---start path.lec.03.18.97----
dr donna dambach again.

joke: told by patrick joseph farley

what's long and green with an IQ of 5?
the st patrick's day parade.

ha ha

remember - need to find out etiology, pathogenesis, morphological 
changes, and clinical signs. these are the important things to find out 
about a disease process.

things in cell that are affected by disease;

cell membrane
ability to produce energy
ability to make protein
ability to replicate DNA or RNA

Common mechanisms of cell injury and death:

-free radical injury: injurious effects of OH* include lipid 
peroxidation, crosslinking of proteins by the formation of disulfide 
bonds, and interactions with DNA. the reactive oxygen species LOVE to 
grab onto things. they grab the hydrogen groups of FAs, which make up our 
cell membrane. When a FR gloms onto an FA, it causes an autocatalytic 
situation. the FA becomes an FR, and this is called LIPID PEROXIDATION. 
this is a major problem, causes major structural damage to the membrane, 
screws up ribosome attachment site and disrupts protein syntheses. 
disrupts rough AND smooth ER (so also get decreased enzymatic rxns). also 
allows leakage of stuff into and out of cell. FRs cause double bonds, 
holes in membrane, aldehyde group formation (toxic to cell). also FRs 
attack the H in DNA, which is an acid. then DNA can't replicate well, 
might break.
cell also won't be able to make ATP.

-hypoxic/ischemic injury:
-virus induced injury:
-chemical toxicity:
-physical trauma:

INACTIVATION OF FRs

spontaneous dismutation of superoxide 

cellular enzymes (cytosolic, peroxisomal, mitochondrial)
- the rxn is catalyzed by superoxide dismutase.
also catalase, and selenium dependent glutathione peroxidase and 
glutathione, which accept electrons and reduce FRs.

non-enzyme antioxidants that bind or block FRs
vitamin E, C, beta carotene, glutathione, ceruloplasmin (binds 
copper)(Cu), transferrin (iron is used to make FRs, so transferrin, which 
binds iron, is important), albumin.
albumin is a professional binding agent. 

really neat thing about vit E and C. vit E lives in membranes and binds 
FRs, prevents lipid peroxidation.. when it binds an FR, it moves to 
surface. vit C comes along, takes the FR, and frees up the vit E to be 
re-used to snag another FR.

white muscle dz/nutritional myopathy -- seen in lambs a lot, i guess.
lambs and goats fed on some pastures low in selenium and vit E get weak 
when weaened. they fall down and don't thrive. can see white streaks in 
leg, back, and heart muscle. why are organs red, usually? myoglobin and 
hemoglobin make them red. so what are the white streaks doing in there? 
when you have a selenium deficiency and the animal can't stabilize the 
FRs, the cells are dying. the myocytes are dying. this is because the 
animals can't stabilize the NORMAL FR reactions in their cells. the cells 
sustain irreversible injury. there is no blood in dead tissue, so it is 
white or pale tan.
now, if you treat these animals with selenium, they can do much better, 
compensate, and go on.

a moment to describe the liver.
it has multifocal to coalescing tan irregularly-surfaced variably sized 
nodules throughout its parenchyma. they are hard to firm but we can't see 
that of course. morphologic diagnoses? um. what could cause this? uh, 
neoplasia. also, could be granulomatous inflammation. this one is a 
hepatocellular carcinoma.

slide: section of cat liver. focal area of fluctuant mass which exudes 
clear fluid when cut. a solitary fluid filled mass in a liver is usually 
a cyst. cysts are usually lined w/epi. this is probably a biliary cyst 
adenoma.

HYPOXIC/ischemic cell injury"

most common cause of cell injury and death.
may arise from a number of routes which reduce oxygen supply to 
mitochondria:
-reduced oxygen supply
-anemia - reduced oxygen carrying capacity in blood
-reduced amount of blood
-poisoning of cellular oxidative enzymes- eg from cyanide, which binds 
cytochrome C and breaks the electron transport chain.

ischemia is when no blood gets tothe cells. a thrombus can block an 
artery and cause distal ischemia. ischemia is most common cause of 
cellular hypoxia. 
anemia also common.

what's anoxia? no oxygen. in cases of ischemia, there are anoxic areas, 
and those cells there die.

