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– Teeth– Specialized groupings of bone cells

Sesamoid– 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 vesselsNutrition, sensation

This is where the tendons & ligaments attach to the bone.

Yellow Marrow

Red marrowspaces(surrounded by trabeculae)

Epiphysis

At the end of each boneMade of cancellous or spongy bone

Network of bone called trabeculaeSpaces contain red marrowSite of hematopoiesis (blood cell

production)Outer surface is compact boneWithin 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 TubeMade of compact bone:

organized into osteonsRigid but light

Medullary Cavity

Hollow area inside diaphysisBordered by spongy boneLined by a thin membrane called the

endosteumCapable of generating new bone cells

Adults: contains soft, yellow bone marrowMostly adipose tissueFood reserve for bone cells

Children: more red marrow

Two kinds of bone

Cancellous/Trabecular (Spongy)

80% of bonemany 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

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 OsteonNutrients 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– 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 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

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. 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– 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

1. Fracture2. Granulation3. Callus4. Lamellar bone5. Normal contour