LECTURE 3 (Cartilage III) Flashcards
What is Cartilage?
A tough, durable form of supporting connective tissue characterised by an extracellular matrix with high concentrations of GAGs and proteoglycans interacting with collagen and elastic fibers
What are the functions of cartilage?
- Firm consistency -> allows the tissue to bear mechanical stresses without permanent distortion
- In respiratory tract, ears and nose -> framework for supporting softer tissues
- Resiliency and smooth lubricated surface -> Provides cushioning and sliding regions within skeletal joints
- Facilitates movement
- Guides development and growth of long bones
Cartilage consists of cells called ______________
Chrondocytes
What is the function of chrondocytes?
synthesise and maintain all ECM components and are located in matrix cavities called lacunae
What do the physical properties of cartilage depend on?
Electrostatic bonds between type II collagen fibrils, hyaluronan and sulphated GAGs on densely packed proteoglycans
What allows cartilage to serve as a shock absorber?
The high content of bound water
Describe the blood supply of cartilage
- Cartilage lack vascular supplies but chrondocytes receive nutrients by diffusion from capillaries in surrounding connective tissue
- Avascular -> chrondocytes exhibit low metabolic activity
- Cartilage lacks nerves
What is the Perichondrium?
A sheath of dense connective tissue that surrounds cartilage in most places, forming an interface between the cartilage and the tissues supported by the cartilage
What is the function of the Perichondrium?
It harbours the blood supply serving the cartilage and a small neural component
Articular cartilage lacks _______________
Perichondrium
Therefore it is sustained by the diffusion of oxygen and nutrients from the synovial fluid
What are the three main types of cartilage?
- Hyaline Cartilage
- Elastic Cartilage
- Fibrocartilage
What are the properties of Hyaline Cartilage?
- Most common of the three types of cartilage
- Homogenous and semi-transparent in the fresh state
Where is Hyaline Cartilage located in adults?
- Articular surfaces of movable joints
- Walls of larger respiratory passages
- Ventral ends of ribs
- Epiphyseal plates of long bones
Where is Hyaline Cartilage located in the embryo?
Forms the temporary skeleton that is gradually replaced by bone
Describe Osteoarthritis
A chronic condition that commonly occurs during ageing and involves the gradual loss or changed physical properties of the hyaline cartilage that lines the articular ends of bones in joints
Fragments released by wear-and-tear to the articular cartilage trigger secretion of MATRIX METALLOPROTEINASES and factors from MACROPHAGES in adjacent tissues -> Exacerbate damage and cause pain and inflammation within the joint
In histologic preparations, what is seen in the matrix?
Proteoglycans make the matrix basophilic and thin collagen fibrils are barely discernible
What is the most abundant proteoglycan of hyaline cartilage?
Aggrecan
150 GAG side chains of chondroitin sulfate and keratan sulfate. Hundreds of these proteoglycans are bound non-covalently by link proteins to long polymers of hyaluronan.
What is Chondronectin?
- Structural multi adhesive glycoprotein in cartilage matrix
- Binds specifically to GAGs, collagen and integrins mediating the adherence of chrondocytes to the ECM
- Stains differently since richer in GAGs than collagen
Describe the arrangement of Chrondocytes in cartilage
- At the PERIPHERY = young chrondocytes/chrondoblasts have an ELLITIC SHAPE with long axes parallel to the surface
- DEEPER = round and appear in groups of up to 8 cells that originate from mitotic division of chrondoblasts (ISOGENOUS AGGREGATES)
- Chrondocytes become more active in secreting collagens -> aggregated cells and pushed apart and occupy separate lacunae
What is the difference between chrondocytes in living tissue and in histologic preparation?
LIVING TISSUE - fill their lacunae completely
IN HISTOLOGIC PREPARATION - irregular shape and retraction from matrix since cartilage cells shrink
What does calcification to hyaline cartilage result in medically?
Hyaline cartilage is susceptible to partial or isolated regions of calcification during ageing -> Calcification of hyaline matrix with degenerative changes in chrondocytes -> Cells of cartilage give rise to BENIGN (CHONDROMA) or slow-growing MALIGNANT (CHONDROSARCOMA) tumours that can metastasise -> Removed surgically
All hyaline cartilage is covered by a layer of dense connective tissue, the _______________, which is essential for growth and maintenance of cartilage
Perichondrium
Describe the Perichondrium
Outer region consists of COLLAGEN TYPE I FIBERS and FIBROBLASTS but the inner layer adjoining the cartilage matrix contains MESENCHYMAL STEM CELLS which provide a source for NEW CHRONDOBLASTS that divide and differentiate into CHRONDOCYTES
What differentiates Elastic Cartilage from Hyaline Cartilage?
- Abundant network of elastic fibers
- Fresh elastic cartilage is a yellowish colour
- Elastic fibers provide greater flexibility
