1.04 - Bone & Cartilage Flashcards
Describe Bone
A specialised form of connective tissue
Cells in an abundant extracellular matrix
Describe the Extracellular Matrix of Bone
The Extracellular matrix is made up of fibres (Type I collage of tensile strength) in ground substance (called osteoid) that becomes mineralised by the deposition of calcium hydroxyapatite (hardness)
What are the types of cells involved in bone formation and regulation?
Osteoprogenitor cells
Osteoblasts
Osteocytes
Osteoclasts
Describe Osteoprogenitor cells
Precursor cells that self replicate or differentiate into bone-forming cells
Describe Osteoblasts
Bone forming cells that deposit osteoid and control subsequent mineralisation
Describe Osteocytes
Modified osteoblasts that become surrounded by newly formed bone - regulate homeostasis
Describe Osteoclasts
Large multinucleate phagocytic cells that resorb bone and break down calcified matrices
Originate from haemopoietic stem cells
Describe the process of ECM calcification in bone
The matrix comprises: 70% inorganic salts (calcium and phosphate) and 30% organic matrix (90% Type I collagen)
Calcification begins a few days after the deposition of osteoid by the osteoblasts
Calcium phosphate precipitates on the collagen molecules.
About 75% of the calcium hydroxyapatite is deposited in the first few days but complete calcification may take several months.
What are the two types of bone and their respective subtypes?
Woven (or immature bone)
Lamellar (orderly strata of bone matrix)
- Compact Bone
- Cancellous Bone (Trabecular & spongy)
Describe Woven or immature bone
Randomly arranged collagen fibres in the osteoid
Produced when osteoid is produced rapidly
Eventually remodelled to form Lamellar Bone
Under what conditions is Woven (or immature) bone produced?
When osteoid is produced rapidly, such as in foetal bone, healing of fractures and in bone diseases such as Paget’s disease
Describe Lamellar bone
Mature bone
Regular parallel bands of collagen fibres in the osteoid
Stronger and more resilient than woven bone
What structures is compact bone made up of?
Lamellae Haversian canals Haversian systems (osteons) Lacunae Canaliuli
What is Lamellae?
Concentric layers of mineralised bone matrix
What are Haversian Canals?
Neurovascular channels surrounded by lamellae. Provide nutrients to the tissue.
Canals run parallel to the surface along the axis of the bone
What are Haversian System (or osteons)?
Lamellae + Haversian canals
What are Lacunae?
Small hollows in the matrix in which osteoblasts become encased
What are canaliculi?
Small channels within the bone matrix formed by the thin processes of osteocytes that extend from the lacunae.
Canaliculi rising from one lacuna man anastomose with those of other lacunae and then eventually with larger, vessel containing canals within the bone
What is the function of Canaliculi?
Provide the means for the osteocytes to communicate with each other and to exchange substances by diffusion
Describe Cancellous bone
Also called Spongy or Trabecular bone
Mature bone with irregular lamellae
Bony trabeculae separated by interconnecting spaces containing bone marrow
Lamellae in cancellous bone do not form aversion systems
List the steps in bone remodelling
Damage repaired
Ion homeostasis maintained
Bone reinforced for increased stress
Bone growth
What are some important factors influencing bone remodelling?
Nutrition Hormones (Vitamin D, Parathyroid Hormone - PTH) Physical Activity Age Growth Factors
What are the two types of bone development and growth, and where do they occur?
Intramembranous ossification: direct replacement of primitive mesenchymal tissue by bone (vault of the skull, maxilla and most of the mandible)
Endochondral ossification: Cartilage bone is replaced by normal bone (long bones, vertebrae, pelvis)
What are the major functions of bone?
Largely structural (movement, protective)
Source of calcium and phosphate
Haemopoiesis (marrow)
Gives the skeleton the necessary rigidity to function as an attachment and lever for muscles and supports the body against gravity
Describe Cartilage
Few cells with abundant extracellular matrix (ground substance)
Cells include: chondroblasts, chondrocytes
Does not contain vessels or nerves. Depend on the diffusion of nutrients which limits the thickness of cartilage
Surrounded by a layer of dense connective tissue, the perichondrium
Contains about 75% water
What are chondroblasts and chondrocytes?
Chondroblasts are precursor cells in cartilage
Chondrocytes are mature cells in cartilage
Describe the ECM in Cartilage
A gel like matrix with firers (collagen and elastin fibres) in ground substance (sulphated proteoglycans and hyaluronic acid)
What are the functions of cartilage?
Provides semi-rigid and bone rigid structural support
Supports soft tissues (ear, nose, epiglottis, trachea)
Shock absorption in joints
Important in development, growth and healing of bones
What are the types of Cartilage?
Hyaline cartilage (glassy, blue) Fibrocartilage (white) Elastic cartilage (yellow)
Describe Hyaline Cartilage
Most common type Fibres - Type II Collagen Ground Substance - Sulphated GAGs Found in nasal septum, larynx, tracheal rings, most articular surfaces and sternal ends of ribs Forms the precursor of bone
Describe Articular Cartilage
A specialised form of hyaline cartilage Transforms the articulating ends of bones into well lubricated, wear-proff, slightly compressible surfaces Partly vascularised Components (including collagen fibres) are arranged in such a way as to maximise biomechanics functions Composition: - 70% water - 15% Proteoglycans - 15% Collagen (Type II) - 1% Chondrocytes
Describe Fibrocartilage
Fibres: Collagen
Ground Substance: Sulphated GAGs
Found in intervertebral discs, some articular cartilage, pubic symphysis
Appearance: alternating layers of hyaline cartilage and thick layers of dense collagen fibres orientated in one direction
Describe Elastic Cartilage
Fibres: Elastic and Collagen
Ground Substance: Sulphated GAGs
Found in external ear, auditory canals, epiglottis, part of laryngeal cartilages and walls of eustachian tubes
Describe the Formation of Cartilage
Precursor cells become round and form densely packed cellular masses –> centres of chondrification
The cartilage forming cells, chondroblasts, begin to secrete the components of the ECM of cartilage
As the amount of matrix increases, chondroblasts become separated from each other
Chondroblasts become isolated in small cavities within the matrix –> Lacunae
Chondroblasts differentiate into mature cartilage cells –> chondrocytes
What are the two mechanisms by which cartilage can grow?
Interstitial Growth
Appositional Growth
Describe Interstitial Growth
Chondroblasts within existing cartilage divide and form small groups of cells, which produce matrix to become separated from each other by a thin partition of matrix
Interstitial growth occurs mainly in immature cartilage
Describe Appositional Growth
Mesenchymal cells surrounding cartilage in the deep part of perichondrium (or the chondrogenic layer) differentiate in to Chondroblasts. Appositional growth also occurs in immature and mature cartilage.
