Histology: Bone Structure Flashcards
How are bones classified?
according to shape
What is the structure of long bones?
- tubular in shape
- consist of 2 ends
a) proximal end
b) distal end - consist of 1 long shaft
a) diaphysis
What is metaphysis?
The junction between the diaphysis and the epiphysis.
(between the bones center and beginning/end)
What structure covers the bone?
the periosteum
What is the periosteum?
A connective tissue membrane that attaches to the outer surface of bones.
What are bone cavities lined by?
endosteum
What is the endosteum?
A single layer of cells that contains osteoprogenitor (endosteal) cells.
What layers does the periosteum consist of?
1) the outer fibrous layer
2) the inner cellular layer
Describe the structure of the outer fibrous layer of the periosteum.
- irregular
- dense connective tissue type
- high percentage of collagenous matrix & small percentage of cells
- divides into 2 layers: the superficial and deep layer.
What two layers does the periosteum (outer fibrous layer) divide into?
1) the superficial layer
2) the deep layer
How does the superficial and deep layer of the periosteum compare?
the superficial layer is more VASCULAR and receives PERIOSTEAL VESSELS.
the inner layer is a fibro-elastic layer.
What does the deep layer of the periosteum consist of?
the fibrio-elastic layer
What is the inner cellular layer of the periosteum made up of?
osteoprogenitor cells
What is another name used for the inner cellular layer?
the osteogenetic layer
What does the inner layer contain? (osteo-) Where?
osteoblasts in young developing bones
Are osteoblasts in adult bones present or absent?
- can be absent
- appear whenever required (eg. fracture healing)
What are osteoprogenitor cells?
- multipotent stem cells
- undergo mitosis divisions
- differentiate into osteoblasts
What is the endosteum? How is it identified?
- a membrane lining the inner surface of the bony wall
- identified as the lining membrane of the bone marrow cavity
What does the endosteum line?
- the Haversian canal
- all the internal bone cavities
What does the endosteum consist of?
- a layer of flattened osteoprogenitor cells
- type III collagenous fibers (reticular fibers)
What is thinner, the endosteum or the periosteum?
The endosteum is noticeably thinner.
What is an immature (woven) bone?
bone tissue formed during development
What is bone tissue called which is formed during development?
immature (woven) bone
How does immature (woven) bone differ from mature (lamellar) bone?
collagen fiber arrangement.
How is bone tissue classified?
1) compact
2) spongy
Where is compact bone located?
outside and beneath the periosteum.
What forms internal spongy bone?
a meshwork of trabeculae
What is the development of bones classified as?
1) ENDOCHONDRAL (a cartilage model serving as the precursor of the bone)
2) INTRAMEMBRANOUS OSSIFICATION (without the involvement of a cartilage presursor)
What is endochondral development?
a cartilage model serving as the precursor of the bone.
What is intramembranous ossification?
a cartilage precursor is not involved.
What bones develop by intramembranous ossification?
- flat bones of the skull
- mandible (lower czaszka)
- clavicle (obojczyk)
What bones develop by endochondral ossification.
all bones except:
- mandible
- clavicle
- flat bones of the skull
What does hyaline cartilage undergo in early fetal development?
the process of endochondral ossification.
What is hyaline cartilage in the process of endochondral ossification?
the precursor of bones
What happens during the development process? What happens to hyaline cartilage?
most of the hyaline cartilage is replaced by bones.
residual cartilage at the proximal and distal ends of the bone served as growth sites (EPIPHYSEAL GROWTH).
What is EPIPHYSEAL GROWTH?
residual cartilage at the proximal and distal ends of the bone served as growth sites.
When does the cartilage at the proximal and distal ends of the bone remain functional (epiphyseal growth)?
as long as the bone is growing in length.
What is the model formed in endochondral ossification?
the hyaline cartilage model
What do osteoprogenitor cells surrounding the hyaline cartilage model differentiate into?
1) bone-forming cells that initially deposit bone onto the cartilage surface (periosteal BONY COLLAR)
2) penetrate the diaphysis (to form the PRIMARY OSSIFICATION CENTER)
What is “periosteal BONY COLLAR”?
bone forming cells that deposit bone in the cartilage surface
How is the primary ossification center formed?
bone forming cells penetrate the diaphysis.
How is the secondary ossification center developed?
within the epiphyses.
What separates the primary and secondary ossification centers?
the epiphyseal growth plate
What does the epiphyseal growth plate do?
it provides a source for new cartilage involved in bone growth (children and adolescents).
Does the epiphyseal growth plate have several zones?
yes, eg.
- reserve cartilage
- zone of proliferation
- zone of hypertrophy
- zone of calcified cartilage
- zone of resorption
What happens during intramembranous ossification?
bone formation is initiated by condensation of mesenchymal cells that differentiate into osteoblasts.
How are ossification centers formed?
some spindle shaped, pale staining mesenchymal cells migrate and aggregate in specific areas
(eg. the region of flat bone development in the head)
What initiates the process of intramembranous ossification?
condensation of cells within the mesenchymal tissue
What do mesenchymal cells in ossification centers elongate and differentiate into?
osteoprogenitor cells
What do osteoprogenitor cells further differentiate into?
osteoblasts
What do osteoblasts deposit?
unmineralized bone matrix (the osteoid).
Where do the osteoblasts accumulate?
at the periphery of the ossification center
What do osteoblasts do at the periphery of the ossification center?
continue to secrete osteoid toward the center of the nodule.
What happens when the process of ossification continues (after osteoblasts secrete the osteoid towards the center of the nodule). What happens to osteoblasts?
osteoid undergoes mineralization and trapped osteoblasts become osteocytes.
