Human anatomy

Human anatomy describes the structure of the body, and physiology describes how that structure works. The body is organised into levels: cells form tissues, tissues form organs, and organs cooperate in organ systems, each responsible for a major function. Because these systems operate continuously and interact with one another, animations are a helpful way to show processes such as a heartbeat, a breath or the passage of a nerve impulse that cannot be captured in a single image.

Several systems support movement and protection. The skeletal system of bones provides a frame, protects organs and allows movement at joints, while the muscular system, including muscles such as the biceps, contracts to move the skeleton. The nervous system — the brain, spinal cord and nerves — senses the environment and coordinates the body's responses, working alongside the hormone-secreting glands of the endocrine system to regulate activity.

Other systems sustain the body's cells. The respiratory system brings in oxygen and removes carbon dioxide; the circulatory system transports blood carrying oxygen, nutrients and waste; the digestive system breaks down food into absorbable nutrients; and the urinary system removes waste and balances water. The immune system defends against infection, and the reproductive system enables the production of offspring. A recurring principle across all of them is homeostasis, the maintenance of stable internal conditions despite changes outside the body.

Frequently asked questions

How is the human body organised?

Cells form tissues, tissues form organs, and organs work together in organ systems, each carrying out a major function such as circulation or digestion.

What does the nervous system do?

The nervous system, made up of the brain, spinal cord and nerves, senses the environment and coordinates the body's responses, often together with the endocrine glands.

Which systems supply the body with oxygen?

The respiratory system takes in oxygen and removes carbon dioxide, and the circulatory system carries that oxygen in the blood to every cell.