skeletal system. types of bones n long: humerus n short: carpals n flat: frontal bone n irregular:...
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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
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