Difference between revisions of "Healing and Repair - Pathology"

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{{review}}
 
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|linkpage =General Pathology
 
|linktext =General Pathology
 
|maplink = General Pathology (Content Map)
 
|pagetype =Pathology
 
|sublink1=Inflammation - Pathology
 
|subtext1=INFLAMMATION
 
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<br>
 
 
==Introduction==
 
==Introduction==
 
 
* There are several factors on which the ability to heal and repair depends:
 
* There are several factors on which the ability to heal and repair depends:
 
*# '''Species'''
 
*# '''Species'''
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==Repair==
 
==Repair==
 
 
* Repair occurs through one of two mechanisms:
 
* Repair occurs through one of two mechanisms:
 
** '''Regeneration'''
 
** '''Regeneration'''
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===Regeneration===
 
===Regeneration===
 
 
* In mammals, only epithelial and connective tissues regenerate extensively.
 
* In mammals, only epithelial and connective tissues regenerate extensively.
 
* The ability of tissue to regenerate depends upon whether the tissue is
 
* The ability of tissue to regenerate depends upon whether the tissue is
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====Labile Tissues====
 
====Labile Tissues====
 
 
* Labile tissues constantly replenish their cells throughout life.
 
* Labile tissues constantly replenish their cells throughout life.
 
** For example skin and mucous epithelia normally desquamate their outer layer of cells during life, maintaining their overall composition by division of their basal layers.  
 
** For example skin and mucous epithelia normally desquamate their outer layer of cells during life, maintaining their overall composition by division of their basal layers.  
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====Stable Tissues====
 
====Stable Tissues====
 
 
* Stable tissues have a limited ability to replace themselves.
 
* Stable tissues have a limited ability to replace themselves.
 
* They retain the ability to  
 
* They retain the ability to  
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====Permanent====
 
====Permanent====
 
 
* Permanent tissues have poor or no regenerative capacity.  
 
* Permanent tissues have poor or no regenerative capacity.  
 
* This group includes tissues in which the cells are highly specialised and generally have only one function, for example:
 
* This group includes tissues in which the cells are highly specialised and generally have only one function, for example:
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===Replacement===
 
===Replacement===
 
 
* Replacement is essentially endothelial and fibrous tissue proliferation to replace severely damaged tissue.
 
* Replacement is essentially endothelial and fibrous tissue proliferation to replace severely damaged tissue.
 
** This classical dual replacement gives rise to granulation tissue.
 
** This classical dual replacement gives rise to granulation tissue.
  
==Repair in the Skin==
+
==[[Skin Repair|Repair in the Skin]]==
''Back to [[Integumentary System - Pathology|Integumentary System Pathology]]
 
* Healing of a wound or surgical incision may be by:
 
** '''First intention'''
 
** '''Second intention'''.
 
 
 
===Healing by First Intention===
 
 
 
* Healing by first intention occurs when the incised ends remain in close apposition to each other anf bacterial contamination is minimal.
 
** This may be induced by suturing.
 
** For example, a surgical incision.
 
* Results in minimal scarring.
 
 
 
====Process====
 
 
 
* Initially, the incision ruptures the dermal blood vessels.
 
** The exuded blood forms a fibrinous clot between and above the incision.
 
*** The clot functions to:
 
***# Stem the flow of blood from the injured site.
 
***# Adhere the two ends together.
 
***# Prevent infection from entering the injured area.
 
* The basal layer of epithelium wthin 1mm of the wound edge begins to lose its connections with adjacent basal and overlying epithelium.
 
** Undergoes mitosis.
 
** Begins to migrate down both sides of the wound under the clot using pseudopodia.
 
*** As they are migrating, cells differentiate to some degree to form more superficial layers of the epithelium.
 
**** Gives a rather thick, if not very strong, barrier of epidermis.
 
*** In the area of migration, the skin is usually hypopigmented and lacks hair follicles.
 
* Within 2-4 days, the migrating basal layer of epithelium from either side meet together under the clot.
 
** It is thought that there is passage of substances, from one side to another that prevents further migration and mitosis.
 
** This gives reconstituion of an intact barrier to micro-organisms.
 
* While the epithelial changes are occuring, there is a sudden proliferation of local fibroblasts and accompanying endothelial cells in the dermis surrounding the incision.
 
