CogKnoSys

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

Physical

Skeletal System

The skeletal system is the body's internal framework of bones and joints, which supports, protects and moves the body.

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The idea

The skeletal system is the internal framework of the human body. A newborn baby has around 270 bones, but as some of these bones gradually fuse together, the total drops to around 206 by adulthood. Bone makes up about 14 percent of total body weight, and it reaches its greatest mass between the ages of 25 and 30.

The axial skeleton, with 80 bones, runs down the middle of the body and includes the spine, the rib cage and the skull. The appendicular skeleton, with 126 bones, is made up of the shoulder and hip girdles and the bones of the arms and legs. Joints link the bones together, and skeletal muscles, which are attached to the bones at various sites, pull on them to produce movement.

The skeleton performs six major functions: support, movement, protection, making blood cells, storing minerals and regulating hormones. The skull protects the brain, while the rib cage, spine and breastbone guard the heart and lungs. Blood cells develop in the bone marrow, and the hard bone around it stores calcium. Bone cells even release a hormone called osteocalcin, which helps regulate blood sugar.

Check yourself

Question 1 of 3

Around how many bones does an adult human have?

Pick one. The first pick counts.

Composition

what it's made of

  • Axial skeleton — The 80 bones of the skull, spine and rib cage along the body's center.
  • Appendicular skeleton — The 126 bones of the shoulders, hips, arms and legs.
  • Bone marrow — Soft tissue inside bones where blood cells develop.
  • Joints — Places where bones meet, letting the skeleton bend and move.
  • Ligaments — Tough bands of tissue that support the bones of the spine and other joints.

Connection

how it relates

Under Human Body

Cause and effect

  1. Central Nervous Systemstrength 80 of 100

    The skeleton shields the central nervous system, as the skull protects the brain and the vertebrae protect the spinal cord.

Related

  1. Skeletal Musclestrength 80 of 100

    Skeletal muscles attach to bones and pull on them, so muscle and bone work together to move the body.

  2. Muscle Contractionstrength 60 of 100

    Each muscle contraction tugs on a bone, which swings at a joint like a lever.

  3. Gravitystrength 50 of 100

    The axial skeleton carries the weight of the head and trunk down to the legs, holding the body upright against gravity.

Change

how and why it evolves

Past
The ancient Indian medical text Sushruta Samhita spoke of 360 bones. In 1543, Andreas Vesalius published the first edition of his anatomy books, De Humani Corporis Fabrica Libri Septem. The work contained many illustrations of the skeleton and corrected some old theories handed down from Galen.
Now
Today, osteoporosis, in which bones lose density and break more easily, is one of the most common skeletal disorders.
Next
Doctors will likely keep using bone density scans to catch osteoporosis early, since it usually causes no symptoms until a bone breaks.

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

Skeletal System

The skeletal system is the body's internal framework of bones and joints, which supports, protects and moves the body.

Learn, discuss, create, buy or invest

The idea

The skeletal system is the internal framework of the human body. A newborn baby has around 270 bones, but as some of these bones gradually fuse together, the total drops to around 206 by adulthood. Bone makes up about 14 percent of total body weight, and it reaches its greatest mass between the ages of 25 and 30.

The axial skeleton, with 80 bones, runs down the middle of the body and includes the spine, the rib cage and the skull. The appendicular skeleton, with 126 bones, is made up of the shoulder and hip girdles and the bones of the arms and legs. Joints link the bones together, and skeletal muscles, which are attached to the bones at various sites, pull on them to produce movement.

The skeleton performs six major functions: support, movement, protection, making blood cells, storing minerals and regulating hormones. The skull protects the brain, while the rib cage, spine and breastbone guard the heart and lungs. Blood cells develop in the bone marrow, and the hard bone around it stores calcium. Bone cells even release a hormone called osteocalcin, which helps regulate blood sugar.

Check yourself

3 quick questions, instant feedback.