The process during infancy and childhood in which cartilage is replaced by bone.

A skin structure in which a strand of hair grows and oil is secreted

A break in a bone

A gland that secretes oil into a hair follicle in the skin; the oil softens and moistens hair and skin.

An overstretched or torn ligament.

A condition in which a significant loss of bone mass causes bones to become weak and break easily.

Involuntary muscle that causes movements inside your body, such as those involved in breathing and digestion.

Involuntary muscle that is found only in the heart.

Voluntary muscle that is attached to and moves your bones

A thick strand of tissue that attaches a muscle to a bone.

A condition in which muscles that cannot contract or are not used often weaken and shrink

A pulled muscle

A lesion that forms when excess oil and dead cells plug a hair follicle.

The outermost layer of skin

A dark pigment that gives skin some of its color