** These grow across the narrow divide from each side and link up in the middle.
 
*** Takes about 12 hours to accomplish.
 
** In the early stages (days 4-7), their alignment may be vertical,  but in later stages (7-21 days) both fibroblasts and capillaries line up horizontally across the incision.
 
** This dermal repair forms the major portion of strength between the two sides at this time.
 
*** Gains in strength over a long period of time as the collagen contracts and remodels according to the stresses imposed upon it.
 
 
 
====Factors Inhibiting Healing====
 
 
 
* Factors inhibiting proper wound healing include:
 
*# '''Protein deficiency'''
 
*#* May be absolute, as in starvation, or resolute, as in some of the endocrine deficiencies.
 
*#**  E.g. [[Thyroid Gland - Pathology#Hypothyroidism|hypothyroidism]]
 
*# '''Vitamin C deficiency '''
 
*#* Vitamin C is essential for fibroplasia and to maintain the integrity of endothelial and epithelial cells.
 
*# '''Cold'''
 
*# '''Ageing'''
 
*# '''Contamination'''
 
*#* Infection tends not to be a complication as bacteria are generally excluded.
 
*#** Retained foreign material such as hair portions or suture material inadvertently left in the wound will cause infection and/or a foreign body reaction.
 
*# '''Movement'''
 
*#* Gives persistent trauma.
 
 
 
===Healing by Second Intention===
 
 
 
* Healing by second intention occurs when the gap between the ends of the incision is too wide to allow close approximation of the ends.
 
* This process of granulation tissue repair in a large wound is also the underlying process in the repair of:
 
** Infarcts and thrombi in vessels.
 
** Surface ulcers and diphtheresis.
 
** Pyogenic membrane in abscesses.
 
** Diffuse fibrosis ( cirrhosis ) in the [[Liver - Anatomy & Physiology|liver]].
 
 
 
====Process====
 
 
 
* In comparison to healing by first intention, there is a more massive fibroblastic and endothelial proliferation in the wound which fills and repairs the defect.
 
* There is also considerable surface exudation.
 
** The exudate is composed of fibrinous fluid and numerous inflammatory cells, mainly [[Neutrophils|neutrophils]] and macrophages.
 
*** The cells are scavengers, and engulf necrotic debris and any bacteria present
 
*** Macrophages and their secretions are also important for the promotion of fibroplasia.
 
* The fibroblasts tend to align themselves roughly horizontal to the surface, but the endothelium is perpendicular to the surface.
 
** The upper vessels form loops near to the surface.
 
*** Gives the gross appearance of red granules - this is [[Granulation Tissue|granulation tissue]].
 
* Well-formed granulation tissue tends to be fairly resistant to surface infection; however, it is rather delicated and so susceptible to trauma and subsequent introduction of infection.
 
** Infection is therefore a common complication in the early stages of healing.
 
* Once the gap has been filled with granulation tissue and is free of infection, the epithelium migrates across.
 
** As it migrates, the epithelium secretes collagenolytic substances.
 
* The epidermis is usually hypopigmented and lacks hair follicles unless they have survived in the granulation tissue.
 
 
 
==== Factors Inhibiting Healing====
 
 
 
* Several factors inhibit healing by second intention.
 
*# '''Movement'''
 
*#* Movement before sufficient strength has been attained in the bond between the edges can inhibit healing.
 
*# '''Infections'''
 
*# '''Corticosteroids'''
 
*#* Prevent proper collagen matrix formation.
 
*#* Inhibit leukocyte emigration and phagocytosis.[[Image:scar tissue.jpg|thumb|right|150px|Scar tissue (Courtesy of BioMed Archive)]]
 
*#* Diminish any acute inflammatory response by generally stabilising cellular membranes.
 
 
 
====Scarring====
 
 
 
* As the fibroblasts mature into fibrocytes, the collagen also matures and contracts and there may be extensive scar formation.
 
** There may be considerable depression of the surface in such a scar.
 
** The scar may interfere with movement in the area.
 
* The scar tends to diminish in size over a long period of time, as the underlying collagen remodels according to the stresses imposed upon the area.
 
 
 
==Repair in the Bones==
 
 
 
===Causes of Fracture===
 
 
 
* The causes of fracture fit into two distinct categories:
 
*# '''Fracture of trauma'''
 
*#* Breakage of normal healthy bone due to excessive stress pressure of short duration.
 
