The Skeletal System Parts of the skeletal system Bones (skeleton) Joints Cartilages Ligaments Two subdivisions of the skeleton Axial skeleton Appendicular skeleton

Functions of Bones Support the body Protect soft organs Allow movement due to attached skeletal muscles Store minerals and fats Blood cell formation

Bones of the Human Body The adult skeleton has 206 bones Two basic types of bone tissue Compact bone Homogeneous Spongy bone Small needle-like pieces of bone Many open spaces Figure 5.2b

Classification of Bones on the Basis of Shape Figure 5.1

Classification of Bones Long bones Typically longer than they are wide Have a shaft with heads at both ends Contain mostly compact bone Example: Femur Humerus

Classification of Bones Figure 5.1a

Classification of Bones Short bones Generally cube-shape Contain mostly spongy bone Example: Carpals Tarsals

Classification of Bones Figure 5.1b

Classification of Bones Flat bones Thin, flattened, and usually curved Two thin layers of compact bone surround a layer of spongy bone Example: Skull Ribs Sternum

Classification of Bones Figure 5.1c

Classification of Bones Irregular bones Irregular shape Do not fit into other bone classification categories Example: Vertebrae Hip bones

Classification of Bones Figure 5.1d

Anatomy of a Long Bone Diaphysis Shaft Composed of compact bone Epiphysis Ends of the bone Composed mostly of spongy bone Start Here

Anatomy of a Long Bone Figure 5.2a

Anatomy of a Long Bone Periosteum Outside covering of the diaphysis Fibrous connective tissue membrane Sharpey’s fibers Secure periosteum to underlying bone Arteries Supply bone cells with nutrients

Anatomy of a Long Bone Figure 5.2c

Anatomy of a Long Bone Articular cartilage Covers the external surface of the epiphyses Made of hyaline cartilage Decreases friction at joint surfaces

Anatomy of a Long Bone Figure 5.2a

Anatomy of a Long Bone Medullary cavity Cavity inside of the shaft Contains yellow marrow (mostly fat) in adults Contains red marrow (for blood cell formation) in infants

Anatomy of a Long Bone Figure 5.2a

Bone Markings Surface features of bones Sites of attachments for muscles, tendons, and ligaments Passages for nerves and blood vessels

Microscopic Anatomy of Bone Osteon (Haversian system) A unit of bone containing central canal and matrix rings Central (Haversian) canal Opening in the center of an osteon Carries blood vessels and nerves Perforating (Volkman’s) canal Canal perpendicular to the central canal

Microscopic Anatomy of Bone Figure 5.3a

Microscopic Anatomy of Bone Lacunae Cavities containing bone cells (osteocytes) Arranged in concentric rings Lamellae Rings around the central canal Sites of lacunae

Microscopic Anatomy of Bone Figure 5.3b–c

Microscopic Anatomy of Bone Canaliculi Tiny canals Radiate from the central canal to lacunae Form a transport system connecting all bone cells to a nutrient supply

Microscopic Anatomy of Bone Figure 5.3b

Types of Bone Cells Osteocytes—mature bone cells Osteoblasts—bone-forming cells Osteoclasts—bone-destroying cells Break down bone matrix for remodeling and release of calcium in response to parathyroid hormone Bone remodeling is performed by both osteoblasts and osteoclasts

Bone cells that aid in remodeling Osteoblast Builds new bone Mature bone cell Osteocyte OsteoblastsOsteoblasts are responsible for building new bone and lie at the centre of bone physiology. Their functions include the synthesis of collagen and the control of mineralisation. OsteoclastsOsteoclasts are specialised cells that resorb bone. They work by sealing off an area of bone surface then, when activated, they pump out hydrogen ions to produce a very acid environment, which dissolves the hydroxyapatite. OsteocytesBone adapts to applied forces by growing stronger in order to withstand them; it is known that exercise can help to improve bone strength. Osteocytes are thought to be part of the cellular feed-back mechanism which directs bone to form in the places where it is most needed. They lie within mineralised bone and it is thought that they may detect mechanical deformation and mediate the response of the osteoblasts. Osteoclast Eats bone

Bone Fractures Fracture—break in a bone Types of bone fractures Closed (simple) fracture—break that does not penetrate the skin Open (compound) fracture—broken bone penetrates through the skin Bone fractures are treated by reduction and immobilization

