The Excretory System

ICSE Class 10 · Biology · Chapter 9

What this chapter covers

Excretion and the excretory organs of the human body
Parts of the urinary system
Blood vessels entering and leaving the kidney
External structure of the kidney
Internal structure of the kidney
The kidney tubule or nephron
Urine formation: ultra-filtration in the Malpighian capsule
Urine formation: selective reabsorption
Urine formation: tubular secretion
Composition of blood plasma and urine

Key definitions

Excretion is the process by which the waste products of metabolism, especially nitrogenous wastes, are removed from the body.

Nitrogenous wastes are waste substances containing nitrogen that are produced when the body breaks down excess amino acids and other nitrogen compounds.

Egestion is the removal of undigested food from the alimentary canal as faeces.

Osmoregulation is the maintenance of the correct balance of water and salts in the blood and body fluids.

The urinary system is the set of organs that forms urine, stores it for a while and passes it out of the body.

Urine is the watery fluid formed by the kidneys that contains urea, other nitrogenous wastes, excess salts and excess water removed from the blood.

The renal artery is the blood vessel that brings oxygenated blood, loaded with urea and other wastes, to each kidney.

The renal vein is the blood vessel that carries purified, deoxygenated blood away from each kidney.

The kidney is a bean-shaped, dark red organ that filters the blood and forms urine.

The hilum is the notch on the concave inner side of the kidney through which the renal artery enters and the renal vein and ureter leave.

The renal capsule is the thin fibrous membrane that covers the outer surface of the kidney and protects it.

The renal cortex is the dark, reddish, granular outer region of the kidney, lying just under the renal capsule.

Key points

Excretion removes metabolic wastes, mainly nitrogenous wastes such as urea; egestion removes undigested food.
Excretory organs: kidneys (urine), skin (sweat), lungs (carbon dioxide and water vapour), liver (bile pigments; makes urea) and large intestine (some salts).
The urinary system is two kidneys, two ureters, a urinary bladder and a urethra.
The renal artery, a branch of the dorsal aorta, brings blood to the kidney; the renal vein takes it to the inferior vena cava and has the least urea in the body.
The kidney is bean-shaped, covered by a renal capsule, with a hilum on its concave side for the renal artery, renal vein and ureter.
Internally the kidney shows an outer granular cortex, an inner striped medulla of renal pyramids, and a pelvis with calyces leading to the ureter.
The nephron is the structural and functional unit of the kidney: Malpighian capsule (Bowman's capsule + glomerulus), proximal convoluted tubule, loop of Henle, distal convoluted tubule and collecting duct.
The afferent arteriole is wider than the efferent arteriole, which raises the pressure in the glomerulus.
Ultra-filtration in the Malpighian capsule forms about 180 L of protein-free filtrate a day.
Selective reabsorption, mainly in the proximal tubule, returns all glucose and amino acids and about 99 per cent of the water to the blood.
Tubular secretion, mainly in the distal tubule, adds hydrogen ions, potassium ions, creatinine and some medicines to the urine.
Normal urine is about 95 per cent water with urea as the main solid, and has no glucose, proteins or blood cells.

Questions answered

Define excretion. How is it different from egestion?

Excretion is the removal of the waste products of metabolism, especially nitrogenous wastes, from the body. Egestion is the removal of undigested food as faeces; that food never entered the cells, so its removal is not excretion.

Name four excretory organs of the human body and one waste each removes.

Kidneys remove urea; skin removes salts and water in sweat; lungs remove carbon dioxide; liver removes bile pigments.

Name the parts of the urinary system in the order in which urine passes through them.

Kidney, ureter, urinary bladder, urethra.

Which blood vessel brings blood to the kidney, and from which vessel does it arise? Which vessel takes blood away, and where does it open?

The renal artery brings blood; it arises from the dorsal aorta. The renal vein takes blood away and opens into the inferior vena cava.

Give a reason: blood in the renal vein has the least urea of any blood in the body.

The kidneys have just removed most of the urea from this blood and sent it into the urine, so the blood leaving them is the cleanest in terms of urea.

