http://www.ck12.org Chapter 1. Human Biology
1.38 Kidneys
- Outline how the kidneys filter blood.
Why are the kidneys important?
These kidney beans are named after a very important organ in your body. You can’t live without at least one kidney.
The kidneys have several essential functions. For example, kidneys filter your blood, removing wastes and regulating
the amount of water in your body.
The Kidneys
The kidneys (Figure1.67) are important organs in maintaininghomeostasis, the ability of the body to maintain a
stable internal environment despite a changing environment. Kidneys perform a number of homeostatic functions.
- They maintain the volume of body fluids.
- They maintain the balance of salt ions in body fluids.
- They excrete harmful nitrogen-containing molecules, such as urea, ammonia, and uric acid.
There are many blood vessels in the kidneys (Figure1.67). The kidneys remove urea from the blood through tiny
filtering units called nephrons.Nephrons(Figure1.68) are tiny, tube-shaped structures found inside each kidney.
Each kidney has up to a million nephrons. Each nephron collects a small amount of fluid and waste from a small
group of capillaries.
Nitrogen-containing wastes, together with water and other wastes, form theurineas it passes through the nephrons
and the kidney. The fluid within nephrons is carried out into a larger tube in the kidney called aureter, which carries
it to the bladder (Figure1.68).