Skeletal System 2

Skeletal System 2

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Skeletal System 2...

Skeletal System 2:

The skeletal system provides a unique and rigid framework and support for the entire body. Bones are living organs and have the ability to change as our environment changes. The skeletal system is comprised of 206 individual bones in the adult body. Some bones are hinged while others are fused.

The skeleton begins to form in the fetus while in utero. During this time it is made of cartilage and fibrous structures that are shaped like bones. Over time these structures transform into real bones when the cartilage is replaced with calcified bone matrix. This remodeling and changing can happen due to the continuous activity of bone forming cells called osteoblasts and the bone resorbing cells called osteoclasts. The process of bone sculpting and resorbing allows bones to respond to stress or injury by their ability to change their shape size and density.

Most bones are formed from cartilage models and this process is called endochondral ossification. Ossification literally means the development of bone.

An example of this is with the embryo’s skeleton. It consists of collagenous protein fibers and hyaline (clear) cartilage. Infant bones are very soft and pliable because of incomplete ossification at birth. The fontanel is the soft spot on the baby’s head. The bone has not been completely formed there.

Let’s look at the make up of a typical long bone.

The small centers on the bone ends are called epiphyses.

The shaft or center of the bone is called the diaphysis.

As long as any cartilage between the epiphysis and the diaphysis is present there is continued growth. The epiphyseal plate is also referred to as the growth plate. Fractures within the growth plate is always a concern when the child is in the developmental stages.

In the center of the shaft is a hollow cylinder of hard, compact bone. This is what makes a long bone hard yet light enough for movement. The outer, fibrous layer of the bone is called the periosteum, while the inner lining is the endosteum. Within the medullary cavity there is the nutrient artery and the red and yellow bone marrow. The red bone marrow is present in both infants and adults and is critical in the formation of blood cells. The red bone marrow is found in adults only in flat bones. This is because as we age, grow and develop the red bone marrow is replaced by the yellow (fat containing) bone marrow in adults.

The skeletal system has five specific functions:

1. Supports- body structures and provides shape to the body.

2. Protects- the soft and delicate internal organs. For example, the cranium protects the brain, the inner ear and parts of the eye. The ribs and breastbone protect the heart and lungs; the vertebral column protects the spinal cord.

3. Movement and anchorage of the muscles. Muscles which are attached to the skeleton. are called skeletal muscles. Upon contraction, these muscles exert a pull upon a bone and so move it. In this manner, bones play a vital part in body movement serving as passively operated levers.

4. Mineral storage. Bones are a storage for minerals like calcium and phosphorous. In case of inadequate nutrition, the body is able to draw upon these reserves. For example, if the blood releases the necessary amount of stored calcium into the blood stream. When calcium levels exceed normal, calcium released from the skeletal system is inhibited. In this way the skeletal system helps to maintain the blood calcium homeostasis.

5. Hemopoeisis- The red marrow of the bone is the site for blood cell formation.

Classification of bones:

Long bones: bones of the arm and legs

Short bones: bones of the wrist and ankles

Flat bones: bones of the ribs, shoulder blades, pelvis and skull

Sesamoid bones: round bones that are found near joints

Irregular bones: bones of the vertebrae and face

PARTS OF THE SKELETON

The skeletal system is comprised of two main parts. The axial skeleton consists of the skull, spinal column, ribs, breastbone and hyoid bone. The hyoid bone is the “U” shaped bone in the neck and the tongue is attached to this bone.

The appendicular skeleton includes the upper extremities: shoulder girdles, arms, wrists and hands. It also includes the lower extremities: hip girdle, legs, ankles and feet.

AXIAL SKELETON

skull- composed of the cranium and the facial bones

cranium- houses and protects the delicate brain

facial bones- guard and support the eyes, ears, nose and mouth.

CRANIAL BONES

Cranial bones are thin and slightly curved. During infancy these bones are held together by an irregular band of connective tissue called a suture. As the child grows and develops this tissue ossifies and turns into hard bone. Thus the cranium turns into a highly efficient shield for the brain. Collectively there are 22 bones in the skull. There are 8 bones in the cranium.

CRANIAL BONES (8)

1- frontal- forms the forehead

2- parietal- forms the roof and sides of the skull

2- temporal- house the ears

1- occipital- forms the base of the skull

1- ethmoid- located between the eyes and forms part of the nasal septum

1- sphenoid- which resembles the shape of a bat, is considered the key bone of the skull; all other bones connect to it

FACIAL BONES (14)

5- nasal- 2 are nasal bones which form the bridge of your nose, 1 is the vomer which forms the lower part of the nasal septum and 2 are the inferior concha bones which make up the side walls of the nasal cavities

2- maxilla- make up the upper jaw

2- lacrimal- inner aspect of the eyes which make up the tear ducts

2- zygomatic which form the prominence of the cheek

1- mandible- which is the lower jaw and the only movable bone in the face

The skull contains large spaces within the facial bones referred to as paranasal sinuses. These sinuses are lined with mucous membranes. When these membranes become inflamed we may experience copious amounts of drainage and inflamed swollen membranes.

SPINE

The spine or vertebral column is strong and flexible. It supports the head and provides attachment for the ribs. The spine also encloses the spinal cord of the nervous system. This column is formed in such a way that they form a flexible curved rod.

The spine consists of small bones called vertebrae which are separated from each other by pads of cartilage tissue called intervertebral disks.

The vertebral column is divided into 5 sections from the first to the last vertebrae.:

cervical or neck- 7

thoracic or chest- 12

lumbar or lower back- 5

sacral or hip

coccyx or tail bone

When you study the model of the human skeleton, you will notice that the spine is curved instead of straight. A curved spine has more strength than a straight one. Normal curves in the spine will give us enough strength to support our body and also provide us with the balance that we need for us to stand tall and erect on two feet.

Normal curvatures of the spine are: cervical, thoracic, lumbar and sacral. This starts with the cervical spine jutting out and the thoracic bending inward, as well as the lumbar jutting out and the sacral bending inward.

The typical vertebra, contains three basic parts: body, foramen and processes. The large part of the vertebra is known as the body or the central opening for the spinal cord or foramen.