1. Bone as an organ. Types of bones – description, structure - compact and spongy bone tissue. Perios-teum – structure. The skeleton - definition, function.

BONES

• Bone is calcified, living, Connective tissue that forms the majority of skeleton.

Composition:

• It consists of an intercellular calcified matrix, which also contains collagen fibers, & several types of cells.

Cell types:

1. Osteoblasts → produce bone matrix
2. Osteoclasts → Responsible for bone resorption & remodeling
3. Osteocytes → Mature bone cells, embedded within the bone matrix.

Functions:

• supportive structures for the body,
• protectors of vital organs,
• reservoirs of calcium and phosphorus,
• levers on which muscles act to produce movement, and
• containers for blood-producing cells.

Types:

• According to the structure:

1. Compact bone - form the outer shell of all bones & surrounds spongy bones.
2. Spongy bone - consists of spicules of bone enclosing the marrow.

• by shape:

1. Long bones are tubular (e.g., humerus in upper limb; femur in lower limb).
2. Short bones are cuboidal (e.g., bones of the wrist and ankle).
3. Flat bones consist of two compact bone plates separated by spongy bone (e.g., skull).
4. Irregular bones are bones with various shapes (e.g., bones of the face).
5. Sesamoid bones are round or oval bones that develop in tendons.