Skeletal System Anatomy and Physilogy 1
Functions of the Skeletal System
Besides contributing to body shape and form, our bones perform several important body functions.
1. Support. Bones, the <steel girders= and <reinforced concrete= of the body, form the internal framework
that supports the body and cradle its soft organs; the bones of the legs act as pillars to support the body
trunk when we stand, and the rib cage supports the thoracic wall.
2. Protection. Bones protect soft body organs; for example, the fused bones of the skull provide a snug
enclosure for the brain, the vertebrae surround the spinal cord, and the rib cage helps protect the vital
organs of the thorax.
3. Movement. Skeletal muscles, attached to bones by tendons, use the bones as levers to move the body
and its parts.
4. Storage. Fat is stored in the internal cavities of bones; bone itself serves as a storehouse for minerals, the
most important of which are calcium and phosphorus; because most of the body’s calcium is deposited in
the bones as calcium salts, the bones are a convenient place to get more calcium ions for the blood as
they are used up.
5. Blood cell formation. Blood cell formation, or hematopoiesis, occurs within the marrow cavities of
certain bones.
Anatomy of the Skeletal System
The skeleton is subdivided into two divisions: the axial skeleton, the bones that form the longitudinal axis of the
body, and the appendicular skeleton, the bones of the limbs and girdles.
,Skeletal System Anatomy and Physilogy 2
, Skeletal System Anatomy and Physilogy 3
Classification of Bones
The adult skeleton is composed of 206 bones and there are two basic types of osseous, or bone, tissue: compact
bone and spongy bone, and are classified into four groups according to shape: long, short, flat, and irregular.
Compact bone. Compact bone is dense and looks smooth and homogeneous.
Spongy bone. Spongy bone is composed of long, needle-like pieces of bone and lots of open space.
Long bones. Long bones are typically longer than they are wide; as a rule, they have a shaft with heads
at both ends, and are mostly compact bone.
Short bones. Short bones are generally cube-shaped and mostly contains spongy bone; sesamoid bones,
which form within tendons, are a special type of short bone.
Flat bones. Flat bones are thin, flattened, and usually curved; they have two thin layers of compact bone
sandwiching a layer of spongy bone between them.
Irregular bones. Bones that do not fit one of the preceding categories are called irregular bones.
Long Bone
The structure of a long bone is shown both through gross anatomy and microscopic anatomy.
Gross Anatomy
Functions of the Skeletal System
Besides contributing to body shape and form, our bones perform several important body functions.
1. Support. Bones, the <steel girders= and <reinforced concrete= of the body, form the internal framework
that supports the body and cradle its soft organs; the bones of the legs act as pillars to support the body
trunk when we stand, and the rib cage supports the thoracic wall.
2. Protection. Bones protect soft body organs; for example, the fused bones of the skull provide a snug
enclosure for the brain, the vertebrae surround the spinal cord, and the rib cage helps protect the vital
organs of the thorax.
3. Movement. Skeletal muscles, attached to bones by tendons, use the bones as levers to move the body
and its parts.
4. Storage. Fat is stored in the internal cavities of bones; bone itself serves as a storehouse for minerals, the
most important of which are calcium and phosphorus; because most of the body’s calcium is deposited in
the bones as calcium salts, the bones are a convenient place to get more calcium ions for the blood as
they are used up.
5. Blood cell formation. Blood cell formation, or hematopoiesis, occurs within the marrow cavities of
certain bones.
Anatomy of the Skeletal System
The skeleton is subdivided into two divisions: the axial skeleton, the bones that form the longitudinal axis of the
body, and the appendicular skeleton, the bones of the limbs and girdles.
,Skeletal System Anatomy and Physilogy 2
, Skeletal System Anatomy and Physilogy 3
Classification of Bones
The adult skeleton is composed of 206 bones and there are two basic types of osseous, or bone, tissue: compact
bone and spongy bone, and are classified into four groups according to shape: long, short, flat, and irregular.
Compact bone. Compact bone is dense and looks smooth and homogeneous.
Spongy bone. Spongy bone is composed of long, needle-like pieces of bone and lots of open space.
Long bones. Long bones are typically longer than they are wide; as a rule, they have a shaft with heads
at both ends, and are mostly compact bone.
Short bones. Short bones are generally cube-shaped and mostly contains spongy bone; sesamoid bones,
which form within tendons, are a special type of short bone.
Flat bones. Flat bones are thin, flattened, and usually curved; they have two thin layers of compact bone
sandwiching a layer of spongy bone between them.
Irregular bones. Bones that do not fit one of the preceding categories are called irregular bones.
Long Bone
The structure of a long bone is shown both through gross anatomy and microscopic anatomy.
Gross Anatomy
