What types of tissue are cartilage and bone considered?
specialized types of connective tissue
True or false: There are more cells than ECM in cartilage and bone.
False. There is more ECM than cells in cartilage and bone.
What resident cells in cartilage are responsible for its production? What cells have the same function in bone?
What are the 2 main components of the ECM of cartilage and bone? What makes them special?
collagen fibers and GAGs (as is true for all connective tissues) but these components are arranged in such a way that makes cartilage and bone well suited to their skeletal functions
What type of embryonic connective tissue are cartilage and bone originated from?
mesenchymal connective tissue
What are the 3 types of cartilage? Generally, how do they differ?
4. largely differ in the fiber content of their matrix
True or false: Cartilage is avascular and aneural.
True. Nutrients and wastes are supplied/taken away via diffusion. Pain in joints due to cartilage damage occurs in surrounding tissues.
What are characteristics of hyaline cartilage? (location, function, composition)
- embryonic skeleton
- costo-chondral junctions (junction btwn costal cartilage of ribs and sternum)
- articular surfaces of synovial joints
- external ear
- supporting structures: trachea, nose
- eustacian tube (links nasopharynx to middle ear)
- epiphyseal plates
- resist compression
- provide smooth surfaces for articulation at diarthrodial joints
- Collagens: primarily type II collagen but also minor amounts of types VI, IX, X, and XI which fxn to crosslink collagenous and non-collagenous components of the ECM
- aggrecan: rich in chroitin sulfate and keratan sulfate
- chondronectin: glycoprotein that mediates adherence of chondrocytes to type II collagen
- growth factors
What are lacunae?
small cavities containing chondrocytes
What are the territorial and interterritorial matrices (in cartilage)? What are the differences in their affinity for basophilic staining?
territorial matrix: matrix surrounding a group of chondrocytes (lacunae)
interterritorial matrix: matrix btwn chondrocytes in a lacunae
territorial matrix is slightly more basophilic (stains darker purple)
What are isogenous groups (in cartilage)?
groups of 2-8 cells in one lacuna suggesting that a cell has divided but daughter cells have not yet produced sufficient matrix to be separated
What is the perichondrium in cartilage?
cellular dense connective tissue layer containing stem cells that produces chondrocytes and ECM.
True or false: Articular surfaces of joint cartilage contain a perichondrium.
False. They do not contain a perichondrium which accounts for the poor capacity of articular cartilage to repair after injury (think of OA)
What are the 2 forms of cartilage growth and how do they differ?
interstitial growth: occurs from within cartilage by mitotic division of chondrocytes and expansion of the flexible matrix
appostional growth: growth by maturation of chondroprogentiors in the perichondrium and formation of new matrix below the perichondrium
What are the characteristics of elastic cartilage? (location, function, composition). What type of stain is used to identify it and why?
- pinna of ear
- internal and external auditory tubes
is similar in appearance to hyaline cartilage with H&E staining. dense bundles of elastic fibers must be visualized with Orcein/Weigert staining. elastic fibers allow for deformability and resilience
What is fibrocartilage? (location, function, composition)
- intervertebral discs
- pubic symphysis
- tendon insertions of bone
is similar in structure of hyaline cartilage only with a dense network of collagen type I (stains with eosin) that is produced by fibroblasts within cartilage. looks very much like dense regular connective tissue with differences in lacunar arrangements and fiber arrays that are sometimes pinnate rather than linear in organization
What are the ways in which bone differs from cartilage?
- is mineralized (with exception of mineralization of hyaline cartilage in endochondral ossification and fibrocartilage during bone repair)
- highly vascular
- has nervous supply
- dynamic: able to remodel and repair itself. does so ~ every ten years
- is interactive with other tissues: produces hormones, growth factors to act on other cells
What are the functions of bone?
- protection to vital tissues/organs
- locomotion: tendon and ligament attachments
- mineral deposition (calcium and phospate homeostasis). its ability to remodel allows it to play role in mineral homeostasis
- stroma for hematopoiesis
Bone has both an organic and inorganic matrix. Describe the compositions of each.