*# '''Pathological fracture'''
 
*#* Breakage of bone weakened by some underlying metabolic, inflammatory or neoplastic condition.
 
 
 
===Description of a Fracture===
 
 
 
* There are various terms to describe a fracture's appearance.
 
* Separation of the ends of the fracture may be '''complete''' or '''incomplete'''.
 
* When there is no penetration of the overlying skin, a the fracture is described as '''closed'''.
 
* When the sharp ends penetrate the overlying skin, the fracture is '''compound'''.
 
** In this scenario there is the danger of introducing infection.
 
*'''Comminuted''' describes a fracture where there are multiple small fragments of bone at the site of breakage.
 
* Where the edges of the fracture are impacted into each other, the fracture is said to be '''compressed'''.
 
* When one side of the fracture is depressed below the plane of the other, the term '''depressed''' is used.
 
** This occurs in the flat bones of the skull.
 
* '''Microfractures''' are fractures that are only visible on histological section as cracks in the bone.
 
** Grossly, there might be evidence of some haemorrhage in the area.
 
 
 
===Fracture Repair===
 
[[Image:fracture repair.jpg|thumb|right|150px|Fracture repair (Courtesy of BioMed Archive)]]
 
* On breakage, there is rupture of the periosteal, cortical and medullary vessels, causing:
 
** A blood clot in the breakage area.
 
*** Fibrin is the important component.
 
** Local necrosis of tissue supplied by these vessels.
 
*** This lowers the local pH.
 
* The fate of the blood clot depends upon its location.
 
** The periosteal portion is lysed and disappears;
 
** The medullary portion is removed by macrophages.
 
* The necrotic material is removed by phagocytosis.
 
** Necrotic [[Bone Marrow - Anatomy & Physiology|bone marrow]] is removed by [[Macrophages|macrophages]].
 
*** This is a fairly rapid process.
 
** Osteoclasts remove necrotic bone.
 
*** This is a slow process.
 
* On the periosteal side, the periosteum proliferates into the clot.
 
** Forms a fibrous collar around the bone called the soft callus.
 
* The cells in the inner aspect of the soft callus, particularly those near the fracture fragments, differentiate into osteoblasts. [[Image:fracture callus.jpg|thumb|right|150px|Fracture callus (Courtesy of BioMed Archive)]]
 
** Grow across the divide between the two fragments, laying down coarse woven bone.
 
* The woven bone laid is known as the hard callus.
 
**  This periosteal coarse bone is of utmost importance in repair.
 
*** It is responsible for much of the strength of the fracture repair.
 
** This is replaced over a period of time by mature compact bone.
 
*** Aligns itself according to the stresses applied to it.
 
* Periosteal cells that are further away from the fracture fragments differentiate into cartilage-producing cells.
 
** Produce a cone of cartilage between the two fragments.
 
*** As the local pH changes to more alkaline conditions, this cartilage undergoes calcification, with invasion by blood vessels and osteoblasts.
 
**** The cartilage is replaced by bone - endochondral ossification.
 
* On the medullary side, the endosteum proliferates and invades the clot, laying down bone.
 
** This bone may totally occlude the medulla and is later remodelled to reconstitute a patent lumen.
 
 
 
===Complications===
 
 
 
* There are several possible complications that may arise in the repair of bone.
 
# Inadequate immobilisation of the fractured ends will lead to incomplete repair by callus formation.
 
#* An intervening mass of fibrocartilage remains, forming a false joint.
 
#** In some cases the false joint can even appear to form a synovial lining.
 
#* If the fractured ends are sufficiently far apart, no substantial callus forms.
 
#** The intervening space is taken up by connective tissue organisation.
 
# Failure to align the fractured ends in proper apposition to one another will produce excessive callus.
 
#* This takes a longer time to be remodelled by the adult compact bone.
 
# [[Healing and Repair - Pathology#Description of a Fracture|Comminution]] delays healing due to persistent irritation.
 
# Infection delays healing due to the effects of the toxins on theproliferating cells.
 
#* May give rise to a systemic infection affecting the rest of the body.
 
 
 
  
 +
==[[Fractures|Repair in the Bones]]==
  
 
==Repair in the Respiratory Tract==
 
==Repair in the Respiratory Tract==
 
 
* Severe damage to the alveolar wall results in fibrous tissue organisation of the entire alveolus.
 
* Severe damage to the alveolar wall results in fibrous tissue organisation of the entire alveolus.
 
