The Skeletal System

The Skeletal System

Introduction… The entire framework of bones (206) and their cartilage make up the skeletal system. The study of bone structure and the treatment of bone disorders is osteology.

The skeletal system has 6 functions… Support Protection Assisting in movement Mineral homeostasis Production of blood cells Triglyceride storage

What is bone ?? Bone is a living, growing tissue made mostly of collagen. Collagen is a protein that provides a soft framework, and calcium phosphate is a mineral that adds strength and hardens the framework. This combination of collagen and calcium makes bone strong and flexible enough to withstand stress. 99 percent of the body’s calcium is contained in the bones and teeth.

There are 4 bone types: Long bones: Irregular bones: ~ Longer in length than width. ~ Curved for strength. ~ Include the femur (thigh), arm (humerus). Irregular bones: ~ Have complex shapes and cannot be grouped into another category. ~ Includes the vertebrae.

3. Short bones: 4. Flat bones: ~ Cubed in shape. ~ Nearly equal in width and length. ~ Includes wrists and ankle bones. ~ Thin. ~ Provides considerable protection. ~ Provide surfaces for muscle attachment. ~ Includes the cranium and sternum.

4 Bone Types

Macroscopic Bone Structure A typical bone has 3 parts: Diaphysis Epiphyses (2) Metaphyses (2) Articular cartilage Periosteum Medullary cavity Endosteum

Microscopic Bone Structure 3 Major Cell Types: Osteoblasts: Bone building cells, synthesize and secrete collagen fibers to build matrix of bone. Osteocytes: Mature bone cells, that maintain the bone’s daily metabolism Osteoclasts: Large cells formed from WBC, concentrated in the endosteum.

Bone Marrow: Red Marrow: Yellow Marrow: Red bone marrow produces new red cells. When red marrow is depleted, yellow marrow produces red cells. Yellow Marrow: Bone marrow containing mostly fat cells (for lipid storage) is called yellow marrow.

Compact and Spongy Bone

Compact (cortical) bone. 2 Types of bone: Compact (cortical) bone. Dense & compact. Forms the outer layer of bone. Spongy (trabecular) bone. Makes up the inner layer of bone. Has a spongy, honeycomb-like structure.

Compact Bone (Dense Bone): Contains few spaces. Forms the exterior layer of all bones. Makes up bulk of diaphyses of long bones. Provides protection & support. Resists stresses of weight & movement.

Spongy Bone (Cancellous): Made up of trabeculae and osteocytes. Does not contain osteons. Forms most of epiphyses in long bones. Makes up most of the bone in the flat, short and irregularly shaped bones. Lightweight, moves more readily. Trabeculae supports and protects red bone marrow.

Ossification: Bone Formation Infants and young children do not have bones like those of adults. Their bones are made mostly of cartilage, a firm, elastic, fibrous material. As an individual gradually grows and matures, the cartilage is replaced by bone cells. These bone cells deposit crystals of calcium carbonate and calcium phosphate, a process called ossification. By the mid-twenties, ossification is complete and bone growth is complete. Some cartilage remains flexible for our lifetime and serves as pads at the ends of bones where one meets the other. The pads serve as shock absorbers during motion.

Bone Development in Infants: Many bones in a newborn are composed almost entirely of CARTILAGE. The Cells that make up Cartilage are scattered in a Network of Fibers composed of an ELASTIC PROTEIN called COLLAGEN. The cartilage is eventually replaced during OSSIFICATION, or the process of bone formation.

Bone development begins about 6 wks. Long bone development Bone development begins about 6 wks.

The bones of the human body. ( There are 206 bones in the human body)