consists of the bones of the skull, hyoid apparatus, cartilages of the larynx and the bones of the thorax(ribs and sternum) and vertebral column
bones of the thoracic girdle and forelimbs and the pelvic girdle and hind limbs
What are the functions of the skeleton?
- supports the body
- levers for locomotion
- protects organs (soft parts)
- mineral homeostasis for calcium, phosphate and other ions
"skeleton" is derived from the Greek word meaning?
- "dried up"
- skeleton soma, "dried up body"
Skeletal system comprises?
- passive part of locomotor apparatus
"Osseous" is derived from the Latin meaning?
"of bone" or "boney" (osseus)
"Osteo-" is derived from Greek meaning?
for "bone" (osteon)
long, straight main body of a long bone.
Location of primary ossification.
end regions of bone.
Location of secondary ossification.
epiphyseal plate; physis; metaphyseal plate
region of bone lying between epiphysis and diaphysis; growth plate resides in this region.
membrane that lines the outer surface of a bone; rich in nerves and blood vessels; source of osteoprogenitor cells.
lines inner surface of bone
center space where bone marrow is stored
Where do bones originate from?
- -paraxial mesoderm(endochondral axial skeleton from sclerotomes)
- -somatic mesoderm(endochondral appendicular skeleton)
- -ectomesenchyme(intramembranous bones of calvaria and face from neural crest)
Ligaments, tendons, and muscle-related connective tissue originate from?
local mesenchyme or ectomesenchyme
Most bones are formed by?
bones of the calvaria(top of the skull) and the face are formed by?
-ectomesenchyme cells become osteoblasts directly rather than becoming chondroblasts
bones formed from cartilaginous precursor
-primary development of long bones
-local mesenchyme undergoes condensation; some cells differentiate into chondroblasts
-chondroblasts secrete matrix to produce a cartilage model of bone
cartilage forming cells
a normal developmental boney outgrowth which has a separate ossification center and fuses with the bone in later development and often serves as an important insertion point for tendon or ligament (e.g. tuber calcanei)
can be present in both long and short bones
cartilage maldevelopment that prevents normal lengthening of bone through secondary centers of ossification; genetic condition that results in dwarfism.
e.g. dachshund, bulldog, basset hound
What is unique about the ossification of vertebrae?
It is formed by both endrochondral and Intramembranous ossifications. The body of the vertebrae is formed by endochondral ossification.
bones formed directly from mesenchyme. Development of flat bones and processes of irregular bones. Mesenchymal stem cells differentiate into osteoblasts which secrete osteoid(primitive bone material). Development of flat bones and is critical in healing bone trauma.
List the types of bones:
Describe long bones.
- length is greater than the diameter
- multiple ossification centers (growth plates)
Describe short bones.
- approximately equal dimensions, cube-shaped
- only one ossification center
- no epiphyseal plates
- apophyseal ossification center(e.g. calcaneal tuber)
e.g. carpal and sesamoid bones
Describe flat bones.
present when either extensive protection or large muscle attatchment area is necessary.
Diploë: cancellous tissue enclosed by 2 thin layers of cortical bone. In certain areas of the skull, this is absorbed to form air sinuses.
Describe irregular bones.
short bones with multiple processes, can't be classified in any other category.
formed by both endochondral and intramembranous ossification.
Describe sesamoid bones.
- small and seed-like bones
- embedded in tendons
all sesamoids are short bones, all short bones are not sesamoids
Name 3 purposes of sesamoid bones.
- Eliminates tendon shear
- Redirects lines of force
- Increases torque
What are bones designed for?
adequate strength with minimal material.
such design allows evolutionary advantages; faster reaction, reduced metabolism requirements
What are the 2 types of bones identified macroscopically?
