Structure and Function of Loose and Dense Connective Tissues Flashcards
What is connective tissue?
Tissue of mesodermal origin which provides structural and metabolic support for other tissues and organs throughout the body
What is loose connective tissue? Where is it found and what is its function?
- Surrounds blood vessels and underlies the basement membrane of epithelia
- Highly hydrated, it is the site for metabolic and gaseous exchange
What is dense connective tissue? Where is it found and what is its function?
- Provides tough physical support and protection, such as in ligaments, tendons and the dermis of the skin
What are the three basic components of connective tissue?
- Fibres
- Ground substance (together termed the extracellular matrix
- Cells
What are the two classes of fibres?
- Collagen
- Elastin
What are the characteristics of collagen fibres?
- Flexible
- High tensile strength
- Break if stretched over 3% of original length
What are the characteristics of elastin fibres?
- Provide connective tissue with ability to stretch and recoil back to its original shape
- The more elastin content in the matrix of a tissue the more elastic the tissue is
- e.g. cartilage (high elastin content) is more elastic whilst ligaments and tendons (low elastin content) less elastic
Where is the ground substance found?
Component of connective tissue occupying space between fibres and cells
What is the ground substance composed of?
- Clear, viscous substance that is slippery due to being highly hydrated
- Proteoglycans - highly hydrophilic molecules that trap water within the matrix
What type of cell is found in dense and loose connective tissue?
- Only one type of cell which produces fibre and ground substance in dense connective tissue
- In both the cells are called fibroblasts
What is bone? What is its function?
- Specialised, mineralised connective tissue
- Provides strength and protection to organs
What is the function of strong, fibrous tissue?
Provide protection and tensile strength
What is the function of elastic connective tissue?
Provides flexibility and recoil in in structures
What is the function of fat/adipose tissue?
Provides cushioning and involved in energy storage and metabolism
What is the function of blood as a connective tissue?
Specialised function in immune defence
What are basic connective tissues?
- Loose and dense connective tissue
- Non-specialised connective tissue
What are the three main types of fibres?
- Elastin
- Collagen
- Reticular fibres
What is embedded in the ground substance in the extracellular matrix?
Fibres
What is the ground substance?
Clear, viscous, gel-like substance that fills the space between the cells and fibres
What does the ground substance contain?
- Glycosaminoglycans
- Proteoglycans
- Water
What do the properties of connective tissue depend on?
The balance between cells and extracellular matrix within tissues
What do tissues involved in mechanical strength contain a lot of? What are examples of these?
- Extracellular matrix fibres
- Ligaments, tendons and bones
What is the role of fibroblasts?
Produce and maintain the extracellular matrix
What structure do fibroblasts have?
- Spindle-like cell shape
- ‘Cigar-shaped’ nucleus
What forms do fibroblasts come in? What are their functions?
- Inactive fibrocyte
- Activated myofibroblasts (involved in wound healing and fibrosis, and can become chronically activated in chronic wounds)
What are adipocytes?
Fat cells which can be white or brown fat cells
How are white adipocytes viewed as in microscopy?
- Has a big hole-like structure
- Formed in the middle of the cell when the lipid filled centre is washed away in processing
- Cytoplasm is pushed to the periphery of the cell along with the nucleus
- ‘Signet ring’ appearance
What are macrophages?
- Role in phagocytosis
- Engulf a wide range of foreign materials such as bacteria, dust particles, dead cells
What are macrophages derived from?
Monocytes
What are other cell types seen in specialised connective tissue?
Chondrocytes (cartilage), osteoblasts (bone) and odontoblast (teeth)
What is wandering connective tissue?
- These cells migrate into the connective when needed.
- Tend to be immune cells
What is the structure and function of a plasma cell?
- Stereotypical oval ‘clock face’ nucleus
- Actively involved in producing antibodies
What are eosinophils?
- Eosin stains a lot of granules within the cells
- Two-lobed nucleus
- Involved in inflammatory reactions
- Eosin granules show up as red on a microscope
What are neutrophils?
- Multi-lobed nucleus
- Role in phagocytosis
What are lymphocytes?
- Rounded nucleus similar to plasma cells
- Plasma cells are mature lymphocytes
- Smaller cytoplasm
- Involved in antibody production
- Specialised ones involved in protection against viruses
What are mast cells?
- Basophilic granules
- Granules show up as dark purple on a microscope
- Involved in the inflammatory response
What substances do mast cells produce?
- Histamine
- Heparin
- Bioactive substances which mediate inflammation
What term is used to describe ground substance?
- Amorphous
- Doesn’t have a clear shape, instead fills the space between cells and fibres
What colour are carbohydrates and collagen fibres stained in the ground substance when using eosin stain?
- Carbohydrates are blue
- Collagen fibres are pink
What is the main structure of ground substance?
- Hyaluronic acid backbone which contains glycoproteins and complex carbohydrates known as glycosaminoglycans (GAG)
What are the characteristics of GAGs?
- Complex carbohydrates
- Negative side chains
- Highly hydrophobic and this allows them to trap water within the matrix
What is the benefit of high water retention in ground substance?
