Chapter 7 Skeletal System

Functions of the skeleton

support, movement, protection, blood formation, electrolyte balance-bone is the body's reservoir for minerals, particularly calcium. Bone is storage for calcium.

Axial Skeleton

At birth, the skull is incompletely developed, with fibrous membranes connecting the cranial bones. These membranous areas are called fontanels (soft spots). The fontanels permits some movement between the bones which enable the infant's skull to pass through the birth canal. Eventually the fontanels will close as the cranial bones grow together ( by the end of the second year).

Factors affecting bone development

Bone development is influenced by nutrition exposure to sunlight, hormonal secretions, and physical exercise.

Bone marrow

Bone marrow is soft material that occupies the marrow cavity and spongy bone. Red bone marrow- abundance of red blood cells. This tissue is blood-forming and is responsible for creating all blood cells (producing cells). Yellow bone marrow- replaces red bone marrow as we age. Contains high amounts of fat and is no longer responsible for creating blood cells (fat adipose tissue).

Skull

Facial bones include: maxilla, palatine, zygomatic, lacrimal, nasal, inferior nasal conchae, vomer, mandible.

Endochondral Bones

In a long bone, bony tissue begins to replace hyaline cartilage in the center of the diaphysis. This region is called the primary ossification center. Bone develops from this region in both directions. (This is the first area of bone formation). The epiphyses of developing bone remain cartilaginous and continue to grow.

Skull

It consists of 22 bones that are rigidly joined by sutures. The cranial bones are: frontal bone, parietal bone, temporal bone, occipital bone, sphenoid bone, ethmoid bone.

Appendicular Skeleton

Pelvic Girdle: a complete ring composed of 3 bones: 2 hip bones ( ossa coxae) and sacrum. Each hip bone is composed of by 3 bones: Ilium, Ischium, and Pubis. The ilium is the largest portion, the ischium is the inferior portion, and the pubis is the anterior portion.

Pituitary Gigantism and Dwarfism

The pituitary gland secretes growth hormone, which stimulates division of cartilage cells in the epiphyseal plate. (Make it grow rapidly). If excessive hormone is produced, the long bone grows rapidly and result in pituitary gigantism a condition in which an individual may reach 8 feet in height. If low levels of hormone are produced, the long bone fail to reach a normal length and result in pituitary dwarfism. These individuals exhibit normal body proportion but are very short in stature.

Axial Skeleton

Bones of the head and neck: Seven bones are closely associated with the skull but are not considered to be part of its structure. Auditory ossicles: Incus, Malleus, and Stapes. Three bones which transmit sound into the ear.

Inframembranous Bone

Develops directly from a sheet of connective tissue below the skin. The connective tissues are relatively undifferentiated but contain a dense network of blood vessels. Osteoblasts develop in this tissue and deposit a bony matrix around themselves. Cells that exist in the connective tissue surrounding the bone develop the periosteum. This process is responsible for forming the bones of the skull.

Long bone structure

Diaphysis- shaft containing marrow (medullary) cavity. Epiphysis- expanded head containing spongy bone. Periosteum- a sheath covering the outside of the bone, consists of fibrous tissue and bone-forming cells. Nutrient foramina- minute holes in the bone that carry blood vessels. Endosteum- a thin layer of reticular connective tissue on the internal surface of the bone. Articular cartilage- hyaline cartilage at the ends of the bone for joint cushioning.

The Skeleton

It is divided into two regions: axial and appendicular. The axial skeleton forms the central supporting axis of the body and includes the skull, vertebral column, and thoracic cage.

Endochondral Bones

Later, secondary ossification centers appear in the epiphyses. A band of cartilage called the epiphyseal plate remains between the two ossification centers. Within the epiphyseal plate cartilaginous tissue continues to develop and lengthen the bone. Once the ossification centers of the disphysis and epiphyses meet eachother the epiphyseal plate ossifies and growth stops. `

Appendicular Skeleton

Lower limb: Divided into four regions: femoral region: thigh, extends from hip to knee, contains only the femur. Crural region: leg proper, extends from knee to ankle, contains the tibia, and fibula. Tarsal region: ankle, strictly a joint, no bones contained within. Pedal region: foot, contains 7 tarsal bones, 5 metatarsal bones, and 14 phalanges.

Bone Development

Parts of the skeletal system begin to form during the first few weeks of prenatal development. Bones continue to develop into adulthood( fully mature by 25 years of age). Bone is formed by two processes: Intramembranous ossification-inside of a membrane bone formation. Endochondral ossification- inside of the cartilage bone formation.

Appendicular Skeleton

Pelvic Girdle: Supports the arm and links it to the axial skeleton. Consists of the clavicle( collar bone) and scapula (shoulder blade).

General features of the bone

Recall that bone consists of an outer layer called compact bone usually enclosing a more loosely organized osseous tissue called spongy bone.

Skeleton

The average number of bones in a human skeleton is 206. At birth there are about 270 bones, but many fuses to create a single structure.

Bone Composition

The majority of bone contains central canals, canaliculi, and lacunae. Bone is highly vascularized and innervated.

The Skeleton

The skeletal system consists of bones, cartilages, and ligaments tightly joined to form a strong, flexible, framework for the body.

Bone cells

There are technically 4 types of bone cells. You are responsible for knowing these two and their functions: osteoblasts- bone-forming cells. osteoclasts- bone-dissolving cells found on bone surfaces.

Endochondral Bones

They are proceded by a model of hyaline cartilage in roughly the same shape of the bone. Cartilage is replaced by osseous tissue as the individual matures. Most of the bones of the skeleton are enchondral bones. (The skeleton starts out as cartilage. Cartilage is easier to build with we can expand it and build on it).

Axial Skeleton

Thoracic Cage: Encloses the heart and lungs in a flexible protective cage. Consists of the 12 thoracic vertebra, sternum, and ribs. There are 12 pairs of ribs (no difference between the sexes). Each attaches at its posterior end with a thoracic vertebra. There are 3 types of rib depending upon the anterior attachment: true ribs: 1-7 has own costal cartilage connecting it to the sternum.( 14) False ribs: 8-10 share costal cartilage of rib 7. False floating ribs: 11-12, do not attach to costal cartilage. there are 24 ribs all together.

Appendicular Skeleton

Upper limb: Divided into four segments: Brachium: arm proper from shoulder to elbow. Antebrachium: forearm, front elblow to wrist, contains the radius and ulna. Carpus: wrist, contains 8 carpal bones. Manus: hand, contains 5 metacarpals and 14 phalanges.

Axial Skeleton

Vertebral column: Supports the skull and trunk, allows for movement, protects the spinal cord. Consists of a chain if 33 vertebra with intervertebral discs. Vertebrae are divided into 5 groups: cervical, thoracic, and lumbar. (breakfast, lunch and dinner).

Rickets

Vitamin D is necessary for proper absorption of calcium in the small intestine. Without this vitamin, low levels of calcium in the blood results. In turn, the bone matrix lacks calcium and is considerably 'softer'. As a result, the bone deforms under the weight of the developing child. In children the condition is known as rickets. Note: Sunlight is very necessary for our body to produce Vitamin D, and very food serve as a source of the vitamin.