The Role of Blood in Forensics and Biology

Importance of Blood Study

• Blood can be used as evidence in legal cases.
• Blood analysis can help determine disputed parentage in custody cases.
• Blood can be used for DNA typing instead of buccal swabs.
• Blood can help determine the time of death and how long the victim survived the attack.
  • A pool of blood indicates the victim may have been alive after the attack.
  • No pool of blood suggests immediate death.
• Blood spatter analysis can determine the direction of escape for the victim or assailant.
  • Circular blood spatter indicates dripping blood.
  • Angled blood spatter indicates blood being projected.

Nature of Blood

• Blood is the largest circulating tissue in the body.
• It has a fluid-like consistency due to its vital substances.
• It contains blood cells, nutrients, and electrolytes.
• It circulates within the cardiovascular system.
  • Transports oxygen, nutrients, and waste products.

Functions of Blood

• Transportation:
  • Gases (oxygen and carbon dioxide)
  • Nutrients
  • Waste products
• Temperature Regulation
• pH Regulation:
  • Maintains a slightly alkaline pH (7.35-7.45).
  • Metabolic acidosis can cause disease, such as arthritis.
• Medication Transport:
  • Delivers medicine to affected parts of the body.

Kinds of Blood

• Arterial Blood (Capillary Blood):
  • Bright red in color due to oxygen transport.
  • Oxygenated blood.
• Venous Blood:
  • Increased amount of CO2.
  • Dark red in color.
  • Non-oxygenated blood.

Characteristics of Blood

• Color:
  • Bright red (arterial blood)
  • Dark red (venous blood)
• Volume: 70% of total body weight.
  • 80-85 mL/kg body weight.
• Viscosity:
  • Resistance of blood to flow.
  • Thick and sticky.
  • 4-5 times more viscous than water.
• Specific Gravity:
  • Blood = 1.065 due to cellular elements.
  • Water = 1.000.
• pH Reaction:
  • Slightly alkaline (pH = 7.35-7.45).
  • Lower than 7 is acidic.
  • Higher than 7 is basic (alkaline).

Composition of Blood

• A. Formed Elements (35%)*

• Red Blood Cells (Erythrocytes):

  • Number: 5,000,000 RBCs/mm3.
  • Shape: Biconcave disc.
  • Hemoglobin (Hb):
    • Coloring matter of blood.
    • Pigment found in the cytoplasm of RBCs.
    • Carries and transports oxygen.

• White Blood Cells (Leukocytes):

  • Number: 5,000-10,000/mm3.
  • Soldiers of the Body.
    • Agranulocytes:
      • Monocytes
      • Lymphocytes
    • Granulocytes:
      • Eosinophils
      • Neutrophils
      • Basophils

• Platelets (Thrombocytes):

  • Number: 150,000-350,000/mm3.
  • Function: Blood coagulation (blood clotting).

• B. Liquid Portion (65% of total blood volume)*

• Plasma: Straw liquid portion of the blood.

• Serum: Straw-yellowish liquid when blood is allowed to clot

  • Used for testing such as drug analysis.

Collection, Preservation, Packing, and Transportation of Blood Specimens

• Blood on Removable Materials:
  • Remove the whole object.
  • Pack in a paper bag or envelope, keep dry and cool.
• Pools of Blood:
  • Collect samples by swabbing from various locations.
  • Pack in an envelope, store dry and cool.
• Blood in Water:
  • Collect water with a clean pipette or syringe.
  • Pour into a clean, dry test tube or vacuum tube with a purple cork.
• Dry Blood:
  • Moisten a swab with sterile/distilled water.
  • Rub the swab on the stain until it becomes brown/red or absorbs all the blood.
  • Pack in a swab wrapper or folded paper, store dry and cool.

### Problems in the Study of Blood

• Locating Blood:
  • Determining where to search for blood.
• Specimen Collection:
  • Proper preservation and transportation of blood specimens.
• Blood Stain Identification:
  • Determining if the stain is blood.
• Blood Source Identification:
  • Determining if the blood is human or animal.
• Blood Origin Identification:
  • Determining if the blood came from the victim, accused, or other persons.