Cartilage and Bone Flashcards

Question

Tissue Distribution in Bone

Answer 1

1. **Cancellous bone** (aka spongy bone, trabecular bone) * Plates of bone organized into interconnected vertical and horizontal struts * Marrow occupies the spaces in spongy bone * Found primarily in: * Flat bones of the skull * Ends of long bones * Inside other "spongy" bones such as vertebrae 2. **Compact bone** (aka cortical bone) * Densely packed bone matrix * Forms the outer cortex of all bones * Found in abundance along the shafts of long bones

Answer 2

* Covers the exterior of a bone except at articular surfaces * Continuous with CT of tendons and skeletal muscles * Two layers * Outer fibrous * Inner cellular * _Sharpey's fibers_ insert into the bone surface and connect the periosteum to the bone tissue * Provides the vascular supply to the bone * Serves as a source of osteoprogenitor cells

Answer 3

* Thin single cell layer of CT which covers the interior surfaces of bone * Covers most internal surfaces of bone including Haversian canals, Volkmann's canals, and marrow cavity * Contains osteoprogenitor cells

Answer 4

* Bundles of collagen fibers that insert into bone tissue * Prominent where tendons and ligaments insert on bone * Also connect the periosteum to the bone tissue

Answer 5

* Spaces of spongy bone filled with bone marrow * Forms the inner portion of the bone * Contains hemopoietic cells * Bone marrow sinusoids provide a barrier between the hemopoietic compartment and the peripheral circulation

Answer 6

* Fairly extensive blood supply * Nutrient arteries * Long bones usually have a nutrient artery that penetrates the bony collar of the diaphysis and divides in the marrow cavity * Branches then enter the Haversian canals * Periosteal arteries enter the Haverisan canals from the outer surface of the bone * Metaphyseal and epiphyseal arteries

Answer 7

* **Collagen** * Major organic constituent of bone - about 90% of the organic matrix * Type I collagen * **Ground substance** * About 10% of the organic matrix * _Proteoglycans_ * GAG's * Chondroitin sulfate * Keratin sulfate * _Glycoproteins_ * _Osteocalcin_ * binds to hydroxyapatite crystals * _Osteonectin_ * binds calcium * important in regulating mineralization * _Osteopontin_ * binds to hydroxyapatite and other components for adhesion of cells to matrix * _Sailoproteins_ * For cell adhesion to the matrix

Answer 8

* About 65% dry weight of bone * Ca₁₀(PO₄)₆(OH)₂ crystals similar to hydroxyapatite * Crystals deposited in the gaps between collagen fibers * Calcification lags behind fiber formation * New unmineralized bone called _osteoid_

Answer 9

* Determined but not differentiated mesenchymal cells * Derived from pluripotent stromal cells in bone marrow and other CT * When activated, divide and produce osteoblasts * Characteristics: * Flattened cells * Found in inner layer of periosteum or endosteal lining of bone * Resembles young fibroblasts

Answer 10

* Cells that synthesize bone * Secretes collagen and ground substance as unmineralized _osteoid_ * Secrete _matrix vesicles_ that contribute to the mineralization process * Vesicles slowly accumulate mineral over time * Forms a single layer of cells on surfaces of developing or remodeling bone * Characteristics: * Cuboidal * Typical characteristics of protein-secreting cells * Connected to each other by processes that end in gap junctions * Once they become surrounded in matrix that they produce cells are considered osteocytes * Quiescent osteoblasts that line the surfaces of a bone formation region after osteoid production is complete are called **bone lining cells** * Has receptors for parathyroid hormone (PTH), Vit D₃ * Important in regulation of osteoclast activity and calcium levels * Has estrogen receptors * Cell membranes rich in **alkaline phosphatase** ⇒ used as a marker enzyme

Answer 11

* Mature, differentiated cells, derived from osteoblasts that have become buried in mineralized bone matrix * Reside in _lacunae_ * Communicate with one another through cell processes joined by gap junctions * Processes run through small fluid filled canals called _canaliculi_ * Functions: * Involved in mineral homeostasis * Can likely remove mineral from a limited region surrounding the lacuna via _osteogenic osteolysis_ * Have _mechano-sensory role_ in the stimulation of remodeling

