Blood

Blood

Blood is the red liquid that circulates in the arteries and veins of humans and other vertebrate animals, carrying oxygen to and carbon dioxide from the tissues of the body.

Types of Blood

All blood is made of the same basic elements, not all blood is same. In fact, there are eight different common blood types, which are determined by the presence or absence of certain antigens – substances that can trigger an immune response if they are foreign to the body. Since some antigens can trigger a patient's immune system to attack the transfused blood, safe blood transfusions depend on careful blood typing and cross-matching.

There are four main blood groups determined by the presence or absence of two antigens – A and B – on the surface of red blood cells:

    Group A – has only the A antigen on red cells (and B antibody in the plasma)
    Group B – has only the B antigen on red cells (and A antibody in the plasma)
    Group AB – has both A and B antigens on red cells (but neither A nor B antibody in the plasma)
    Group O – has neither A nor B antigens on red cells (but both A and B antibody are in the plasma)

Blood facts

    - Approximately 8% of an adult’s body weight is made up of blood.
   -  Females have around 4-5 litres, while males have around 5-6 litres. This difference is mainly due to the differences in body size between men and women.
    - Its mean temperature is 38 degrees Celcius.
    - It has a pH of 7.35-7.45, making it slightly basic (less than 7 is considered acidic).
    - Whole blood is about 4.5-5.5 times as viscous as water, indicating that it is more resistant to flow than water. This viscosity is vital to the function of blood because if blood flows too easily or with too much resistance, it can strain the heart and lead to severe cardiovascular problems.
    - Blood in the arteries is a brighter red than blood in the veins because of the higher levels of oxygen found in the arteries.
    - An artificial substitute for human blood has not been found.

 Functions of blood

BloodBlood has three main functions:

1.  Transport,

2.  Protection and 

3.  Regulation.

1. Transport

Blood transports the following substances:

    - Gases, namely oxygen (O2) and carbon dioxide (CO2), between the lungs and rest of the body
    - Nutrients from the digestive tract and storage sites to the rest of the body
    - Waste products to be detoxified or removed by the liver and kidneys
    - Hormones from the glands in which they are produced to their target cells
    - Heat to the skin so as to help regulate body temperature

2. Protection

Blood has several roles in inflammation:

    a) Leukocytes, or white blood cells, destroy invading microorganisms and cancer cells
    b) Antibodies and other proteins destroy pathogenic substances
    c) Platelet factors initiate blood clotting and help minimise blood loss

3. Regulation

Blood helps regulate:

    - pH by interacting with acids and bases
    - Water balance by transferring water to and from tissues

To Know more :

Composition of blood