Lecture 11 - Connective tissue defects and deficiencies. Role in healing and repair. Flashcards
The main transmembrane protein involved in hemidesmosomes and focal adhesions is
integrin
________ is an almost universal response to tissue damage
inflammation
Damaged cells quickly release molecules that stimulate acute inflammation which is important for getting immune cells to the area quickly and destroying any foreign bodies or pathogens that might reside there
Acute inflammation flow chart
cells can regrow - regeneration - restoration of normal structure and function
cells cannot regrow - healing by repair - scar formation (loss of specialised function)
damaging agent persists - chronic inflammation - damaging agent overcome
two options…
no - persistance - keep having chronic inflammation
yes - healing by repair - scar formation (loss of specialised function)
Three main interrelated stages of acute inflammation
Vascular dilation (after initial brief (secs) phase of arteriole constriction) - blood vessels near where we have had the injury occur dilate and allow increased blood flow to that area mediated by histamine (tissue mast cells) and nitric oxide (endothelial cells)
Endothelial activation - endothelial cells lining the blood vessels are activated which allows various different molecules to enter the area of the tissue damage which actually causes the swelling that we see
Neutrophil activation and migration - migration to the area of damage and getting rid of any foreign bodies or pathogens that could be there as a result of the injury
Vasodilation, increased blood flow
Chemical mediators act on local blood vessels
Blood vessels get bigger, increases our blood flow to the area of damaged tissue and it is chemical mediators that cause this increase in local blood flow, cells in this damaged tissue are already damaged such as mast cells which then release substances that can act on blood vessels particularly histamines can be released and these then act on our blood vessels. Histammines can directly act on the smooth muscle cells that control vasodilation and vasoconstriction and they can also act on endothelial cells that then can produce nitrous oxide which indirectly causes vasodilation
Substances released from dead/damaged tissues act on blood vessels (e.g. histamines)
Endothelial contraction
Allows the tissue become swollen
Endothelial activation cell swelling and retraction
Increased permeabiliry.. Immune cells also enter the area. Water, salts and proteins have various functions and this allows the tissue to become swollen
Leukocyte migration and activation
The damaged area becomes progressively replaced by components of the exudate
As the blood vessels dilate, we get more neutrophils rolling along the outsides of blood vessels and in addition the endothelial cells themselves actively secrete molecules that attract our leukocytes (various types of white blood cells) to them so that they stick to the endothelial cells and these molecules adhere to the epithelium and they move in via the gap between the endothelial cells known as margination. SO now we have our neutrophils actively migrating to the area of damage using chemotaxis as they are sensing molecules coming from the damaged tissue and move to that damaged area and at the same time we get production of fibrin which is polymerised from fibrinogen so this is effectively our coagulant that is temporarily filling the space where we have lost tissue so getting coagulation of the area so effectively blocking where we might have a gash in the tissue
MAcrophages emigrate into the area of damage - clear damaged foreign debris and dead cells. Promote vascularisation and fibroblast migration
Neutrophils adhere to endothelium (margination) - neutrophils actively migrate into the area of damage (migration) - fibrin is polymerised in tissue from fibrinogen (this occurs over hours)
Outcomes of acute inflammation
Regeneration (or)
Organisations and repair - healing by fibrosis (or)
Chronic inflammation
Outcomes of acute inflammation are affected by …
Severity of tissue damage (if we lost the stroma and the connective tissue below then need to build ECM and can’t completely replicate what was there before so effectively need to make up for that tissue deficit
Capacity of specialised cells to replicate and regrow (regenerate) (for example damage to just the epithelial cells then we know that they have a high regenerative capacity and a high level of cell turnover as such they are going to be able to regenerate and make up for where we have lost epithelial cells)
Type of agent which has caused the tissue damage
Extent of healing will depend on …
the level of tissue deficit
For restoration of normal function without scarring …
stroma (connective tissue framework of tissue) must be intact
and damaged cells must be capable of regeneration (e.g. epithelial cells)
Organisation and repair of damaged tissue
Macrophages enter damaged area and remove the debris
Granulation tissue is then laid down
Vascular granulation tissue
Damaged area is first replaced by a complex of interconnecting capillaries, macrophages, and support cells
First thing we are getting after the macrophages have entered this damaged tissue area is vascular regeneration os we actually get capillary buds moving into the damaged tissue area so growth of new capillaries from the existing blood vessel and moving to form a network within the damaged tissue area to form a network and this effectively causes granulation of the tissue which is where this tissue forms a granular appearance, process of the capillary buds forming from the existing blood vessels and moving to the damaged tissue area is mediated by the macrophages that are moved to this area and the macrophages secrete angiogenic factors and these macrophages guide the growth of capillaries
Macrophages are surrounding in the formation of blood capillaries, growth towards direction of damage
Collagen is making up the new area, stained blue with trichrome staining
Fibroblasts/myofibroblasts also attracted to the area
occurring over hours/days
Fibrous granulation tissue
Eventually fibroblasts begin to proliferate and then they can deposit collagen
Capillaries gradually regress and damaged area is replaced with collagen
Fibroblasts lay down collagen
Few remaining lymphocytes
Collagenous scar formation
The fibroblasts align so the collagen is deposited for maximum strength, collagen is dense
Initially just vertically from the wound usually and then can be laid horizontally for maximum strength
Lose the blood capillaries that were produced (vascularity is reduced)
Fibroblasts become inactive (fibrocytes)
Occurring over days
Scar formation
clotting occurs caused by clotting proteins and plasma proteins, and a scab is formed. Inflammatory chemicals are released from injury. White blood cells seep into the injured area = removing debris or infectious substances
2 - epithelial cells multiply and fill in over the granulation tissue, granulation tissue restores the vascular supply, macrophages enter the area, increased capillary growth to the area of damage, fibroblasts enter the area in preparation for production of collagen
3- now the area is covered with collagen so we have an underlying area of scar tissue, the epithelia has thicker and completely covered but still have loss of the initial tissue structure below it, restored epithelia thickens and the area matures and contracts, underlying area of scar tissue is present
Fibrous scar formation
Permanent scar forms
Contraction may result in reduction of size of scar
keliod scar
Keliod scar = raised scar, overproduce collagen within the scar area
Why are surgical cuts so much better at healing?