Common Types of Fractures Table 5.2

Repair of Bone Fractures Hematoma (blood-filled swelling) is formed Break is splinted by fibrocartilage to form a callus Fibrocartilage callus is replaced by a bony callus Bony callus is remodeled to form a permanent patch

Stages in the Healing of a Bone Fracture Hematoma External callus Bony callus of spongy bone Healed fracture New blood vessels Internal callus (fibrous tissue and cartilage) Spongy bone trabecula Hematoma formation Fibrocartilage callus formation Bony callus formation Bone remodeling Figure 5.5

Stages in the Healing of a Bone Fracture Hematoma Hematoma formation Figure 5.5, step 1

Stages in the Healing of a Bone Fracture Hematoma External callus New blood vessels Internal callus (fibrous tissue and cartilage) Spongy bone trabecula Hematoma formation Fibrocartilage callus formation Figure 5.5, step 2

Stages in the Healing of a Bone Fracture Hematoma External callus Bony callus of spongy bone New blood vessels Internal callus (fibrous tissue and cartilage) Spongy bone trabecula Hematoma formation Fibrocartilage callus formation Bony callus formation Figure 5.5, step 3

Stages in the Healing of a Bone Fracture Hematoma External callus Bony callus of spongy bone Healed fracture New blood vessels Internal callus (fibrous tissue and cartilage) Spongy bone trabecula Hematoma formation Fibrocartilage callus formation Bony callus formation Bone remodeling Figure 5.5, step 4

The Axial Skeleton Forms the longitudinal axis of the body Divided into three parts Skull Vertebral column Bony thorax

The Axial Skeleton Figure 5.6a

The Axial Skeleton Figure 5.6b

The Skull Two sets of bones Cranium Facial bones Bones are joined by sutures Only the mandible is attached by a freely movable joint

Human Skull, Lateral View Figure 5.7

Human Skull, Superior View Figure 5.8

Human Skull, Inferior View Figure 5.9

Human Skull, Anterior View Figure 5.11

Paranasal Sinuses Hollow portions of bones surrounding the nasal cavity Functions of paranasal sinuses Lighten the skull Give resonance and amplification to voice

Paranasal Sinuses Figure 5.10a

Paranasal Sinuses Figure 5.10b

The Hyoid Bone The only bone that does not articulate with another bone Serves as a moveable base for the tongue Aids in swallowing and speech

The Hyoid Bone Figure 5.12

Inflammatory Conditions Associated with Joints Tendonitis—inflammation of tendon sheaths Arthritis—inflammatory or degenerative diseases of joints Over 100 different types The most widespread crippling disease in the United States

Clinical Forms of Arthritis Osteoarthritis Most common chronic arthritis Probably related to normal aging processes

Clinical Forms of Arthritis Rheumatoid arthritis An autoimmune disease—the immune system attacks the joints Symptoms begin with bilateral inflammation of certain joints Often leads to deformities

Clinical Forms of Arthritis Gouty arthritis Inflammation of joints is caused by a deposition of uric acid crystals from the blood Can usually be controlled with diet

Osteoporosis a medical condition in which the bones become brittle and fragile from loss of tissue, typically as a result of hormonal changes, or deficiency of calcium or vitamin D.

Formation of the Human Skeleton In embryos, the skeleton is primarily hyaline cartilage During development, much of this cartilage is replaced by bone

Developmental Aspects of the Skeletal System At birth, the skull bones are incomplete Bones are joined by fibrous membranes called fontanels Fontanels are completely replaced with bone within two years after birth

Ossification Centers in a 12-week-old Fetus Figure 5.32

Skeletal Changes Throughout Life Fetus Long bones are formed of hyaline cartilage Flat bones begin as fibrous membranes Flat and long bone models are converted to bone Birth Fontanels remain until around age 2

Skeletal Changes Throughout Life Adolescence Epiphyseal plates become ossified and long bone growth ends Size of cranium in relationship to body 2 years old—skull is larger in proportion to the body compared to that of an adult 8 or 9 years old—skull is near adult size and proportion Between ages 6 and 11, the face grows out from the skull

Skeletal Changes Throughout Life Figure 5.33a