Chapter 2 Skeletal system

Anatomy and physiology Skeletal system composed of 206 separate bones. Bone is a type of connective tissue its matrix consists of calcium phosphate. Periosteum: fibrous membrane that encloses all of the bone except the joint surface and is crucial in supplying blood to the underlying bone

Tissue types Epithelial tissue: covers the body surface and forms the lining for most internal cavities.  The major function of epithelial tissue includes protection, secretion, absorption, and filtration.  The skin is an organ made up of epithelial tissue which protects the body from dirt, dust, bacteria and other microbes that may be harmful. Connective tissue is the most abundant and the most widely distributed of the tissues.  Connective tissues perform a variety of functions including support and protection.  The following tissues are found in the human body, ordinary loose connective tissue, fat tissue, dense fibrous tissue, cartilage, bone, blood, and lymph, which are all considered connective tissue.    

Tissue types cont. There are three types of muscle tissue: skeletal, smooth, and cardiac.  Skeletal muscle is a voluntary type of muscle tissue that is used in the contraction of skeletal parts.  Smooth muscle is found in the walls of internal organs and blood vessels.  It is an involuntary type.  The cardiac muscle is found only in the walls of the heart and is involuntary in nature.  Nerve tissue is composed of specialized cells which not only receive stimuli but also conduct impulses to and from all parts of the body. 

Anatomy of Bone periosteum cancellous

Osteoblasts Are bone forming cells that line the medullary canal and are Interspersed throughout the periosteum. They are responsible for bone growth and thicknening.

Osteoclasts Is a type of bone cells that removes (old) bone tissue by breaking down bone and releasing minerals resulting in transferring calcium from bone fluid to the blood (bone resorption) its function is maintenance and repair. Osteoclasts and osteoblasts are instrumental in controlling the amount of bone tissue. Osteoblasts form bone, osteoclasts resorb bone.

Epiphysis Metaphysis Diaphysis The bones of the skeletal system may also classified according to their shape Epiphysis Metaphysis Growth zone bet. Epi.&Dia. Diaphysis

Bone Radiography Plain Films: • Good for fracture, dislocation, tumors. Bone Scan: • Allows screening entire skeleton. • Good for metastatic disease. • Helps answer whether osteomyelitis. CT: • Allows cortical disruption, soft tissue extension to be assessed. MR: • Good for assessing marrow involvement. • Good for soft tissues around joint (collateral ligaments, menisci in knee)

Normal Bone Appearance

The radiographic image of the bone is due to its calcium content. Pathological lesions will be visible when there are: • Change in structure continuity (as in fractures). • Change in position (as in dislocations). • Change in shape (as in congenital development defects). • Lessening of density (reduced radio-opacity). • Localized demineralization with disappearance of the trabeculae (bone erosion). • Increased density from a high calcium content (bone sclerosis). • New bone formation.

Metabolic bone disease Generalized reduction of bone density The main causes of generalized reduction in bone density are: Osteoporosis. Osteomalacia and rickets. Hyperparathyroidism. Gout Paget disease

Osteoporosis-disease characterized by low bone mass & structural deterioration of bone tissue normal bone osteoporotic bone

Bone is a living, constantly changing tissue, and normally a balance exists between the amount of old bone being removed (an osteoclastic process) and the amount of new bone replacement (an osteoblastic process). Osteoporosis is usually caused by accelerated resorption of bone. Causes: Endocrine disorders. Drug induced osteoporosis (prolonged steroid administration). Dietary deficiencies (especially in proteins). Post menopausal osteoporosis.

Radiographic appearance Loss of mineral salts causes osteoporotic bone to become more lucent than normal. This may be difficult to detect, because about 50% to 70% of the bone density must be lost before. So it is essential to use lowest practical kVp.

Osteomalacia لين العظام and rickets الكساح In histology, osteoid is the unmineralized, organic portion of the bone matrix that forms prior to the maturation of bone tissue. Osteoblasts begin the process of forming bone tissue by secreting the osteoid as several specific proteins. When the osteoid becomes mineralized, it and the adjacent bone cells have developed into new bone tissue. When there is insufficient nutrient minerals or osteoblast dysfunction, the osteoid does not mineralize properly, and it accumulates. The resultant disorder is termed rickets in children and osteomalacia in adults.

Causes: Normal Abnormal Dietary deficiencies of vitamin D, or lack of exposure to sunlight. Malabsorption causing impaired absorption of vitamin D and calcium from the gut.

Hyperparathyroidism Excess parathyroid hormone secretion mobilizes calcium from the bones resulting in decrease in bone density. Causes: Hyperparathyroidism may be: • Primary, from hyperplasia or tumor of the parathyroid glands. • Secondary to chronic renal failure.

• A generalized loss of bone density, with loss of different The signs of hyperparathyroidism • A generalized loss of bone density, with loss of different ion between cortex and medulla. • Bone resorption (Fig.3a) • Brown tumors (Fig.3b) • Vascular calcification(Fig.4) • Soft tissue calcification(Fig.5) (Fig 3 a) (Fig 3 b) (Fig 4) (Fig 5)