cell types vary in susceptibility to hypoxia. some muscle cells can 
undergo anaerobic respiration pretty well. but neurons in the brain MUST 
HAVE glucose and oxygen ALLTHE TIME. kidneys also are very sensitive to 
hypoxia. 

connective tissue has low sensitivity to hypoxia - tendon, ligament, etc. 
they can tolerate it ok

so if someone has an MI and some myocytes in the heart die, what happens? 
the fibroblasts nearby will fill in the area. it becomes white, firm, 
contracted, scarred with FIBROSIS. fibrous CT is very strong and very 
stable.

what happens to a cell w/o enough oxygen? membrane ATPase pumps don't 
work. Na/K aren't exchanged right. pH changes. can't undergo aerobic 
respiration. anaerobic resp creates alcohols. pH changes. acidosis. 
ribosomes fall off ER. decreased protein synthesis.get swelling of 
membranes from pH change, many cell functions decrease. pH and energy 
required enzyme functions majorly affected.

REPERFUSION INJURY:
sometimes when blood isn't getting to an area for a while, and then flow 
is reestablished...eg, thrombus is lysed or whatever...depending on how 
long the cells were ischemic, they aren't normal anymore. some are dead. 
when blood comes back in, reperfusing the area, it brings in RBC and WBC. 
this area is controversial. what happens is those WBC start attacking the 
injured/dead tissue. that's normal for the WBC...something has happened 
to the injured cells and it triggers the WBCs to release their toxic 
enzymes. this can be very very bad, causing a lot ofdamage eg in lg 
animal intestinal dz. so peopleare trying to learn how to dampen that 
inflammatory response.

FR source? neutrophils vs xanthine oxidase. hotly debated. xanthine 
oxidase is a normal enzyme for purine synthesis. in hypoxic state it 
produces FRs that can damage cells.

all depends on length of ischemia. if cells aren't too damage, they'll be 
ok. if it lasts longer, some will  be really bad off....if ischemia lasts 
long enough, all cells willdie from it.

also, during reperfusion, calcium binds to dead cells....
role of Ca++ in reperfusion injury, cell injury and death...
some folks say ca++ CAUSES death. if cell is damaged, Ca++ will go into 
that cell and make things worse by bindnig things and activating 
things...
ca++is a marker of irreversible cell injury aka cell death. we will often 
see mineralization. ca++ will helpto destroy a cell. the ER is a calcium 
sink, so when it is damaged Ca++ leaks out....

slide: lamb with white muscle dz. in some of the dead cells, wherelipids 
were falling apart etc, there were all these new Ca++ binding sites, so 
the normal calcium in the area started binding, and accumulating, and 
mineralizing the tissue. the mineralyzed myocytes appear a deep purple 
blue on this slide.
grossly it's white, chalky, crunchy in the tissue.

virus induced cell injury and death:
two major classes of virus:

cytolytic/cytopathic eg parvovirus- get into cell, destroy it, are 
released. HIV does this too.

latent/oncogenic eg herpesvirus. these viruses enter a cell, insert viral 
genome into host cell genome. if you insert a foreign genome into a cell, 
it will disrupt the cell function in some way. in most cells it goes in 
there and can cause a proliferation of those cells...

valley forge: 45 mi bike ride from here, mostly flat. highly recommended.


anyway. viruses causing injury.
one: they get in, uncoat, replicate, release, kill cell via trauma
two: they get into GENOME and disrupt it, or make tumors, or whatever.

 virus protein can be exteriorized onto cell surface. macrophages 
recognize this, and try to kill the target cell. if this happens to 
enough cells, you get disease.

herpesvirus of dogs/foals/birds...
herpesvirus is a latent virus in nerves. it hides in there. but 
herpesvirus of the LIVER is a lytic/cytopathic virus, and it kills 
animals. causes necrosis of hepatocytes. it infects hepatocytes, 
replicates, lyses the hepatocyte, and moves on. body inflammatory cells 
come in to clean up. also, viruses can leave tell tale signs. here we see 
a bright pink thing - "viral inclusion" body, inside a cell. it's an 
accumulation of viral particles that builds up in nucleusor cytoplasm. 
some viruses do this all the time. so you can make a diagnosis based on 
seeing that kind of thing sometimes.

grossly, the liver has multifocal, flat, white, circular lesions varying 
in size from pinpoint to 2 cm.
dx: multifocal hepatic necrosis caused by herpesvirus.
signs: young dog comes in in hepatic and renal failure.
histo: hepatic necrosis and intranuclear pink viral inclusion bodies.

