CT, Cartilage, and Bone Histology Flashcards
What are the three components of CT?
Cells, fibers, ECM
What is the resident cell of CT?
Fibroblast
What are the features of loose CT?
More cells than collagen fibers
Where is loose CT usually found?
Surrounding blood vessels, nerves, and muscles
What are the features of dense CT?
More collagen fibers than cells
What are the features of dense regular CT?
Preferentially oriented collagen fibers
What are the features of dense irregular CT?
Randomly oriented collagen fibers
What is the structure of GAGs?
Long, unbranched polysaccharides consisting of repeating disaccharide units; highly negatively charged
What is the function of GAGs?
Associate with large amounts of water to create hydrated gels with high viscosity and low compressibility
What are the four main components of the ECM?
Glycoaminoglycans (GAGs), proteoglycans, adhesive glycoproteins, and collagen
What is the structure of proteoglycans?
Protein core with at least one covalently bound GAG; highly negatively charged
What are the functions of proteoglycans?
Organization and stabilization of the ECM by interaction with other molecules; component of the basal lamina of epithelial cells to create a barrier to the passage of positively charged molecules
What is the structure of adhesive glycoproteins?
Proteins with disulfide-bound subunits and binding sites for cells and other ECM components
What are the functions of adhesive glycoproteins?
Facilitate the attachment of cells to the ECM; affect growth, survival, morphology, differentiation, and motility of cells
What are the two primary glycoproteins?
Laminin and fibronectin
What is the general function of type I, II, and III collagen?
Providing tensile strength to tissues
What is the structure of mature collagen fibers?
Multiple associated triple helices formed by three individual α-chains
How is collagen formed?
Fibroblast translates and modifies individual α-chains; assembly of α-chains into soluble triple helix (procollagen); secretion of procollagen into extracellular space; cleavage via proteases (C and N propeptidase) into insoluble tropocollagen; spontaneous assembly of tropocollagen into collagen fibrils; association of collagen fibrils into immature collagen fibers; crosslinking of immagture collagen fibers via lysyl oxidase to form mature collagen fibers
What are the three types of cartilage?
Hyaline, elastic, and fibrous
What are the primary cells that form cartilage?
Chondrocytes
What type of cartilage is this?
Hyaline cartilage
What type of cartilage is this?
Elastic cartilage
What type of cartilage is this?
Fibrous cartilage
What is the connective tissue layer that surrounds most cartilage?
Perichondrium
What is the function of the perichondrium?
Contains stem cells that differentiate into chondroblasts, then chondrocytes
What are the two mechanisms by which chondrocytes grow?
Interstitial growth by division of existing chondrocytes; appositional growth by the production of new cells from the perichondrium
Not a real question, but did you know that cartilage and dense regular connective tissue are avascular and therefore heal poorly?
*In the voice of Cecil from WTNV*: …neat!
What is the structure of hyaline cartilage?
Surrounded by perichondrium; chondrocytes surrounded by type II collagen, proteoglycans, and water (provides compressive strength)
Where is hyaline cartilage found?
Skeleton of the embryo, articular cartilage in joints, cartilage of respiratory tract
What is the structure of elastic cartilage?
Surrounded by perichondrium; surrounded by type II collagen, proteoglycans, and elastic fibers
Where is elastic cartilage found?
External ear and epiglottis
What is the structure of fibrous cartilage?
No perichondrium; surrounded by type I collagen; resembles dense fibrous connective tissue
Where is fibrinous cartilage found?
Intervertebral disks, menisci of the knee, pubic symphysis
What is the composition of the organic matrix of the bone (osteoid)?
Type I collagen and proteoglycans (osteocalcin, osteopontin, osteonectin)
What is the composition of the inorganic matrix of the bone (bone mineral)?
Hydroxyapatite (calcium and phosphate salt)
What are the four major cell types in bone?
Osteoblasts, osteocytes, osteoclasts, and osteoprogenitor cells
What are the functions of osteoblasts?
Deposit osteoid along the osteoblast-bone interface; initiate and control mineralization of the osteoid
Maybe make a card that says: What are some of the proteins that osteoblasts express?
Cool
What is the first bone matrix produced by the osteoblast?
Primary or woven bone
What are the characteristics of primary/woven bone?
Loose, randomly oriented collagen fibers; low amounts of hydroxyapatite
What is the primary/woven bone matrix remodeled into?
Secondary or lamellar bone
What are the characteristics of secondary/lamellar bone?
Organized sheets of collagen fibers (lamella); high amounts of hydroxyapatite
What is the function of osteocytes?
Respond to forces on the bone, release factors that stimulate bone remodeling or turnover
What are the characteristics of osteocytes?
Highly branched cells; cell bodies occupy lacunae within the layers of bone matrix; processes pass through canaliculi and interconnect
How are osteocytes formed?
Osteoblasts flatten out and transform into osteocytes when bone formation is complete
What is the primary function of osteoclasts?
Degradation of the bone matrix
What are the characteristics of osteoclasts?
Large, multinucleated cells; highly polarized with a ruffled border; contains high levels of carbonic anhydrase II (creates acidic microenvironment for solubilizing mineralized component of bone; lots of steps that I don’t really care to memorize unless McGuire says we have to)
How are osteoclasts formed?
Derive from monocyte precursors in the bone marrow; undergo osteoclastogenesis (lots of steps that I don’t really care to memorize unless McGuire says we have to)
What is the function of calcitonin?
Decreases bone turnover by activating osteoclast calcitonin receptors (CTR), which inhibits osteoclast activity, causing immobilization and retraction away from the bone surface
What are the two classifications of bone structure?
Cortical or compact bone; trabecular or cancellous bone
What are the features of cortical/compact bone?
Osteocytes and bone matrix are arranged into osteons
What is the structure of an osteon?
Central (Haversian) canal with blood vessel; canal surrounded by concentric layers (lamellae) of bone cells and matrix; canaliculi traverse the lamellae to form connections between lacunae and central canals
What is the structure of trabecular/cancellous bone?
Layers of lamellae form bony trabeculae that project into the marrow cavity; randomly distributed osteocytes within trabeculae; surface of trabeculae covered with osteoblasts and osteoclasts
What hormone is released in response to hypocalcemia?
Parathyroid hormone (PTH)
What are the functions of PTH?
Decreases osteoid matrix synthesis by activating osteoblast receptors; increase bone turnover by secretion of osteoclast activating factors, which cause the differentiation of osteoclasts
What hormone is released in response to hypercalcemia?
Calcitonin
