W5 Aatomy And Histology Of Bone Cartilage And Ossification Flashcards
What is cartilage?
Avascular connective tissue
Consists of cells and extracellular matrix (fibres and ground substance)
What does avascular mean for the cartilage?
It has no nerve supply or lymphatic drainage. Nutrition is by diffusion.
What is cartilage surrounded by?
Perichondrium (except articular cartilage and fibrocartilage)
What is the function of cartilage?
Tensile strength to provide a firm structural support for soft tissues, allowing flexibility without distortion and is resilient to compression.
What are the 3 types of cartilage?
Hyaline
Elastic
Fibrous
Where is hyaline cartilage found?
Covers articular surfaces, synovial joints, nasal septum, trachea, larynx etc
Describe hyaline cartilage
Collagen type II
Many chondrocytes
Perichondrium
Why are there no fibres in the hyaline cartilage?
The matrix is homogeneous. The matrix and fibres have the same retractive index so do not appear separate, leaving a glassy appearance.
Describe elastic cartilage
Has many chondrocytes
Has a perichondrium
ECM has fine elastic fibres
Where can elastic cartilage be found?
External ear, epiglottis
Describe fibrocartilage
Type I collagen fibres
Few chondrocytes
No perichondrium
Where is fibrocartikage found?
TMJ, intervertebral disc
Describe the outer and inner layer of the perichondrium
Outer layer - dense vascular connective tissue
Inner layer - chondrogenic = stem cells which give rise to new chondroblasts
Function of the perichondrium
Protection, nutrition, repair
Which cartilages have perichondrium and which don’t?
Articular cartilage and fibrocartilage are not lined by perichondrium but hyaline and elastic are.
What types of cells are found in cartilage?
Chondroblasts - synthesis the matrix. Enlarge the cartilage by both interstitial and appositional growth.
Chondrocytes - mature cartilage cells, enclosed in lacunae (maintain the matrix)
What does the matrix of cartilage contain?
Glycosaminoglycans (chonrdoitin sulfate) and fibres (collagen or elastic)
What is the function of the matrix of cartilage?
Allows diffusion and acts as a semirigid shock absorber.
What are the roles of bone?
Haemopoiesis, reservoir for calcium and minerals
What is the bone covered by?
Periosteum except articular surfaces.
Why is the bone matrix highly vascularised?
To aid diffusion in the calcified matrix
What do the organic and inorganic components of the bone matrix do?
Organic components resist tension
Mineral components resist compression
What are the 4 types of bone cell?
Osteoblasts, osteogenic, osteoclasts, osteocyte
What is the initial bone matrix called and what secretes it?
Osteoblasts secrete components of the initial matrix = osteoid (before it becomes mature, consists of the inorganic component)
What are the osteoid components?
Type I collagen, osteocalcin (a protein), which then vines calcium and phosphate ions forming hydroxyapatite crystals
What do osteocytes do?
They are enclosed within lacunae and maintain the matrix. They detect mechanical stresses on bone. They maintain communication with adjacent cells via a network of long dendritic processes (pass through canaliculi radiating from each lacuna.
How does bone grow?
Interstitial growth: bone grows in length and height - important in growing age
Apositional: growth in bone girth/width - important in fractures and repairs
New bone is deposited and old bone is degraded
How is bone repaired, e.g., after fracture? (Min 37 zoom)
- Hematoma - accumulation of blood
- Hematoma replaced by a fibrocartilaginous (soft) callus forms and blood vessels start to revascularise
- A hard (bony) callus forms (woven bone) after a few days
- Eventually the bone is remodelled to lamellar bone
What do PTH and calcitonin do?
PTH decreases blood calcium levels and calcitonin increases blood calcium levels.
