lecture 1: post-mortem changes

lecture 1 content. 1-2 in book.

Define autolysis.

Type of post-mortem change.

Self-digestion by tissue enzymes present in or released into the cytoplasm of the cell after death. The degree of it varies among tissues - content of proteolytic enzymes.

• Fast changes occur in liver, pancreas and kidney

• slow changes occur in muscle tissues

How does fleece affect autolysis in sheep?

Post-mortem changes are very early in sheep, due to the fleece having an insulating effect. Thus, trapping heat and slowing down the cooling process (algor mortis) → warmer environment → promotes faster bacterial growth + enzymatic activity (autolysis).

The same in larger swine, due to their insulating layer of fat.

most sensitive tissues to autolysis are?

• Retina, which becomes separated from the choroid

• Seminiferous tubules, in which vacuolation in and between cells occurs

• intestine, in which the epithelium over the villi peels off.

What is rigor mortis and how does it occur?

Post-mortem change.

Rigor mortis is the stiffening of muscles after death caused by the contraction of muscle fibers as ATP decreases.

• ATP decrease → actomyosin formation (death cells - efflux of Ca → gets actin + myosin together) → muscle contracts.

• To be relaxed, the connection has to be destroyed, but this step needs energy → thus, muscles remain stiffed (rigor mortis).

In animals, dying from tetanus, strychnine poisoning or during hunting, rigor mortis is rapid due to starvation or strong muscle contraction → glycogen stores have been reduced.

• the low storage of glycogen → means that ATP may not be remade from glycogen → rapid rigor mortis without any ATP.

In cachectic animals with little or no energy stores, rigor mortis will typically occur at what rate?

slow rate, or not occur at all (in extremely emaciated animals).

• This is because, the depletion of glycogen and ATP is a slow, gradual process.

• The body has broken down its reserves for a longer period of time (can be due to malnutrition, chronic disease) → meaning there is not much glycogen to begin with, muscles are not undergoing any sudden contraction, little ATP is present and used little by little over time → rigor mortis is thus slight or absent as muscles are already weak and depleted.

How long does rigor mortis typically last?

Rigor mortis begins 2 to 6 hours after death, peaks after 24 to 48 hours, and disappears within another 48 hours. (total of 4 days).

• disappears with autolysis or putrefaction (bacterial decomposition).

Progression: heart → jaw → cervical muscles → thorax → extremities. (disappears in same order).

Define algor mortis.

Gradual cooling of the body after death. (post-mortem change).

• some infections, like tetanus and anthrax will make the body temperature increase after death.

What is livores mortis?

Livores mortis refers to the gravitational settling of blood to the lower side of the body after death, creating discoloration spots. (post-mortem change).

Most evident in the lungs and skin as a dark red coloration, or in the kidney as a black zone of coloration on one side of the cortex. (hypostasis - discoloration, same mechanism as livores mortis).

Define Pseudomelanosis.

Pigmentation of tissues after death by blood pigments. (post mortem change).

• Hydrogen sulphide released by putrefaction → diffused from intestines → tissues.

• Chemical reaction bw. hydrogen sulphide + iron → iron (III) sulphate → dirty green color.

What is imbibition?

Process where tissues absorb fluids → swelling of tissues or organs. Post-mortem changes.

• Imbibition of blood

  • it is when red-tinged plasma leaks into surrounding tissue due to the breakdown (haemolysis) of RBCs in blood vessels.

  • Process:

    1. Hemolysis happens → Hb is released into blood plasma

    2. Vessel weakening happens due to autolysis

    3. The red-tinged plasma leaks out → distinct dark red color along the course of each blood vessel. Seen on white tissues easily like mesentery or omentum.

• Imbibition of bile

  • leaking of bile through gall bladder wall due to autolysis.

  • stains adjacent tissues like liver, stomach and mesentery fat.

What is distention? And why does it happen?

Refers to the expansion or swelling of an organ or body part due to pressure/accumulation of gas/fluid. (post mortem change).

• Occurs mainly due to fermentation from gas produced in the digestive tract.

  • The gas distends all the parts of the digestive tract from the stomach downward.

  • Large areas of liver can become pale as the blood is forced out, myocardium may also have large pale areas + within muscles.

• Stomach and diaphragm may rupture, abdominal muscles may tear, hernia may develop.

post-mortem clots (cruor) are caused by?

Characteristic: Blood clots that form after death. Components are RBCs, leukocytes, fibrin and precipitated protein (mainly albumin). Caused by:

1. Protein denaturation in dead cells

2. Release of tissue thromboplastin (activation of blood clotting)

3. Weaker than normal anti-coagulation effect in endothelial cells

What are post-mortem clots?

Post-mortem clots are clots formed after death characterized by a dark red color, smooth texture, and unattached to blood vessels.

Describe the appearance of a post-mortem clot.

Post-mortem clots are dark red, smooth, and shiny on the outside, moulded to the vessel like jelly in its container, and are entirely unattached to the vessel.

What is a chicken-fat clot?

A chicken-fat clot is a type of post-mortem clot characterized by the settling and separation of red cells from the fluid phase of the blood.

• typically found in the chambers of the heart when post-mortem clotting is delayed.

• It has a smooth, shiny surface resembling currant jelly but appears yellow due to plasma.

What is the difference between post-mortem clots and ante-mortem thrombi?

Post-mortem clots (cruor) are unattached, smooth, and jelly-like. Formed after death.

ante-mortem thrombi are irregularly shaped, firmly attached to vessel walls, and have a friable, dull, and irregularly rough surface. Mix of red/grey color.

• formed in the flowing blood (before death).

What is putrefaction?

Process of Enzymatic decomposition (especially of proteins), caused by bacterial enzymes → foul smells (hydrogen sulphide, ammonia and mercaptans).

• often results in very friable, structureless, greyish/greenish tissues.