Flashcards in ToB 9 Connective Tissues Deck (148)
Define 'connective tissue':
Tissue which links together muscle, nerve and epithelial tissues, providing structural support, and metabolic and physiological support.
Name the 6 functions of connective tissue:
1) Provide substance and form to the body and organs
2) Provide a medium for diffusion of nutrients and wastes
3) Attach muscle-to-bone, and bone-to-bone
4) Provide a cushion between tissues and organs
5) Defend against infection
6) Aid in injury and repair
Name the 6 main types of connective tissue:
1) Loose connective tissue
2) Dense connective tissue
6) Lymph system
What are the 4 basic types of tissue in the human body?
What tissue is the tissue is the most abundant, widely distributed, and varied type?
What are the 2 general components of connective tissue?
2) Extracellular matrix
What are the 2 general components of the extracellular matrix within connective tissue?
1) Ground substance
What 3 types of fibres may be found in connective tissue?
What type of fibres are found in the lung connective tissue?
What type of fibres are found in the lymph node connective tissue?
What type of connective tissue is present in the umbilical cord?
Mucous connective tissue
The dermis is an example of what kind of connective tissue?
Dense irregular connective tissue
Tendons are examples of what kind of connective tissue?
Dense regular connective tissue
What are the 3 main classes of connective tissue?
1) Embryonic connective tissue
2) Connective tissue proper
3) Specialised connective tissue
What are the 2 types of embryonic connective tissue?
2) Mucous connective tissue
Give an example of mucous connective tissue:
What are the different types of connective tissue proper?
Loose/areolar connective tissue
Dense connective tissue (Regular or irregular)
Name the 6 types of specialised connective tissue:
1) Adipose tissue
5) Lymphatic tissue
6) Haemopoetic tissue
Lymphatic tissue would come under what main class of connective tissue?
Specialised connective tissue
Loose/areolar connective tissue would come under which main class of connective tissue?
Connective tissue proper
What type of embryonic connective tissue is pluripotent?
Cells which can give rise to many different cell types
What type of cells form the mesenchyme?
Mostly mesodermal cells, but also some ectodermal cells.
Maturation and proliferation of mesenchyme cells give rise to what?
- Various connective tissues
- Serous membranes
- Vascular system
- Urogenital system
What cell type forms cartilage?
What is the main function of chondroblasts?
Formation of cartilage
What cell type forms adipose cells?
What is the main function of lipoblasts?
Formation of adipose cells
What cell type forms supporting tissues such as ligaments/tendons?
What is the main function of fibroblasts?
Formation of supporting tissues such as ligaments/tendons
What cell type forms bone?
What is the main function of osteoblasts?
Formation of bone
What cell type forms skeletal muscle cells?
What is the main function of myoblasts?
Formation of skeletal muscle cells
Why is it important for mesenchymal cells to persist in the adult?
To produce new connective tissue when required for healing
What is the general constitution of mucous connective tissue?
- Mostly specialised ground substance
- Few mesenchymal cells
- Few fibres
What is the main constituent of cartilage ground substance?
Proteoglycans, made up of core proteins each with approx. 100 glycosaminoglycan (GAG) units joined. These core proteins are linked onto hyaluronic acid, to form a hyaluronate proteoglycan aggregate.
Why does cartilage ground substance form a hydrated gel?
The glycosaminoglycans give the ground substance a high density of negative charge, attracting water
What is meant by 'GAG'?
What is formed when GAG units attach to a hyaluronic acid molecule?
Hyaluronate proteoglycan aggregate
Describe cartilage extracellular matrix:
Hyaluronate proteoglycan aggregates form an interwoven network with collagen fibrils
What are the 3 main properties of GAGs, and why?
1) Highly negative charge
3) Strongly hydrophilic
Allows attraction of water to form gel-like substance, and makes the connective tissue good at resisting compressive forces.
What proportion of our whole-body protein content is collagen?
Between 1/4 to 1/3
What is gelatin?
Collagen which has been hydrolysed irreversibly, and is used in the food industry
What is the most common type of collagen?
Describe Type I collagen:
Collagen fibrils aggregate into fibres and fibre bundles.
Give 3 examples of where you can find collagen Type I:
2) Capsules of organs
3) Skin dermis
Which types of collagen form fibres?
Types I and III
Describe Type II collagen:
Collagen fibrils do not form fibres
Where is Type II collagen found?
What type of collagen is present in hyaline cartilage?
What type of collagen is present in tendons?
Describe Type III collagen:
Collagen fibres form fibres called Reticulin.
What is an alternative name for Type III collagen?
What is an alternative name for Reticulin?
Type III collagen
What type of collagen is found in the basal lamina of a basement membrane?
Where is type IV collagen found?
In the basal lamina of the basement membrane ONLY
Define and explain the appearance of a type I collagen fibril after staining:
It has repeating periodic banding every 68nm, which is produced because each collagen fibril is composed of staggered collagen molecules. Adjacent molecules have a small gap between them, where heavy metal stains, therefore 'gap' zones produce the dark staining bands.
What is the length and width of a type I collagen molecule?
300nm long, 1.5nm wide
What is a type I collagen molecule composed of?
