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dr weber
handout: inflammation and repair

first 7 pages deal with lab; detailed descriptions of the slides. only 
need to see 2 or 3 slides today. can ignore 331 'cause we don't have that 
one.
next week, try to answer the questions on page 8.

acute inflammation is by definition a continuous spectrum of events.
granulomatous inflammation is a subset. chronic inflammation is a 
continuation of acute inflammation.
repair and healing follow inflammationn.

acute infl.response is response of living, viable tissue to injury. if 
tissue has already undergone necrosis, those cells are dead. they can't 
undergo an inflammatory response. but the tissue around the necrosis can 
be inflamed.
by definition, acute inflammation is an exudative phenomenon. this is not 
like chronic, which is proliferative response eg fibroblast 
proliferation, collagen deposition, etc. acute inflammation is 
characterized by dilation of blood vessels, eg arterioles and venules. 
associated with that is increased vascular permeability, so plasma fluid 
extravasates and the fluid varies with intensity of response. can be very 
watery or can have lots of protein in it if more severe.  also there is 
accumulation and emigration of WBCs into extravascular space. exudate == 
high protein fluid with high WBC count. causes of acute inflammation 
vary. exposure to extreme heat or cold, trauma, are some nonspecific 
causes. infection - viruses, bacteria, fungi, parasites. with bacteria, 
depends largely on whether bacteria produce toxins that kill cells or if 
they have cell walls, and live intracellularly. viruses by nature tend to 
kill cells, usually lytic. often have predilection for specific cell 
type. some viruses like endothelial cells and kill those, causing 
hemorrhagic inflammatory response. in GI tract, virus may select 
superficial epi cells causing watery fluid diarrhea. now, thinnk back to 
immuno. some highly specific rxns - autoimmune dz and hypersensitivities 
are inflammatory rxns based on highly specific immunological mechanisms.

know this about acute inflammation: the mechanisms involved inn causing 
vascular dilation, emigration of WBCs, etc etc. the photos in the lab 
should be helpful. if you have a hard time seeeing things under the 
scope, check out the wall. also in the computer lab is a video called 
"the inflammatory respose" which is 20 yrs old but still useful. has 
lovely time-lapse cinematography of vascular respose to inflammation.

focusing on the small blood vessels:

slide: venule or capillary - no smooth muscle around the vessel- just 
endothelium and basement membrane. inside are the WBC and platelets. in 
the periphery are some important cell types to remember: mast cells, 
fibroblasts, monocyte/macrophage, and elastic, collagen, fibers in ECM. 
collagen type IV, fibronectin, proteoglycans: in basement membrane. 

these components are active in acute, and chronic, inflammation, and 
healing. in acute infl.rxns, you have vasodilation occuring. if you look 
at skin, and look at blood vessels, there are many small vascular spaces 
that often carry no blood. an occasional rbc sneaks through to keep 
tissue viable. but, during infl response, these vessels dilate, and all 
of a sudden lots more blood is going through the area. this is largely 
responsible for the hyperemia (redness) we see. of course, you only see 
this on an area that's normally PALE. doesn't show up well on liver or 
other dark tissue. the dilation occurs to capillaries, arterioles, and 
venules, but the increased permeability is primarily in the venules.  
most of the exudate comes out of the venules. if you look at pressure 
relationships, hydrostatic v oncotic, etc, it's not 
difficult....normally, the colloid osmotic pressure between arteriole and 
venule is about 25 mmHg, straight across. but BP is higher on arteriole 
side - 32 and 12. so, because BP in arteriole side is higher, there is 
normally fluid being pushed out of small bvs, but because oncotic 
pressure is high on venule side, fluid gets pulled back in, so you don't 
really see much edema. the little excess fluid that stays out of the 
system gets picked up by lymphatics.but, in inflamed tissue, you have 
dilated vessels. the blood pressure is tremendously icreased, up to 50 
and 30. compare that to the 32 and 12 of normal vessels. now, colloid 
osmotic pressure is lowered compared to normal - about 20 all the way 
across. this is because the fluid that leaks out carries some protein 
molecules with it. this protein builds up outside the vessel, and that 
causes more inflammatory edema

there are other forms of edema. we're talking about edema secondary to 
damaged endothelium.

why is hydrostatic pressure raised? if the blood vessels dilate, as the 
fluid on the venule side is escaping, because the endothelium becomes 
leaky, the bloodstream isn't flowing normally...blood actually aggregates 
in clumps. there is "sludging" of RBCs due to fluid loss. the RBCs 
partially block the exits on the venule side, causing back pressure to 
build up. because there is less fluid on the venule side, see. so these 
are the main pressure effects taht occur. the fluid goes out the venule 
side because endothelial cells physically contract when they are 
irritated, and the spaces between them get larger.

if you have mild inflam. rxn, fluid exudate is mostly watery. if more 
intense, more protein, more WBC.

exudate vs transudate

exudate: inflammatory, caused by inflammation/infection. SG 1.020, 
protein content over 4%, often clottable due to platelet presence and 
clotting factors, often contains inflammatory cells eg neutrophils(almost 
always), and often has bacteria.