Name the three structures that pass through the hilum of the kidney.

Renal artery, renal vein and ureter.

Why does the cortex of the kidney look granular and the medulla look striped?

The cortex is packed with the round Malpighian capsules, which make it look granular. The medulla contains the long, straight loops of Henle and collecting ducts lying side by side, which make it look striped.

What is a nephron? Name its parts in order.

A nephron is the structural and functional unit of the kidney in which urine is formed. Its parts in order are Bowman's capsule with the glomerulus (together the Malpighian capsule), proximal convoluted tubule, loop of Henle, distal convoluted tubule and collecting duct.

Past board exam questions

ICSE 2027 sample paper · 1 mark

While playing cricket on a hot, summer afternoon, Rohan felt a little dizzy though he had a balanced meal. The doctor advised him to take an oral rehydration solution. What was most likely the reason for Rohan’s condition?

Excessive urination
Asphyxiation
Low blood glucose level
Excessive perspiration

Show answer

Excessive perspiration

ICSE 2027 sample paper · 1 mark

Which of the following correctly describes the level of urea in the two blood vessels after a meal containing protein?

Renal Artery - High; Renal Vein – High
Renal Artery - High; Renal Vein - Low
Renal Artery - Low; Renal Vein - Low
Renal Artery - Low; Renal Vein - High

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Renal Artery - High; Renal Vein - Low

ICSE 2027 sample paper · 1 mark

A patient suffering with severe cholera:

passes very little urine due to severe dehydration.
passes excessive urine due to kidney overactivity.
has blood in the urine as the first symptom.
produces normal amounts of urine despite severe fluid loss.

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passes very little urine due to severe dehydration.

ICSE 2027 sample paper · 1 mark

Which parts of the nephrons are present in the renal cortex and renal medulla? The parts of a nephron are numbered as follows: 1 and 3 – the two blood vessels (arterioles) entering and leaving the glomerulus; 2 – the glomerulus within Bowman’s capsule; 4 – the proximal convoluted tubule; 5 – the distal convoluted tubule; 6 – the loop of Henle; 7 – the collecting duct.

Renal Cortex – 1, 2, 3; Renal Medulla – 4, 5, 6, 7
Renal Cortex – 1, 2, 3, 4, 5; Renal Medulla – 6, 7
Renal Cortex – 4, 5, 6, 7; Renal Medulla – 1, 2, 3
Renal Cortex – 1, 2, 3, 4; Renal Medulla – 5, 6, 7

Show answer

Renal Cortex – 1, 2, 3, 4, 5; Renal Medulla – 6, 7

ICSE 2026 board paper · 1 mark

A person suffering from kidney failure has proteins in the urine. What is this condition called?

Haematuria
Glycosuria
Albuminuria
Anaemia

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Albuminuria

ICSE 2026 board paper · 5 marks

Study the table given below and match the structure with its functions: Example: Pelvis – (f) | Structure (labelled in a longitudinal section of the kidney) | Functions | |---|---| | Renal Medulla | (a) Has Malpighian capsules | | Renal Artery | (b) Carries oxygenated blood | | Renal Vein | (c) Transports urine to urinary bladder | | Renal Cortex | (d) Has Henle's loops | | Pelvis | (e) Carries deoxygenated blood | | Ureter | (f) Receives urine which flows into ureter |

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Renal Medulla – (d) Has Henle's loops Renal Artery – (b) Carries oxygenated blood Renal Vein – (e) Carries deoxygenated blood Renal Cortex – (a) Has Malpighian capsules Ureter – (c) Transports urine to urinary bladder (Pelvis – (f) is the given example.)

ICSE 2026 sample paper · 1 mark

What is Excretion?

Show answer

Excretion is the removal of harmful (mainly nitrogenous) metabolic waste products from the body.

ICSE 2026 sample paper · 2 marks

Mention the regions of the kidney where we can find glomerulus and Henle’s loop.

Show answer

Glomerulus – renal cortex Henle’s loop – renal medulla