Bone Histology Flashcards
What is the cement line?
separates osteon from interstitial lamellae
Where is red marrow found in an infant?
everywhere
What is in the outer layer of periosteum?
blood vessels and nerves
fibroblasts
collagen fibers
sharpey’s fibers
What are osteoblasts?
epithelial-like cells w/ cuboidal/columnar shapes
form matrix of bone tissue
deposit osteoid and control mineralization
give strong cytochemical rxn for alkphos
Where are Osteoclasts found?
Howship’s Lacuna
What is osteomalacia?
adult form of rickets - progressive softening and bending of bone
vit d deficiency or GI disease
How much of bone matrix is organic (not minerals)?
35%
What percentage of inorganic bone makes up the matrix?
What is in it?
65%
calcium phosphate, hydroxyapatite
What is compact bone?
outer solid cortex surrounding spongy bone
lamellar bone
What are osteoprogenitor cells?
mesenchymal origin w/ stem cell properties
found in inner layer of periosteum and endosteum
give rise to osteoblasts
reactivated in times of bone repair
What would you find at the center of an osteon?
a haversian canal that houses capillaries and post-capillary venules
What are the 2 layers of the periosteum?
inner layer
outer layer
What are canaliculi?
tiny little channels in an osteon that allow osteocytes to have projections to connect to other osteocytes and get nutrients
What is in the inner layer of the periosteum?
osteoprogenitor cells
osteogenic layer
What are inner circumferential lamellae?
internal surface of bone
subjacent to endosteum
What is spongy bone?
also known as trabecular/cancellous bone
inner layer
spaces for bone marrow
lamellar or woven
What happens to Alkaline Phosphatase when osteoblasts become osteocytes?
alkphos disappears
What is rickets?
calcium or vit D defficiency –> defect in mineralization of cartilage in growth plate –> bowed limbs, delayed closure of fontanelles
What type of collagen is predominant in bone?
type I
Where is red marrow found in an adult?
skull, vertebrae, ribs, clavicle, scapula, pelvis, heads of femur and humerus
What is woven bone?
immature/primary replaced by lamellar loose arrangement of collagen more cells, less mineral content forms during Fx repair/remodeling
What is the general composition of bone matrix?
90% ECM and 10% water
What are interstitial lamellae?
between osteons
separated from osteon by cement line
What is a volkmann’s canal?
transverse vascular channel that connect haversian canals
What are sharpey’s fibers
found in the outer layer of the periosteum
anchoring collagen fibers penetratint the outer circumferential lamellae
What is the outer circumferential lamellae?
external surface of compact bone
under the periosteum
Where is the periosteum?
lines bone on the outside
What makes up organic bone?
type I collagen
osteoid (unmineralized bone)
ground substance = proteoglycans, glycoproteins, growth factors/cytokines, Vit K-dep proteins
What are osteocytes?
osteoblasts trapped in lacunae in matrix
deposit osteoid matrix
branches in canaliculi
What is osteoporosis?
imbalance btw osteoclast resorption of bone and osteoblast deposition
elderly and postmenopausal females
What is achondroplasia caused by?
autosomal dominant mutation in FGFR3 –> endochondral growth inhibitted too early –> short limbs
What is the function of osteoclasts?
generate a secluded acidic environment for bone resorption
mediated by H+-ATPase –> degradation of organic matrix via cathepsin K protease
impt in bone remodeling and renewal
What is an osteon/ haversian system?
concentrically arranged lamellae around a vascular channel
Where is the endosteum?
lines marrow cavity
covers spongy walls
extends into all cavities of bone
contains osteoprogenitor cells
What is lamellar bone?
mature/secondary
regular parallel arrangement of collagen
not visible on H&E stains
form of most adult bone = strong, forms slowly
How do osteoclasts form?
NOT from osteoblasts
monocytes –> enter bone –> osteoclasts
Why do you feel pain if you break a bone?
bc periosteum is innervated by nerves
outer layer
What enzyme helps degrade organic bone matrix?
Cathepsin K protease
