SKELETAL SYSTEM

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

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

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

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.

Red marrow spaces (surrounded by trabeculae) Yellow Marrow

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 Also called the “growth plate”; indicates that additional bone growth is possible Site of bone elongation 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) Compact (cortical) many spaces filled with marrow Compact (cortical) 20% of skeleton structure 80% of skeletal weight Structural unit = osteon

The structural unit of bone 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 Mature bone cells = osteocytes Secrete bone matrix Composed of collagen fibers and protein (osteocalcin) The cell resides in a space called a lacuna 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: Structural Functional Tissue composition, structural complexity Cartilaginous, fibrous, synovial Functional Type of movement allowed Synarthrotic, amphiarthrotic, diarthrotic

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

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

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

Diarthrotic/Synovial Joint Allows much movement; joint cavity lined by synovial membranes 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 The first crystals of bone that form are pointed and needle-like: called spicules. 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.

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

Ossification

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

An osteoclast in action. Here an osteoclasts is eroding bone 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 Epiphyseal plate made of hyaline cartilage is responsible for long bone growth. The direction of growth is toward the diaphysis 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.

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

healing

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

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

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

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

Healing stages Fracture Granulation Callus Lamellar bone Normal contour