Skeletal System

2 Subdivisions of the skeleton

1. Axial Skeleton

2. Appendicular Skeleton

Parts of the skeletal system

- Bones (skeleton)

- Joints

- Cartilages

- Ligaments

Functions of Bones

- Support body

- Protect soft organs (skull and vertebrae protect brain and spinal cord. Rib cage protects inner organs in chest)

- Attached skeletal muscles allow movement

- Store minerals and fats (Like Ca and P. Fat in internal marrow cavity.)

- Hematopoiesis

Hematopoiesis

- Blood cell formation

Adult Skeleton has ...

- 206 bones

Two basic types of bone tissue

1. Compact bone (dense, smooth, homogeneous)

2. Spongy bone (small needle-like pieces of bone with many open spaces)

Classification of bones

- Classified based on shape

- Long, short, flat, or irregular

Long Bone

- Typically longer than wide

- Shaft with heads situated at both ends.

- Contain mostly compact bone

- All of the bones of the limbs (except wrist, ankle, and kneecap) are long bones

- Examples: Femur and Humerus

Short Bones

- Generally cube-shaped

- Contain mostly spongy bone

- Include bones of the wrist and ankle

- Sesamoid bones are a type of short bone that form within tendons (patella)

- Examples: Carpals and Tarsals

Flat Bones

- Thin, flattened, and usually curved

- Two thin layers of compact bone surround a layer of spongy bone

- Examples: Skull, ribs, and sternum

Irregular Bones

- Irregular shape

- Don't fit into other bone classification categories

- Examples: Vertebrae and Hip Bones

Anatomy of a Long Bone

- Diaphysis

- Periosteum

- Epiphysis

- Articular cartilage

- Epiphyseal Plate

- Epiphyseal Line

- Marrow (Medullary) Cavity

- In adults, red marrow is situated in cavities of spongy bone and epiphyses of some long bones.

Diaphysis

- Shaft

- Makes up most of bone's length

- Composed of compact bone

Periosteum

- Outside covering of the diaphysis

- Fibrous connective tissue membrane

- Perforating (Sharpey's) fibers secure periosteum to underlying bone

Epiphysis

- Ends of the bone

- Composed mostly of spongy bone enclosed by thin layer of compact bone

Articular Cartilage

- Covers the external surface of the epiphyses

- Made of hyaline cartilage

- Decreases friction at joint surfaces and acts as a cushion against gravity (like when jumping or running or etc.)

Epiphyseal Plate

- Flat plate of hyaline cartilage seen in young, growing bone.

- Causes lengthwise growth of a long bone

Epiphyseal Line

- Remnant of the epiphyseal plate

- Seen in adult bones

Marrow (Medullary) Cavity

- Cavity inside he shaft

- Contains yellow marrow (which is mostly fat) in adults

- Contains red marrow for blood cell formation in infants

- In adults, red marrow is situated in cavitites of spongy bone and epiphyses of some long bones

Bone Markings

- Surface features of bones

- Sites of attachments for muscles, tendons, and ligaments

- Passages for nerves and blood vessels

- Categories of bone markings

- Projections or processes - grow out from the bone surface (terms often begin with "T")

- Depressions or cavities - indentions (terms often begin with "F")

Microscopic Anatomy of Compact Bone

- Lacunae

- Lamellae

- Osteonic (Haversian) Canal

- Osteon (aka Haversian System)

- Canaliculi

- Perforating (Volkmann's) Canal

Lacunae

- Cavities which house osteocytes

Lamellae

- Concentric rings that contain the lacunae

- Situated around the central canal (Osteonic/Haversian Canal)

Osteonic (Haversian) Canal

- Opening in center of Osteon

- Runs lengthwise through bone

- Carries blood vessels and nerves

Osteon (Haversian System)

- A unit of bone containing central canal and matrix rings

Canaliculi

- Tiny canals

- Radiate from central canal to lacunae

- Form a transport system connecting all bone cells to a nutrient supply

Perforating (Volkmann's) Canal

- Canal perpendicular to the central canal

- Carries blood vessels and nerves

Bone Components

- Organic parts of the matrix make bone flexible

- Calcium salts deposited in the matrix make bone hard

Ossification

- Process of bone formation

- Occurs on hyaline cartilage models or fibrous membranes

- Long bone growth involves two major phases

Ossification Phases

1. Osteoblasts

- Bone-forming cells

- Cover hyaline cartilage model

2. Enclosed cartilage is digested away, opening up a medullary cavity

Bone Formation and Growth

- By birth, most cartilage is converted to bone except for two regions in a long bone: Articular cartilages and epiphyseal plates

- New cartilage is formed continuously on external face of these two cartilages

- Old cartilage is broken down and replaced by bony matrix

- Bones grow in length and width. Which is also known as appositional growth (aka growth in diameter)

- Controlled by hormones such as growth hormone.

- Epiphyseal plates are converted to bone during adolescence (Gwoth in length ends)

Bone Remodeling

- Bones are lengthened until growth stops