transudate: noninflammatory, noninflammatory edema. SG below 1.015, 
protein below 3.0%, rarely clottable, rarely contains inflammatory cells, 
almost never contains bacteria.

you can have a transudate with a very mild inflammatory rxns. mostly, 
though, transudate caused by cirrhosis of liver which causes back 
pressure and therefore ascites, or a malfunctioning heart causing a 
transudate into the lungs (that often predisposes patient to pneumonia). 


can characterize exudates eg serosanguinous, etc.

chemical mediators:

cells: produce preformed or newly synthesized mediators
preformed: histamine (4 main functions: vasodilation, increased vascular 
permeability, contraction of extravascular smooth muscle (bronchioles, 
uterus), and increased mucus secretion. only responsible for early 
infl.response. is quickly inactivated by histaminase.), lysosomal enzymes 
(both hist. and lys. enz. are from mast cells, basophils); serotonin
new: prostoglandins, leukotrienes, platelet activating factor (first 
three here are more responsible for the prolonged phase of the acute 
inflammatory rxn.), cytokines, NO (nitric oxide)

plasma: complement activation and hageman factor activation.
complement: C3a, C5a, C5b-9
hageman: kinin system and coagulationn system
all of these are considered plasma proteases.

Mast cell/basophil: what triggers these suckers? immunologically specific 
factors. recall crosslinking of IgE. also nonspecific trauma...neutrophil 
basic protein, anaphylatoxins, bee venom or other chemicals, and also 
just plain trauma to the cell. variety of immunologically specific and 
nonspecific triggers cause these cells to release preformed vasoactive 
agents. very important cell. histamine a main component but only early. 
can also make cytokines, leukotrienes, and prostoglandins later in the 
inflamm rxn.

[my n key keeps skipping and sticking. argh]

p 12 of handout: arachadonic acid derivatives
all starts with cell membrane phospholipids, present in all cells of 
course.
phospholipase A2 (inhib by steroids) changes them into arachadonic acid. 
then there are two pathways: cyclooxygenase pathway forms endoperoxide 
intermediaries, and then specific enzymes produce prostacycline, 
thromboxane, and prostoglandins. prostacyclin mainly made by endothelial 
cells. inhibits platelet aggregation. is antithrombotic. prevents 
thrombus formation, causes some vasodilation, can potentiate edema 
formation. but thromboxane, made by platelets, causes platelet 
aggregation and vasoconstriction. so these things antagonize each other. 
the way different cells respond in an area of acute infl rxn depends on 
the sum of signals the cells recieve. there are positive and negative 
signals. now, you can inhibit the cyclooxygenase pathway with aspirin, 
indomethacin. at age 30, you may start taking a baby aspirin every couple 
of days to drop down the thromboxane production. now, steroids block both 
pathways, the cyclooxygenase and lipoxygenase pathway. lipoxygenase 
pathway makes leukotrienes, LTB4 a WBC chemotactic agent, and LTC4, LTD4 
and LTE4 which vasoconstrict, cause bronchospasm, and increased vascular 
permeability. how does that happen? well, constriction is on arteriolar 
side, and increased permeability is on the venule side. these three 
leukotrienes used to be called slow reactive substances. they keep an 
inflammatory response going.

question: why does bronchospasm occur? evolutionarily, it seems 
maladaptive. well, we don't know. we consider it an unfortunate 
consequence that when you have smooth muscle in blood vessels relaxing, 
bronchiolar smooth muscle constricts.

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[note: 10 years ago, people were all concerned about which cell made what 
mediator, etc. but it is now clear that multiple cell types make the same 
thing. many cells in the vicinity of infl.rxn will form these factors.]

from the standpoint of efficiency and potency, leukotrienes are about 
100-1000x more potent than histamine is. they're serious stuff.

complement system plays active role in acute inflamm rxn:

C3a and C5a are anaphylatoxins, induced via alternative or classical 
pathway. they trigger mast cells to release histamine, and they also 
dilate blood vessels, cause inncreased vsc perm, and bronchoconstriction. 
they perpetuate the inflammatory response after complement activation and 
during gram neg bacterial sepsis.

C3b functions as an opsonizer. most cells have receptors for C3b and 
phagocytose bacteria more easily when it is present.

complement in acute infl rxns - the MAC will lyse bacteria and foreign 
cells, smooth musc contraction, mast cell degranulation and increased 
vasc perm are caused by anaphylatoxins. also anaphylatoxins activate 
neutrophils and make more adhesion molecules show up on neutrophils. 

C5a is major anaphylatoxin. activates neutrophils, causes neutrophil 
adhesion to endothelium, is chemotactant for neutrophils, stimulates 
monocytes to make factors which play role in inflammation, and triggers 
mast cells. also vasc perm, etc.

Hageman factor (XII) p 11 of handout

subendothelial collagen (damaged endothelium, basement membrane, laminin, 
collagen type IV, etc) activates factor XII
activated factor XII (XIIa) converts plasminogen to plasmin, prothrombin 
to thrombin, and prekallikrein to kallikrein.

when injury occurs, endothelium is damaged. so, factor XII is activated 
and becomes XIIa.