* The appearance of inflammation in the respiratory tract varies with the route of entry of the agent.
 
* The appearance of inflammation in the respiratory tract varies with the route of entry of the agent.
  
 
===Airborne Agents===
 
===Airborne Agents===
 
 
* Infectious droplets tend to deposit in the anterior ventral portions of the lobes.
 
* Infectious droplets tend to deposit in the anterior ventral portions of the lobes.
 
** I.e. in the apical, cardiac and anterior portions of the diaphragmatic lobes.
 
** I.e. in the apical, cardiac and anterior portions of the diaphragmatic lobes.
* Airborne agents produce '''bronchopneumonia'''.
+
* Airborne agents produce [[Bronchopneumonia|'''bronchopneumonia''']].
 
** So-called because the inflammation is initiated and centred upon the airways.
 
** So-called because the inflammation is initiated and centred upon the airways.
 
* The usual appearance of bronchopneumonia in ruminants and the pig is as the name suggests.  
 
* The usual appearance of bronchopneumonia in ruminants and the pig is as the name suggests.  
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*** Air trapped distal to the blockage is gradually absorbed into the bloodstream.
 
*** Air trapped distal to the blockage is gradually absorbed into the bloodstream.
 
**** This causes increased pressure on the injured wall, dilating it further.  
 
**** This causes increased pressure on the injured wall, dilating it further.  
*** This is a progressive process and results in irreversible dilatation of the airway lumen and is called '''bronchiectasis'''.
+
*** This is a progressive process and results in irreversible dilatation of the airway lumen and is called [[Bronchiectasis|'''bronchiectasis''']].
 
* Bronchopneumonia in the dog and cat often tends to be more diffusely spread.  
 
* Bronchopneumonia in the dog and cat often tends to be more diffusely spread.  
 
** These species have a poorly-developed interlobular septum and collateral ventilation between alveoli from different respiratory units.  
 
** These species have a poorly-developed interlobular septum and collateral ventilation between alveoli from different respiratory units.  
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===Blood-borne Agents===
 
===Blood-borne Agents===
 
 
* Blood-bourne agents tend to have a patchy distribution throughout the lung.
 
* Blood-bourne agents tend to have a patchy distribution throughout the lung.
* Cause '''interstitial pneumonia'''.
+
* Cause [[Interstitial Pneumonia|'''interstitial pneumonia''']].
  
 
====Circulating Toxins====
 
====Circulating Toxins====
 
+
* For example, [[Acute Bovine Pulmonary Emphysema and Oedema|"Fog Fever"]] in adult cattle.
* For example, "Fog Fever" in adult cattle.
 
 
** Interstitial emphysema.
 
** Interstitial emphysema.
 
** 3-methyl indole is selectively toxic to Type 1 alveolar epithelium.
 
** 3-methyl indole is selectively toxic to Type 1 alveolar epithelium.
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====Micro-organisms====
 
====Micro-organisms====
 
 
* A predominantly mononuclear reaction in the alveolar wall can be caused by:
 
* A predominantly mononuclear reaction in the alveolar wall can be caused by:
 
** Viruses
 
** Viruses
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*** E.g. [[Salmonella|''Salmonella'']]
 
*** E.g. [[Salmonella|''Salmonella'']]
 
** Protozoa
 
** Protozoa
*** E.g. [[Toxoplasma]]
+
*** E.g. ''[[Toxoplasma gondii]]''
  
 
====Parasites====
 
====Parasites====
 
 
* Lungworms (''Dictyocaulus vivipara'') tend to affect the dorsocaudal areas of the diaphragmatic lobes in their invasion stage as larvae in the blood.  
 
* Lungworms (''Dictyocaulus vivipara'') tend to affect the dorsocaudal areas of the diaphragmatic lobes in their invasion stage as larvae in the blood.  
 
* Later adult stages irritate the airways and also release larvae which are inhaled deeper into the lung.
 
* Later adult stages irritate the airways and also release larvae which are inhaled deeper into the lung.
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===Traumatic Implantation===
 
===Traumatic Implantation===
 
 
* Traumatic implantation is fairly rare.
 
* Traumatic implantation is fairly rare.
 
* Initially causes a pleural inflammation, with some extension to the adjacent lung tissue.
 
* Initially causes a pleural inflammation, with some extension to the adjacent lung tissue.
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** Stake wounds in horses.
 
