Ch.8 Bone Flashcards
(29 cards)
what is bone?
- a connective tiss characterized by an extracellular matrix that’s mineralized by calcium phosphate in the form of hydroxyapatite crystals
- for support and protection
- storage site for calcium and phosphate, in homeostatic regulation of blood Ca2+ levels
What does bone matrix contain?
- collagen type I, some collagen type V
- Ground substance:
1. glycoaminoglycans (hyaluronic acid, chondroitin sulfate, keratin, sulfate)
2. glycoproteins (osteocalcin, osteonectin, osteopontin)
3. sialoproteins
Lacunae spaces have:
-osteocyte, that extends numerous processes into canaliculi, that connect adjacent lacunae by gap junctions, forming continuous network.
3 cell types:
- osteoprogenitor
- osteoblasts
- osteoclasts
- ->osteoblasts (and secrete bone matrix)
- secrete extracell matrix, once surrounded its an osteocyte
- bone-resorbing cells on bone surfaces where its being removed or remodeled (reorganized) or where bone has been damaged (phagocytotic cells derived from bone marrow)
what other conn tiss is bone associated?
- hemopoietic
- fat
- blood vessels
- nerves
- compact (dense)
- spongy (cancellous)
- outside bone
- sponge-like, inside. consist of trabeculae. occupied by marrow and blood vessels
bones classified by shape, location of spongy and compact bone varies by shape:
- long bones
- short
- flat
- irregular
- periosteum
- shaft, 2 ends-diaphysis, epiphysis, metaphysis, medullary cavity (tiba, metacarpals)
- almost entire shaft is compact. - equal length, diameter (carpals)
- made of shell of compact bone, spongy bone, marrow space. usually forms joints w/ neighbors - thin, plate-like (skull, sternum)
- complex (vertebrae)
- fibrous connective tiss cap. covers the outer surface of bone
Periosteum
- a sheath of dense fibrous conn. tiss containing osteoprogenitor cells, covering bones
- coll fibers arranged parallel to surface of bone in form of a capsule
- Sharpey’s fibers, angled in ligaments/tendons
Periosteal cells
-capable of undergoing division, becoming osteoblasts under appropriate stimulus.
Parts of long bone
- diaphysis: shaft
- epiphysis: ends
- metaphysis: flared portion bet dia and epi
- medullary cavity: large filled with marrow, inner portion
articular cartilage which is exposed to joint cavity:
- hyaline, not covered by perichondrium
* diarthrosis: 2 parts-external fibrous layer, synovial layer that lines articular cavity except for cartilaginous area
bone cavities lined by endosteum:
*endosteal cells
- layer of conn tiss that contain osteoprogenitor cells, usually one cell layer thick and can differentiate into osteoblasts
- flattened cells resemble fibroblasts
What is bone marrow?
- network of reticular cells and fibers that serve as a supporting framework for developing blood cells and vessels
- doesn’t increase in proportion to bone growth, as individual grows
what is yellow bone marrow?
- when rate of blood cell formation is diminished in adults, tissue consists of fat cells
- in response to stimuli (blood loss), yellow->red
- in adults, red is restricted to spaces of spongy bone in sternum and iliac crest
mature bone is composed of:
-osteon (Haversain sys) structural units
osteons
-consist of lamellae which are concentric bony plates surrounding a Haversian(osteonal) canal which contains vascular and nerve supply of osteon
- typically develop in preexisting compact bone
- in dev’t a tunnel is bored through compact bone by osteoclasts
- compact adult bone contains haversian systems of varying age and size
blood supply to shaft of long bone is by:
- arteries that enter marrow cavity through nutrient foramina
- greatest number being in diaphysis and epiphysis
blood supply to bone tiss is:
- centrifugal
- moves from marrow cavity into and through bone tiss and out via periosteal veins
Osteoprogenitor cells found in:
-external and internal surfaces of bone such as periosteal cells that form innermost layer of periosteum and endosteal cells that line the marrow cav, osteonal canals, and volkman’s
Osteoblasts
- retains its ability to divide since its a versatile secretory cell like the fibroblasts and chondroblasts
- secretes osteoid (initial unmineralized bone)
- calcification of the matrix
- cuboidal, polygonal, single layer of cells lying in apposition to forming bone
- basophilic cytoplasm w/ clear Golgi app, next to nucleus
- respond to mechanical stimuli to mediate changes in the bone growth and bone remodeling
Osteocyte
- maintains bone matrix by synthetic and reabsorptive activities
- helps maintain homeostasis of blood Ca2+
- each occupies lacuna
- 3 functional states:
1. Quiescent-exhibit a paucity of rER, Golgi ap,
2. Formative-show evidence of matrix deposition and similar to osteoblast
3. Resorptive-contain numerous ER and Golgi ap
Osteoclast
- large, multi-nucleated cells found at sites where bone is being removed. As a result, a shallow bay called resorption bay (Howship’s lacuna) can be observed in bone directly under osteoclast.
- release lysosomal hydrolases, w/ collagenase, they digest organic components of bone matrix, after matrix is decalcified by acids
Endochondral ossification:
- cartilage precursor (vertebrae, extremities)
- mesenchymal cells -> chondroblasts -> cartilage matrix
1. hyaline cart model w/ the general shape of bone is formed(interstitial and app. growth)
2. 1st sign is the appearance of cuff of bone around cart. model - perichondrial cells in midregion do not become chondrocytes, instead osteoblasts produced.
3. w/ the est periosteal bony collar, perichondrium becomes PERIOSTEUM (becoz of altered role), resulting in a LAYER OF BONE is formed around cart model.(can be classified at periosteal bone or intramembranous bone) - Chondrocytes in the midregion of cart model become hypertrophic. thus surrounding matrix is resorbed forming thin irregular cart plates between hypertrophic cells.
4. calcified cartilage matrix inhibits diffusion of nutrients, causing death of the chondrocytes in the cart
5. periosteal cells migrate into the cavity along w/ growing blood vessels
*synthesize alkaline phosphatase
Intramembranous ossification:
- w/o cart precursor (flatbones of skull, face, mandible, clavicle
- formed by differentiation of mesenchymal cells into osteoblasts. they elongate, migrate, and aggregate in specific areas where the sites of bone is destined to form.
- 8th week of gestation
- becomes more vascularized, larger, rounded
- changes from eosinophilic to basophilic w/ clear Golgi ap
- result in osteoblast
- with time, matrix becomes calcified and interconnecting cytoplasmic processes of osteocytes are contained in canaliculi
- concomitantly, more of surrounding mesenchymal cells in membrane proliferate, giving rise to a pop of osteoprogenitor cells
- through continued MITOTIC activity, the OSTEOPROGENITOR CELLS, maintain their numbers and provide a constant source of osteoblasts for growth of the bone spicules(Appositional growth). the new osteoblasts, lay down bone matrix in successive layers, giving rise to WOVEN BONE.