-----break-----

ok, we went over FR, selenium, vit E; hypoxia, infarc, thrombus; viruses, 
lytic, latent; and now....

CHEMICAL TOXICITY

someone asked what we need to know for the test.
know concepts. what are FR, how do they act? etc.
some examples from lecture may fit into exam. know the concepts she's 
teaching us. anyway. don't have to know everything about herpesvirus, but 
know it is a virus, and know viruses are cytopathic or latent, and what 
thsoe kinds of viruses do.

anyway. chemical toxicity:

this includes toxins (eg, bacterial toxins) and xenobiotics
xenobiotic: foreign compound from other living organism. usually implies 
man-made.

two major categories of injury:

direct action by heavy metals, phalloidin (amaranthin mushroom 
toxin)(destroys cell membrane)(kills liver), microcystin (made by 
bluegreen algae, kills cattle/dogs that drink infested water). iron, 
binds things, activates enzymes and free radicals. mercury, lead, etc. 

 - or, indirect action, eg
by an active metabolite (metabolized by host cells) eg acetominophen, 
carbon tetrachloride. when body metabolizes the substance, it forms a 
toxic compound. cats have problem with acetominophen since they don't 
haveenough glutathione, can't metabolize FRs made when metabolize 
acetominophen. also, makes methemoglobin form. CCl4 - drycleaning fluid. 
well worked out pathogenesis. it's in our notes. causes disease b/c the 
hepatic P450 system metabolizes it and metabolite forms FR. P450 lives in 
smooth ER in cell. the enzymes are stuck to the membrane. so if you 
metabolize CCl4, you make lots of FR and they glom onto the smooth ER 
membrane and fuck it up. if the liver is exposed to enough CCl4, and 
enough toxic metabolites are formed, the hepatocytes die! the smooth ER 
is attacked, cell mmbrane attacked, cells swell, rough ER ribosomes fall 
off, no protein synthesis occurs, this is very very bad, bcause the liver 
needs to metabolize glucose and make glycogen, and it can't, and will 
start having fatty changes. apoprotein won't be formed. you get a 
sublethally injured liver accumulating fat. or if enough damage occurs, 
you get disruption of mitochondria, increased permeability, calcium 
influx,cell death, liver failure.

chemicals...detoxified by liver and kidney, so liver and kidney are very 
vulnerable to effects of toxic metabolites. if you have an animal with 
severe blood loss,  what part of liver is going to be hypoxic first? 
central vein area. portal vein area will resist hypoxic change because 
the blood that goes there has more oxygen.

say an animal ingests a directly acting hepatotoxin. the portal area will 
accumulate the most of the toxin.

if it ingests an indirectly acting hepatotoxin eg CCl4 (works in 
drycleaning store). knowing that central lobular hepatocytes have the 
most P450in them, which cells are most affected? central lobular cells. 
affected by free radical formation

bluegreen algae toxicity. bluegreen algea lives in water and blooms, like 
red tide. is often on farms. may see whole pond covered with green scum. 
now, a farmer may have a die off of cattle. may find green scum on nose. 
dogs, too. this is Microcystis aeruginosa. what does it do? well it's an 
interesting toxin. this toxin affects the liver. it takes advantage of 
the bile receptors in the liver. the toxin also binds to those receptors, 
and gets into hepatocyte readily that way. once in there, it acts by 
binding to actin and altering the structure. hepatocytes start to ball 
up. so the hepatocytes lose their cell to cell interaction. (argh. 
lecturer had to hunt and kill giant cockroach just now...) so, what 
happens then? hepatocytes now have spaces between them. in the slide, 
near the central vein, hepatocytes are balled up, with blood filled 
spaces between them. they become much less efficient. also the 
hepatocytes become dysfunctional due to altered structure. why are the 
cells near central vein affected? This toxin uses BILE RECEPTORS and 
there are more of them enar the central vein. as toxicity increases, 
cords of hepatocytes are disrupted and blood filled spaces occur between 
hepatocytes. dead cells slough into central vein. hepatic failure occurs.


slide: ugly ass kidney
multifocal to coalescing cysts of varying size, predominantly in cortex, 
filled with clear yellowish fluid (urine). morph dx: polycystic 
nephropathy. can be congenital, either inherited or acquired.

