Skeletal System Functions

Skeletal System

Functions of Bone

• Provides the framework for the attachment of other organs
• Stores minerals (e.g., calcium ions, 98% of the body's calcium ions)
• Produces blood cells (erythrocytes, leukocytes, and platelets)
• Acts as a leverage system for muscle movement
• Protects internal organs (e.g., heart, lungs, brain, spinal cord, and reproductive organs)

Components of the Skeletal System

• Bones (skeleton)
• Joints
• Cartilages
• Ligaments (connect bones to bones)
• Tendons (connect bones to muscles)

Classification of Bones

According to Location

• Axial Skeleton (long axis of the body, 80 bones, 3 major regions: skull, vertebral column, and bony thorax)
• Appendicular Skeleton (bones of upper and lower extremities and girdles, 126 bones, 3 major regions: girdles, upper extremity, and lower extremity)

According to Shape

• Long Bones (e.g., femur, tibia, fibula, humerus, ulna, and radius)
• Short Bones (e.g., carpals, tarsals, and metacarpals)
• Flat Bones (e.g., sternum, ribs, and scapula)
• Irregular Bones (e.g., vertebrae, pelvis, and bones of the face)
• Sesamoid Bones (e.g., patella)

Long Bones

• Typically longer than wide
• Have a shaft with heads at both ends
• Contain mostly compact bone tissue
• Examples: femur, tibia, fibula, humerus, ulna, and radius

Structure of Long Bones

• Diaphysis (shaft)
• Epiphysis (ends of the bone)
• Periosteum (outside covering of the diaphysis)
• Sharpey's fibers (secure periosteum to underlying bone)
• Arteries (supply bone cells with nutrients)
• Articular cartilage (covers the external surface of the epiphysis)
• Medullary cavity (cavity of the shaft, contains yellow marrow or red marrow)

Cells Present in Bone

• Osteogenic cells
• Osteoblasts
• Osteocytes
• Osteoclasts

Changes in the Human Skeleton

• In embryos, the skeleton is primarily hyaline cartilage
• During development, much of this cartilage is replaced by bone
• Cartilage remains in isolated areas (e.g., bridge of the nose, parts of ribs, and joints)

Skull

• Bony skeleton of the head
• Most complex bony structure in the body
• Begins to close one to two months after birth, but closure is not generally complete until the age of one year

Facial Bones

• Provide the basic shape of the face
• All are paired except vomer and mandible
• Consist of about 14 bones
• Examples: mandible, maxilla, zygomatic bones, nasal bones, and lacrimal bones

Bones of the Thoracic Wall

• Includes: 12 pairs of ribs and costal cartilages, 12 thoracic vertebrae, and sternum

Appendicular Skeleton

• Superior appendicular skeleton (pectoral girdle and bones of the free part of the upper limb)
• Pectoral girdle (consists of two bones: clavicle and scapula)
• Scapula (shoulder blade)
• Clavicle (collar bone)
• Humerus (arm bone)
• Radius and ulna (forearm bones)
• Carpals (wrist bones)
• Metacarpals (hand bones)
• Phalanges (finger bones)

Bones of the Lower Limb

• Pelvic girdle (hip bone)
• Femur (thigh bone)
• Patella (knee cap)
• Tibia and fibula (leg bones)
• Tarsals (ankle bones)
• Metatarsals (foot bones)
• Phalanges (toe bones)