CogKnoSys

Knowledge you can walk. Read the idea below, then step up to the general, across to peers or down to the specific.

Physical

Human Body

The human body is built from cells, tissues, organs and organ systems that work together to keep us alive.

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The idea

The human body is built in levels. Many different types of cells come together to form tissues, which in turn form organs, and organs work together in organ systems. An organ is a group of tissues joined to do a shared job, like the heart pumping blood. An organ system, such as the digestive or nervous system, is a group of organs that work together. Scientists count about 79 organs in the human body, though the exact number depends on how an organ is defined.

On the outside, the body has a head, neck, torso, arms, hands, legs and feet. Inside are organs, bones, muscles, tendons, ligaments, blood vessels, blood and lymph. The skeleton gives support, muscles create movement, and the nervous system carries the signals that control both.

All these systems interact to keep conditions inside the body steady, a balance called homeostasis. For example, the body keeps safe levels of sugar, iron and oxygen in the blood. Much of this works by negative feedback: sensors notice a change, and other parts of the body act to reverse it. Anatomy studies the body's structure, and physiology studies how its systems and organs work.

Check yourself

Question 1 of 3

Roughly how many organs do scientists count in the human body?

Pick one. The first pick counts.

Composition

what it's made of

  • Cells — The smallest living units; many different types make up the body.
  • Tissues — Groups of cells of the same type working together, such as muscle tissue.
  • Organs — Tissues joined to do a shared job, such as the heart or liver.
  • Organ systems — Groups of organs that work together, such as the digestive system.
  • Homeostasis — The steady inner balance that all the systems help maintain.

Connection

how it relates

Under Physical

Related

  1. Fight or Flight Responsestrength 60 of 100

    During a threat, nerves and hormones change how the whole body works, preparing it to fight or flee.

  2. Emotions and Feelingsstrength 50 of 100

    Emotions come with changes in the body, such as a faster heartbeat or tense muscles.

  3. Dreaming and Sleep Statesstrength 40 of 100

    The body needs regular sleep to rest and recover.

Change

how and why it evolves

Past
In the 19th century, the French physiologist Claude Bernard developed the idea that the body regulates its internal environment. Walter Bradford Cannon named this balance homeostasis in 1926.
Now
Today the body is studied by health professionals, physiologists, anatomists and even artists.
Next
The body's balancing systems can become less effective with age. Research on keeping them working well into old age is likely to keep growing.

Knowledge you can walk. Read the idea, then step up, across or down.

Human Body

The human body is built from cells, tissues, organs and organ systems that work together to keep us alive.

Learn, discuss, create, buy or invest

The idea

The human body is built in levels. Many different types of cells come together to form tissues, which in turn form organs, and organs work together in organ systems. An organ is a group of tissues joined to do a shared job, like the heart pumping blood. An organ system, such as the digestive or nervous system, is a group of organs that work together. Scientists count about 79 organs in the human body, though the exact number depends on how an organ is defined.

On the outside, the body has a head, neck, torso, arms, hands, legs and feet. Inside are organs, bones, muscles, tendons, ligaments, blood vessels, blood and lymph. The skeleton gives support, muscles create movement, and the nervous system carries the signals that control both.

All these systems interact to keep conditions inside the body steady, a balance called homeostasis. For example, the body keeps safe levels of sugar, iron and oxygen in the blood. Much of this works by negative feedback: sensors notice a change, and other parts of the body act to reverse it. Anatomy studies the body's structure, and physiology studies how its systems and organs work.

Check yourself

3 quick questions, instant feedback.