Clean cut into the connective tissue and through the epithelial cells can heal better
Less damage to epithelial layer, less fibrin and inflammation
Less granulation tissue, particularly less angiogenesis. Collagen initially laid vertically
Collagen fibres can meet horizontally, with less space to fill
Healing scar on skin
Healing biopsy site on skin a week following excision
Skin surface re-epithelialised
Below this is granulation tissue with small capillaries and fibroblasts forming collagen
After a month, only a small collagenous scar will remain
Connective tissue defects and deficiencies
> 200 disorders of connective tissue
Some are result of infections (e.g. cellulitis) - e.g. some sort of immune response
Some as result of injuries (e.g. scars) (no efficient repair mechanisms)
Some are genetic
Others have no known cause
Diseases due to collagen defects
Usually arise from mutations in genes for particular collagen types
Point mutation in collagen I genes produce fragile bones
osteogenesis imperfecta - brittle bone disease
Other mutations for collagen produce abnormally stretchy skin and joint laxity
Ehlers-Danlos syndrome- ‘Rubber Man Syndrome’
point mutation in collagen I genes produces…
osteogenesis imperfecta - brittle bone disease
Other mutations for collagen produce abnormally stretchy skin and joint laxity …
Ehlers-Danlos syndrome- ‘Rubber Man Syndrome’
Osteogenesis imperfecta (brittle bone disease)
Deficiency of Type I collagen
Less collagen/poorer quality (or both of these
Results in weak/fragile bones, in addition to other connective tissue deficits
Usually autosomal dominant disease (only one mutant copy required)
Mutations in COL1A1 and COL1A2, type 1 collagen genes (there are 2 collagen genes that make up type 1 collagen)
Often thinner bones with reduced cortical and trabecular components
Sometimes these individuals actually have more osteoclasts but this is unable to counteract the loss of collagen so these individuals still have lesser quality bone despite having more of these collagen producing support cells in the bone
Type 1 - half as much collagen but still able to make normal triple helices, the collagen they have is normal but they have less of it
Type 2 and 3 - Normal quantity of collagen but have an amino acid substitution/point mutation within some of these collagen molecules and as a consequence the triple helices that is produced that actually goes into the structure of the collagen fibres is not effective
Type 1 - Blue sclera ( blue in the whites of the eyes), brittle bones (lots of fractures throughout their lives)
Brittle bone disease name
osteogenesis imperfecta
Type I Brittle bone disease
Type 1 - half as much collagen but still able to make normal triple helices, the collagen they have is normal but they have less of it
Type 1 - Blue sclera ( blue in the whites of the eyes), brittle bones (lots of fractures throughout their lives)
most common, produce less collagen
Type 2 brittle bone disease
Type 2 and 3 - Normal quantity of collagen but have an amino acid substitution/point mutation within some of these collagen molecules and as a consequence the triple helices that is produced that actually goes into the structure of the collagen fibres is not effective
less common, produce mutated collagen
Type 3 brittle bone disease
Type 2 and 3 - Normal quantity of collagen but have an amino acid substitution/point mutation within some of these collagen molecules and as a consequence the triple helices that is produced that actually goes into the structure of the collagen fibres is not effective
less common, produce mutated collagen
Ehlers-Danlos Syndromes
Less of an effect on the bones so less of the brittle bone phenotypes
Group of heritable connective tissue disorders
Can affect skin, ligaments and internal organs
Characterised by
Loose joints
Stretchy skin
Abnormal scar formation
Increased risk of
Dislocations
Scoliosis
Osteoarthritis
Collagen is weaker in affected individuals
Can occur due to many mutations in collagen synthesis pathway
Collagen genes
Formation/processing of microfibrils (triple helices)
Formation/processing of fibrils
Stability between fibrils
Alport syndrome
Mutation in genes encoding Type IV collagen
Type IV makes up some of the basement membranes we find in cells and in particular in places like the kidney and eyes
Inherited kidney disease
Characterised by kidney dysfunction, deafness and visual abnormalities
Glomerular basement membrane disrupted
Blood and proteins (not normally filtered) are excreted in urine
Leads to metabolic & Inflammatory pathologies (since the kidney is not working)
Marfan syndrome
Due to mutation of fibrillin gene on chromosome 15
Fibrillin important protein in the synthesis/adhesion of elastin fibres - fibrillin makes up the outside of the fibres and helps them to attach to various components of the extracellular matrix
Component of blood vessel walls, eyes, ligaments, and lung
Disorder causes skeletal defects & cardiovascular complications
Symptoms
Long limbs
Extended fingers
Chest abnormalities
Curvature of spine
Facial features with highly arched palate, crowded teeth
Cardiovascular abnormalities incl. dilation of base of aorta
Weakness of elastin causes enlarged aorta
Many individuals with Marfan syndrome would die ~40 without surgery
Preventative aortic root replacement and dramatic increase in survival (removes the bit of weak/damaged tissue)
