lecture 1: post-mortem changes

Week 1 Lecture. finished.

Topic:

• introduction, Post-mortal changes and their differentiation from intravital ones.

• Intravital → changes that occur in living tissues or organisms.

Pathologist's Methods

1. Necropsy:

   • Examination of an animal after death.

   • Purpose: Determine the cause of death or extent of disease (e.g., neoplastic).

   • Involves dissection, observation, interpretation, and documentation.

   • Includes sample collection for further examinations.

2. Microscopical Examinations:

   • Histopathology:

     • Common HE staining.

     • Special staining: mast cell granules, glycogen (PAS), mycobacteria (ZN), fungi (Grocott), calcium salts (Von Kossa), amyloid (Congo Red).

   • Cytology

   • Histochemistry: Visualization of specific substances or chemical groups (Fe, digestive enzymes like ALP and AP, muscle fibers, granulocyte granules).

   • IHC (Immunohistochemistry): Uses antibodies to detect antigens (markers) in tissue samples.

   • EM (Electron Microscopy), PCR (Polymerase Chain Reaction), Immunofluorescence

3. Histopathology:

   • Postmortal vs. Intravital: Surgical biopsies provide insight into prognosis and the lesion's influence on the organism.

General vs. Special Pathology

• General Pathology (GP): Study of mechanisms of tissue and cell injury. Covers basic principles applicable to specific diseases.

  • Post-mortal changes.

  • Cell injury.

  • Degenerations.

  • Necrosis.

  • Circulatory disturbances.

  • Disturbances of growth and cellular adaptation (agenesia, aplasia, atresia, hypoplasia, atrophy, hypertrophy, hyperplasia, metaplasia, dysplasia).

  • Inflammations (nonspecific, specific).

  • Tumors.

  • Pathology of immunity.

  • Developmental anomalies.

• Special Pathology (SP): Pathology of specific systems.

  • Respiratory, cardiovascular, liver, gall bladder, gastrointestinal, hemopoietic, male/female genital tract, skin, mammary gland, nervous system, musculoskeletal system.

🧟 Post-Mortem Changes

Autolysis

• Definition:

  Self-digestion by tissue enzymes present in or released into the cytoplasm of the cell after death.

• Variations: The degree of autolysis varies among tissues based on proteolytic enzyme content.

  • Fast changes: Liver, pancreas, and kidney.

  • Slow changes: Muscle tissue.

• Factors Affecting Autolysis:

  • In sheep, fleece has an insulating effect, leading to early post-mortem changes.

  • Larger swine have an insulating fat layer with similar effects.

  • Rapid fixation is needed for some tissues to observe lesions accurately.

  • Sensitive tissues: retina (separates from choroid), seminiferous tubules (vacuolation), and intestine (epithelium peels off).

Rigor Mortis

• Definition:

  Stiffening of muscles after death due to muscle fiber contraction as ATP decreases.

• Mechanism:

  1. ATP decreases post-mortem.

  2. Anaerobic glycolysis may resynthesize ATP hours after death.

  3. Calcium efflux from cells connects actin and myosin (actomyosin formation), requiring energy.

  4. Actomyosin presence leads to muscle contraction.

  5. Relaxation requires energy to break the actin-myosin connection.

  6. When ATP and glycogen are depleted (ATP under 85%), muscles remain stiff.

• Onset and Duration:

  • Rapid onset in animals with reduced glycogen stores due to starvation, tetanus, strychnine poisoning, or hunting.

  • Slight or absent rigor mortis in cachectic animals with little energy.

  • Disappears with autolysis or putrefaction.

• Timeline:

  • Begins 2-6 hours after death.

  • Reaches maximum after 24-48 hours.

  • Disappears after approximately 4 days.

• Progression:

  • Heart (1-2 hours) → jaw → cervical muscles → thorax → extremities. Disappears in the same order.

    • disappears with autolysis/Putrefaction (bacterial decomposition).

Algor Mortis:

• Definition: Gradual cooling of the body after death.

  • influenced by surrounding temperature.

Livores Mortis:

• Definition: Gravitational settling of blood to the lower side of the animal, seen in the skin. - discoloration in skin and tissues.

  • disappears upon pressure.

  • Hemorrhages are not present.

• Hypostasis - discoloration, reflecting livores mortis (same mechanism), particularly visible in lungs and kidneys (dark red coloration).

  • Most evident in the lungs or kidneys → dark red coloration.

  • Related to carcass position after death.

Pseudomelanosis

• Definition: Pigmentation of tissues after death by blood pigments.

• Mechanism:

  1. hydrogen sulfide released during putrefaction diffuses into surrounding tissue.

  2. Chemical reaction between hydrogen sulfide + iron from Hb.

  3. Forms iron (III) sulfate → dirty green color.

Imbibition of Blood is?

• Definition: Red-tinged plasma leaks into surrounding tissue due to hemolysis of erythrocytes in blood vessels.

• Mechanism:

  1. Hb released from RBCs → blood plasma

  2. Post-mortem autolysis (body`s own enzymes start to break down tissues) weakens vessel walls.

  3. Distinct dark red color along the course of each vessel appears.

Imbibition of Bile is?

• Definition: Leaking of bile through the autolysed wall of the gall bladder.

• Stains adjacent liver liver tissue, stomach and mesenterium fat.

Distention/Pressure post-mortem changes:

• Definition: Fermentation from gas produced in the digestive tract → pressure on surrounding organs and potential ruptures.

• Distention of digestive tract parts from the stomach downward. (swelling).

• Effects:

  • extreme pressure to surrounding organs.

  • Large pale areas on the liver where blood has been forced out.

  • Myocardium have large pale areas on the surface and within the muscles.

  • Stomach or diaphragm may rupture, or abdominal muscles may tear (no vessel reaction).

Post-Mortem Clots (Cruor) is?

• Post-mortem clots are caused by:

  • Protein denaturation in dead cells.

  • Release of tissue thromboplastin (activates blood clotting).

  • Weaker normal anti-coagulation effect in endothelial cells.

• Components: Erythrocytes, leukocytes, fibrin and precipitated proteins (mainly albumin).

• Types:

  1. Post-mortem clots: Dark red, smooth, shiny outside, molded to the vessel like jelly, and entirely unattached to the vessel.

  2. Chicken fat clot: settling and separation of RBCs from fluid phase of blood, found in heart chambers, delayed post-mortem clotting.

     • smooth, shiny surface with yellow plasma color. Looks like

In contrast, an ante-mortem clot or thrombus is formed in flowing blood. It has friable, dull and irregularly rough surface with a mixture of red and grey color, usually in irregular laminated layers, firmly attached to the surface.

Putrefaction is?

• Definition: Enzymatic decomposition by bacterial enzymes, characterized by foul odors and breakdown of tissue structure.

  • results in foul smells (hydrogen sulfide, ammonia, mercaptans)

  • very friable, structureless, greyish-greenish.