Lesson 3 of 13 · 5 min
Human excretory system
NCERT §16.1
When Meher's doctor pressed on her lower back during the check-up, she was feeling for something that sits much higher than most people guess. Where exactly are the kidneys?
The lesson in notes
In short
Four organs make up the human excretory system: two kidneys, two ureters, one urinary bladder and one urethra.
The kidneys are reddish brown and bean shaped. They sit high against the back wall of the abdominal cavity, on its inner dorsal side, between the levels of the last thoracic and the third lumbar vertebra.
An adult kidney is 10–12 cm long, 5–7 cm wide and 2–3 cm thick, and weighs on average 120–170 g.
The hilum is a notch at the centre of the kidney's inner concave surface; the ureter, blood vessels and nerves enter through it.
Just inside the hilum is the renal pelvis, a broad funnel-shaped space with projections called calyces (singular calyx).
A tough capsule covers the kidney. Inside, the tissue forms two zones: the cortex on the outside and the medulla within.
The medulla is split into a few cone-shaped medullary pyramids that project into the calyces. The cortex dips in between the pyramids as the renal columns, the columns of Bertini.