3 alpha chains twisted into a triple helix (2 alpha1 chains, and 1 alpha2 chain)
Which AA is present in every 3rd position of an alpha chain of collagen type I?
Which cell is mainly responsible for the production of collagen?
What is it called when collagen fibres aggregate in some areas?
What type of fibres are present in the dense irregular connective tissue of the testis capsule?
Collagen type I
Where is type III collagen found?
Around muscle and nerve cells, and within lymphatic tissues and organs
What type of fibres are found in lymph nodes?
Reticulin/Type III collagen
What is the function of trabecula present in lymph nodes?
The trabecula extend from the capsule into the node, so as they contain collagen bundles they give strength to the structure
What are the components of elastic fibres?
Name 3 sites at which elastic fibres have a particularly important role:
2) Artery walls
3) Sites containing elastic cartilage
Why can you define the elastin and fibrillin within elastic fibres, under a TEM?
Fibrillin microfibrils are more electron dense than elastin fibres, so appear darker under TEM.
Why is elastic fibres abnormal in Marfan syndrome sufferers?
Expression of the fibrillin gene is abnormal, resulting in abnormal elastic fibres
Describe the genetic inheritance of Marfans's syndrome:
What are the 4 typical characteristics of Marfan syndrome sufferer's?
1) Abnormally tall
3) Frequent joint and lens dislocation
4) Heart defects
What is 'arachnodactyly'?
Abnormally long and slender limbs, fingers and toes
What is the 'tunica intima'?
The innermost layer of an artery or vein, compromised of one layer of endothelial cells.
What is the latin name for the innermost layer of an artery or vein, compromised of the endothelium?
What is the 'tunica media'?
The middle layer of an artery and vein. It consists of muscle and elastic fibres, and is thicker in arteries than veins.
What is the 'tunica adventitia'?
The outermost layer of an artery or vein, consisting mainly of collagen, but also elastic fibres in arteries.It is much thicker in veins than arteries.
What type of cell produces the elastin, collagen and matrix within the tunica media?
Smooth muscle cells
What types of fibres and cells are present in the tunica media?
Elastin fibres, collagen fibres, smooth muscle cells
Why are fibroblasts not required to produce the connective tissue present in the tunica media?
The smooth muscle cells present in the tunica media can synthesise the elastin and collagen required.
What cell most commonly synthesises collagen fibres?
What is the main component of the extracellular matrix in connective tissue?
Define loose irregular connective tissue:
It holds organs in place, and attaches epithelial tissue to underlying tissues. It consists of many cells (fibroblasts and macrophages), a loose arrangement of fibres, and a moderately viscous extracellular matrix.
Define dense connective tissue:
It consists of a dense interwoven network of fibres, few cells, and a viscous extracellular matrix. It is found in joint capsules, muscle fascia and the dermis.
What type of connective tissue is found in mammary tissue?
Loose irregular (around glandular tissue), and dense irregular.
What type of connective tissue is makes up the submucosa of the colon?
Loose irregular connective tissue
The nuclei present in loose connective tissue are mainly of what cells?
What type of connective tissue compromises the dermis?
Dense irregular connective tissue
What is meant by dense IRREGULAR connective tissue?
The bundles of fibres (particularly collagen) are densely packed but irregularly arranged, so are orientated in multiple directions.
Why is it important that the dermis is made of dense irregular connective tissue?
It allows the skin to resist forces in multiple directions, without tearing.
Why is it important for there to be elastic fibres present in the dermis?
They allow a degree of stretch and restoration to original shape, after the skin is bent or folded.
What type of stain enables elastic fibres within connective tissue to be seen? (in black)
What type of connective tissue is leather made of?
What is a capsule?
A membrane of connective tissue which surrounds tissues such as glands, to protect. It can vary from loose to dense irregular.
What is the function of a tendon?
To connect muscle to bone, withstanding high tensile force in one direction.
Why can tendons only withstand a high tensile force in one direction?
The collagen fibres within tendons are lined up in the same direction (parallel), densely packed, so can withstand in one direction, but will be pulled apart if force applied in other directions.
What type of cells lie between the collagen fibres in tendons?
Describe the appearance of a fibroblast cell within a tendon:
Elongated and flattened, packed inbetween the collagen fibres
What is the name of the junction where skeletal muscle fibres meet the tendon collagen bundles?
What is the function of a ligament?
To connect bone to bone
Describe the arrangement of collagen bundles within ligaments:
They are arranged in a densely packed undulating parallel arrangement, and form fascicles, which are separated by loose connective tissue
How do ligaments and tendons differ in terms of their structure?
- In tendons the collagen bundles lie in a straight line, in ligaments the bundles undulate
- In tendons the collagen bundles are very long and connect muscle to bone. In ligaments the bundles are short and form fascicles, which are separated via loose connective tissue
Where are the rectus abdominis?
At the front of the abdomen, joining the sternum to the pubis
What are the rectus abdominis?
A pair of long flat muscles at the front of the abdomen, joining the sternum to the pubis
What separates the rectus abdominis, and in some people define the '6-pack'?
