Bone & Cartilage Flashcards
What is the difference between chondroblasts and chondrocytes?
-blasts are precursor cells. -cytes are when the cell is surrounded by the matrix it has made
What is the embryologic origin of chondrocytes?
mesoderm. mesenchymal cells
What is the perichondrium?
Mesenchymal cells that immediately surround the matrix become perichondrium
Perichondrium covers most cartilage EXCEPT?
articular cartilage at the synovial joint and fibrocartilage
What is the name for the gap in the matrix that chondrocytes sit in?
lacuna
What is the major reason cartilage can withstand compression?
Its water content. ~60-80%
What is the composition of cartilage?
-60-80% water
-type 2 collagen
-9% proteoglycans
-5% glycoproteins
What is the type of collagen incorporated into cartilage?
type II
What are the two types of proteoglycans in cartilage? what type of cartilage are they in respectively?
-Aggrecan : hyaline & elastic
-Versican: fibrocartilage
Describe the structure of cartilage
- aggrecans attach through their core protein to linear hyaluronic acid molecules. This linkage is stabilized by a link protein.
What is a proteoglycan aggregate?
aggrecan attached to the hyaluronic acid molecule (hyaluronin)
What is the main reason cartilage is difficult to repair?
no blood vessels or lymphatics
How is nutrition provided to cartilage?
diffusion through the hydrated gel of the matrix
What are the two types of cartilage growth?
-Appositional
-Interstitial
Where does appositional growth occur?
Perichondrium
What are the 3 types of cartilage?
-Hyaline
-Elastic
-Fibrocartilage
What is the most common type of cartilage?
hyaline
Why is hyaline cartilage so basophilic?
aggrecan
What are the 6 main locations of hyaline cartilage?
-fetal skeleton
-synovial articular surfaces
-epiphyseal plates
-larynx
-nasal cartilage
-trachea & bronchi
How can you tell the difference between fetal and mature cartilage histologically?
Most chondrocytes/lacunae are single in mature cartilage. In fetal cartilage there are usually groups of chondrocytes called isogenic clusters
What is an isogenic cluster?
a pair/group of chondrocytes. Found mainly in fetal cartilage
What is the main difference between hyaline and elastic cartilage?
elastic cartilage has elastic fibers in it, which can be seen with H&E but need to be highlighted by special stain. Chondrocytes often appear larger/more plump
Where can you find elastic cartilage? (4)
-Pinna
-Auditory tube
-Epiglottis
-Laryngeal cartilages
Describe the structure of fibrocartilage
light blue hyaline cartilage matrix, mainly interstitial growth, relatively parallel bundles of type 1 collagen.
What is a defining feature of fibrocartilage?
no perichondrium
Why is there no appositional growth in fibrocartilage?
no perichondrium
Where can you find fibrocartilage?
Tendon insertions, intervertebral discs, pelvic symphysis, menisci of the stifle joint.
What type of collagen makes up most of the organic material in bone?
type I
What gives bone its hardness?
hydroxyapatite
What is hydroxyapatite?
A form of calcium phosphate that gives bone its hardness
What is the bone precursor cell?
osteoblast
What is the term for the bone matrix produced by osteocytes?
Osteoid
What triggers mineralization of osteoid?
alkaline phosphatase
How can you identify a bone tumor?
Stain for alkaline phosphatase
Do osteocytes communicate? if so how?
gap junctions
What are bone lining cells?
cells derived from osteoblasts that are inactive, but can be reactivated if needed for remodeling
What are the roles of osteoclasts?
remodel bone through decalcification, reabsorption of bone matrix
What two things are need for osteoclasts to reabsorb bone?
-acid to demineralize
-proteolytic enzymes to break down collagen
What is an osteoclast?
a multi nucleated cell derived from the fusion of blood monocytes
What is the “docking station” of osteoclasts?
howship’s lacunae
What is the first bone formed at any site including when you fracture a bone?
woven bone
What is woven bone replaced with ?
lamellar bone
What is the structure of a long bone?
-Epiphysis
-Epiphysis plate
-Metaphysis
-Diaphysis
-Marrow cavity
-Periosteum
-Endosteum
What are the two types of bone based on architecture?
-Cancellous
-Compact
What is the basic structural unit of compact bone?
The osteon
What is the center of an osteon called? 3 poss names
-Osteonal canal
-central canal
-Haversian canal
Where do blood vessels and nerves travel in bone?
Through the osteon
What are the two types of histological preparations of bone tissue?
-decalcified (all mineral removed)
-Ground section (no organic material)
What carries blood vessels between osteons?
transverse (volkman’s) canal
What are the two ways to form new bone in the fetus?
Intramembranous ossification
Endochondral ossification
What is Intramembranous ossification? What type of bone does it occur in?
Bone is formed by direct replacement of embryonic mesenchyme. Flat bone
What is Endochondral ossification? What type of bone does it occur in?
Cartilage model serves as the template bone. Long bones
Describe the process of intramembranous ossification
Embryonic mesenchyme condenses into a vascular CT, then mesenchymal calls differentiate into osteoblasts, osteoid is deposited into the mesenchyme, which is the formation of bone islands. A bone tissue surface is now available for appositional growth.
Describe the process of endochondrial ossification
-Relies on a template of hyaline cartilage
-This template continues to grow as ossification proceeds
-Bone collar forms around diaphysis, chondrocytes in inner diaphysis hypertrophy, chondrocytes secrete alkaline phosphatase causing mineralization and death of cartilage.
-Invading osteoblasts (via vessels that have broken through collar) lay down osteoid on the calcified cartilage, calcified cartilage provides surface for appositional growth.
-Secondary ossification center forms at epiphyseal plate where growth of bone in length continues
What are the 5 layers of the epiphyseal plate?
-Reserve cartilage
-Proliferation
-Hypertrophy
-Calcified cartilage
-Resorption
When does bone remodeling occur?
-Developmentally
-Throughout life
-Fracture repair
What cells make up the cutting cone?
osteoclasts
What cells make up the closing cone?
osteoblasts
