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Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.
Key concept
Each kidney has an outer cortex and inner medulla. Nephrons span both regions: the Bowman's capsule and glomerulus are in the cortex, while the loop of Henle extends into the medulla. Urine collects in the renal pelvis and drains through the ureter to the bladder.
Kidney structure questions typically involve labelling a diagram or describing the path of urine from formation to excretion. Know the three main regions (cortex, medulla, pelvis) and where the key parts of the nephron are located.
External and internal structure
Humans have two kidneys, located at the back of the abdomen. Each receives blood via the renal artery and returns filtered blood via the renal vein. Urine leaves each kidney through the ureter and drains into the bladder, where it is stored before leaving the body through the urethra.
Internally, the kidney has three regions: the outer cortex, the inner medulla, and the central renal pelvis (a funnel-shaped cavity that collects urine and channels it into the ureter).
Where nephron components are located
Each kidney contains approximately one million nephrons: the functional units that filter blood and produce urine. The Bowman's capsule and glomerulus are located in the cortex. The proximal convoluted tubule (where most reabsorption occurs) is also in the cortex.
The loop of Henle dips down from the cortex into the medulla and returns to the cortex. The collecting duct passes through the medulla toward the renal pelvis, where urine is collected.
Blood supply to the kidney
The renal artery branches into smaller arterioles, each leading to a glomerulus: a knot of capillaries inside a Bowman's capsule. Blood pressure in the glomerulus forces small molecules out of the blood into the capsule (filtration). The blood leaving the glomerulus flows through capillaries surrounding the rest of the nephron, where useful substances are reabsorbed.
Filtered blood then exits through the renal vein. The blood in the renal vein has less urea, the correct water and ion balance, and normal glucose levels (all glucose has been reabsorbed).
Try a focused question (3 marks)
Name the blood vessel that carries blood to the kidney and state what happens to this blood in the kidney.
Show the answer and marking guidance
The renal artery carries blood to the kidney.
In the kidney, small molecules are filtered from the blood in the glomerulus into the Bowman's capsule.
Useful substances are selectively reabsorbed back into the blood, and waste products remain to form urine.
Original Cambridge-style practice written for this site. It is not an official Cambridge past-paper question.
Common mix-ups to avoid
Check these points against your own answer before moving on.
Confusing the renal artery (to the kidney) with the renal vein (from the kidney).
Not knowing that the glomerulus is in the cortex and the loop of Henle extends into the medulla.
Describing the kidney as a single structure rather than containing millions of nephrons.
Confusing ureter (from kidney to bladder) with urethra (from bladder to outside).