Skeletal System

Funtions of the Skeletal System

• Support

• Protection

• Leverage

• Storage of Minerals

• Blood Cell production

Skeletal is divided into 2 parts

Axial skeleton & appendicular skeleton

Axial skeleton =

(80 bones) consists of the bones of the

skull, hyoid, sternum, rib cage, vertebral column,

sacrum, and coccyx.

Appendicular skeleton =

(126 bones) includes bones of

the limbs and the pectoral and pelvic girdles that

attach the limbs to the axial skeleton.

Bones are classified according to shape and structure

1. Flat Bones

2. Long Bones

3. Irregular Bones

4. Short Bones

2 types of ossification that occur in the embryo

Endochondral Ossification & Intramembranous Ossification

Steps of Intramembranous Ossification

• Embryonic connective tissue (mesenchyme)

moves to the future bone site

• Mesenchymal cells enlarge and differentiate

into osteoblasts

• Osteoblasts deposit bony matrix around

themselves

• Spongy bone forms in all directions by

following blood vessels

• Mesenchyme outside the developing bone

forms the periosteum. The periosteum has a

thin layer of osteoblasts that form compact

bone on top of the spongy bone

Steps of Endochondral Ossification

• Start as masses of hyaline cartilage

• The cartilage cells die and a periosteum

forms from connective tissue

• Blood vessels move in and connective

tissue cells differentiate into osteoblasts

• Spongy bone is formed in the space that

held hyaline cartilage

• Periosteum osteoblasts lay down compact

bone around the spongy bone

Hematoma formation

1. Blood vessels in bone tear and hemorrhage occurs.

2. Over a period of several hours, a large blood clot, or

hematoma, develops.

Fibrocartilage callus formation

1. Capillaries grow into the hematoma and phagocytic cells

invade the area.

2. Fibroblasts and osteoblasts migrate to the fracture.

3. Fibroblasts secrete collagen fibers and/or differentiate

into chondroblasts that secrete a cartilage matrix.

4. Osteoblasts form spongy bone.

5. The mass of repair tissue is referred to as a

fibrocartilage callus.

6. An internal callus connects bone ends and an external

callus protrudes from the outer bone surface.

Bony callus formation

1. Osteoblasts and osteoclasts continue to migrate inward

and multiply rapidly in the fibrocartilaginous callus.

2. As the material calcifies, the tissue becomes a bony

callus.

Fractures are classified on the basis of:

1. Whether the bone penetrates the skin

2. Orientation of the break

Simple (closed) break

bone breaks cleanly, but does not penetrate the skin

Compound (open) break

Broken ends of the bone protrude through the tissue and the skin

Transverse break

break occurs perpendicular to the long axis of the bone

Linear break

Breaks parallel to the long axis of the bone

Comminuted fracture

Bone fragments into many pieces

Compression fracture

bone is crushed from upward and downward forces

Depressed fracture

broken bone is pressed inward (skull)

Spiral fracture

ragged break as a result of excessive twisting of the bone

Epiphyseal break

break occurring along the epiphyseal plate

When blood calcium levels are too LOW…

the parathyroid gland secrets parathyroid hormoneor PTH

when blood calcium levels are too HIGH…

the c cells of the throid gland secrets calcintonin

The middle ear consists of

Three parts: malleus, incus, and stapes

the skull has … bones

22 bones

The vertebral column contains ______________ vertebra, including the __________ and the _____________

• 33 bones

• Sacrum and the coccyx

The thoracic cage contains of the ______ and the sternum

Ribs, thoracic cavity, and the sternum

____ bones make up the appendicular skeleton

126 bones