- Tendinous intersection (across)
- Linea alba (down the middles)
What is an aponeurosis?
A fibrous sheet of flattened tendons
Where are the external oblique muscles?
One of the outermost abdominal muscles, extending from the lower half of the ribs around and down to the pelvis
What are the 3 common cell types found in connective tissue?
3) Mast cells
Why are fibroblast nuclei not circular within dense irregular connective tissue?
The collagen bundles are arranged densely and tightly packed, so fibroblast cells are squeezed and deformed.
When visualising a fibroblast via a TEM, what are the 3 main characteristics which allows recognition?
1) Large amount of euchromatin in the nucleus
2) Abundant rER
3) Many secretory vesicles located at the edge of the cell
How are the long collagen fibrils formed?
Fibroblasts secrete procollagen, which self-assembles into collagen fibrils
Which cell is responsible for synthesising and secreting the extracellular matrix of connective tissue? (Fibres and ground substance)
Why do fibroblasts have abundant amounts of rER?
To allow them to synthesise and secrete large amounts of fibres and substance.
Which cells are primarily responsible for the formation of scar tissue?
From what cell are macrophages derived from?
Macrophages are matured monocytes
What are the 3 main visual characteristics of a macrophage, when looking through a TEM?
1) Phagocytic vacuole
3) Many pinocytic vesicles around the end of the cell
What is the function of a macrophage?
To phagocytose foreign organisms and cell debris
Why do macrophages have a large amount of lysosomes within the cell?
To degrade the foreign organisms and cell debris which are engulfed.
Describe the process of phagocytosis:
Performed by macrophages:
- Foreign body or cell debris is engulfed by the macrophage, which forms a small pocket around the particle = phagosome
- Lysosomes present within the macrophage containing hydrolytic enzymes fuse with the phagosome, and release their contents
- The digested contents are then released from the cell via exocytosis, (for reabsorption by body)
What is meant by 'professional antigen presenting cells'?
Cells which can present foreign material to the T lymphocytes of the immune system, initiating immune response
Name the 4 main professional antigen presenting cell types:
2) Dendritic cells
3) B lymphocytes
4) Langerhans cells
What is the main visual characteristic of a mast cell?
Many granules present in the cytoplasm
What do the granules of mast cells contain?
- Substances to attract eosinophils and neutrophils
What is heparin?
Substance which inhibits blood coagulation
How does histamine affect blood vessel walls?
Dilates blood vessels and increases the permeability of the walls
Where is histamine primarily stored in the body?
In the granules of mast cells
Why is the release of histamine important in an immune response?
It dilates blood vessels allowing increase in blood flow, and also increases the permeability of the blood vessel walls, allowing fluid and cells such as leukocytes and blood plasma proteins, to leak from the bloodstream through the vessel walls and migrate to the site of tissue injury or infection, where they begin to fight the infection and nourish and heal the injured tissues = inflammation
Where are mast cells usually found?
In connective tissues near blood vessels (apart from the CNS)
Why are mast cells absent from the CNS?
To prevent the damaging effects of oedema occuring there.
What causes mast cells to release their granules?
The binding of a specific allergen to one of the Immunoglobulin E (IgE) molecules expressed on the surface of the cell.
Which cell type is mainly responsible for inflammation?
What is released quickly after damage/trauma, leading to inflammation?
The granules of mast cells
Where in a mast cell are the granules located?
Within the cytoplasm
Adipocytes are derived from what cell type?
What are the 2 types of adipocytes, and what is the difference?
1) Brown adipocytes - contain multiple lipid droplets in their cytoplasm
2) White adipocytes - contain one large lipid droplet in their cytoplasm, which displaces all other cell organelles and cytoplasm (original multiple lipid droplets fuse together)
What is the difference in nuclei placement between brown and white adipocytes, and why?
In brown adipocytes the nuclei are centrally located, however in white adipocytes the single lipid droplet displaces the cytoplasm and pushes the nuclei to the very edge of the cell.
What type of adipocyte is unilocular?
White adipocyte (has one lipid droplet)
Why are adipocyte cells empty when stained with H&E?
The use of toluene/xylene in the fixing process dissolves away the lipid
What are the 3 main reasons of storing lipid in adipocytes?
1) Fuel storage
3) Shock absorption
What gives brown adipocytes their colour?
Large amount of mitochondria within the cells, and is also due to their rich vascular supply.
What type of adipocyte is multilocular?
Brown adipocytes (have many lipid droplets)
Why are brown adipocytes described as 'thermogenic'?
Because they contain high amounts of mitochondria which release heat rather than ATP, using uncoupling proteins.
Where are brown adipocytes found?
Close to the scapula, sternum and axillae, also in the upper chest and neck of adults.
Why are brown adipocytes more common in newborns than adults?
Newborns have a high surface area to volume ratio, so lose heat readily. The brown adipocytes allow newborns to generate heat. Also newborns cannot shiver, so cannot generate heat that way.
Why is non-shivering thermogenesis important for babies and small hibernating animals?
They have a high surface area to volume ratio, so can readily lose heat, so require ways of generating heat. (Particularly in animals which have inability/reluctance to shiver)
Name the three granulocytes: