Postmortem changes in muscles

test three topic

what is homeostasis

in the living state, all organs and systems within the body interact to maintain an environment under which each can perform its functions efficiently

what effects the narrow range of physiological conditions

• oxygen concentration

• pH

• temperature

• energy supply

what marks the beginning of postmortem physiological changes

exsanguination (drop in blood pressure)

what homesotasis mechanisms kick in after exsanguination

• protective/survival mechanism to compensate

• increase in heart rate to maintain circulation

• peripheral vessels constrict to prioritize blood flow

• 50% of remaining blood redirected to vital organs

What is the result?

muscle is not converted to meat until ____ stops

metabolism

what halts metabolism

• oxygen supply deplated : TCA cycle and electron transport failing

• shifts to anaerobic metabolism (continues until glucose in body depleted)

what does the decline of muscle pH lead to

• accumulation of lactic acid

• greatly variable rate of decline

what is the normal decline pattern of pH

• gradually from 7 to 5.7 w/in 6-8 hrs postmortem

• ultimate pH: 5.5 w/in 24 hrs postmortem

what else can impact ph change?

…..

factors effecting muscle temp change

• rate of metabolism

• size and location of muscles

• predominate muscle fiber type

• duration of metabolism

• fat insulation

• slaughter methods

ph ___ ~ temp ___

decline / rise

consequences of pH decline ~ temp rise

• microbial growth

• protein denaturation

• oxidation

energy is ____ depleted

gradually

what are the two sources of atp

• glycolytic/anaerobic metabolism

• creatine phosphate

how is atp used

• muscle contraction (how?)

• metabolism (how?)

rigor sets in when

atp depletes (why?)

what is another word for rigor mortis

stiffness of death

what are the phases of rigor mortis

delay, onset, completion

what characterizes the delay phase of rigor mortis

immediately after exsanguination

what characterizes the onset phase of rigor mortis

w/in hrs, species dependent

what characterizes the completion phase of rigor mortis

w/in 24 hrs, species dependent

compare rigor phases in regards to

• atp availability

• cp availability

• formation of actomysosin cross birdges

• extesnibility of muscel

…..

at rigor completion

• how many binding sites used

• what about length of sarcomeres

• what about muscle tension

• what is special about actomyosin bonds

…..

onset of riger in hours for various species

beef- 6-12

lamb- 6-12

pork- 1/4-3

turkey- <1

chicken- <1/2

fish- <1

binding sites used in rigor mortis

100%

binding sites used in normal contraction

20%

what is resolution of rigor mortis

decrease in tension with time postmortem

during resolution, actomyosin bonds are

still not broken

what makes meat tender in resolutio

….

during resolution there are changes in muscle ___

structural integrity

there is subtle ___ right after exsanguination

degradation

the most notable change in resolution is ____ post mortem

48-72 hrs

what is degraded in resolution

z disk

what enzymatic activity occurs postmortem

proteolytic degradation of myofibril proteins

what is involved in the calpain system

• 2 calcium dependent enzymes and a specific inhbitor

  • m-calpain: millimolar (high) Ca conc

  • µ-calpain: micromolar (low) Ca conc

  • calpastatin?

• acitvated by Ca++ released from mitochondria and SR during storage

what is involved in failure of protective mechanisms during post mortem

• connective tissues slightly degrde

• cell membranes slightly degrade

• lymphatic system fails

• circulating white blood cells

what are microbial risks during psot mortem

• spread

• proliferation

• contamination

(what causes these)