SKELETAL SYSTEM

OVERVIEW Functions Classification of bones Bone structure Microscopic structure of bone Formation of bone Joints

Functions of bone Bones and cartilage together forms the skeletal system performing several functions. Functions: 1.Support The bones of the legs, pelvic girdle, and vertebral column support the weight of the erect body. The mandible (jawbone) supports the teeth. Other bones support various organs and tissues.

Functions of bone 2.Protection The bones of the skull protect the brain. Ribs and sternum (breastbone) protect the lungs and heart. Vertebrae protect the spinal cord. 3. Movement Skeletal muscles use the bones as levers to move the body.

Functions of bone 4. Reservoir for minerals and adipose tissue 99% of the body’s calcium is stored in bone. 85% of the body’s phosphorous is stored in bone. Adipose tissue is found in the marrow of certain bones. 4.Hematopoiesis All blood cells are made in the marrow of certain bones.

Classification of Bones There are 206 bones in the human body. They are divided into two large groups: I. Axial skeleton Forms long axis of the body. Includes the bones of the skull, vertebral column, and rib cage. Involved in protection, support, and carrying other body parts.

II. Appendicular skeleton Bones of upper & lower limbs and the girdles (shoulder bones and hip bones) that attach them to the axial skeleton. Involved in locomotion and manipulation of the environment.

Classification of Bones

Classification of Bones Four types of bones based on shapes: 1. Long Bones Much longer than they are wide. All bones of the limbs except for the patella (kneecap), and the bones of the wrist and ankle. 2. Short Bones Roughly cube shaped. Bones of the wrist and the ankle

Classification of Bones Types of bones: Flat Bones Thin, flattened, and usually a bit curved. Scapulae, sternum, (shoulder blades), ribs and most bones of the skull. Irregular Bones Have weird shapes that fit none of the three previous classes. Vertebrae and hip bones.

Structure of Bone Bones are organs and are composed of multiple tissue types. Bone tissue (osseous tissue). Fibrous connective tissue. Cartilage. Vascular tissue. Lymphatic tissue. Adipose tissue. Nervous tissue.

Bone Structure Externally bone is covered by a thin layer of dense connective tissue known as Periosteum. It is a double-layered membrane Covers entire external surface of bone except for joints. Outer fibrous layer is dense irregular connective tissue containing fibroblast. Inner cellular layer contains osteoprogenitor cells and osteoblasts. Below compact bone lies more porous and light weight bone-spongy or cancellous bone.

Bone structure It is a thin layer found just inside the compact bone. The centre of the bone shaft is hollow-Medullary Cavity. This contains both red and yellow bone marrow

The centre of the bone shaft is hollow-Medullary Cavity. This contains both red and yellow bone marrow

Endosteum Delicate connective tissue membrane covering internal surfaces of bone Covers the trabeculae of spongy bone in the marrow cavities and lines the canals that pass through compact bone. Contains both osteoblasts and osteoclasts.

Structure of Bone

Bone cells Bone consist of cells and extracellular matrix. A. Bone cells Osteoblasts Bone-building cells. Synthesize and secrete collagen fibers and other organic components of bone matrix. Initiate the process of calcification. Found in both the periosteum and the endosteum

Bone cells 2. Osteocytes Mature bone cells. Osteoblasts that have become trapped by the secretion of matrix. No longer secrete matrix. Responsible for maintaining the bone tissue.

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3. Osteoprogenitor Cells Mesenchyme stem cells that divide to produce osteoblasts Are located in inner, cellular layer of periosteum Assist in fracture repair

4. Osteoclasts Giant, mutlinucleate cells Secrete acids and protein-digesting enzymes Dissolve bone matrix and release stored minerals Concentrated in the endosteum. Are derived from stem cells that produce macrophages

Bone Matrix Consists of organic and inorganic components. Consists of several materials that are secreted by the osteoblasts. Mainly consist of collagen fibers and other organic materials . These (particularly the collagen) provide the bone with resilience and the ability to resist stretching and twisting.

Inorganic component Consists mainly of two salts: calcium phosphate and calcium hydroxide that interact to form a compound called hydroxyapatite. Bone also contains smaller amounts of magnesium, fluoride, and sodium. These minerals give bone its characteristic hardness and the ability to resist compression.

Structure of Long Bone Long bone consist of a diaphysis and an epiphysis. Diaphysis Tubular shaft that forms the axis of long bones Composed of compact bone that surrounds the medullary cavity (central marrow cavity) In adults, the marrow cavity contains fat - yellow bone marrow.

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http://www.wbais.org/~usalant/Gallery/Anatomy_physiology/Skeletal/images/long_bone_shaft.jpg

Structure of Long Bone Epiphyses Expanded ends of long bones Exterior is compact bone, and the interior is spongy bone Joint surface is covered with articular (hyaline) cartilage that cushions the bone ends and reduces friction during movement.

Microscopic Structure of Compact Bone In cross section, compact bone is seen to consists of tightly packed multiple cylindrical structural units -osteons or haversian systems. They are arranged parallel to one another along the long axis of a compact bone.

Osteons/Haversian systems Each osteon consists of a single central canal, known as a haversian canal, surrounded by concentric layers of calcified bone matrix (lamella). Haversian canals are interconnected with one another via Volkmann's canals. Between the lamella are present concentric rings of fluid filled spaces-lacuna containing osteocytes. Tiny hair-like channels/canaliculi extend from lacuna through which osteocytes communicate and receive nutrients. Haversian canals allow the passage of blood vessels, lymphatic vessels, and nerve fibers.

Structure of Bone

Haversian canal system

Microscopic Anatomy of Bone

Compact Bone

Microscopic Structure of Bone: Compact Bone

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