Inflammation and Repair Practical

Question 1

Major characteristics of necrosis? (4)

Answer 1

Passive, often occurs because the cells run out of ATP

Kills surrounding cells forming an infarct

Stimulates an acute inflammatory response (provided we’re alive)

Only associated with pathology

Question 2

Major characteristics of apoptisis? (4)

Answer 2

Active process where cells use energy/ATP to kill themselves

A single cell can delete itself without impacting neighboring cells

Does not cause inflammation

Part of physiological and pathological processes

Question 3

What are the cardinal signs of acute inflammation and how are they related to vascular changes?

Answer 3

Red, heat, pain, swelling & loss of function.

Heat due to hyperaemia

Redness due to hyperaemia

Swelling due to hyperaemia & increased vascular permeability

Pain due to stretching of the tissue by oedema & stimulation of pain fibres

Loss of function due to oedema & pain

Extra information not assessed in CSB520: Arachidonic acid released from plasma membranes by phospholipase A2 is processed through two enzymatic pathways, cyclooxygenase and lipoxygenase, to produce prostaglandins and leukotrienes. These chemical mediators cause vasodilation leading to hyperaemia (redness and heat); increased vascular permeability resulting in exudate or oedema (swelling); stimulation of pain fibers and sensitization/amplification of pain signals. The pain and oedema results in loss of function.

Question 4

What are the three microscopic features of acute inflammation?

Answer 4

Hyperaemia, oedema & the recruitment of neutrophils

After a transient reflexive period of vasoconstriction, vasodilation leads to hyperaemia. The increased permeability of the vessels allows serum & proteins to enter the affected tissue forming oedema, which because of its high protein content can be referred to as exudate. Neutrophils are activated and are attracted to the acutely inflamed tissue, migrating through the vessel walls.

Neutrophils are phagocytic and the primary cell to associate with acute inflammation, however they have a short lifespan and will be aided my macrophages that will finish the job of neutrophils as well as remove apoptotic neutrophils.

Acute inflammation can result in resolution, organization or chronic inflammation.

Question 5

The acute inflammatory process is critical for repair yet in some cases may be detrimental and even life-threatening, can you think of examples where this might be the case?

Answer 5

Brain, lungs & throat, lungs (alveoli), pericardium, pleura and peritoneum.

The brain. The brain is suspended in cerebrospinal fluid (CSF) within the closed skull.
Oedema or haemorrhage will act as a space occupying lesion that increases the intracranial pressure. Initially the pressure will be countered by reduced secretion of CSF and decreased blood supply to the brain. However, these adaptations are limited and continued increase in pressure can lead to herniation of the brain which is lethal.

The lungs & throat. Swelling within the walls of the conductive airways, larynx or oropharynx can close the airway lumen leading to breathing difficulties.

The lungs. Excessive oedema in the alveoli can impair gas exchange and place greater demands upon the heart.

Pericardium, pleura & peritoneum. Excessive oedema with a high content of fibrin protein can perpetuate inflammation in areas of the body covered with a mesothelial lining. This can result in organization and abnormal adhesions to form between organs. This can be observed in response to invasion of cancers as well acute and chronic inflammatory processes, in some cases even surgery can cause the formation of adhesions.

Question 6

b. What type of oedema is observed in acute inflammation and how does it occur?

Answer 6

Exudate, which is an oedematous fluid which is high in proteins or pus which has proteins, cellular debris/necrotic cells, white blood cells and sometimes microorganisms.

In acute inflammation the HYPERAEMIA RESULTS IN INCREASED HYDROSTATIC PRESSURE which forces fluid from the vessels into the tissue (transudate) but there is also INCREASED VASCULAR PERMEABILITY which allows plasma proteins to also enter the fluid hence why we get an exudate.

Question 7

What are the three possible outcomes of acute inflammation?

Answer 7

Resolution = Healing without scarring

Organisation = Healing by scarring

Chronic inflammation

Question 8

What factors may prevent complete repair from occurring?

Answer 8

Resolution is the term for healing without scarring. Permanent tissues like the brain and heart will never heal by resolution as neurons, skeletal and cardiac myocytes do not divide. In labile/stable tissues resolution is not possible when a lot of tissue has been lost or when there is overlying infection, poor immunity, poor nutrition or interruption of healing.

Question 9

What are the three components of granulation tissue?

Answer 9

Granulation tissue is composed of:
1. Fibroblasts secreting collagen protein.

2. Macrophages coordinating events & cleaning up debris
3. Angiogenesis, the formation of new blood vessels to provide nutrients and blood gases during the repair process.

Once the dead tissue is removed and the space filled with collagen, the fibroblasts and macrophages migrate away leaving the largely acellular protein (collagen) scar. Because of the acellular nature of the scar, the new vessels regress through apoptosis and the collagen fibers contract as it matures.

Question 10

Under what circumstances does granulation tissue occur?

Answer 10

Granulation tissue is the immature scar, the tissue that forms the scar and so will occur in acute inflammation that heals through organization and it will always be present in chronic inflammation as part of the repeated attempts at repair.

