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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

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
OrganSubstances excreted
LungsCarbon dioxide
KidneysUrea, excess water and excess ions

The urinary system

Parts of the urinary system
PartFunction
KidneysFilter the blood and make urine
Renal arteryBrings blood to the kidney
Renal veinTakes blood away from the kidney
UretersTubes that carry urine from the kidneys to the bladder
BladderStores urine
UrethraTube that carries urine out of the body
The urinary system: two kidneys connected to the aorta by renal arteries and to the vena cava by renal veins, with a ureter from each kidney to the bladder and the urethra leading out of the bladder. (opens full size in a new tab)
The urinary system. The renal artery brings blood to each kidney and the renal vein takes it away.
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 (what this means)Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels mean

Inside the kidney

Supplement (what this means)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 (what this means)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. (opens full size in a new tab)
The cortex is the outer region of the kidney and the medulla is the inner region.
Supplement (what this means)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.