BLOOD
Blood can be characterized as a fluid mixture, consisting of cellular components and plasma that circulates throughout the body via the arterial, venous and capillary systems. It accounts for approximately 8% of the total body weight. For a normal adult the total blood volume may range from 4.5 to 6 liters.
Also Read: Substances That Resembles Bloodstains
CELLULAR COMPONENTS OF BLOOD
1. Red blood cells (RBCs)
Also known as Erythrocytes, contain Hemoglobin which transports oxygen from the lungs throughout the body via arterial system and returns carbon dioxide to the lungs for expiration through the venous system. The oxygen rich blood in the arteries is due to the oxyhemoglobin complex which imparts a bright red color to the blood whereas the blood in the veins is somewhat darker in color due to oxygen deficiency. Oxygen can also be released from hemoglobin by exposure to atmosphere. This causes the blood which has been shed to become darker as it loses its oxygen to the surrounding environment.
2. White Blood Cells (WBCs)
Also known as leukocytes, perform vital functions related to immunological response of the body to foreign substances and infections.
3. Platelets
An important element of the clotting mechanism of the blood.
4. Plasma
The liquid portion of the blood constitutes approximately 55% of the total blood volume. It has numerous chemical compounds both solid and gases dissolved in it. It is a medium of blood circulation and also carries nutritive substances, hormones, electrolytes and antibodies throughout the body and assists with removal of waste products of metabolism. Once the blood has clot, the liquid portion is referred to as Serum. It is the pale yellow liquid which appears around an exposed blood clot which has jelled and often observed at crime scenes.
5. Hemoglobin
Is a tertiary structure formed by symmetric pairing of four polypeptide chains, two alpha globin and two beta globin and all the four chains are connected together to a haem group that contains an iron atom at its center.
The Physical Properties Of Blood
Whenever blood is exposed to external environment and subjected to various forces, it will behave according to the principle of physics. The application of the principles of fluid in motion and the physical properties of blood form the basis for the determination of location, shape, and size relative to the forces that produced them. This, it is important to acquire a basic knowledge of the principles that govern the fluid motion.
Viscosity of a liquid is defined as its resistance to change form or flow due to mutual attraction of molecules to each other. The more viscous a fluid the more slowly it will flow. The viscosity of the blood increases greatly as a result of clothing.
Specific Gravity is defined as the weight of a substance compared to an equal volume of water. The specific gravity of blood is only slightly higher than blood.
Surface tension is defined as the force that pulls the surface molecules towards the interior of a fluid and decreases the surface area and causes the liquid to resist penetration. It is measured in force per unit length. The surface tension of Blood is 50.0.
Functions Of Blood
The function of blood is to maintain the consistency of the internal body. The circulating blood makes adaptability possible to changing life. Some of the regulatory mechanism in which blood is involved, includes sensors that detect alterations in pH, temperature, oxygen and constituents of blood.
Apart from these, some of the major functions of blood are Respiration, Excretion, Nutrition, in providing immunity and temperature regulation by Hemostasis.
Clotting Process
A blood clot is formed by a complex mechanism involving the plasma protein fibrinogen, platelets, and other clotting factors. This occurs as a network of fibrin and red blood cells. Subsequently, the blood clot begins to retract causing a separation of the remaining liquid portion which is referred to a Serum. Blood clots and serum stains surrounding them as well as the degree of observed drying of blood should be recognized as important information at crime scenes.
Importance of Blood in Forensic Science
Blood as a physical and biological evidence is found in a number of violent crimes, for which investigators pay attention in crime scene investigations in order to provide crucial information to determine the type of crime and to link a suspect to the scene of crime. Criminals often attempt to remove these bloodstains from the crime scene by partial or complete washing using detergents or acids. The major task of the experts is to examine the crime scene with different search methods to collect and lift evidences left by the criminal and to examine them with every possible scientific technique.