- Trabecular bone
- Cortical bone
cancellous or spongy bone, lattice shaped, greater surface area
compact bone, dense "cortex", outer shell of bones
How is bone blood supplied to bones?
nutritional vessels enter the diaphysis and epiphysis.
majority of long bones have a single nutrient foramen entering mid-diaphysis
What supplies the cortical bone with bone blood?
vessels in the periosteum
proximal articular end of bone
small pit in the head
small projection or bump
rounded, knuck-like articular process
projection near condyle but not part of joint
raised, roughened surface for muscular attachment
large process on femur
broad, shallow depressed area
opening through bone
long, tunnel-like foramen
small, flattened articular surface
narrow, prominent ridge
sharp, slender process
line remaining after two bones have joined
a small oval plate located cranial to the shoulder within the clavicular tendon in the brachiocephalicus muscle of the dog.
one of the first bones to show a center of ossification in the fetal dog, but in the adult it is partly or completely cartilaginous. It is frequently visible in dorsoventral radiographs of the trunk, medial to the shoulder joint.
bone forming cells that secrete osteoid which is then mineralized into calcified boney tissue; derived from mesenchymal stem cells.
osteoblasts that are entrapped in bone matrix; most abundant bone cell (>70%)
small transverse canals through which osteocytes communicate via cytoplasmic processes
bone resorbing cells; multinucleated and derived from hematopoietic stem cells; "dissolve" bone by forming resorption pits termed Howship's lacunae by secreting acids and proteases
*note: Howship's lacunae...bite out of sandwich
functional unit of cortical bone;includes the osteon and haversian canal
Haversian system (osteon)
central canal, nerve/blood supply
Concentric layers (_________) of ________ surround Haversian canal; composed of osteocytes, canaliculi and extracellular matrix
complex of self-assembled macromolecules composed of the inorganic component hydroxyapatite (~70%) and the organic component primarily Type I collagen(~30%) but also contains proteoglycans, glycosaminoglycans, glycoproteins, osteonectin, and osteocalcin.
Bone Extracellular Matrix (ECM)*know abb.
What 2 types of bone are identified microscopically?
ECM organized haphazardly and is mechanically weak, formed rapidly and then remodeled into lamellar bone.
regular alignment and mechanically strong, formed by osteons.
a delicate balance of bone formation (osteoblasts) and resorption (osteoclasts); occurs continuously throughout life; occurs in response to loads on bone; increases in response to injuries and disease
local groups of osteoblasts and osteoclasts that remodel bone.
Bone multicellular unit (BMU)
How is bone remodeling used as an important diagnostic tool to identify bone injury?
Bones can be "labeled" with radionucleotides or fluorescent markers that are deposited in extracellular matrix when new bone is formed via nuclear scintigraphy, double tetracycline/calcein labeling(mostly in humans)
Describe Wolff's Law.
- Normal bone remodels in response to stress upon it.
- If load increases on a particular area, bone will remodel to become stronger to resist those forces.
- Works in opposit direction.
- "use it or lose it"
Name the functions of bones.
- biological "storage"
- Blood production
How do bones function as support/movement?
serves as attachment point for muscles and leverage for these muscle attachments.
How do bones function as protection?
- skull/vertebral column protects the central nervous system
- Thoracic cage protects heart, lungs, liver, spleen, and great vessels
- Pelvic girdle protects organs like reproductive organs
- Marrow cavity protects hematopoiesis(the process by which immature precursor cells develop into mature blood cells.)
What do bones store biologically?
calcium, phosphorous, fat (yellow marrow), endogenous stem cells (red marrow)
the predominant marrow in young individuals, when blood production is high. Primarily found in vertebrae, pelvis, sternum, ribs and ends of long bones in adults.
Hematopoietic stem cells are located in the ____________________ and will differentiate into precursor cells of erythrocytes, leukocytes, and thrombocytes, aiding in growing and maintaining blood cell populations.
Red marrow can serve as a source for other endogenous stem cells such as ______________ and ____________________.
- endothelial progenitors
fatty tissue predominant in marrow cavities of long bones in adults, serves as fat storage and used as "last resort" as an energy source in cases of extreme starvation.
___________ and _____________ are oriented within bone according to the forces exerted.
the amount of force bone can withstand without breaking.
bone's capacity to resist axially directed pushing forces. Bone is best at resisting these forces.
bone's capacity to resist pulling or stretching
bone's capacity to resist a force in a direction perpendicular to extension of the bone. Bone is worst at resisting these forces.
a diagnostic tool that can identify bone remodeling and can pick up fractures that may not be visible on radiographs. Can assist in diagnosis of osteoarthritis and can be used to identify "bone bruises"; fracture of trabeculae or subchondral bone that does not result in a classical "fracture".
The approximate strengths of bones in: