Disorders of the excretory system

Disorders of the excretory system

In plain words: if the kidneys stop clearing the blood, urea piles up. A machine can then do the kidneys’ cleaning from outside the body, letting wastes leak out of the blood through a thin membrane into a clean fluid; or a working kidney can be given by a donor. Stones and inflammation are two other things that go wrong in the kidney.

Uraemia and kidney failure

• Malfunctioning kidneys let urea accumulate in the blood: uraemia (NCERT spells it “uremia”), which is highly harmful and may lead to kidney failure (NCERT page 213). Give this in an NCERT-based answer.
• Beyond the NCERT text: in medical usage, a rise in blood urea and creatinine is azotaemia, and uraemia is the illness caused by the retained wastes; it is usually the result of kidney failure (NLM MeSH, “Uremia” and “Azotemia”, public domain).
• In such patients, urea can be removed by haemodialysis (page 213).

Haemodialysis and the artificial kidney

NCERT describes the process (pages 213–214):

1. Blood is drained from a convenient artery, and an anticoagulant such as heparin is added (see coagulation).
2. It is pumped into a dialysing unit called the artificial kidney, which contains a coiled cellophane tube surrounded by dialysing fluid.
3. The dialysing fluid has the same composition as plasma, except that it has no nitrogenous wastes.
4. The porous cellophane membrane lets molecules pass according to their concentration gradient. Since the dialysing fluid has no nitrogenous wastes, these move freely out of the blood, clearing it.
5. The cleared blood is pumped back into the body through a vein, after anti-heparin is added.

NCERT calls the method a boon for thousands of uraemic patients all over the world (page 214). Beyond the NCERT text, the US National Institute of Diabetes and Digestive and Kidney Diseases describes haemodialysis as “a treatment to filter wastes and water from your blood, as your kidneys did when they were healthy”. Today the blood leaves and returns through a vascular access, which may be an arteriovenous (AV) fistula, an AV graft or a catheter, and in the filter the dialysis solution flows the opposite way to the blood, on the other side of thin hollow fibres, taking up the wastes (NIDDK, Hemodialysis; public domain). The diagram below shows NCERT’s textbook model.

Kidney transplantation

• A functioning kidney from a donor, preferably a close relative, is transplanted, to minimise the chance of rejection by the immune system of the host. Modern clinical procedures have increased the success rate of this complicated technique (NCERT page 214). Beyond the NCERT text: a relative’s kidney is more likely to be a good tissue match, but the donor can also be a spouse, a friend or someone who has recently died; the team tests the donor’s blood against the patient’s (cross-matching), and the patient takes medicines every day so that the immune system does not reject the new kidney (NIDDK, Kidney Transplant; public domain).
• NCERT calls transplantation “the ultimate method in the correction of acute renal failures (kidney failure)” (page 214); use NCERT’s words in NCERT-based answers. Beyond the NCERT text: NIDDK notes that some children with acute kidney injury need dialysis “for a short time while their kidneys recover” (NIDDK, Kidney Disease in Children). NIDDK describes a kidney transplant as “a treatment for kidney failure; it’s not a cure”, and notes that end-stage renal disease is “kidney failure that is treated by dialysis or kidney transplant” (NIDDK, Kidney Transplant; What Is Kidney Failure?).

Renal calculi and glomerulonephritis

• Renal calculi: a stone, or insoluble mass of crystallised salts (oxalates and others), formed within the kidney (NCERT page 214).
• Glomerulonephritis: inflammation of the glomeruli of the kidney (page 214).

Solved examples

Common mistakes to avoid

Quick revision summary

• Uraemia: urea accumulates in the blood when the kidneys malfunction; it is harmful and may lead to kidney failure (NCERT). Beyond the NCERT text: in medical usage uraemia is the illness of retained wastes, usually the result of kidney failure, and azotaemia the raised blood urea and creatinine (NLM MeSH).
• Haemodialysis: blood from an artery, with heparin, passes through a cellophane tube in dialysing fluid (plasma without nitrogenous wastes); wastes diffuse out down their gradient; anti-heparin is added and the blood returns through a vein (NCERT).
• Kidney transplantation: a functioning kidney from a donor, preferably a close relative, to minimise rejection; NCERT calls it the ultimate method for acute renal failures (NCERT). Beyond the NCERT text: it is a treatment for kidney failure, not a cure, and anti-rejection medicines are taken every day (NIDDK).
• Renal calculi are stones of crystallised salts such as oxalates; glomerulonephritis is inflammation of the glomeruli.

