Excretion, the lungs and the urinary system

Excretion in humans · Excretion in humans · note 1 of 3

Spec 13.1.1, 13.1.2, 13.1.3, 13.1.4Download all Excretion in humans notes (PDF)Download all notes (PDF)6 pages

Excretion, the lungs and the urinary systemSpec 13.1.1, 13.1.2, 13.1.3, 13.1.4

In short

Excretion is the removal of the waste products of metabolism and substances in excess of requirements. The lungs excrete carbon dioxide made in respiration, and the kidneys excrete urea, excess water and excess ions in urine. Urine passes from the kidneys down the ureters to the bladder, where it is stored, then leaves through the urethra.

Excretion is the removal of the waste products of metabolism and substances in excess of requirements. Waste products are made by the chemical reactions inside cells. If they build up, they can harm the body.

Carbon dioxide is made in cells during respiration. It is carried in the blood to the lungs and leaves the body when you breathe out. So the lungs excrete carbon dioxide.

The kidneys excrete urea and excess water and excess ions. These leave the body dissolved in urine.

Excretory organs and the substances they excrete
Organ	Substances excreted
Lungs	Carbon dioxide
Kidneys	Urea, excess water and excess ions

The urinary system

Parts of the urinary system
Part	Function
Kidneys	Filter the blood and make urine
Renal artery	Brings blood to the kidney
Renal vein	Takes blood away from the kidney
Ureters	Tubes that carry urine from the kidneys to the bladder
Bladder	Stores urine
Urethra	Tube that carries urine out of the body

Common mistake:

Do not mix up the ureter and the urethra. The ureter goes from the kidney to the bladder. The urethra goes from the bladder out of the body.

Supplement

Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels mean

Inside the kidney

Supplement

Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels mean

A section through a kidney shows two main regions. The cortex is the outer region. The medulla is the inner region. The ureter leaves the kidney, and the renal artery and renal vein join it.

Supplement

Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels mean

Longitudinal section through a kidney showing the outer cortex and the inner medulla, with the renal artery and renal vein joining the kidney and the ureter leaving it. — The cortex is the outer region of the kidney and the medulla is the inner region.

Supplement

Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels mean

Exam tip:

Cortex is the outer region and medulla is the inner region. In a diagram question, look at which region is on the outside.

Written and checked against the Cambridge IGCSE Biology (0610) specification · Updated October 2026

Frequently asked questions

How does the kidney filter blood?

Supplement The kidney filters blood in tiny tubes called nephrons. Blood in the glomerulus is under high pressure, so water, glucose, urea and ions are forced out into the nephron, while proteins and blood cells stay in the blood. All the glucose, some ions and most of the water are reabsorbed, and what is left becomes urine.

What is the difference between the ureter and the urethra?

The ureter carries urine from the kidney to the bladder, while the urethra carries urine from the bladder out of the body. Each kidney has its own ureter, and the bladder stores the urine until it leaves. Students often mix the two up, so link the ureter with the kidney and the urethra with the way out.

Why is there no glucose in urine?

Supplement There is normally no glucose in urine because all of it is reabsorbed into the blood from the nephron. Glucose is small enough to be filtered out of the blood at the glomerulus, so it does enter the nephron. It is then all taken back into the blood as the filtered liquid passes along the nephron.

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