Skeletal system

introduction Bone consists of a variety of very active, living tissues: Bone tissue cartilage Dense connective tissue Blood Nervous tissues

Physiology of bone: Provide point attachment for muscles Protect and support softer tissues House blood-producing cells Store inorganic salts Form passageways for blood vessels and nerves

Bone classification Bones are classified according to their shapes: Short Flat Irregular Sesamoid (round) Long

Short bone Short bones are somewhat cube like, with their lengths and widths roughly equal Bones of the wrists and ankles

Flat bones Flat bones are plate like structures with broad surfaces Ribs Scapulae Some bones of the skull

Irregular bones Irregular bones have a variety of shapes and are usually connected to several other bones. Vertebrae Many facial bones

Sesamoid (round) bones Small and nodular and are embedded within tendons adjacent to joints Patella (kneecap)

Long bones Long bones have long longitudinal axes and expanded ends Examples of long bones: Forearm thigh

Epiphysis of a long bone At each end of a long bone is an expanded portion called an epiphysis. The epiphysis articulates (forms a joint) with another bone. The proximal epiphysis is nearest to the center of the body. The distal epiphysis is farthest from the center of the body. The shaft of the bone between the epiphysis, is called the diaphysis

Articular cartilage of a long bone The outer surface of the articulating portion of the epiphysis is coated with a layer of hyaline cartilage called articular cartilage.

periosteum Except for the articular cartilage on the bone’s ends, the long bone is completely enclosed by a tough, vascular covering of fibrous tissue called the periosteum

Periosteum continued The periosteum is firmly attached to the bone The periosteal fibers are continuous with the connecting ligaments and tendons The periosteum helps form and repair bone tissue

Shape determines function A bone’s shape makes its functions possible Processes are bony projections that provide sites where ligaments and tendons attach Grooves and openings form passageways for blood vessels and nerves Depression of one bone may articulate with a process of another.

Compact bone The wall of the diaphysis is mainly composed of tightly packed tissue called compact bone or cortical bone. This type of bone has a continuous extracellular matrix with no spaces.

Spongy bone The epiphysis are composed of spongy (cancellous) bone. Spongy bone consists of numerous branching bony plates. Irregular connecting spaces between these plates help reduce the bone’s weight. The bony plates are most highly developed in the regions of the epiphysis that are subjected to compressive forces.

Medullary cavity Compact bone in the diaphysis of a long bone forms a semi rigid tube, which has a hollow chamber called the medullary cavity that is continuous with the spaces of the spongy bone

Endosteum cells The endosteum is a thin membrane which consists of connective tissue and lines the medullary cavities. It is highly vascular and contains osteoclasts and osteoblasts.

Yellow marrow A specialized type of soft connective tissue that fills the medullary cavity Yellow marrow stores fat which the body consumes as a last resort in cases of extreme starvation. It also turns into red marrow in emergencies such as blood loss or anemia