post mortem change

3 types of change

• due to disease- lesions

• occur just prior to or at the time of death- agonal change

• those that occur after death and before the cadaver is examined- post mortem change

post mortem change

1. algor mortis- cooling

2. rigor mortis- rigidity

3. post mortem clotting

4. livor mortis- hypostatic congestion

5. post mortem staining

6. autolysis

7. putrefication

algor mortis

• cooling of the cadaver to the temp of the environment

• practical importance in meat production- reduces post mortem bacterial growth, affects tenderness of meat for consumption

• may aid in estimating time of death

rigor mortis

• what is it

• what does it lead to

• when does it begin

• what is affected first and last

• stiffening of skeletal muscle after death

• leads to immobilisation of joints

• begins 1-6hr after death

• smaller muscles affected first and those in excessive use before death affected last

skeletal muscle post mortem

• immediately after death the cell tries to maintain ATP production by ADP to ATP through the phosphagen system and the glycogen/lactic acid ssytem

• reduced atp availability reduces ca sequesteration in sr and build up of ca in cytosol

• myosin heads cant be released from binding sites in actin

• only released when there is sufficient enzymatic digestion of the contractile proteins to remove cross bridges

• when you forcibly break rigor you are mechanically overcoming the cross bridges

rigor mortis- variation in

• time of onset

• intensity

• between species- poultry 1-2hrs, pork 4-6 and beef/lamb 7-15

what is rigor mortis influenced by

• pre mortem glycogen reserves- low levels quick onset

• ph of muscles at time of death- low ph quick onset

• env temp- warm is quick

algor and rigor morits

• Warm and flaccid – Dead less than 3 hours

• Warm and stiff – Dead 3-8 hours

• Cold and stiff – Dead from 8-36 hours

• Cold and flaccid – Dead more than 36 hours

Body held at 10-20ºC

timing of rigor mortis

• what does it occur rapidly in

• when might it not develop

• what is this called

• occurs rapidly in exccited or stressed- as total energy supply is less and critical level of atp needed to delay it is soon reached

• may not develop in emaciated animals

• cadaveric spasm

in emaciated

• normally l ventricle stiffens leaving it empty of blood

• in extreme emaciation rigor mortis wont occur and blood will remain in both chambers of the blood

post mortem clotting

• 2 layers

• colours

• how to distinguish between post mortem clotting and thrombus

-separates into an upper plasma layer and a lower red blood layer

upper is translucent and lower is intense red

no damage to the inner surface of the vessel and the clot can be easily removed

thrombus is firmly attached to the underlying vascular endothelium, has a white interior and is layered.

hypostatic congestion- livor mortis

• when does it begin

• when can it become fixed

• where is it best appreciated

• hypostatic congestion discolouring the skin of man and pigs

• gravitational pooling of blood which occurs post mortem

• begins an hour after death and clotted blood can become fixed in place 12-24 hours so movement will not influence distribution

• may be apparent in animals with little hair cover

• best appreciated in the dependent lung and kidneys in animals

post mortem imbibition of haemoglobin

• haemoglobin pigment diffuses out of erythryocytes and through the walls of small vessels

• in cases where there has been a haemolytic crisis, staining of tissues occurs early after death

• most common obscurer of lesions in post mortem examination

post mortem imbibition of bile pigment

• cholebillirubin readily diffuses out of the gall bladder

• very common finding which occurs within hours of death

• stains tissues adjacent to gall bladder yellow/green

pseudomelanosis

• what is it caused by

• caused by iron sulphide (hydrogen sulfide produced by bacteria reacts with iron from haemoglobin)

staining

• haemolytic staining- red

• biliary imbibition- yellow

• pseudomelanosis- green

autolysis

tissue breakdown due to anoxia and cell death

• in a hypoxic or anoxic cell ATP levels fall and are depleted

• cellular membrane damage which destory selective permeability that retains proteins and electrolytes within the cell and restricts na, ca and water entry from extracellular spance

• involves no inflammatory responses

• process is enhanced by higher temps and failure to cool body after death

putrefication

• what is it and hwat happens

• what is produced and examples

• what other process can occur as as result

• dead tissue is invaded by anaerobic saprophytic bacteria

• proteins, fats and carbs in the body substances are attacked by enzymes produced by these putrefactive bacteria

• producesgas and colour change

• foul smelling substances, hydrogen sulphide , indole/skatole (degredation product of tryptophan)

• pseudomelanosis

gaseous distention of the alimentary tract

• bacterial fermentation producing gas continues after death

• may be surface pallor of adjacent organs due to pressure of this distension squeexing blood out of this adjacent tissue

• abdominal viscera may be pale in comparison to thoracic viscera or the musculature of hind lumbs

• gas rises- distended loops may be pale and lower loops hypostatically congested

• if gaseous distention is excessive, distended intestine may tear

autolysis and putrefaction

• autolysis plus putrefaction equal decomposition

• decomposition occurs faster at high temps

• is faster in air compared to water

• deep burial is equivalent to storage at 4 degrees

post mortem damage by insects

• bluebottles and flies

• maggots

• eggs are laid on the lips, nostrils or genitals of the fallen carcase

• secrete digestive fluid that soften tissue

• creophilus maxillosus feed on larvae- imply longer

mummification

• occurs in dry conditions

• dryness inhibit bacterial groth

• skin and tissue become hard and leathery

• occurs in foetuses when hte skin is thick enough to resist autolysis and fluids are resorbed

why freeze a carcass

• to preserve and halt decomposition i immediate pm not possible

• body outside in cold env, ay have diet from hypothermia

• poach fish/ deer out of season then freeze and thaw in legal

• to hide evidence

freeze thaw artefact

• damage occurs to tissues during freezing due to fluid movement between intra and extra cellular spaces, due to ice crystal formation

• alters the gross and histological appearance of tissues which may mimic or obscure lesions

effects of multiple freeze thaw cycles