Answer 12

* Cells responsible for the resorption of bone * Large, multinucleated cells * Structural syncitium * Derived from a common bone marrow precursor as monocytes * Differentiate first into uninucleate osteoclast precursors * Activated precursors fuse to produce mature multinucleated osteoclasts * Create resorption bays called _Howship's Lacunae_ along the surface of bone being removed * _Ruffled border_ formed by folds of the plasma membrane that increase cell surface area and represents the zone of contact with bone * _Actin_ microfilaments in the _clear zone_ surrounding the ruffled border healp seal the cell to the bone surface * Release of acid (H⁺) by the osteoclasts into the Howship's lacunae to dissolve the mineral crystals * Organic matrix degraded by lysosomal enzymes ⇒ _collagenases_ * Activity indirectly stimulated by PTH through osteoblasts * Activity directly inhibited by calcitonin

Answer 13

* Role of Parathyroid Hormone * When [PTH] high, osteoblasts stimulate maturation of osteoclasts through release of _macrophage colony stimulating factor_ and expression of RANKL molecules on their own membrane * Osteoclast precursors have RANK receptors which bind the RANKL stimulating them to differentiate and fuse with one another * When [PTH] low, osteoblasts release _osteoprotegerin_ * This can bind RANKL to prevent it from stimulating differentiation of osteoclasts * Role of Estrogen * High [estrogen]: * increases osteoblast production of osteoprotegerin. * Binds more RANKL, decreasing production of osteoclasts * Suppresses RANKL production * Prolongs life of osteoblasts * Post-menopausal women have decreased estrogen levels thus favoring bone loss leading to osteoporosis

Answer 14

Cancellous vs compact bone Differentiated based on the amount of space (porosity) of the bone.

Answer 15

Applies to both cancellous and compact bone. AKA immature bone * A form of immature non-lamellar bone tissue * First bone to appear during bone formation * Eventually replaced by lamellar bone during the growth and remodeling process * Found in areas of injury repair * Characteristics: * Deposited quickly during growth and fracture repair * Randomly oriented collagen fibers and cells * Highly cellular * More porous & less dense than lamellar bone * Not as strong as lamellar bone

Answer 16

* Bone organized into layers of aligned collagen called lamellae * Layers usually seperated from one another by a single layer of osteocytes * Slow deposition due to highly organized structure * Stronger material better able to resist biomechanical loads than woven bone * Found in both cancellous and compact bone tissue types * In cancellous bone * lamellae will not form Haversian systems * Instead form layers on the surface of the trabeculae that make up cancellous bone * In compact bone * Lamellae will either be circumferential or in Haverisan systems **Circumferential Lamellar Bone** * Organized into linear sheets that encircle the bone * In adults primarily found as the outer circumferential lamellae and inner circumferential lamellae * Encircles the bone just deep to the periosteum and just superficial to the endosteum respectively **Haversian System** (Secondary Osteons) * Represents bone that has formed by the secondary remodeling process * Forms much of the bone matrix in adult human compact bone * As we age, more lamellar bone will remodel to form Haversian systems

Answer 17

* Layers of lamellae arranged concentrically around a central Haversian canal * _Haversian canal_ * Long tubular branching structures that run predominantly longitudinally through the bone * Act as vascular channels which run longitudinally through the center of the osteon * Contains blood vessels and nerves which supply the bone tissue * _Volkmann's Canals_ * Obliquely oriented vascular canals linking the Haversian canals of neighboring osteons * Allows blood to pass through a large network throughout the bone * Some also connect with vessels in the marrow cavity or periosteum * Cells within an osteon communicate with one another via cellular processes/gap juctions that run along the _canaliculi_ * Communication between osteons limited due to cement lines * _Cement lines_ * Marks the outer edge of each Haversian system * Represent reveral lines where osteoclasts stopped resorbing bone and osteoblasts started refilling the space * Functionally seperates neighboring osteons since canaliculi *generally* do not cross cement lines * _Interstitial lamellae_ * Remnants of old Haversian systems or circumferential lamellae * Found between exsiting HAversian systems * Formed as a result of the remodeling process