XIIa is active in the intrinsic pathwayy of coagulation which culminates 
in production of fibrin. XIIa helps prothrombin to become thrombin. 
thrombin converts fibrinogen into fibrin. fibrinogen is a protein formed 
in liver, always present in peripheral blood. should be always 
intravascular. thrombin causes it to polymerize into fibrin, which 
usually happens OUTSIDE the vessel when there has been vascular damage. 
but, how does body deal with fibrin? it has to be removed to allow 
healing and repair. can't really recognize fibrin usually but if you have 
say severe hepatitis or splenitis, ad you have fibrin building up on 
surface of organ, you recognize it as a grey white elastic membranous 
material which can at first be readily stripped away. it's a polymerized 
protein. after time goes by, fibrin won't be able to be stripped off. 
potentially, you can have fibrin formation inside blood vessels during an 
acute inflammatory response. eg, inflammatory response going on on a 
heart valve can cause fibrin formation and accumulation on the heart 
valve, which is very damaging, because you get thrombi and clots forming, 
and some will maybe break free as emboli, and they can go to brain, 
kidney, spleen, heart (lung?). then they cause infarcts. it's not 
pleasant.as fibrin is being produced, fibrinopeptides are splitting off. 
they increase vascular permeability and cause vasodilation.
coagulation system is countered by fibrinolytic system. end product of 
that is plasmin, which comes from plasminogen. plasminogen is activated 
by plasminogen activator. plasmin has several main functions, the main 
one being it breaks down fibrin, which is good. it also activates the 
alternative complement pathway, producing anaphylatoxins which perpetuate 
infl. response.  also feeds back and activates more factor XII.
kinin system activated by XIIa and culminates in bradykinin production. 
bradykinin acts like histamine...vasodilation, increased vasc perm. short 
acting. broken down by kininases. also, it is one of few molecules which 
can induce intense pain. it is a pain inducing compound which is formed 
during inflammatory response. it also feeds back and activates more 
factor XII.

during acute infl response, not all of these factors have to be taking 
part in it. it depends on the etiology and severity of the reaction. main 
thing, you need to have damage to the endothelium and activation of XII, 
and that will cause these things to occur.

easiest way to learn this is to learn it as these four systems and pick 
out key points.

in terms of mechanisms, we're stopping for now. now, jumping ahead to 
some histology and what we actually see in inflammatory rxns. what 
happens to WBCs? how and why do they extravasate, etc. 

how do we term acute infl rxns?

usually call these things somethingitis. hepatitis, nephritis, 
prostatitis - these are acute inflammations. pneumonia also :)
may be suppurative, nonsuppurative, fibriopurulent, etc. may be 
interstitial, broncho-, glomerulo-, submandibular, etc. can be mild, 
acute, diffuse, etc


cardinal signs of inflammation: rubor, dolor, calor, turgor,loss of 
function

eg, redness/hyperemia, pain due to swelling and stretched nerve endings, 
heat due to vasodilation, swelling due to edema, loss of function due to 
pain.

histologically, we see an exudate- lots of PMNs. if you see lots of 
eosinophils, probably acute infl response to parasites. if mononuclear 
infiltrate, is chronic infl response. will see eosinophilic background 
material: protein. when tissues are fixed, any protein will precipitate. 
if fluid were not protein rich, would not have precipitated. so might be 
fibrinogen or other protein, could look w/special stain.

slide: SI of cat. mostly pale pink. one part is bright red. intense 
hemorrhagic inflammation - hemorrhagic panenteritis. severe hyperemia and 
hemorrhage through all layers of intestine. panleukopenia

slide: bladder with hemorrhagic inflammation. even mild bacterial infxn 
can cause hemorrhagic cystitis. bladder is predisposed to this kind of 
thing. you will see pinpoint hemorrhages - petechiae - and ecchymosis.

slide: GI tract with hyperemia and mucus/WBC/protein/exudate covering the 
mucosal surface in patches. this is hemorrhagic and catarrhal 
inflammation.

slide: lung showing alveoli. normal.
slide: lung, showing pale pink staining stuff in alveoli. looks rather 
uniform and acellular. this is pulmonary edema. mild accumulation of 
protein. no cellular infiltrate. this cow got into severe toxin exposure 
and died quickly with massive pulmonary edema, so never had chronic 
inflammatory response. was primarily vascular event.

slide: lung. cat with pneumonia. can't even see alveoli well. mostly see 
neutrophils everywhere. acute pneumonia. occasional monocytes seen.

slide: another look at the cat lung.

slide: dark pink background stuff with white spaces in it - more 
honeycombed appearance, fibrillar arrangement. also has cells in it. what 
protein is it? fibrin? fibrin indicates severe acute inflammatory rxn. 
special stain will cause fibrin to show up well, looks orange red.  so 
yes, mostly fibrin. fibrillopurulent bronchopneumonia in cow, bacterial 
in origin. if there's fibrin there, that means endothelial gaps were 
large enough that fibrinogen, which is big, got out of the vessel. 
indicates severe damage to endothelium/severe inflammatory response.  


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