Skeletal System

• The skeletal system is usually thought of as the framework of the body, but the skeletal system has many other functions
• Functions of the Skeletal System

  • Organ Protection and Body Support
  • Body Movement
  • Mineral Storage
  • Blood Cell Production
• The average adult has 206 bones However, the actual number of bones varies between people and decreases with age as bones become fused.
• Bones are divided into two:

  • Axial
  • Appendicular
• Axial Skeleton

  • Consists of the bones of the head and the trunk; forms the upright axis of the body.
  • It protects the brain, the spinal cord, and the vital organs housed within the thorax.
• Bones in the Head:

  • Cranium
  • Mandible
• Vertebral Column

  • Has five major functions: It supports the weight of the head and trunk, (2) it protects the spinal cord, (3) it allows spinal nerves to exit the spinal cord, (4) it provides a site for muscle attachment, and (5) it permits movement of the head and trunk.
• The vertebral column usually consists of 26 bones, called vertebrae, which can be divided into five regions: cervical vertebrae, thoracic vertebrae, lumbar vertebrae, sacral bone, and coccygeal bone.
• Rib Cage and Sternum

  • AKA Thoracic Cage
  • protects the heart and lungs within the thorax and forms a semirigid chamber, which can increase and decrease in volume during respiration.
• True Ribs

  • Superior 7 pairs of ribs
  • they articulate with the thoracic vertebrae and attach directly through their costal cartilages to the sternum.
• False Ribs

  • Inferior 5 pairs
  • articulate with the thoracic vertebrae but do not attach directly to the sternum.
• Floating Ribs

  • 11th and 12th ribs
  • Are not attached to the sternum
• Costal Cartilages

  • flexible and permit the rib cage to expand during respiration.
• Pelvic Girdle

  • The right and left hipbones (coxal bones) join each other anteriorly and the sacrum posteriorly to form a ring of bone called the...
  • Each hipbone is formed by the fusion of the ilium, the ischium, and the pubis.
• Upper Limb

  • Femur - only bone contained by the thigh.
  • Patella - a large sesamoid bone located within the tendon of the quadriceps femoris muscle
  • Tibia and Fibula - part of the lower limb between the knee and the ankle
  • Foot - composed of seven tarsal bones then five metatarsal bones. The toes have three phalanges each, except for the big toe, which has two.
• Long Bones

  • are longer than they are wide;
  • e.g., bones of the upper and lower limbs are long bones
• Flat Bones

  • have a relatively thin, flattened shape; usually curved;
  • e.g., skull bones, the ribs, the breastbone and the shoulder blades
• Short Bones

  • are round or nearly cube-shaped;
  • e.g., bones of the wrist and ankle
• Irregular Bones

  • are shapes that do not readily fit into the other three categories;
  • e.g; vertebrae and facial bones
• Bones in the Trunk:

  • Sternum
  • Ribs
  • Vertebral Column
  • Sacrum
  • Coccyx
• Cranium

  • protects the brain and houses our eyes, ears, nose, and mouth. Special effort is needed to separate the other bones.
• Mandible

  • is inferior to the maxilla and attaches posteriorly to the temporal bone.
• Appendicular Skeleton

  • Consists of the bones of the upper limbs, the lower limbs, and the girdles
• Girdle

  • a belt or a zone, refers to the two zones, pectoral and pelvic, where the limbs are attached to the body
• Pectoral Girdle

  • consists of scapula (shoulder blade) and a clavicle (collarbone)
• Scapula

  • a flat, triangular bone
• Clavicle

  • is a long bone with a slight sigmoid (S-shaped) curve.
• Upper Limb Bones

  • Arm - Humerus
  • Forearm
  • Ulna - medial side (little finger)
  • Radius - lateral or thumb side
  • Wrist - Eight carpals
  • Hand - Five metacarpals with phalanges
• Osteogenic Cells

  • are undifferentiated and develop into osteoblasts.
• Osteoblasts

  • get trapped within the calcified matrix, their structure and function changes; they become osteocytes.
• Osteoclasts

  • develop from monocytes and macrophages and used in breaking down bone.
• Ossification (Osteogenesis)

  • is the process of bone formation by osteoblasts.
• Two Patterns formed by Bones

  • Intramembranous Ossification
  • Endochondral Ossification
• Intramembranous Ossification

  • bone forms from preexisting connective tissue membranes
  • process of bone development from fibrous membranes (sheets of mesenchymal connective tissue)
  • involved in the formation of the flat bones of the skull, the mandible, and the clavicles
• Endochondral Ossification

  • bone forms from a preexisting cartilage model
  • process of bone development from hyaline cartilage; the cartilage serves as a template to be completely replaced by new bone.
  • All of the bones of the body, except for the flat bones of the skull, mandible, and clavicles, are formed
• Bone Remodeling

  • is the replacement of old bone tissue by new bone tissue. It involves the processes of bone deposition by osteoblasts and bone resorption by osteoclasts.