Organic: Type I collagen, aggrecan composites (GAGs and proteoglycans)
inorganic: hydroxyapatite (calcium phosphate)
collagen type I and mineral are the major compositions of bone
What are the 3 main cell types in bone? (just list them)
What are the main features of osteoblasts? (derivation, location, function)
- derived from primitive osteoprogenitor cells (which are derived from mesenchymal stem cells)
- located on internal bone surfaces and beneath the periosteum
- secrete organic bone matrix called osteoid which when mineralized, becomes bone
- become osteocytes when surrounded by a mineralized matrix
What are the main features of osteocytes? (derivation, location, function)
mature bone cells (matured osteoblasts) that reside in lacunae surrounded by bone matrix that they have produced. are deeper in bone than osteoblasts (which reside at surface). send extensive spiderlike cytoplasmic processes into tiny canaliculi in the matrix (canaliculi are microscopic canals btwn lacunae of ossified bone. radiate like wheel spokes from each lacunae to connect with canaliculi of adjacent lacunae and with the Haversian canal). communicate with other osteocytes via gap junctions btwn cytoplasmic processes-forms a cell network within the bone. function in turnover and maintenance of bone maintenance through mechanotransduction: sense mechanical stress on bone and can send signals to osteoblasts to proliferate. also fxn in immobilized osteoporosis. their ability to remove caclium (osteocytic osteolysis) from bony matrix makes them key players in Ca2+ homeostasis.
What are the main features of osteoclasts? How are they stimulated and inhibited? (derivation, location, function)
developed from pluripotent hematopoietic cells that traveled to bone. specialized type of macrophage. multinucleated (up to 200, at least 3-8) large cells (20-100 µm) formed from fusion of monocytes. function in bone resporption by attaching to bony surface through cell membrane integrins and removing inorganic matrix and digesting organic matrix. found in Howship's lacunae that they have created in trabecular surgace of spongy bone or may be active in resorption cavities within compact bone
osteoclast development from monocytes is stimulated by both cytokines (M-CSF and RANKL) and direct interaction with osteoblasts. PTH activity through osteoblasts stimulates osteoclast activity. osteoclasts are directly inhibited through binding of calcitonin.
define the following terms:
- epiphysis: head of a long bone
- diaphysis: long shaft part of bone
- metaphysis: region that connects epiphysis and diaphysis
- epiphyseal line: also known as growth plate. is cartilaginous
- periosteum: dense lining outside of bone
- osteogenic layer: inner cellular layer of periosteum that can give rise to new bone on the outside
- endosteum: single layer of osteogenic cells lining the marrow cavity
True or false: The epiphysis of bone typically contains articular cartilage.
What are the two types of bone marrow?
red marrow: hematopoietic
yellow marrow: is more fatty. increases with age.
What are the 2 types of bone? (just list them). How may they be further classifed by maturity?
spongy aka trabecular, alveolar, cancellous
compact aka lamellar, Haversian, cortical, compacta
woven: immature. not very well organized
lamellar: mature. is well organized
What are characteristics of spongy (aka trabecular, alveolar, cancellous) bone? What is it composed of?
interconnected network of trabeculae or bone spicules that provide a supporting framework beneath or above compact bone. can remodel in response to stress. marrow permeates the space btwn bone spicules.
trabeculae contain entrapped osteocytes. a layer of osteoblasts cover the surface and produce a layer of organic matrix called the osteoid on teh surface of mineralized trabeculae. a similar layer of cells on the inner surface of the marrow cavity forms the endosteum (contains osteogenic cells)
True or false: Since trabeculae (in spongy bone) are thin and surrounded by capillaries of the marrow cavity, osteocytes are nourished by diffusion from the surface through canalicular channels.
What are characteristics of compact (aka lamellar, Haversian, cortical, compacta) bone? What is it composed of?
dense outer subunits of bone consisting of calcified layers arranged in concentric layers of lamellae (osteons, Haversian systems) around a core of vessels and nerves. may lack regular Haversian systems in woven bone (immature bone)
more detail about above:
Haversian systems/osteons are organized around Haversian canals which contain a neurovascular bundle conisiting of an artery, a vein, and a nerve.
Volkmann's canal: interconnect Haversian canals. are perpendicular to the longitudinal axis of osteons
when picturing a step ladder, can think of Haversian canals as long sides of step ladder and Volkmann's canals as the steps
osteoclasts: can be found periodically on trabecullar surface or in erosion pits called Howship's lacunae. attachments at their perimeter and ruffled border at the bony surface create an acidic microenvironment for demineralization and lysosomal digestion of organic matrix