Cartilage and Bone Flashcards
What does cartilage consist of?
Extracellular matrix, chondrocytes and proteoglycans
What do chondrocytes do?
Produce and maintain the ECM
What type of GAG is abundant in cartilage and why?
Hyaluronic acid and its negative charges means it attracts water to produce a hydrated gel that allows for diffusion and resistance to pressure
What type of collagen is found in the ECM of cartilage?
Type 2
What are the 3 types of cartilage?
Hyaline, elastic and fibrocartilage
What is hyaline cartilage composed of?
Proteoglycans, hyaluronic acid and type 2 collagen
What are groups of chondrocytes called?
Isogenous groups
Where is hyaline cartilage found?
At articulating surfaces, nose, ribs, larynx, trachea and bronchus
What is the perichondrium?
A layer of dense CT that surround hyaline cartilage except at the articulating surfaces
What is the perichondrium responsible for?
Appositional growth as the fibroblasts in the perichondrium develop into chondrocytes which secrete the ECM causing growth of the cartilage from the edges
What is interstitial growth of cartilage?
Where the isogenous groups deep into the cartilage produce ECM and move away from each other causing growth of the cartilage
What is the composition of elastic cartilage?
The same as hyaline cartilage but with elastic fibres
Where is elastic cartilage found?
In the pinna of the ear and the epiglottis
What is fibrocartilage composed of?
Hyaline cartilage, dense regular CT (lots of type 1 collagen), fibroblasts (elongated) and rows of chondrocytes
Where is fibrocartilage found?
Pubic symphysis, knee joint, intervertebral discs
What is the role of fibrocartilage?
To act as a shock absorber in pressure areas
What is endochondrial ossification?
Where hyaline cartilage is replaced by bone
What types of bone are made from endochondrial ossification?
Long bone
Outline the steps of long bone development
Starts with hyaline cartilage. Periosteal (compact) bone forms in the shaft. The central cartilage calcifies and arteries protrude in supplying osteogenic cells to the area, which develop into osteoblast which lay down osteoid. This is the primary ossification centre. Secondary centres forms at the epiphyses. These then calcify forming bone. Epiphyseal plate remains to allow lengthening of bone.
What is osteoid?
Substance secreted by osteoblasts containing type 1 collagen and ground substance. It is unmineralised
What are the 5 zones found at the epiphyseal growth plates
Zones of reserve cells, proliferation, hypertrophy, calcified cartilage and resorption.
What is a synovial joint?
Articulating joint covered by hyaline cartilage. Contains synovial fluid lined by a synovial membrane
What are osteogenic cells?
Bone cells that can divide and differentiate into osteoblasts
What are osteoblasts?
Cells that produce osteoid found on the periosteum and endosteum
What are osteoclasts?
Multi-nucleated cells that break down bone for remodelling.
Where are osteoclasts found?
In depressions called Howship Lacunae
What are osteocytes?
Osteoblasts that are surrounded by bone
How do osteocytes reach to adjacent cells?
Through cytoplasmic extensions called canaliculi connecting cells via gap junction to exchange nutrients
What type of bone develops from intramembranous ossification?
Flat bone e.g. Skull, pelvic, scapula and clavicle
Outline the process of intramembranous ossification
A cluster of mesenchymal stem cells forms a nidus. These cells then develop RER and Golgi and differentiate into osteoblasts, which start to lay down the osteoid. The osteoid then mineralises forming bone spicules which merge to form trabeculae giving cancellous bone. The trabeculae can then merge together to form layers of lamellae, making up compact bone
What is cancellous bone?
Network of trabeculae which combines strength and lightness. The spaces are filled with bone marrow
What is compact bone?
The external surfaces of bone made up of layers of lamallae
What is a lacuna?
The space where a chondrocyte lies
What is the structure of compact bone?
The lamallae are arranged in concentric layers called osteons. Haversian Channels run down the middle of osteons where the arteries, Lymphatic and nerve vessels lie. Osteocytes are arranged in the osteons of mature bone.
How is bone remodelled?
Osteoclasts real down bone forming a cutting cone. The osteoblasts then follow to form new osteons
Why does bone need remodelling?
To meet the mechanical needs e.g. You want thicker stronger bone if you are exercising more
Outline how bone repairs itself
- Haematoma form as blood vessels break. Bone at edges die. There is swelling and phagocytes remove damaged tissue and blood clot
- Fibrocartilaginous callus forms as new blood vessels infiltrate allowing fibroblast and osteoblasts to enter and form new bone, collagen and cartilage.
- Bony callus formation. The fibrocartilaginous callus is converted into spongy bone
- Bone remodelling
What is osteoporosis?
Where more bone is broken down then is formed
What are the 2 types of primary osteoporosis
- Where there is an increase in osteoclasts
2. Where there is a decrease in osteoblasts
What is type 1 osteoporosis?
Resorption of bone in post menopausal women
What is type 2 osteoporosis
Bone resorption in the elderly
What are the 2 different types of type 2 osteoporosis
Increased Osteoclast activity and decreased osteoblast activity
