Connective tissue

Question 1

Origin of CT

Answer 1

-Mainly derived from undifferentiated mesenchymal cells
-Also, haematopoietic stem cell line:
Monocytes, macrophages, lymphocytes and mast cells, blood cells

Question 2

Constituents of CT

Answer 2

• Cellular component-fibroblasts/adipocytes, Adipose cells.
• Visible fibres- collagen, elastic, reticulin.
• Ground substance (hydrophilic jelly)-proteoglycans and glycosaminoglycans (GAGs). Invisible fibres-laminin and fibronectin.
• Ground substance doesn’t stain with H and E therefore appears as white spaces on histological slides.

Question 3

Types of Connective Tissue (CT)

Answer 3

• Fibrous-loose and dense
• Hard-cartilage and bone
• Fatty-white and brown

Question 4

Collagen: principle extracellular fibre

Answer 4

• Tropocollagen-triple helix of peptides
• Fibroblasts-secrete tropocollagen subunits
• Fibroblasts produces elastic fibres and sheets
• Fibres-assembled extra-cellularly
• Collagen cells may be longer than the cells that produce them
• Not elastic or contractile

Question 5

Types of Collagen

-More than 20

Answer 5

• Type 1 skin and bone, tendons
• Type 2-cartilage
• Type 3 liver, bone marrow, spleen
• Type 4 basement membranes of epithelia
• Type 5 placenta

Question 6

Collagen Fibres

Answer 6

• Extracellular fibres that stain pink with H&E
• Variable thickness and length, often run in bundles
• Sometimes confused for muscle fibres (intracellular-nucleus lies within them) that also stain pink but collagen fibres are extracellular.
• Most forms of collagen form linear fibres

Question 7

Loose Connective Tissue

Answer 7

• widely spaced thin collagen fibres
• fibroblasts/fibrocytes that secrete them (blasts when immature and cytes when matured)
• Unstained ground substance

Question 8

Dense Connective Tissue

Answer 8

• closely packed thick collagen fibres
• Fibroblasts/fibrocytes
• Unstained ground substance (less abundant than seen in loose ct)
• May be irregular or regular depending on arrangement of collagen fibres and fibroblasts/fibrocytes within it.
• Irregular-arranged haphazardly, found in penis
• Regular- collagen fibres and fibroblasts regularly arranged running parallel to one another, found in tendons.

Question 9

Reticulin

Answer 9

• Type 3 collagen.
• Forms branched fibres.
• Fibrillar collagen
• Forms a supporting scaffold in blood cells and many organs: bone marrow, liver, kidney, lymph node and spleen
• Not visible on H&E-need silver stain

Question 10

Elastin

Answer 10

• Elastic tissue contains fine fibres and sheets of elastin
• Elastin fibres may be branched/unbranched
• Produced by fibroblasts
• Stain pink on H&E
• Easily confused with smooth muscle cells

Question 11

White Adipose (fatty) Tissue

Answer 11

• Large cells with single fat globule in each cell. Pushes remainder of cytoplasm and nucleus to edge of cell
• Usually appear empty (white) in conventional slides as fat is extracted during processing
• Don’t confuse with alveoli of lungs. Lung tissue contains airways but white adipose tissue doesn’t.

Question 12

Brown Adipose (Fatty) Tissue

Answer 12

• Cells with many globules of fat. Pink foamy appearance.
• Found across shoulders and down back of neck
• Important in neonatal thermo-regulation (generate heat on breakdown).

Question 13

Cartilage: 3 Types

Answer 13

-Cells-chondroblasts, chondrocytes

Extracellular matrix:

• Glycosaminoglycans-Hyaluronic acid.
• Proteoglycans-Condroitin sulphate, keratin glycan
• Extracellular fibres-collagen, elastin
• Cartilage is avascular- derives blood supply from vessels on either side of cartilage.

Question 14

Hyaline Cartilage

Answer 14

• Found in synovial joints
• Chondrocytes in lacunae surrounded by a glassy amorphous matrix (blue/grey)
• Chondrocytes appear in clumps in matrix
• No visible fibres
• Perichondrium-fibroblasts and collagen.

Question 15

Elastic Cartilage

Answer 15

• Found in pinna of ear and epiglottis
• Visible elastic fibres in matrix (blue/grey)
• Perichondrium-fibroblasts and collagen

Question 16

Fibrocartilage

Answer 16

• Type 2 collagen
• Found in annulus fibrosus, pubic symphysis
• Visible collagen fibres in matrix
• Perichondrium-fibroblasts and collagen

Question 17

Synovium: Type of CT that binds synovial joints

Answer 17

• Lines inside of the joint capsule
• 1-4 layers of synovial cells
• Type A-phagocytes
• Type B-rich in RER
• Variable shapes-squamous to cuboidal
• Richly vascular, highly innervated.

Question 18

Muscle Types

Answer 18

• Visceral (smooth) muscle- arterial wall, wall of intestine, airways of lungs
• Voluntary (skeletal) muscle-skeletal muscles, larynx, diaphragm
• Cardiac muscle-heart, base of great vessels
• Other contractile cells-pericytes, myo-fibroblasts, myo-epithelial cells.

Question 19

Smooth Muscle

Answer 19

• Involuntary muscle
• Fusiform cells
• Central nucleus
• No striations but eosinophilic
• Non-branching
• Found in walls of arteries, arterioles, venules and veins. In muscular wall layers of intestines and around bronchioles and bronchi in lungs.

Question 20

Skeletal Muscle

Answer 20

• Formed by multiple myoblasts
• Long fibre like structures with multiple nuclei. Hundreds of nuclei in 1 muscle fibre, located at edge.
• Striated and Eosinophilic
• Not branched, they are straight.

Question 21

Cardiac Muscle

Answer 21

• Each myocyte has single nucleus, located in centre.
• Branched-connect with neighbours via intercalated discs
• Striated