What are the main functions of connective tissue?
- Join to underlying tissues and provide support
- Protect underlying organs
- Defend against infection
- Provide a medium for diffusion
What tissue is the most abundant and widespread in the body?
What three general features make up connective tissue?
- Cellular components
- Ground substance
What is ground substance?
- amorphous ECM consisting of linear aggregates of hyaluronic acid with many proteoglycan monomers (glycoaminoglycans attached to a core protein)
- Link proteins attach the proteoglycan monomers to the hyaluronic acid molecules
Why does ground substance form a hydrated gel?
-The high density of gags gives the ground substance a high negative charge which attracts water
What type of fibres can be found in connective tissue?
What protein is the most abundant in the body?
-Collagen (specifically Type 1)
What secretes collagen?
-Fibroblasts secrete procollagen which are then arranged into fibres
What is type 3 collagen and where is it found?
- Lymphatic tissues
What do reticular fibres look like?
- Messy network of fibres
Where is type 4 collagen found?
-Basal lamina in basement membrane
What is type 2 collagen?
-Elastic and hyaline
Name the two types of embryonic connective tissue?
Where is mucous connective tissue found? Describe its features
- Wharton’s jelly of the umbilical cord
- Gelatin-like ground substance
- Large intercellular spaces
- Spindle-shaped cells
Where is mesenchyme derived from?
Describe mesenchymal cells
- Tapered/spindle appearance due to cytoplasmic processes
What 5 things are derived from mesenchyme?
- Fibroblasts->ligaments/tendons/supporting tissues
- Skeletal muscle
What are the types of connective tissue proper?
What are the specialised types of connective tissue?
- Adipose tissue
- Haematopoetic tissue
Why does mesenchyme persist in the adult?
-To give rise to new connective tissue during healing
Where would you find elastic fibres?
- Artery walls
- Elastic cartilage
Describe the structure of elastic fibres, and it’s appearance under a TEM
- Primarily elastin surrounded by a microfibril protein called fibrillin
- Elastin is less electron dense than fibrillin ->lighter on the inside with surrounding darker area
Name the three layers of arterial walls and what do they consist of?
- Tunica intima -> epithelia
- Tunica media -> elastic lamella capable of being stretched, smooth muscle, collagen and ECM
- Tunica adventitia -> collagen
What is the inheritance pattern of marfans syndrome?
What is special about the smooth muscle of the aorta wall?
-Secretes elastic, collagen and matrix
What do elastic fibres look like?
- Usually black
- Branched network (not as messy as reticular)
What causes marfans syndrome?
-Abnormal fibrillin gene leading to abnormal elastic tissue
What is the clinical picture of marfans syndrome?
- Abnormall tall
- Frequent joint dislocations
- Abormally stretchy skin
- Risk of aortic rupture
Describe the connective tissue of the mammory gland
- loose connective tissue with wispy collagen and many fibroblasts surrounds the glandular epithelium
- Dense irregular connective tissue lies further away from the glandular epithelium with thick and abundant collagen and few fibroblasts
What is the main function of loose connective tissue?
- Attach epithelium to underlying tissues
- Allow diffusion of nutrients to cells
Which layer of epithelial tissue is normally loose connective tissue?
-Submucosa (eg, in colon)
What type of fibres does loose connective tissue contain?
-Collagen and elastic
What is a specialised loose connective tissue?
What type of connective tissue are organ capsules?
-Loose or dense irregular depending on anatomical location
What is the purpose of organ capsules?
-To provide protection
What are the main purposes of dense irregular connective tissue?
- Withstand tension
- Provide structural support
What type of connective tissue is the dermis?
What is the general organisation of dense irregular connective tissue? How does its structure relate to its function?
- Collagen bundles which are densely packed but irregularly arranged
- The different orientations of the fibres allows the connective tissue to resist force in multiple directions and prevents tearing
What is the function of the elastic fibres in the dermis?
-Allows a degree of stretch and restoration
What are the colours of the dermis with silverstain?
- Collagen bundles - pink
- Elastic fibres - dark red
What is the main function of dense regular connective tissue?
-To have high tensile strength to resist high force in one direction
Where is dense regular connective tissue found?
What is the structure of tendons and how does this relate to its function?
- Very dense collagen bundles tightly packed arranged in parallel lines to the direction of the exerting force
- Rows of elongated flattened fibroblasts between bundles
- Provides high tensile strength of the tendon which is needed to attach muscle to bone
What is the function of ligaments?
-Attach bone to bone
How does the structure of ligaments differ from tendons?
-Arranged in fascicles of dense connective tissue separated by loose connective tissue
What 4 cell types are found in connective tissue?
- Mast cell
What is the most common cell type in connective tissue?
What are the function of fibroblasts?
- Provide and maintain ECM
- Synthesise and secrete collagen, elastin, proteoglycans and gags
Describe the appearance of a fibroblast?
- Slightly spindle nuclei
- Tapered cytoplasm
- Abundant rER
What other function are fibroblasts important in?
In what connective tissue are macrophages found?
What are the functions of the macrophages in connective tissue?
- Degrade foreign organisms
- Remove cell debris and dead cells
Where are mast cells found in connective tissue?
-Near blood vessels, absent from CNS
What are mast cells involved in?
What causes mast cells to release their granules?
- Become coated in IgE
- Bind allergen
- Release granules
What do the granules contain?
What are the two types of adipocytes?
-Brown and white
Describe the features of a white adipocyte
- Numerous lipid droplets merge to form one large droplet
- Displaces all other cell contents to the side
Describe the features of a brown adipocyte
- Lipid droplets remain separate
- Central nucleus
- Abundant mitochondria (non-shivering thermogenesis)
Why do adipocytes look empty when stained with H and E?
-Preparation with toluene and xylene dissolves the lipid
Where is brown adipose tissue found?
-Scapula, sternum, axillae