** Stake wounds in horses.
 
*** Usually fatal and cause extensive purulent, smelly inflammation.
 
*** Usually fatal and cause extensive purulent, smelly inflammation.
** Purulent pleuritis in dogs and cats due to [[:Category:Nocardia|''Nocardia'']] from a distant wound.  
+
** Purulent pleuritis in dogs and cats due to ''[[:Category:Nocardia species]]'' from a distant wound.  
 
*** Not uncommon in cats.
 
*** Not uncommon in cats.
 
*** May take some time to develop fully after the initial wound or cause has healed.  
 
*** May take some time to develop fully after the initial wound or cause has healed.  
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==Repair in the Alimentary Tract==
 
==Repair in the Alimentary Tract==
 
 
===The Gut===
 
===The Gut===
 
 
* The gut is quite prone to infections.
 
* The gut is quite prone to infections.
 
** These are generally kept at bay by the profuse gut associated lymphoid tissue and the continuous movement of ingesta.
 
** These are generally kept at bay by the profuse gut associated lymphoid tissue and the continuous movement of ingesta.
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===The Liver===
 
===The Liver===
 
 
* The [[Liver - Anatomy & Physiology|liver]] retains limited powers to regenerate and has considerable functional reserve.
 
* The [[Liver - Anatomy & Physiology|liver]] retains limited powers to regenerate and has considerable functional reserve.
 
* Acute inflammation is often due to viruses and bacteria.
 
* Acute inflammation is often due to viruses and bacteria.
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===The [[Pancreas - Anatomy & Physiology|Pancreas]]===
 
===The [[Pancreas - Anatomy & Physiology|Pancreas]]===
 
 
* The [[Pancreas - Anatomy & Physiology|pancreas]] suffers both acute and chronic disease.
 
* The [[Pancreas - Anatomy & Physiology|pancreas]] suffers both acute and chronic disease.
 
* The acute form called acute pancreatic necrosis is the important type in dogs.
 
* The acute form called acute pancreatic necrosis is the important type in dogs.
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==Repair in the Urinary Tract==
 
==Repair in the Urinary Tract==
 
 
* The kidney has a great functional reserve.
 
* The kidney has a great functional reserve.
 
** Only 30% of the tissue is required to function properly.
 
** Only 30% of the tissue is required to function properly.
  
 
===Glomerulonephritis===
 
===Glomerulonephritis===
 
 
* Glomerulonephritis and glomerular deposition of amyloid may cause loss of substantial quantities of protein into the urine.  
 
* Glomerulonephritis and glomerular deposition of amyloid may cause loss of substantial quantities of protein into the urine.  
 
* Oedema develops in the body, generally first in the back legs, then the ventral subcutis, and perhaps in the abdominal cavity.  
 
* Oedema develops in the body, generally first in the back legs, then the ventral subcutis, and perhaps in the abdominal cavity.  
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===Pyelonephritis===
 
===Pyelonephritis===
 
 
* Important in the cow and sow.
 
* Important in the cow and sow.
 
** It tends to be quite acute in the sow, and chronic in the cow.
 
** It tends to be quite acute in the sow, and chronic in the cow.
 
* Arises from infection ascending the urinary tract.
 
* Arises from infection ascending the urinary tract.
 
*  There is progressive loss of tissue.
 
*  There is progressive loss of tissue.
** Starts with necrosis in the pelvic area, then the inflammation spreads up into the cortex. *P oor prognosis even with therapy.
+
** Starts with necrosis in the pelvic area, then the inflammation spreads up into the cortex.  
 +
*Poor prognosis even with therapy.
  
 
===Cystitis===
 
===Cystitis===
 
 
* Bladder inflammation.
 
* Bladder inflammation.
 
* Common in females.  
 
* Common in females.  
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==Repair in the Genital Tract==
 
==Repair in the Genital Tract==
 
 
 
===Female===
 
===Female===
 
 
* '''Inflammation of the uterus''' in livestock can take place at two periods:
 
* '''Inflammation of the uterus''' in livestock can take place at two periods:
 
*# At service.
 
*# At service.
Line 422: Line 226:
 
**# Chronic mastitis.
 
**# Chronic mastitis.
 
**#* Results in progressive destruction of the glandular tissue and replacement by fibrous tissue.
 
**#* Results in progressive destruction of the glandular tissue and replacement by fibrous tissue.
**#* E.g. [[Streptococcal mastitis - bovine|''Streptococcus agalactiae'']].
+
**#* E.g. [[Streptococcal Mastitis - Cattle|''Streptococcus agalactiae'']].
 