Question 11

What has happened to the heart in response to ischaemia?

Answer 11

The heart tissue affected by ischaemia would have survived using anaerobic metabolism for a short period of time before succumbing to necrosis. The infarcted tissue would stimulate the acute inflammatory response so there would be hyperemia, oedema and the infiltration of the tissue by neutrophils. Because the heart is a permanent tissue, the formation of granulation tissue would follow; macrophages will move into the necrotic tissue and continue to remove it along with the increasingly apoptotic population of neutrophils. Fibroblasts would migrate into the area and secrete collagen fibres to fill in the space once occupied by dead myocytes and new capillaries would sprout into the area to provide growth factors, oxygen and nutrients for the granulation tissue. Once the dead cells are removed and the tissue deficit filled with collagen, the macrophages and fibroblasts migrate away and the new capillaries regress (die of by apoptosis). As this is a case of organization as part of acute inflammation, the granulation tissue would mature into a collagen scar which contracts over time pulling the edges of parenchymal tissue together.

Question 12

hyperaemia means?

Answer 12

active increase in blood to an area (e.g. injury)

Question 13

congestion means?

Answer 13

increase of blood in area. passive process.

Question 14

exudate means?

Answer 14

inflammatory extravascular fluid with high protein concentration

Question 15

transudate means?

Answer 15

extravascular fluid with low protein concentration

Question 16

What are the positive and negative consequences of healing through organisation?

Answer 16

Scarring allows repair & fills in the tissue deficits so we can survive but it lacks the properties of the tissue that it replaces. In addition, scar tissue contracts over time pulling surrounding tissue with it which can distort the surrounding parenchyma.

Specifically, in the heart the scar represents a weak point that can form an aneurysm & is pro- rather than anti-coagulant predisposing towards thrombus formation. Scar tissue lacks the strength of the normal cardiac muscle & will not relay electrical impulses in the same way as the normal heart muscle.

Question 17

In most of the specimens the process of chronic inflammation is ongoing because the cause persists. If the cause of the chronic inflammation had been treated, what would have happened?

Answer 17

The granulation tissue would have matured into scar tissue as happens with organization .

Question 18

a. What are the three ways in which chronic inflammation occurs?

Answer 18

1. Unresolved acute, so for example when the stimulus causing the acute response remains.
2. Repeated acute
3. “Special” cases where there is little/no acute response preceding the chronic inflammation which includes some infections and autoimmune reactions.

Question 19

What are the three main features of chronic inflammation?

Answer 19

1. Ongoing tissue injury and destruction
2. Lymphocytes
3. Repeated attempts at repair through the formation of granulation tissue and, when occurring in stable/labile tissues, proliferation of parenchymal cells.

Question 20

What has chronic inflammation lead to & why?

Answer 20

Liver is a common site for secondary cancers but rarely gets primaries unless affected by cirrhosis which is a chronic inflammatory condition of the liver. The liver has great regenerative capacity but the cells do not divide unless injury occurs. Cirrhosis results from chronic diffuse injury resulting in scarring complete loss of normal architecture and therefore loss of function. The cirrhotic liver is composed of islands of proliferating hepatocytes surrounded by scar tissue. Proliferation is a risk factor for carcinogenesis and there are a number of primary cancers in specimen 5.0.

The majority of gastric ulcers are now known to be caused by infection with Helicobactor pylori but prior to this discovery, treatment of ulcers was ineffective leading to chronic ulceration. The ulcer base, where the microbes are is composed of necrotic tissue, granulation tissue and lymphocytes while at the edge of the ulcer the normal epithelial cells proliferate in a futile attempt to repair. This increase in proliferation provides a fertile soil for carcinogenesis as observable in specimen 5.1.

In specimen 5.2 the varicose veins have cut off blood and nerve supply to the overlying skin which has died as a result forming an ulcer. Until the veins are surgically removed the ulcer will continue to fester and as with the previous example, the epithelial cells at the edge of the lesion will be prone to mutation and cancer formation.

In all 3 cases the increased proliferation of epithelial cells and oxidative stress as a result of chronic inflammation has led to the development of cancer.

Question 21

(additional info)

Answer 21

In all of the examples it is NOT the inflammatory cells (lymphocytes, macrophages, fibroblasts) that give rise to cancer but the surrounding epithelium.

In specimen 5.0 it is the epithelial cells of the liver that has given rise to the hepatocellular carcinomas.

In specimen 5.1 it is the gastric epithelial cells that have given rise to the gastric carcinoma.

In specimen 5.2 it is one of the epithelial cells of the skin that has resulted in a squamous cell carcinoma.

It is when cells are dividing & copying their DNA that they are most vulnerable to errors occurring. If you make the cells divide more, during to inflammation then there is greater risk for mutation and for that mutation to be passed onto daughter cells. In addition, to proliferation, during inflammation there is often increased levels of oxidants & other mediators capable of damaging DNA.

Question 22

Aims of acute inflammation vs chronic

Answer 22

acute: dilute, destroy, clean-up
chronic: wall-off and contain