15 - Cartilage and Bone Flashcards
What are the three types of cartilage?
- Hyaline cartilage
- Elastic cartilage
- Fibrocartilage
What do all three types of cartilage contain?
- Proteoglycan and hyaluronic acid
- All contain chondrocytes
What type of fibres does each type of cartilage contain?
- Hyaline cartilage - type II collagen
- Elastic cartilage - elastic fibres
- Fibrocartilage - type I collagen
What cell type is present in hyaline cartilage? How do they appear?
- Only chondrocytes
- Present singly or in clusters if they’ve just divided (isogenous groups)
- Isogenous groups separate as they lay down ECM
Where is hyaline cartilage found?
- Precursor for bones that develop by endochondral ossification in foetal development
- Some remains at articulating surfaces and the epiphyseal plate
- Rib cage, nose, trachea, bronchi and larynx
The proteoglycan ground substance is similar in structure to other connective tissues. How does it differ in cartilage from loose connective tissue?
Cartilage has ~100 proteoglycan aggregates per collagen fibril, loose connective tissue is only ~10
Makes a much stiffer gel-like substance
The margin of hyaline cartilage is covered with dense connective tissue called …..
the perichondrium
Growth of cartilage from the periphery into the centre is known as …..
Appositional growth
Growth of cartilage from the centre to the periphery is known as …..
Interstitial growth
Cartilage ECM is highly hydrated, why is this important?
Water is non-compressable, so permits resilience to increased loads
How is the hyaline cartilage in the trachea structured and what is its purpose?
- Tube formed from C-chaped cartilages
- Lined with pseudostratified ciliated epithelium
- Reinforces the trachea to protects and maintain the airway
What cells and fibres are found in elastic cartilage?
- Chondrocytes (no other cells)
- Elastic fibres
What 3 places in the body is elastic cartilage found?
- The pinna of the ear
- The Eustachian tube (drains inner ear)
- Epiglottis
The elastic cartilage in the pinna of the ear grows by which mechanism?
Interstitial growth
What is the structure of fibrocartilage?
- Chondrocytes and fibroblasts
- Mixture of dense regular connective tissue and hyaline cartilage
- Cells often seen in rows
- No perichondrium
Where is fibrocartilage found? What does it do?
- Intervertebral discs
- Articular discs of sternoclavicular and temporomandibular joints
- Menisci of the knee
- Pubic symphysis
Resilience to act as a shock absorber and resist shearing forces
Where and by what mechanism does cartilage become bone?
- In development of the long bones
- Grow by endochondral ossification
- Hyaline cartilage model mineralises to form bone
During growth of the long bones cartilage becomes bone at growth plates, where are the growth plates found?
In the epiphysis
What are the main stages in endochondral ossification?
- Whole bone initially cartilage model
- Collar of compact bone appears in the shaft (diaphysis)
- Central cartilage calcifies, nutrient artery penetrates and supplies osteogenic cells (forms primary ossification centre)
- Medulla of diaphysis becomes cancellous bone, epiphyseal growth plates form and epiphyses develop secondary ossification centres
- Epiphyses ossify and growth plates move apart, lengthening bone
- Epiphyseal growth plates eventually replaced with bone, only articular hyaline cartilage remains
Long bones increase in length by ……… ossification and in girth by ………. ossification
Length - endochondral ossification
Girth - intramembranous ossification
Osteocytes are surrounded by ……….. produced by ……………….., when these cells become trapped they become osteocytes themselves
Osteoid
Osteoblasts
What is an osteoprogenitor cell?
Stem cell that produces osteoblasts and periostium
What is an osteoblast?
Forms inner layer of endosteum and spicules, lays down new bone secreting the organic components of the matrix
What is an osteocyte?
Terminally differentiated bone cell, trapped within the osteon and no longer lays down matrix
What is an osteoclast?
Huge multinucleate cell (fused monocytes) on the surface of cortical bone. Lie in depressions where they are degrading the bone.
Reabsorb existing bone for remodelling
What is the functional unit of compact bone? What is it composed of?
The osteon
Layers of compact mineralised collagen, containing osteocytes (trapped osteoblasts)
Where in the osteon are osteoclasts found?
Not within the bone, only on the edges (endosteum and periosteum) where they degrade bone
Osteons contain canals with blood vessels and neurones, what are these called and in what direction do they go?
Vertical within osteon cylinder - Haversian canal
Horizontal connecting osteons - Volkmann’s canal
What is osteoarthritis?
Age-related degeneration and mechanical failure of articular cartilage
Narrows the joint space and bone rubs against bone
What is rheumatoid arthritis?
Autoimmune disease causing inflammation of the synovial membrane and thickening of the joint capsule
- Damage to underlying bone and cartilage (both begin to disintegrate)
What are osteophytes?
- Bony spurs that grow due to narrowing of the joint space and bones rubbing together
- Cause inflammation and pain
- Cannot be broken down by osteoclasts