** Some organisms such as [[Staphylococcus aureus|''Staphylococcus aureus'']] can cause gangrenous, acute and chronic mastitis.
 
** Some organisms such as [[Staphylococcus aureus|''Staphylococcus aureus'']] can cause gangrenous, acute and chronic mastitis.
  
 
===Male===
 
===Male===
 
 
* '''Prostatitis'''
 
* '''Prostatitis'''
 
** Inflammation of the prostate.
 
** Inflammation of the prostate.
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==Repair in the Central Nervous System==
 
==Repair in the Central Nervous System==
 
 
* '''Encephalitis'''
 
* '''Encephalitis'''
 
** Inflammation of neural tissue of the brain.
 
** Inflammation of neural tissue of the brain.
Line 448: Line 250:
 
** Inflammation of the meninges.
 
** Inflammation of the meninges.
 
** Purulent meningitis follows haematogenous spread of infection from umbilical infections and certain septicaemias.
 
** Purulent meningitis follows haematogenous spread of infection from umbilical infections and certain septicaemias.
 +
[[Category:Inflammation|B]]
 +
[[Category:General Pathology]]

Latest revision as of 16:32, 25 July 2011


Introduction

  • There are several factors on which the ability to heal and repair depends:
    1. Species
      • The ability of the species to cope with that particular inflammation .
      • For example, peritonitis.
        • In cattle, it is often successfully walled off at the initial injury site, preventing spread throughout the whole cavity.
        • In the horse peritonitis is not walled off, and is generally rapidly fatal.
    2. Age
      • Repair is generally more successful in younger animals than older animals.
      • However, in young animals the immune system may still be immature.
        • For example, Pseudorabies virus is more often fatal in pigs under three weeks old, even in the presence of maternal antibody.
    3. Tissue and extent of damage
      • Highly specialised tissue rarely repairs successfully apart from in mild injury.
        • If the functional reserve of the damaged tissue is exceeded, clinical signs of disease related to this insufficiency will occur.
      • When there is substantial fibrosis in the tissue, the tissue may continue to be progressively destroyed.
        • This is due the maturation and contraction of fibrous tissue causing further injury to the adjacent normal tissue.
        • E.g. the liver in cirrhosis, and the kidney in chronic renal disease.

Repair

  • Repair occurs through one of two mechanisms:
    • Regeneration
    • Replacement

Regeneration

  • In mammals, only epithelial and connective tissues regenerate extensively.
  • The ability of tissue to regenerate depends upon whether the tissue is
    • Labile
    • Stable
    • Permanent.

Labile Tissues

  • Labile tissues constantly replenish their cells throughout life.
    • For example skin and mucous epithelia normally desquamate their outer layer of cells during life, maintaining their overall composition by division of their basal layers.
  • Other examples include bone marrow and fat.
  • These tissues regenerate well.
    • Provided the basement membrane is not breached during the inflammatory process, the epithelium migrates to cover the surface defect.

Stable Tissues

  • Stable tissues have a limited ability to replace themselves.
  • They retain the ability to
    • Replace cells that have undergone programmed cell death when the cells age and cannot continue their function.
      • For example, the liver, some endocrine glands and the renal tubular epithelium.
    • Respond to greater need for their function in the body.
  • Blood vessels and fibroblasts are also stable tissues.
    • Have great potential to divide and proliferate.
    • Are the important tissue cells in repair by replacement.

Permanent

  • Permanent tissues have poor or no regenerative capacity.
  • This group includes tissues in which the cells are highly specialised and generally have only one function, for example:
    • Neuronal cell bodies in the CNS
    • The retina of the eye
    • The cells responsible for hearing in the ear.
  • Axons in the peripheral nervous system can regenerate to a limited extent when severed.
  • Cardiac muscle myofibres have very poor regenerative capacity, and undergo repair by

fibrosis or fat replacement.

Replacement

  • Replacement is essentially endothelial and fibrous tissue proliferation to replace severely damaged tissue.
    • This classical dual replacement gives rise to granulation tissue.

