Histology- Connective Tissue Flashcards
Main origin of connective tissue
Mainly derived from undifferentiated pluripotential mesenchymal cells
The undifferentiated pluripotential mesenchymal cells give rise to different types of cells including
Mast cell
Fibroblast and so Fibrocyte
Chondroblast and so Chondrocyte | most cartilage cells
Osteoblast and so osteocyte | most bone cells
Adipocyte (brown adipose tissue) |fat cells
Adipocyte (white adipose tissue)
Some of our connective tissue also come from Haematopoetic stem cell line including
Monocytes
Macrophages
Lymphocytes
Mast cells
Blood cells and others
Constitutes of connective tissue
Cells
Visible fibres-extracellular component
Ground substance (hydrophilic jelly)- this is invisible and is an extra cellular component
Cellular component includes
Fibroblasts/cytes
Adipose cells
Visible fibres include
Collagen
Elastic
Reticulin
Ground substance (hydrophilic jelly) includes
Proteoglycans
Glycosaminoglycans (GAGS)
Laminin
Fibronectin
-invisible fibres
Does not stain with H&E therefore appears as white spaces on histological slides
Types of connective tissue
Fibrous- loose/dense
Hard- cartilage/bone
Fatty- white/brown
What is the principle extracellular fibre of connective tissue?
Collagen
What secretes collagen?
Fibroblasts secrete collagen in the form of precursor units called tropocollagen
What is tropocollagen
Is a triple helix of peptides
The fibres of collagen are assembles extracellularly
Collagen fibres are much longer than the cells which produce them
More than 20 different types of collagen
5 that we must know:
1: skin
2: cartilage
3 (this type is called reticulin): liver, bone marrow, spleen
Provides a scaffold for these organs
4: basement membranes (predominantly in epithelia)
5: placenta
Collagen fibres staining and appearance when stained
Extracellular fibres that stain pink with H&E
Variable thickness and length, often run in bundles
Sometimes all in the same orientation and sometimes in a more haphazard arrangement (lacking any principal of organisation)
Sometime confused for muscle fibres that also stain pink (but are intracellular so the nucleus lies within them)
Loose connective tissues comprises of
Widely spaced thin collagen fibres
Fibroblasts/fibrocytes
Blasts when immature
Cytes when mature
Here the terms are used interchangeably
Unstained ground substance (white areas)
Abundant in this tissue type
Dense connective tissue
Closely spaced thick collagen fibres with intervening nuclei of the fibroblasts/fibrocytes that have produced them
Unstained ground substance (white areas)
Here there is far less abundant unstained ground substance than loose connective tissue
May be described as regular or irregular depending on the arrangement of the collagen fibres of the fibroblasts within it
When there is a haphazard arrangement of the collagen and fibroblasts= irregular tissue (found in penis fascia)
When the collagen fibres and fibroblasts are regularly arranged running parallel to each other= regular tissue (found in tendons)
Reticulin (type 3 collagen)
Forms fibres
Forms a supporting scaffold to epithelial cells in many organs including; liver, kidney
Also provides scaffold to other types of tissue such as blood cells.
So also found in bone marrow, spleen, lymph node
Not easily visible on H&E so need a silver stain
Elastin
Elastic tissue contains fine fibres or sheets of elastic
Elastin fibres may be branched or unbranded
Produced by fibroblasts
Stain pink on H&E
Easily confused with smooth muscle cells
White adipose (fatty) tissue
Large cells with single fat globule in each cell
Usually appear empty (white) in conventional slides as fat is extracted during processing
Can be easily confused with lung, but lung tissue will usually have an airway
Brown adipose (fatty) tissue
Cells with many globules of fat
Found across shoulders and down back of newborn
Important in neonatal thermo-regulation (generate heat on breakdown)
Has multivaculated cells
Fat is present as multiple globules that are not bound by membranes, giving them a pink foamy appearance with white space where the fat was and pink space from other components, eg cytoplasm
Constituents of cartilage
Hard connective tissue
Comprises of two cell types: immature chondroblasts and mature Chondrocytes
These are set in an abundant extracellular matrix
Extracellular matrix:
Glycosaminglycans including hyaluronic acid
Proteoglycans including condroitin sulphate, Keratan glycan
Extracellular fibres: collagen and elastin
Cartilage is AVASCULAR- derives its blood supply from ventricles on either side of cartilage
Hyaline cartilage
Found in synovial joints
Chondrocytes in lacunae surrounded by a glassy amorphous matrix (bluey grey colour)
No visible fibres
Perichondrium- fibroblasts and collagen
Elastic cartilage
Found in the pinnacle and epiglottis
Visible elastic fibres in the matrix (blue grey in appearance)
Perichondrium- fibroblasts and collagen found here
Visible with an H&E stain but much more visible in silver stain that highlights the elastic fibres
Fibrocartilage
Found in the annulus fibrous and pubic symphysis
Visible collagen fibres in matrix
Perichondrium- fibroblasts and collagen
Synovium
Lines the inside of the joint capsule
1-4 layers of synovial cells that comprise of specialised synovial cells
Two types of synovial cells
-Type A- phagocytes
-Type B- rich in rER and secret synovial fluid
Variable shapes ranging from squamous to cuboidal
Richly vascular and highly innervated
Muscle types
Visceral (smooth) muscle
Found in: arterial wall, wall of intensive, airway of lungs
Voluntary (skeletal muscle
Found in: skeletal muscle, larynx, diaphragm
Cardiac muscle
Found in: Heart, base of great vessels
Other contractile cells
Found in: pericytes, myo-fibroblasts, myo-epithelial cells
Smooth muscle
Involuntary muscle
Individual fusiform cells that have central and flattened nucleus
No striations
Non-branching cellular structure
