It happens at the malpighian corpuscle (also called renal corpuscle), which is the glomerulus together with Bowman's capsule. It does NOT happen in the PCT, loop of Henle or DCT. A 2018 NEET question directly matched ultrafiltration with the malpighian corpuscle.
The glomerular capillary blood pressure (hydrostatic pressure) is the force that pushes plasma out of the glomerulus into Bowman's capsule. This high pressure exists because the efferent arteriole is narrower than the afferent arteriole. No energy (ATP) is spent, so it is a passive pressure-driven process.
Match the items given in Column I with those in Column II and select the correct option: Column I (Function): a. Ultrafiltration, b. Concentration of urine, c. Transport of urine, d. Storage of urine. Column II (Part): i. Henle's loop, ii. Ureter, iii. Urinary bladder, iv. Malpighian corpuscle, v. Proximal convoluted tubule.
Match the items in Column-I with those in Column-II: Column-I: (a) Podocytes, (b) Protonephridia, (c) Nephridia, (d) Renal calculi. Column-II: (i) Crystallised oxalates, (ii) Annelids, (iii) Amphioxus, (iv) Filtration slits.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
On average 1100 to 1200 ml of blood is filtered by the kidneys per minute, which is roughly one-fifth (1/5th) of the blood pumped out by each ventricle in a minute.
It is passive. It is driven by glomerular capillary blood pressure and does not use ATP energy, so no active transport is involved in this step.
Filtrate is the fluid just formed in Bowman's capsule; it is almost like plasma without proteins. Urine is the final concentrated fluid formed after reabsorption and secretion in the tubules, so about 99 percent of the filtrate is reabsorbed before it becomes urine.
Plasma proteins are large molecules and cannot pass through the fine filtration membrane and slits. So they stay in the blood. Finding protein in urine is a sign of kidney damage.
The malpighian corpuscle (renal corpuscle) is the glomerulus together with Bowman's capsule. It is the exact site where ultrafiltration takes place.
