BONES Flashcards
What are a few functions of bone?
- provide solid support
- protect organs
- reservoir for calcium and phosphate
- allows us to move
- have cavities for bone morrow
DESCRIBE THE DEVELOPMENT OF THE OSTEON
Osteoclast begin to dig a hole and at somepoint they die and leave a hole. this hole its gonna fill up with vessels, osteoblast. Osteoblast will create bone.
What is the osteon?
It can also be known as Harvesian system. Are concentric lamellae that surrounds a canal in which are blood vessels, nerves and endosteum.
What is the cement line?
boundary of an osteon
Describe some of the structures seen in bone.
picture:
A schematic overview of the basic features of bone, including the three key cell types: osteocytes, osteoblasts, and osteoclasts; their usual locations; and the typical lamellar organization of bone. Osteoblasts secrete the matrix that then hardens by calcification, trapping the differentiating cells now called osteocytes in individual lacunae. Osteocytes maintain the calcified matrix and receive nutrients from microvasculature in the central canals of the osteons via very small channels called canaliculi that interconnect the lacunae. Osteoclasts are monocyte-derived cells in bone required for bone remodeling.
The periosteum consists of dense connective tissue, with a primarily fibrous layer covering a more cellular layer. Bone is vascularized by small vessels that penetrate the matrix from the periosteum. Endosteum covers all trabeculae around the marrow cavities.
What is bone matrix? What are the three major cell types found in bone matrix? Briefly describe them.
- calcified extracellular material. 50% is inorganic: calcium hydroxapatite, mst abundant.
- organic composition: most abundant is collagen type 1 collagen, 90%; proteoglycans and mutiadhesive glycoproteins and osteocalcin, and phosphatase
What are the two linings seen in bone? Describe them.
- All bones are lined on their internal and external surfaces by layers of connective tissue containing osteogenic cells
- endosteum on the internal surface surrounding the marrow cavity
- periosteum on the external surface
osteogenesis
formation of bone; two types of ossification: intramembranous and endochrondral. In both processes woven bone is produced first and then replaced with lamellar bone
How do metabolites diffuse in bone?
- unable to diffuse through the calcified matrix of bone
- exchanges between osteocytes and blood capillaries depend on communication through the very thin, cylindrical spaces of the canaliculi
How is histological preparation of bone different than other tissues?
- Because of its hardness, bone cannot be sectioned routinely.
- Bone matrix is usually softened by immersion in a decalcifying solution before paraffin embedding
- or embedded in plastic after fixation and sectioned with a specialized microtome.
What do osteoblast produce? (function)
- organic components of bone matrix, including type I collagen fibers, proteoglycans, (filler) and matricellular glycoproteins such as osteonectin (junction)
- Deposition of the inorganic components of bone also depends on osteoblast activity
After osteoblast synthetic activity is complete, what is their fate?
- some differentiate as osteocytes entrapped in matrix-bound lacunae
- some flatten and cover the matrix surface as bone lining cells
- the majority undergo apoptosis
By what process do osteoblast secretions become bone matrix?
- Matrix components are secreted at the cell surface in contact with existing bone matrix, producing a layer of unique collagen-rich material called osteoid between the osteoblast layer and the preexisting bone surface.
- Prominent among the noncollagen proteins secreted by osteoblasts is the vitamin K-dependent polypeptide osteocalcin
- also release membrane-enclosed matrix vesicles rich in alkaline phosphatase and other enzymes whose activity raises the local concentration of PO43- ions - together with various glycoproteins binds Ca2+ ions and concentrates this mineral locally
- with high concentrations of both these ions, matrix vesicles serve as foci for the formation of hydroxyapatite [Ca10(PO4)6(OH)2] crystals, the first visible step in calcification
- These crystals grow rapidly by accretion of more mineral and eventually produce a confluent mass of calcified material embedding the collagen fibers and proteoglycans (surrounds collagen fibers and other macromolecules)
How are osteocytes derived? Where are they located? What are some notable structures that are observed in osteocytes?
- some osteoblasts become surrounded by the material they secrete and then differentiate as osteocytes enclosed singly within the lacunae spaced throughout the mineralized matrix
- During the transition from osteoblasts to osteocytes, the cells extend many long dendritic processes, which also become surrounded by calcifying matrix
- The processes thus come to occupy the many canaliculi, radiating from each lacuna
Where are active osteoblast typically located? How are they fixed in these locations and how do they appear?
