Biology · Excretory Products and Their Elimination · NEET
The three steps are: (1) Glomerular filtration (also called ultrafiltration), (2) Tubular reabsorption, and (3) Tubular secretion. They always happen in this order. Filtration makes a first fluid, reabsorption takes back useful parts, and secretion adds extra wastes. NCERT lists exactly these three, so remember the order for NEET.
Reabsorption moves useful substances (glucose, amino acids, most water, Na+) OUT of the filtrate and BACK into the blood. Secretion does the opposite: it moves extra wastes (H+, K+, ammonia) FROM the blood INTO the filtrate. So reabsorption saves things for the body, secretion removes things from the body. This direction is a common NEET trap.
Filtration happens at the Malpighian body (glomerulus + Bowman's capsule). Reabsorption happens mainly in the PCT, and also in the loop of Henle and DCT. Secretion happens in the PCT, DCT and collecting duct. So the renal corpuscle only filters, and the tubules do reabsorption and secretion.
Yes. NCERT calls glomerular filtration 'ultrafiltration' because the glomerular capillaries filter blood so finely that all small molecules pass but blood cells and large proteins stay back. So the filtrate is almost like plasma but without proteins. The words are used for the same first step.
None of the three basic steps alone concentrates urine — concentration is done by tubular reabsorption of water, driven by the counter current mechanism in the loop of Henle and vasa recta plus ADH. So filtration and secretion decide what is in urine, while reabsorption of water decides how concentrated it is.
Because the filter is so fine that even small proteins are stopped, but water, glucose, urea, salts and ions pass through. About 1100–1200 mL of blood is filtered per minute, forming around 180 litres of filtrate a day, of which 99% is reabsorbed. That is why only 1–1.5 litres of urine is released daily.
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
Which of the following diagrams is correct with regard to the proximal (P) and distal (D) tubule of the Nephron (showing reabsorption and secretion directions)?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Glomerular filtration (ultrafiltration), tubular reabsorption, and tubular secretion, in that order.
It begins with filtration at the Malpighian body (glomerulus and Bowman's capsule) inside the renal cortex.
About 180 litres of filtrate form per day, but nearly 99% is reabsorbed, so only about 1–1.5 litres leave as urine.
Tubular reabsorption of water, controlled by ADH and the counter current mechanism, decides how concentrated the urine is.
Secretion ADDS extra wastes such as H+, K+ and ammonia into the filtrate, helping keep blood pH and ion balance correct.
