1.04 - Bone & Cartilage Flashcards Preview

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Flashcards in 1.04 - Bone & Cartilage Deck (37):

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


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?

Haversian canals
Haversian systems (osteons)


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?

Hormones (Vitamin D, Parathyroid Hormone - PTH)
Physical Activity
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
- 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.