- located exclusively at the surfaces of bone matrix
- bound by integrins, typically forming a single layer of cuboidal cells joined by adherent and gap junctions
How does diffusion occur between osteocytes and blood vessels?
-through the small amount of interstitial fluid in the canaliculi between the bone matrix and the osteocytes and their processes
What is the function of osteocytes?
-communicate with one another and ultimately with nearby osteoblasts and bone lining cells via gap junctions at the ends of their processes
mechanoreceptors- giving orders to other cells to form or deform bones
What are some structural differences seen in osteocytes vs osteoblast?
- almond-shaped osteocytes
- exhibit significantly less RER
- smaller Golgi complexes
- more condensed nuclear chromatin than osteoblasts
What are a few functions of osteocytes?
- maintain the calcified matrix, and their death is followed by rapid matrix resorption
- While sharing most matrix-related activities with osteoblasts, osteocytes also express many different proteins, including factors with paracrine and endocrine effects that help regulate bone remodeling
- The extensive lacunar-canalicular network of these cells and their communication with all other bone cells allow osteocytes to serve as sensitive detectors of stress- or fatigue-induced microdamage in bone and to trigger remedial activity in osteoblasts and osteoclasts
What are osteoclast?
-very large, motile cells with multiple nuclei (Figure 8-6) which are essential for matrix resorption during bone growth and remodeling.
** they are big become comes from monocytes**
Why are osteoclast large in size and multinucleated?
-due to their origin from the fusion of bone marrow-derived monocytes
Explain osteoclast development
- It requires two polypeptides produced by osteoblast: M-CSF and RANKL
How does an active osteoclast function?
- the membrane domain that contacts the bone forms a circular sealing zone which binds the cell tightly to the bone matrix and surrounds an area with many surface projections, called the ruffled border
- This circumferential sealing zone allows the formation of a specialized microenvironment between the osteoclast and the matrix in which bone resorption occurs
Explain more in depth how osteoclast preform their function in bone remodeling and how they are regulate to preform this function.
osteoblast sense microcraks in the bone produce RANKL, receptor activator of nucelar factor KB ligand, binds to nearby monocytes to produce multi nucleated osteoclast. The osteoclast secrete lysosomal enzyme (collagenase) and digest and college making the Howship’s lacunae. The osteoclast secretes HCl, and this dissolves hydroxypatite to Ca and PO3. This gets into the blood stream. when they are done they commit suicide.
Osteoblast secrete osteoid seam (mostly collagen) to fill in lacunae. they also secrete Ca and PO3 making hydroxipatite.
What is the periosteum ?
outer fibrous layer of dense connective tissue containing: Type 1 Collagen, fibroblast and blood vessels
-Bundles of periosteal collagen, called perforating (or Sharpey) fibers, penetrate the bone matrix and bind the periosteum to the bone.
inner layer: is more cellular and has osteoblasts, bone lining cells and stem cells .
-With the potential to proliferate extensively and produce many new osteoblasts, osteoprogenitor cells play a prominent role in bone growth and repair
What is the endosteum?
inside the bone. Covers the trabeculae and contains: osteoprogenitors/ mesenchymal cells, osteoblast and bone lining cells.
More delicate because we dont have the fibrous part as the periosteum
Location and appearance Woven bone (type of bone)
Irregular and random arrangement of cells and collagen; lightly calcified/ no mineralized. Its replaced by lamellar bone
It is located in developing and growing bones embryonic development; bones fracture
Location and appearance lamellar bone (type of bone)
multiple layers of calcified matrix, organized on sheets around a canal. Each lamella has type 1 collagen with orthogonal orientation ( different directions)
all normal regions of adult
Compact bone
Parallel lamellae or densely packed osteons, with interstitial lamellae
It is located in the thick, outer region of bones
What are the parts of the long bones?
epiphyses: composed of cancellous bone covered with compact bone.
diaphysis: dense bone with a region of cancellous bone
type of bone in short bones:
cores of spongy bone and covered completely in compact bone
endochondral ossification
process in which bone forms by replacing hyaline cartilage because osteoblast invades.
Happens in most bones of the body.
How many parts have the epiphyseal cartilage plate and their names
zone of reserve
proliferative zone
zone of hypertrophy
zone of calcified cartilage
zone of ossification
