SKELETAL SYSTEM

TYPES OF BONES n LONG: humerus n SHORT: carpals n FLAT: frontal bone n IRREGULAR: vertebrae

Categorizing bones developmentally… n Endochondral –develop from pieces of cartilage deposited as sheets of tissue in embryo –Face, appendages n Dermal –Formed from sheets of fibrous connective tissue –Clavicle, scapula, flat cranial bones

n Alveolar –Teeth –Specialized groupings of bone cells n Sesamoid –Form within tendons due to stress on tendon –Patella, pisiform, various metacarpal, metatarsal bones

n Wormian –Small, irregular, isolated; develop within sutures

BONE STRUCTURE

Periosteum  “To surround the bone”  Fibrous membrane, covers surface of the bone EXCEPT at the joint surfaces.  Contains nerves and blood vessels  Nutrition, sensation  This is where the tendons & ligaments attach to the bone.

Yellow Marrow Red marrow spaces (surrounded by trabeculae)

Epiphysis  At the end of each bone  Made of cancellous or spongy bone  Network of bone called trabeculae  Spaces contain red marrow  Site of hematopoiesis (blood cell production)  Outer surface is compact bone  Within joints, surfaces covered with hyaline articular cartilage

Epiphysial Plate n Also called the “growth plate”; –indicates that additional bone growth is possible n Site of bone elongation n Ossifies over time –then callled epiphysial line

Epiphyseal Plate

Diaphysis  “to grow apart”  Hollow Tube  Made of compact bone: organized into osteons  Rigid but light

Medullary Cavity  Hollow area inside diaphysis  Bordered by spongy bone  Lined by a thin membrane called the endosteum  Capable of generating new bone cells  Adults: contains soft, yellow bone marrow  Mostly adipose tissue  Food reserve for bone cells  Children: more red marrow

Two kinds of bone Cancellous/Trabecular (Spongy)  80% of bone  many spaces filled with marrow Compact (cortical)  20% of skeleton structure  80% of skeletal weight  Structural unit = osteon

The Osteon The structural unit of bone

The OSTEON: Found in compact bone  Matrix is organized into numerous structural units called osteons or Haversian systems.  Consists of calcified matrix arranged in concentric rings called concentric lamellae

The Osteon  The rings surround an opening called the Central (Haversian) Canal  Canal contains blood, lymph vessels and nerves

The Osteon n Mature bone cells = osteocytes –Secrete bone matrix n Composed of collagen fibers and protein (osteocalcin) n The cell resides in a space called a lacuna n Canals, called canaliculi, connect the osteocytes to one another

More on the Osteon  Nutrients pass  from the blood vessel in the central canal  through the canaliculi  to the osteocytes

What can you identify?

The Osteon  Central canals are connected by a horizontal blood vessel housed within the Volkmann’s Canals

JOINTS

Classification: n Structural –Tissue composition, structural complexity –Cartilaginous, fibrous, synovial n Functional –Type of movement allowed –Synarthrotic, amphiarthrotic, diarthrotic

Bursa – Accessory Structure n Sac-like space made of fibrous tissue n Synovial fluid –thick, lubricating fluid –Nourishes, protects joints and surface –Secreted by epithelial cells n Found in articular areas where rubbing between skin, muscle, ligaments, or bones could occur n Can become inflamed/damaged = bursitis

Synarthrotic Joint (Immovable Joints) Fibrous Joint n Produce NO movement n Bone connected to bone by fibrous tissue n Purpose: to securely hold two bones together n Include –Sutures of the skull (synostoses/sutures) –Skull to teeth (gomphosis) –Tibia and fibula (syndemosis)

Amphiarthrotic Joint (Semi-movable) Cartilaginous n Bone connects to bone via cartilage n Allows slight movement n Includes –Pubic symphisis –Vertebrae

Diarthrotic/Synovial Joint n Allows much movement; joint cavity lined by synovial membranes n Some types –Ball & Socket: Shoulder, Hip –Hinge: Knee, Shoulder –Pivot: Atlas/Axis –Gliding: Between carpal bones, between tarsal bones –Saddle: thumb –Ellipsoid/Condyloid: wrist

BONE DEVELOPMENT AND HEALING

Osteowhat?  Osteoblasts secrete a mineralized matrix  Once the osteoblast is surrounded by its matrix, it’s called an osteocyte, a bone cell.  Osteoclasts break down bone. The first crystals of bone that form are pointed and needle-like: called spicules.

Ossification n Conversion of embryonic tissues into recognizable bone n 2 ways: –Endochondral n Long bones –Intramembranous n Flat bones –Combination – irregular bones

Ossification

Ossification n Mesodermal cells form cartilage centers –Cartilage pegs form –Restructured, filled with hydroxylapatite (calcification) n Pegs formed by fibroblasts n Osteoblasts and osteoclasts sculpt growing bones

An osteoclast in action. Here an osteoclasts is eroding bone. The capsule formed by such action is called a Howship's capsule (H). Similar to the cell of the gut, osteoclasts have a ruffled border which increases the surface area for bone resorption.

Direction of Long Bone Growth n Epiphyseal plate made of hyaline cartilage is responsible for long bone growth. n The direction of growth is toward the diaphysis n The newly forming spongy bone (below the growth plate) is not clearly organized as the older spongy bone in the epiphysis above the growth plate.

n Fontanelles – soft spots –Regions of flat bone not fully ossified –Completed during teenage years

HEALING

Fractures n Bone is cracked/splintered due to physical injury n Categorized by severity of break/angle at which break occurs

n Simple: –Crack in bone structure –May not be readily noticeable –Some large; may involve bleeding, pain, swelling –Greenstick fractures n One side frayed from fracture; other twisted, but not broken

n Compound/comminuted –Large fracture –One (more) area is displaced, shattered –Bleeding, swelling n Open –Tearing of skin occurs; easily infected

Angle of break n Transverse (horizontal) n Oblique (angle) n Spiral (twisted) n Angulation – bone changes overall shape n For healing to occur, blood accumulation must occur

Healing stages 1. Fracture 2. Granulation 3. Callus 4. Lamellar bone 5. Normal contour