slide: another ugly ass kidney

multifocal tan, irregular, red-bordered, slightly raised regions on 
capsular surface
on cut surface, wedge shaped tan lesion, wider at the cortex. i'm gonna 
call it an infarct, personally, 'cus a wedge in my experience always 
means an infarct. but, let's see what she says. clues: red rim, wedge 
shape. why is rim around affected area so red? blood. there is hemorrhage 
there. there's death of cells surrounded by hemorrhage. this is typical 
of infarct and reperfusion. (YAY!) remember, the dead area includes 
vessels as well as tubules. as the blood reperfuses the dead vessels, 
they leak. that's why you see the hemorrhage. now, why a wedge? well, the 
thrombus is in the arcuate artery, and the area it feeds dies, and that 
area is wedge shaped. 

take home message: wedge shaped area, light tan, necrosis, rimmed 
w/hemorrhage == infarct. also see this in heart. in heart, arteries are 
on outside and veins inside, so wedge is inverse to this.

cellular morphologic changes and adaptations to injury:

often cell injury is reversible if the "stressor" is removed. if it 
persists, the cell adapts if it can, and we can often see these changes 
at the ultrastructural, light, and gross levels. cells adapt if they can 
restore some level of homeostasis.

-ultrastructural changes (eg organelle changes not visible w/light scope) 
we won't discuss these.

-histologic changes seen in early, reversible cell injury: hydropic 
degeneration (water getting into cell, cell swelling, secondary to 
membrane damage, or failure of pumps or lack of energy), fatty change 
(accumulation of triglyceride/lipid in cells, common in liver).

-histologic changes seen with persistent injury and cellular adaptation: 
atrophy (shrinking), hyperplasia (growth of new cells), hypertrophy 
(increase in size of cells), metaplasia (migration to new cell type), 
dysplasia (this one not really adaptive)

-other unrelated terms: aplasia (organ never formed), hypoplasia (smaller 
than normal or fewer cells than normal)

case: 6 mo old animal: you go to spay it. you see there is only one 
kidney. is it acquird, congenital, infectious, what? well, probably 
congenital aplasia. hypoplasia could be acquired...eg, something could 
happen in utero to cause the kidney to stop developing. but if it isn't 
there AT ALL, it's probably congenital. important to be able to tell 
hypoplasia from atrophy, btw.

hydropic degeneration:
-swollen cell due to osmotic disturbance- why?
plasma membrane problem
membrane gradient pump problem 
energy problem
most commonly seen in epithelial cells and hepatocytes.

slide: skin. the epi cells have extra cytoplasm, and it's clear instead 
of pink, not picking up stain, because proteins aren't there. also, there 
is a halo around the nucleus, a clear perinuclear halo of water. these 
cells are injured and have extra water in them.

if you biopsy sunburnt skin, it looks like this. sunburn is red due to 
influxof blood into area.

fatty change:

triglyceride accumulation in cell cytoplasm in vacuoles. can be 
physiologic (eg, normal, due to pregnancy - pregnant women get fatty 
liver because they NEED to use that fat for energy, it's due to normal 
stuff. also if we eat a lot of fat, you see this change, so it's normal 
in suckling young) or result of sublethal injury, and is seen often in 
hepatocytes, muscle cells, andrenal tubular epi - metabolically active 
cells. liver also prepares lipid into lipoprotein, so is very important 
source of lipoprotein/fat synthesis, which is why it commonly gets fatty 
change when injured. 
 
conditions commonly associated w/fatty change, most commonly in liver:
hepatotoxic agents
starvation
metabolic derangements (diabetes, ketosis)
hypoxia, anoxia
pregnancy (normal)
suckling animals (normal)

is usually reversible but can be fatal in some instances

three possible scenarios for fatty change:
-increased amt of incoming FA into hepatocyte: diabetes, high fat diet, 
etc. fat accumulates in hepatocyte.
-apoprotein which is made in liver doesn't bind triglyceride. then it 
doesn't form lipoprotein, then fat can't get out of hepatocyte. so, not 
making enough apoprotein will cause this.
-as FAs come in, some are shunted to oxidation for energy. if no need for 
that, all go to triglyceride synthesis. if making way more triglyceride 
synth than apoprotein, will have fatty change.

---end----