Repair in the Skin

Repair in the Bones

Repair in the Respiratory Tract

  • Severe damage to the alveolar wall results in fibrous tissue organisation of the entire alveolus.
  • The appearance of inflammation in the respiratory tract varies with the route of entry of the agent.

Airborne Agents

  • Infectious droplets tend to deposit in the anterior ventral portions of the lobes.
    • I.e. in the apical, cardiac and anterior portions of the diaphragmatic lobes.
  • Airborne agents produce bronchopneumonia.
    • So-called because the inflammation is initiated and centred upon the airways.
  • The usual appearance of bronchopneumonia in ruminants and the pig is as the name suggests.
    • These species have a well developed interstitial septum between groups of lobules, and little or no connection between alveoli from different terminal bronchioles.
      • Therefore, one lobule may show extensive pneumonic changes while the adjacent lobule is free from inflammation.
    • The inflammatory exudate commonly gets stuck in the lower airways.
      • Invokes an inflammatory response in the smooth muscle of the wall of the airway.
        • The wall is weakened, causing it to dilate somewhat.
      • Air trapped distal to the blockage is gradually absorbed into the bloodstream.
        • This causes increased pressure on the injured wall, dilating it further.
      • This is a progressive process and results in irreversible dilatation of the airway lumen and is called bronchiectasis.
  • Bronchopneumonia in the dog and cat often tends to be more diffusely spread.
    • These species have a poorly-developed interlobular septum and collateral ventilation between alveoli from different respiratory units.
    • Resolution of bronchopneumonia in the dog and cat is often more or less complete.

Blood-borne Agents

Circulating Toxins

  • For example, "Fog Fever" in adult cattle.
    • Interstitial emphysema.
    • 3-methyl indole is selectively toxic to Type 1 alveolar epithelium.
      • Derived from excess tryptophan in autumn grass.

Micro-organisms

Parasites

  • Lungworms (Dictyocaulus vivipara) tend to affect the dorsocaudal areas of the diaphragmatic lobes in their invasion stage as larvae in the blood.
  • Later adult stages irritate the airways and also release larvae which are inhaled deeper into the lung.
  • In natural outbreaks, both types of lesions are seen.
    • May be complicated by bacterial infection.

Traumatic Implantation

  • Traumatic implantation is fairly rare.
  • Initially causes a pleural inflammation, with some extension to the adjacent lung tissue.
  • For example:
    • Stake wounds in horses.
      • Usually fatal and cause extensive purulent, smelly inflammation.
    • Purulent pleuritis in dogs and cats due to Category:Nocardia species from a distant wound.
      • Not uncommon in cats.
      • May take some time to develop fully after the initial wound or cause has healed.
      • Generally fatal.
      • Clinical signs only developing when the lesions have become very extensive.

Repair in the Alimentary Tract

The Gut

  • The gut is quite prone to infections.
    • These are generally kept at bay by the profuse gut associated lymphoid tissue and the continuous movement of ingesta.
  • In mild infections, the inflammation is usually catarrhal.
    • Particularly in the large intestine where there are numerous goblet cells.
    • There is rapid repair by mucosal epithelium.
  • More severe infections may damage the structure of the mucosa.
    • The villi may be stunted following repair.
      • There is a reduced water absorption compounded by loss of electrolytes - malabsorption.
        • Results in diarrhoea and progressive loss of weight.
        • E.g. in Johne's Disease.

The Liver

  • The liver retains limited powers to regenerate and has considerable functional reserve.
  • Acute inflammation is often due to viruses and bacteria.
    • E.g. Infectious Canine Hepatitis and Salmonellosis in young livestock.
    • The liver is swollen and may display hyperaemia.
    • Small pinpoint foci of necrosis may be seen through the surface.
  • Chronic liver damage results in fibrosis - cirrhosis.
    • Generally the sequel to ingestion of a toxic substance over a long period of time.
    • E.g Aspergillosis.
      • Grossly, the liver shows varying fibrosis imparting a pale or greyish colour.
      • In some cases, there may be attempts at nodular regeneration of the hepatic parenchyma.
    • Ragwort poisoning has a fairly similar appearance.
      • The insidious deposition of fibrous tissue eventually becomes self-perpetuating, causing further damage to remaining hepatocytes as it matures and contracts.
      • Eventually neural signs referable to loss of hepatic detoxifying function occur.

