Histology of Cartilage Flashcards
What are the general characteristics of cartilage? (4)
- Avascular: Low metabolic rate - obtains nutrition by long range diffusion from blood vessels on it periphery (perichondrium)
- Dynamic tissue: Capacity for continued growth and remodelling; low metabolic rate means that regeneration is slow; due to this it can be transplanted and not rejected
- Mechanical tissue: provides high resistance to tension, compression and shearing forces
- Acts as a support in tissues, organs and as a scaffold for bone development
What is it comprised of?
It is comprised of relatively few cells, embedded in extensive extracellular matrix permeated by CT fibres of varying type and orientation, depending on its location and function.
What does Blast mean?
A tissue forming cell
What is a Chondroblast?
A cartilage producer
Chondroblasts are… cells, whilst Chondrocytes are… cells
Immature & Mature
What is the cellular constituents of Cartilage?
- Cells: Chondroblasts (immature)
Originates from mesenchyme - Embryonic CT
Small, flattered or irregular in shape
Mature chondroblasts enlarge with age and become rounder - Chondrocytes
When viewing chondroblasts on a light microscope you see areas around the cells; what are they called?
They are known as lacuna (little lakes). When Chondroblasts lay down cartilage and become condrocytes; they end up in a space within the cartilage (lacuna). They spread apart when laying down cartilage
What are the cellular features of Chondroblasts?
They are metabolically active cells which means their cytoplasm is filled with rER, vesicles, golgi and mitochondria
Their nucleus appears round or oval with one or more nucleoli
What are the cellular features of Chondrocytes?
These are chondroblasts which have become surrounded by the matrix they secrete.
Occupy small lacunae within the matrix
They are less active: Smaller nucleus, less nucleoli, rER, gogli etc
Often accumulate large lipid droplets intracellularly (indicates an older cell)
What is the intracellular matrix composed of?
Ground Substance & Fibres
Collagen Fibres (Mostly Type II)
Some cartilage also has elastin fibres- elastic cartilage
Fibres embedded into a water-permeated & semi rigid ground substance
What are the characteristics of the Ground Substance in Extracellular Matrix?
It is gel like with a firm consistency
Rich in carbohydrates (COH) and water
Dissolved salts are held in a meshwork of long interwoven proteoglycan molecules
Some glycoproteins and lipids are present
What are the characteristics of the collagen fibres in Extracellular matrix?
50% of collagen in cartilage is a chemically distinct form of Type II collagen
Fibres vary with type of cartilage, age an position within the cartaginous mass
What are the 3 different types of Cartilage?
Hyaline** Cartilage
- Glassy, opalescent, firm consistency
- Cells are flat near perichondrium (area of immature chondroblasts) but rounded deep inside tissue
- Cell nests formed of two/4 cells (parent and offspring) (cells dividing in their lacuna)
- Most common cartilage in the body; prominent in head & neck
- Don’t see fibres or black elastic fibres
What are the 3 different types of Cartilage?
Fibrocartilage (white/non-elastic):
- Dense tissue with associated fibroblasts
- Chondrocytes ovoid and surrounded by concentrically striated matrrix
- Mainly type I cartilage in the matrix
- Found in intervertebral discs,
Fibres run parallel to one-another, regularly arranged: direction strength and stability
What are the 3 different types of Cartilage?
Elastic Cartilage (yellow):
- Found in the external ear apices of arytenoid cartilages, epiglottis
- Typical chondrocytes but matrix has preponderance of elastic fibres
- Glycoprotein oxytalan forms fibre framework which is then impregnated by elastin
- Vibrational functions: sound-wave production (larynx), collection and transmission (ear)
You have to stain specifically for these fibres: normally in dark blue/black
How does cartilage gain nutrients?
Even though they are described as avascular, they contain cartilage channels. These are pores from blood vessels into cartilage matrix
Most cells are distant from vascular supply so they use diffusion from surface (perichondrial) vessels
Therefore, cartilage is usually limited to a few mi, thickness
What are the 2 types of cartilage growth?
Interstitial growth: Enlarges the cartilage from within. Chondrocytes in the cartilage matrix divide, and the daughter cells produce additional matrix. Interstitial growth is most important during development. It begins early in embryonic development and continues through adolescence.
Appositional growth:
adds new layers of cartilage to the surface.
Cells of the inner layer of the periochondrium divide repeatedly and become chondroblasts; producing new cartilage matrix. They gradually mature and become chondrocytes and are embedded in the matrix within lacuna; having increased the size of the cartilage.
Interstitial contributes more to the overall mass of adult cartilage. Neither take place in normal adults.
Appositional can occur however in response to damage or stimulated via growth hormone.
