Section 32.2 The Skeletal System

A. Structure of the Skeletal System How many bones are in an adult? 206 Babies are born with more bones. How is this possible? The human skeleton consists of 2 divisions: Axial skeleton  includes the skull, vertebral column, ribs and sternum Appendicular skeleton  includes the bones of the shoulders, arms, hands, hips, legs, and feet

Axial Skeleton Appendicular Skeleton

Compact and Spongy Bone Bone is a connective tissue with many shapes and sizes Bone is classified as long, short, flat, and irregular (all have the same basic structure, with a few slight differences) Long  arm and leg Short  wrist Flat  skull Irregular  facial and vertebrae

Compact bone The outer layers of all bone It is dense and strong It provides strength and protection Osteons: run the length of the compact bone and contain blood vessels and nerves the blood vessels supply oxygen to the bone cells (Osteocytes)

Spongy Bone It is less dense and has many cavities that contain bone marrow It is found in the center of short and flat bones and at the end of long bones It is surrounded by compact bone

Bone Marrow Red Bone Marrow: Produces red and white blood cells and platelets It is found in the humerus bone of the arm, the femur bone of the leg, the sternum and the ribs, the vertebrae, and the pelvis What is also located in each one of these areas? The cavities of infant’s bones are composed of red bone marrow Childrens’ bones have more marrow than adults’ bones

Yellow Bone Marrow It is found in many other bones Consists of stored fat

Formation of Bones Osteoblasts Bone forming cells As an infant, the development of osteoblasts turns cartilage into bones The formation of bone from osteoblasts is called ossification They are also responsible for the growth and repair of bones

Remodeling of Bone Bone is constantly being remodeled Old cells are being replaced by new cells Osteoclasts  cells that break down bone cells Bone growth involves several factors Nutrition Exercise Calcium intake osteoporosis

Repair of Bone Simple Fracture When a bone breaks, but does not come through the skin Compound Fracture A broken bone that protrudes through the skin Stress Fracture A thin crack in the bone

What happens when you break a bone? Fracture: When injured, endorphins (natural pain killers) are released and flood the injured area Reduces the pain temporarily The injured area becomes inflamed and swollen Within 8 hours a blood clot forms between the broken ends of the bone and new bone begins to form The blood clot becomes a callus

Callus Formation: After about 3 weeks, osteoblasts form a callus made of spongy bone Osteoclasts then remove the spongy bone, while osteoblasts produce stronger, compact bone The broken bone must remain in place by a cast Why do you think this is?

Remodeling: Bones require different amounts of time to heal Age, nutrition, location, and severity of the break all play a part in the healing process A lack of calcium will slow bone repair Younger bones will heal more quickly

B. Joints Ball and Socket The ball-like surface of one bone fits into a cup-like depression in another bone This allows for the widest range of motion of any kind of joint Examples: hips and shoulders

Pivot The primary movement is rotation This type of joint allows the lower arm to twist Examples: elbow joint (where the ulna and the radius come together)

Hinge The convex surface of one bone fits into the concave surface of another bone This allows for the back and forth movement like a door hinge Examples: elbows and knees

Gliding This type of joint allows for a side-to-side and back-and-forth movement Examples: joints in the wrist and ankles, and joints in the vertebrae

Suture The joints in the skull that are not moveable There are 22 bones in the adult skull and all are joined by suture joints except for the lower jaw bone (mandible)

C. Functions of the Skeletal System Support The legs, pelvis, and vertebral column hold up the body The mandible supports the teeth Almost all bones support the muscles

Protection The skull protects the brain The vertebral column protects the spinal cord The rib cage protects the heart, lungs, and other organs

Formation of Blood Cells Red bone marrow produces red blood cells, white blood cells, and platelets Reservoir The skeletal system is a storage system for calcium and phosphorus Movement Muscles that are attached to bones pull on the arms and legs The diaphragm allows for normal breathing patterns