The Pancreas

  • The pancreas suffers both acute and chronic disease.
  • The acute form called acute pancreatic necrosis is the important type in dogs.
    • The aetiology is obscure.
    • The mechanism involves the release of pancreatic enzymes into the surrounding fatty connective tissue.
    • Commonly affects obese females.
    • Animals may either die soon after the initial painful episode, or the inflammation smoulders on, often without clinical signs, until there is little pancreatic tissue left.
    • Diabetes mellitus or pancreatic insufficiency are common sequelae.
  • Chronic pancreatitis is seen in the cat.
    • A slow disease often associated with inflammation of both the pancreatic and biliary ducts. *** Fuse before entering the duodenum in cats.
    • Grossly, there is reduction in size and sometimes quite extensive periductal fibrosis and inflammation.

Repair in the Urinary Tract

  • The kidney has a great functional reserve.
    • Only 30% of the tissue is required to function properly.

Glomerulonephritis

  • Glomerulonephritis and glomerular deposition of amyloid may cause loss of substantial quantities of protein into the urine.
  • Oedema develops in the body, generally first in the back legs, then the ventral subcutis, and perhaps in the abdominal cavity.
    • This is called the Nephrotic Syndrome
  • Inflammation can arise in the glomeruli, interstitial tissue and in the renal pelvis.
    • In the later stages of chronic inflammation, it may be difficult to determine the initial site of the inflammation.
  • In severe chronic inflammation, substantial fibrosis of repair can become self-perpetuating.
    • Produces more and more damage until the whole kidney appears shrunken and distorted .
      • Called "end stage".
  • Signs of uraemia develop once the functional reserve has been exceeded.
    • There are also characteristic (though inconsistent) lesions present in other tissues, i.e. the remote effects.
      • Inflammation of the tongue and stomach
      • Atrial endocarditis
      • Parathyroid hyperplasia
      • Widespread calcium deposition
        • Grossly noticeable intercostal muscles from the pleural aspect.
      • Anaemia
      • Hypertrophy of the left ventricle of the heart
      • Facial loss of bone

Pyelonephritis

  • Important in the cow and sow.
    • It tends to be quite acute in the sow, and chronic in the cow.
  • Arises from infection ascending the urinary tract.
  • There is progressive loss of tissue.
    • Starts with necrosis in the pelvic area, then the inflammation spreads up into the cortex.
  • Poor prognosis even with therapy.

Cystitis

  • Bladder inflammation.
  • Common in females.
  • A feature of inflammation in the bladder is the considerable dilation of the submucosal vessels - vascular ectasia.
    • Bracken fern poisoning initially causes vascular ectasia and inflammation, but can progress

to tumour formation in the bladder.

Repair in the Genital Tract

Female

  • Inflammation of the uterus in livestock can take place at two periods:
    1. At service.
      • Mild.
      • An endometritis.
    2. At parturition.
      • Can be very severe and life threatening.
      • Particularly occurs in assisted parturition.
      • Causes a metritis, involving the whole wall.
  • Pyometra
    • Pus in the uterus.
    • Occurs commonly in bitches.
    • Is life threatening
  • Mastitis
    • Inflammation of the mammary gland.
    • There are several forms of mastitis.
      1. Life threatening mastitis.
        • Occurs shortly after parturition.
        • E.g. gangrenous mastitis due to Staphylococcus aureus, and Coliform mastitis.
      2. Chronic mastitis.
        • Results in progressive destruction of the glandular tissue and replacement by fibrous tissue.
        • E.g. Streptococcus agalactiae.
    • Some organisms such as Staphylococcus aureus can cause gangrenous, acute and chronic mastitis.

Male

  • Prostatitis
    • Inflammation of the prostate.
    • Common in dogs.
    • Causes a bag of pus in the tissue.
    • Results from an ascending infection of the tract.
  • Orchitis
    • Inflammation of the testis.
    • Rather uncommon.
    • In bulls, a granulomatous inflammation occurs with Brucella abortus.

Repair in the Central Nervous System

  • Encephalitis
    • Inflammation of neural tissue of the brain.
    • Repairs by the proliferation of astrocytes.
      • Astrocytes are the brain's form of fibrous tissue.
      • Called gliosis.
  • Perivascular lymphocytic cuffing accompanies neural damage in the brain parenchyma.
  • Meningitis
    • Inflammation of the meninges.
    • Purulent meningitis follows haematogenous spread of infection from umbilical infections and certain septicaemias.