Bone and cartilage Flashcards
What are the three types of cartilage?
Hyaline
Elastic cartilage
Fibrocartilage
These all have cells and extracellular matrix.
Where is cartilage found?
On the articular surfaces of all synovial joints.
Forming the cartilaginous model of most developing bones and their epiphyseal growth plate.
Where is flexible cartilage found?
Forming the flexible skeleton of the nose, larynx, pinna of the ear and costal cartilages of the ribs.
In its structural role in the intervertebral disc allowing flexibility to the spine.
What is perichondrium?
Found on peripheries of hyaline and elastic tissue.
The outer layer is dense vascular connective tissue.
The inner layer is chondrogenic.
It’s function is protection, nutrition and repair from stem cells.
What are the cells in cartilage?
Chondroblasts - immature, form all structures of cartilage
Chondrocytes - mature, maintain the cartilage.
What is the role of cartilage?
The highly hydrated nature of cartilage means that it can withstand significant compressive forces.
It also provides an almost frictionless surface across which other cartilages can move.
What are the components of ECM?
Organic components - ground substance and fibres
Inorganic components - water, electrolytes, minerals, vitamins and gases
What are the components of ground substance in cartilage?
Proteoglycan - versican
GAGs: Chondroitin sulphate and dermatan sulphate
What is hyaline cartilage?
Contains glycosaminoglycans and type II collagen fibres.
Located in isogenous groups.
Avascular (poor blood supply) - doesn’t repair itself well.
Predominant in lining articulating surfaces of synovial joints and respiratory tract.
What is the function of hyaline cartilage?
The type II collagen fibres give it good strength, which is needed to provide a friction-surface and act as a shock absorber.
What does hyaline cartilage look like?
Has a white glassy appearance
c = chondrocytes
P = perichondrium
M = matrix
see image
Why does hyaline cartilage look glassy?
Because of the highly hydrated nature of the ground substance which consists of three types of glycosaminoglycans:
hyaluronic acid, chondroitin sulphate and keratin sulphate, all of which trap water.
What is elastic cartilage?
Has type II collagen fibres.
It is more flexible than hyaline cartilage.
Located in the auricle of the ear.
Auditory tubes, epiglottis.
What does elastic cartilage look like?
Histologically it resembles hyaline cartilage, but contains an abundance of elastic fibres which allow to to deform and return to it’s original shape.
see image
Dark lines are elastic fibres.
What is fibrocartilage?
A mixture of hyaline cartilage and dense connective tisuse - type I and II collagen.
Found in intervertebral discs, pubic symphysis and discs of knee joints.
What is the function of fibrocartilage?
Provides strong connections and stability - so contains many collagen fibres.
What does fibrocartilage look like?
see image
How does cartilage survive?
Because cartilage is avascular, it is dependent on diffusion of nutrients and metabolites thorugh the matrix.
The main source of nutrients is from the synovial fluid in the tissue and joint spaces, but there is some diffusion from blood vessels in the bones.
What are the types of bone?
Compact bone - on the outside
Spongy bone - on the inside
What is periosteum?
Bones are enclosed in periosteum except at their articulating surfaces which are covered by cartilage.
It is formed from two fibrocollagenous membranes, contains osteoblasts which are capable of proliferation, and are especially important in healing fractures.
Also has osteoclasts which are bone destroying cells.
What is the structure of periosteum?
The outer layer is fibrous made of dense connective tissue.
The inner layer is cellular osteogenic and contains stem cells - osteoprogenitor cells.
It is secured to the bone by Sharpey’s fibres.
What is endosteum?
Covers the internal bone surface.
Osteogenic - forms bones.
What is the structure of compact bone?
Osteon pillars
Concentric lamellae - circular structures
Haversian system
How is bone formed?
In developing bone, the collagen fibres are arranged in a random orientation - woven bone.
This is broken down by osteoclasts and remodelled to form cortical (compact) bone and spongey (cancellous) bone.
Bones can adapt slowly to environmental stresses.
How is compact bone formed?
Osteoblasts have laid down the matrix in concentric rings known as osteons - Haversian systems.
The osteons surround a central canal containing blood vessels, nerves and a lining of osteoblasts.
Blood vessels enter each bone at nutrient foramina.
Loss of blood supply to a bone causes avascular necrosis.
What does an osteon look like?
see image
What is a lacuna?
After forming bone, immature osteoblasts are trapped inside the concentric lamellae to form a space - lacuna.
The osteoblasts then form mature osteocytes.
What is spongey bone?
Has a sponge like appearance
Trabeculae interlock with each other to form spaces where bone marrow are, and provides strength.
Have few Haversian systems.
Spaces contains haemotopoietic cells (red marrow) or fat (yellow).
What are osteoblasts?
Derived from osteoprogenitor cells.
Present in endosteum and periosteum.
Lined up along the surface of bone matrix.
What is the shape of osteoblasts?
They have a narrow spindle shape when inactive (osteoprogenitors).
Large and broad spindle or cuboidal shape when active.
What is the function of osteoblasts?
Synthesise osteoid and mediate mineralisation.
Produce the organic bone matrix.
Reponsible for deposition of inorganic component of matrix.
What is bone matrix?
Or osteoid:
Highly vascularised
70% is inorganic
30% is organic
What is the inorganic material of bone matrix?
Calcium hydroxyapatie
Bicarbonate
Citrate
Magnesium
Potassium
Na+
What is the organic component of bone matrix?
Collagen type I
Small proteoglycans
Glycoproteins - osteonectin
Osteocalcin and phosphatases promote calcification in the matrix.
What are osteocytes?
Inactive osteoblasts that are trapped in matrix bound lacunae.
When there is a need for more matrix the osteocytes are activated and secrete matrix.
What are osteoclasts?
Phagocytic multinucleated cells.
Essential for bone turnover and remodelling, this releases calcium into bloodstream.
Ca is required for muscle contraction, so when in short supply, osteoclasts are activated to supply this.
Excess calcium is absorbed back into the bone.
How does the structure of osteoclasts link to function?
Has a ruffled border which secretes organic acids which dissolves the mineral component.
Lysosomal proteolytic enzymes destroy the organic osteoid matrix.
It is found in resorption lacunae.
What is ossfication?
Turning into bone - intramembranous or endochondral.
What is intramembranous ossification?
Bone forms directly from mesenchyme.
Most skull bones and the clavicle.
What is endochondral ossification?
It is modelled in hyaline cartilage, then replaced by bone tissue.
This is how all other bones except the skull and clavicle are formed.
How does endochonral ossification occur?
Perichondrium turns into periosteum.
Chondrocytes stop getting nutrition and begin to die.
The periosteum form osteoblasts which invade the cartilage and form a primary ossification centre, where bone matrix is released and replaces cartilage.
Blood vessels then invade the primary ossification centre and bone is deposited into the middle.
What is osteoporosis?
Bone disease caused by a reduction in bone density leading to fragile bones and higher risk of fractures.
For women after menopause, there is less oestrogen, so less osteogenesis - uptake of matrix, and so increased risk in osteoporosis.
What does a calcium deficiency do?
The bone matrix does not calcify normally and the epiphyseal plate is distorted.
This causes bones to grow more slowly and become deformed - leading to rickets or osteomalacia.
This can be due to lack of calcium in diet or lack of vitamin D which is needed for absorption.
