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how is bone and cartilage similar?
both consist of cellular population encased in a matrix
True or false
Bone is innervated and vascularized, and can dynamically update its shape and size in response to tensions from attached ms
anatomy of long bone - diaphysis
long shaft of the bone
Antomy of long bone - epiphyses
rounded ends of the long bone
anatomy of long bone - periosteum
cover entire bone
a dense connective tissue layer that contian vasculature, nerves, lymphatics and bone progenitor cells
Which layer of bone regenerate if it were removed?
Bone structure - type
compact or spongy bone
dense bone found at the external surface
- consists of branching trabeculae and spicules
- that extend from the compact bone layer into the internal marrow cavity.
How is spongy bone arranged?
irregular arrangements of lamellae (layers of matrix), within which reside osteclasts within lacunae
Bone structure - spongy bone - what is marrow cavity?
The spaces between the lamellae
- filled with red marrow (containing
- pregenitor blood cells) or yellow marrow (containing fat).
Osteoblast - location and fxn
- Lining the marrow cavity and the external
- surface of the bone (at the periosteal border)
cuboidal-to-columnar cells that secrete osteoid.
Osteoblast - osteoid
- uncalcified bone matrix- mostly Type I collagen (90% of the organic component of bone, 35% of the dry weight), but also some aggrecan
How is osteoid visualize in histological slide?
Osteoid is visible as the lighter border between the osteoblasts and the underlying bone lamellae in this image
Osteoblast - matrix
mineralized with HA crystal and phosphorous and other miner provide the inorganic component of bone matrix
Osteoblast - inorganic and organic component
- 35% organic is type I collagen
- 65% inorganic is from the mineralization of osteoblast matrix
osteocytes - definition
- Osteoblasts that become surrounded and
- encased by matrix
They resides within lacunae
Osteocytes regulate what and how?
bone homeostasis by incorporating calcium into matrix and by releasing signals for osteoclasts to degrade bone when required.
osteoclasts - morphology and location
- large, multinucleated cells derived from
- the monocyte cell line
- They sit in depressions called Howship’s
- lacunae where active bone resorption is
Osteoclast secretes ...
- collagenases, lysozomal enzymes, and
- protons to reduce the pH of the local environment; the inorganic components of bone are dissolved in the acidic environment while the enzymes degrade the organic components
Osteoclast interaction with osteoblast and hormone involvement
- Osteoblasts signal osteoclasts to
- initiate bone degradation which is inhibited by calcitonin released by the thyroid gland
Compact bone forms
- The outer, dense surface of the long
- bone, can be of two forms:
- woven and lamellar bone
the first form of bone produced in the fetus and during bone repair
Woven bone, also known as primary bone or immature bone
compact bone forms - Lamellar Bone
- known as secondary bone or mature bone;
- this is the adult bone structure that replaces the initial structure of woven bone
Woven bone's histology
- •Woven bone has abundant osteocytes with
- irregularly deposited bundles of collagen.
- •Most woven bone is replaced in the adult
- by lamellar bone, with a few exceptions (tendon attachment sites, sutures in the skull, alevoli of
Lamellar Bone - histology
•Lamellar bone is organized into concentric (parallel) layers (lamellae) with osteocytes populating lacunae at regular intervals between the layers.
•Small canaliculi connect lacunae, allowing the osteocytes to extend processes and form gap junctions with their neighbors.
•These canaliculi allow the osteocytes to exchange nutrients, hormones, and waste products, and gap junctions allow direction communication between cells.
•Canaliculi can be seen extending between osteocytes across lamellae to contact each other.
Osteocytes can sense mechanical stresses and communicate with neighboring cells via gap junctions
•Compact bone contains several systems of lamellae.
- •Outer circumferential lamellae are the outermost layers, deep to periosteum,
- which encircle the circumference of the bone.
- •The inner circumferential lamellae encircle the marrow cavity and enclose
- the spongy bone.
•Osteons contain neurovascular elements and their associated connective tissues, and are lined with osteoblasts.
•These systems of lamellae form the bulk of compact bone.
•Osteons extend for considerable lengths and frequently bifurcate along this dimension.
•A thin cementing line of calcified ground substance with few collagen fibers bounds the osteon.
- Periosteum is an outer covering of dense irregular connective tissue, present on the
- anatomical bone everywhere except at the site of attachment of tendons and
- muscles, at articular surfaces, and in some other rare cases (e.g. sesamoid
- bones are not covered by periosteum).
- It attaches to the bone by Sharpey’s
- fibers, long collagen fibers that penetrate the outer, dense layer of compact bone.
- The outer fibrous layer of periosteum
- delivers neurovasculature to the bone.
- The inner fibrous layer of periosteum
- contains osteoprogenitor cells- mesenchyme-derived cells that can differentiate into osteoblasts.
Roles for Bone
- •Movement in conjunction with muscular
•Protection for vital organs
•Storage for minerals
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