- Provides the volume to the connective tissue
- provides space and allows it to be soft and penetrable to allow other structures like vessels to pass through
How is elastin viewed when stained? What stains can we use?
- Seens as wiggly lines in the aorta
- Can use basic H&E stain or eosin
- Stained black when using elastic van gieson stain e.g. in the skin, arteries, lungs, bladder, ears etc
What is elastin formed of?
- Soluble precursor tropoelastin
- Tropoelastin is secreted from fibroblasts, and elastic fibres are assembled onto a scaffold of microfibrils, using the glycoprotein fibrillin
What structures can elastin form?
- Fibres
- Fenestrated sheets called elastic lamina (seen in major arteries)
What is the main fibre in the extracellular matrix?
Collagen
How many types of collagen are there?
- 25
- Differ based upon morphology
What is the structure of collagen?
- Secreted by fibroblasts as procollagen
- Forms tropocollagen which has a triple helix structure
- This can form fibrils which form collagen fibres
- Thicker and unbranched compared to elastin
What is needed for collagen formation? How can this be affected?
- Many genes
- Several diseases where the production of collagen is altered
How is collagen viewed when stained?
- Pink with basic H&E staining
- Blue with Masson’s trichrome
Where is collagen type 1 found?
Bone, dentine, skin, tendons and ligaments
Where is collagen type 2 found?
Mainly found in cartilage
What is type 3 collagen?
Reticular fibres
What is type 4 collagen?
Found within the basement membrane
What are reticulate fibres?
- Form mesh-like frameworks which are delicate and thin
- Surround organs, glands and blood vessels
What is the function of the basement membrane?
- Support to the overlying epithelium
- Can act as a filter allowing only certain molecules to pass, often small molecules to pass
What stain is used for the basement membrane?
PAS stain not basic H&E
How do we classify different types of connective tissue?
- Density of tissues: loose or dense
- Arrangement of fibres: regular vs irregular (dense CT)
How does loose connective tissue look under a microscope?
What is the structural arrangement of loose connective tissue?
- Fibres are loosely and randomly arranged
- Lots of ground substance
- Many cells present
What other term is used to describe loose connective tissue?
Areolar connective tissue
What is the function of loose connective tisse?
- Bind structures together
- Allows for diffusion to occur due to the loose arrangement of fibres and ground substance
- Allows nerves and blood vessels to pass freely through the connective tissue
What are examples of loose connective tissue?
- Dental pulp
- Lamina propria
What is lamina propria?
Thin layer of loose connective tissue which underlie epithelial tissues which are exposed to the external environment e.g. digestive, reproductive and respiratory tract
What are the advantages and disadvantages of loose connective tissue?
+ Good for diffusion of nutrients and waste products
- Extra space and ground substance environment means that many microbes breed here meaning many immune cells are present here
What is the structure of dense irregular connective tissue? How does this link to function?
- Fewer cells and ground substance
- More extracellular matrix fibres which are randomly arranged, making it strong and able to withstand pressure from several directions
What is an example of dense irregular CT?
Dermis (skin)
How does dense irregular CT look under a microscope?
Strongly stained
What is the structure of dense regular CT? How does this link to function?
- Fewer cells and ground substance
- Lots of extracellular matrix fibres
- Fibres are arranged parallel to each other giving high tensile strength and resists forces in one direction
What are examples of dense regular CT?
Tendons and ligaments
How does dense regular connective tissue look under a microscope?
Strongly stained
What is another type of connective tissue found in the skin?
Hypodermis (found just below the dermis)
What is the hypodermis?
White adipose tissue (most common in humans)
What does the hypodermis (adipose tissue) look like under a microscope?
- Signet ring of an adipocyte
- Appearance is uniocular
- Single large lipid droplet within the cells which looks empty due to the lipid being washed away in processing
What stain can be used to view the lipid present in adipose tissue?
Oil red O or Sudan red
What is the function of white adipose tissue?
- Specialised for storing fat as energy
- Structural role - fill spaces and act as padding or shock absorbing
- Metabolic role
- Thermal insulator under the skin
- Stores and mobilises triglycerides
What is brown adipose tissue? What is its function?
- Multiocular
- Several lipid deposits within a cell
- Really only found in newborns
- Sometimes present around the kidney or adrenal glands
- Rich in mitochondria and capillaries
- Main role is thermogenesis
How does brown adipose tissue look under a microscope?
What does mucosa refer to?
The epithelium and the lamina propria combined
What genetic condition is caused by mutation in collagen type 1?
Brittle bones which can be malformed in osteogenesis imperfecta
- Causes fragile, extra elastic skin and hypermobility of joints
- Issues with blood vessels and eyes
What genetic condition is caused by mutation in collagen type 2?
Collagen defects and joint abnormalities like chondrodysplasia
What collagens types can cause Ehler-Danlos syndrome?
Types I, III, V
What causes Marfan Syndrome? What is the effect?
- Mutations in the fibrillin gene, affecting the formation of the glycoprotein scaffold used for elastin assembly
- Affects tissues rich in elastic fibres like the aorta
- Can lead to aortic aneurysms and rupture due to weakening, and skeletal defects
