Consists of: Bones Joints Cartilage Ligaments The skeletal system consists of 206 bones.
The Skeletal System Functions: Bones of the lower extremities support the weight of the body. Support and protect the soft body organs. Enables the body to move about. Store a number of minerals, calcium and phosphorus are most important. Red bone marrow produces blood cells.
Classification of Bones Bones are classified as follows: Long bones-longer than they are wide. Found in the arms and legs.
Classification of Bones Short Bones-shaped like cubes and are found primarily in the wrists and ankles.
Classification of Bones Flat Bones-thin, flat, curved. Form the ribs, breastbone and skull.
Classification of Bones Irregular Bones-differently shaped, not classified as long, short, or flat. Include hip bones, vertebrae, and various bones in the skull.
Tissue and Bone Formation Osseous tissue-another word for bone. Osteocytes-bone cells. - secrete an intercellular matrix. -contain calcium, minerals and protein fibers.
Compact Bone- Dense hard bone. Found in shafts of long bones and outer surfaces of other bones. Two Types of Bone
Spongy Bone- Also called cancellous bone. Less dense Found at the ends of long bones and in the center of other bones.
Compact Bone Microscopically-compact bone and spongy bone look different. Compact bone is tightly packed, density gives it strength. Osteon or haversion system-microscopic unit of compact bone. Each haversion system consists of mature osteocytes arranged in concentric circles around large blood vessels.
Compact Bone Area surrounding the osteocytes is filled with protein fibers, calcium and other minerals. Protein fibers provide elasticity. Minerals make bone tissue hard and strong. Compact bone consists of many haversian systems running parallel to each other, system looks like a long cylinder. Blood vessels run laterally to the haversian system, this ensures adequate blood supply to the bone tissue.
Spongy Bone Also called cancellous bone. Does not have a haversian canal. Bone tissue is arranged in plates called trabeculae. Bony plates are separated by holes that give it a punched- out “swiss cheese” appearance. Holes are important for: (1)decrease the weight of bone, make it lighter, and (2)contain red bone marrow.
Spongy Bone Red bone marrow richly supplies the spongy bone with blood cells for use throughout the body. Spongy bone is located in short, flat, and irregular bones. Spongy bone is found in the ends of long bones.
Long Bone Made up of an arrangement of compact and spongy tissue, which accounts for its strength. Contains sites of growth and reshaping and structures associated with joints.
Long Bone Parts of a long bone: Diaphysis-long shaft of the bone, composed primarily of compact bone, therefore it provides strength. Epiphysis-enlarged ends of the long bone. Articulates or meets with a second bone at a joint. Consists of a thin layer of compact bone overlying spongy bone. Epiphysis are covered with cartilage.
Long Bone Epiphyseal disc-band of hyaline cartilage located at each end, between the epiphysis and the diaphysis in a growing bone. This band of cartilage is the epiphyseal disc or growth plate. Medullary cavity-hollow center of the diaphysis. The inside is lined with connective tissue called the endosteum.
Long bone Periosteum-tough, fibrous connective tissue membrane that covers the outside of the diaphysis. Anchored firmly to the outside of bone on all surfaces except articular cartilage. Periosteum protects bone, serves as a point of attachment for muscle, contains blood vessels that nourish underlying bone.
Long Bone Injury to the periosteum may have serious consequences to the health of the bone since this structure carries the blood supply. Articular Cartilage-found on the outer surface of the epiphysis, forms a smooth shiny surface that decreases friction within a joint.
Ossification Ossification-the formation of bone. Occurs differently in flat and long bones. In the fetus, flat bones in the skull consist of thin connective tissue membrane. Ossification begins when the osteoblasts (bone forming cells), migrate to the region of the flat bones. The osteoblasts secrete calcium and other minerals into the spaces between the membranes, thereby forming bone. This process involves the replacement of thin membrane with bone.
Ossification of Long Bones Ossification of long bones occurs as bone tissue replaces cartilage. The fetal skeleton is composed largely of cartilage. As the baby matures, osteoblasts invade the cartilage and gradually replace it with bone until all but the articular cartilage and the epiphyseal disc have been replaced by bone. Isolated pieces of cartilage, such as the bridge of the nose and parts of the ribs remain.
Growing Bones Two types of bone growth occurs from infancy to adulthood. (1)Longitudinally-determines the height of an individual. (2)Thicker & wider-to support the weight of the adult. Longitudinally-bone grows at the epiphyseal disc, (also called the growth plate). Cartilage adjacent to the epiphysis continues to multiply and grow toward the diaphysis. Cartilage next to the diaphysis is invaded by osteoblasts and become ossified. As long as the cartilage continues to form within the epiphyseal disc, the bone will continue to lengthen.
Growing Bones Longitudinal bone growth ceases when the epiphyseal disc becomes ossified and fused. Growth hormone stimulates growth at the epiphyseal disc, making the child taller. The sex hormones estrogen and testosterone cause the epiphyseal disc to fuse, inhibiting further longitudinal growth. The epiphyseal disc is more sensitive to estrogen, this causes girls to tend to be shorter than boys.
Growing Bones Longitudinal growth generally ceases after puberty. Injury to the epiphyseal disc may impair longitudinal bone growth. Eg. Injured leg shorter than uninjured leg. Giantism- hypersecretion of growth hormone. Dwarfism- undersecretion of growth hormone.
Growing Thicker and Wider After longitudinal bone growth ceases, bones continue to increase in thickness and width. Bones are continuously being reshaped. Bone reshaping is accomplished by a combination of the actions of osteoblasts and osteoclasts. Osteoblasts- bone forming cells. Osteoclasts- bone destroying cells.
Growing Bones Osteoblastic Activity: While osteoblasts build new bone, osteoclasts, found on the inner bone surface break down bone tissue, thereby hollowing out the interior of the bone. Osteoclastic Activity is like sculpting, the bricklayer lays the bricks and the sculptor will hollow out the middle so that it is not too heavy. Bone resorption-(not reabsorption)-process whereby osteoclasts breakdown bone matrix.
Growing Bones Bone resorption- widens the bone, moves calcium from the bone to the blood. Bone resorption plays a crucial role in blood calcium levels. Weight-bearing – factor that stimulates bone growth. Exercise and weight bearing keep calcium in the bone and increase bone mass. Bedridden and sedentary people tend to lose bone mass causing bones to be easily broken when stressed.
Surface Markings Surface of bones appears bumpy and irregular. Appearance is due to numerous ridges, projections, depressions, and grooves called bone surface markings. These bone surface markings serve as points of attachment for muscles, tendons and ligaments.
Condyle Condyle- large rounded knob that usually articulates with another bone.
Epicondyle Epicondyle- an enlargement near or above a condyle.
Bone Markings Head- an enlarged and rounded end of a bone.
Bone Markings Facet- a small flattened surface.
Bone Markings Meatus-a tunnel or tubelike passageway.
Bone Markings Sinus-a cavity or hollow space.
Fractures Fractures- break in the bone. Simple Fracture- a break in which the overlying skin remains intact. Local tissue damage is minimal. Compound Fracture- a broken bone that also pierced the skin. Ends of the broken bone usually cause extensive tissue damage. Incomplete Fracture- (greenstick)-usually occurs in children, the break is incomplete because the child’s bone is still made up of some cartilaginous material.