Questions students ask

What is the difference between haemodialysis and peritoneal dialysis?

Haemodialysis cleans the blood outside the body, in an artificial kidney, while peritoneal dialysis, which NCERT does not describe, cleans it inside the body, using the lining of the abdomen as the filter (NIDDK, Peritoneal Dialysis). In NCERT’s haemodialysis, the blood is pumped through a coiled cellophane tube surrounded by dialysing fluid in a dialysing unit (NCERT pages 213–214). In peritoneal dialysis, beyond the NCERT text, a solution of water, salt and other additives flows through a catheter into the belly, stays a few hours while wastes pass into it from the blood, and is then drained (NIDDK, Peritoneal Dialysis).

How is an artificial kidney different from a natural kidney?

A dialyser does only part of a natural kidney’s work: beyond the NCERT text, NIDDK says that haemodialysis removes wastes along with extra salt and water but “can replace part, but not all, of your kidney function” (NIDDK, Hemodialysis; public domain). A natural kidney also reabsorbs and secretes: its tubular secretion of H^⁺, K^⁺ and ammonia keeps the ionic and acid–base balance of body fluids, and its juxtaglomerular cells release renin (NCERT page 209) and the hormone erythropoietin (NCERT Chapter 19, page 247). NCERT’s artificial kidney, by contrast, works only by letting molecules cross a porous cellophane membrane down their concentration gradient (pages 213–214).

Is nephritis in the NEET syllabus the same as NCERT’s glomerulonephritis?

Nephritis, the term in the NEET (UG) 2026 syllabus, is wider than NCERT’s glomerulonephritis: beyond the NCERT text, nephritis is inflammation of any part of the kidney (MeSH, “Nephritis”), while glomerulonephritis, the one kind NCERT names, is inflammation of the glomeruli of the kidney (NCERT page 214). The syllabus lists “Disorders; Uraemia, Renal failure, Renal calculi, Nephritis; Dialysis and artificial kidney.” in Unit 5, so learn NCERT’s glomerulonephritis line for it. Beyond the NCERT text, glomerulonephritis usually leads to blood and protein in the urine, high blood pressure and failing kidney function (MeSH, “Glomerulonephritis”).

Why do kidney stones form?

Kidney stones, which NCERT calls renal calculi, form when certain minerals reach high levels in the urine: beyond the NCERT text, NIDDK says they are caused by high levels of calcium, oxalate and phosphorus in the urine, minerals that are normally found in urine and do no harm at low levels (NIDDK, Kidney Stones). NCERT describes the result as a stone of crystallised salts formed within the kidney (page 214), and NIDDK adds that calcium oxalate stones are more common than calcium phosphate stones (NIDDK, Kidney Stones).

What is the difference between uraemia and azotaemia?

Uraemia, as NCERT defines it, is the accumulation of urea in the blood when the kidneys malfunction (page 213); azotaemia, a term from beyond the NCERT text, is a raised level of blood urea nitrogen and creatinine, a biochemical finding that is called uraemia once it comes with a set of clinical signs (MeSH, “Azotemia”). The same MeSH note adds that azotaemia can be caused by kidney diseases or by disorders outside the kidney, so a raised blood urea does not by itself show kidney failure (our reading). For NEET, give NCERT’s definition; azotaemia is in neither the NCERT text nor the NEET (UG) 2026 syllabus.

Practice questions

Try each question first, then open the answer to check your working.

1. Q1. What is the dialysing unit used in haemodialysis called?

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   The artificial kidney (NCERT page 213).

2. Q2. Why is a donor kidney preferably taken from a close relative?

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   To minimise its chances of rejection by the immune system of the host (NCERT page 214).

3. Q3. What are renal calculi made of?

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   Insoluble masses of crystallised salts, such as oxalates, formed within the kidney (NCERT page 214).