BLOOD

DEFINITION:

It is a red colored, viscous, alkaline (pH about 7.4) fluid flowing through the body of higher animals. It is a connective tissues. The adult human body consists of 5-6 liters of blood.
It has two components:
  • Fluid plasma.
  • Solid formed elements. (The elements including corpuscles and postulate)

BLOOD PLASMA/ FLUID PLASMA:

It is the colorless liquid part of the blood. It forms about 55% of the blood (about 3 liters). It is non- living part and its 90% part is composed of water, in which a large number of organic and inorganic substances are dissolved.

Functions of blood plasma:
  • Maintains osmotic pressure and viscosity of the blood.
  • It helps in transport of various substances like food, water and other substances from all parts of the body for many purposes such as assimilation, oxidation and storage.
  • It acts as a protein reservoir.
  • It also helps in clotting of blood.
  • By the circulation of blood heat is distributed throughout the body to maintain the body temperature constant and uniform. 
Its composition is as follows: 
  • Water (92%)
  • Soluble components: Proteins, glucose, amino acid, triglycerides, urea, hormones etc. 


BLOOD CORPUSCLES/ SOLID FORMED ELEMENTS:

  • The blood corpuscles make up the 40-45% of the blood. These blood corpuscles are found freely suspended in the liquid plasma.
  • There are three types of solid elements:
1- Red blood corpuscles or cells (RBC’s)

2- White blood corpuscles or cells (WBC’s)

3- Platelets.

Red blood corpuscles (RBC’s) /Erythrocytes:

  • They are small biconcave circular cells also called erythrocytes.
  • They are thicket at their edges than in the center.
  • The erythrocytes are flexible so that they can pass through the narrow capillaries easily.
  • They number 5.8 million per cubic mm in adult males and 4.2 cubic mm in adult females.
  • Their number is higher in early infancy.
  • The adult red blood cells do not have nucleus, mitochondria or endoplasmic reticulum.
  • Hemoglobin is composed of an iron containing pigment called haeme and a protein called globin. The hemoglobin pigments combine with oxygen to form oxyhaemoglobin in the lungs.
  • The life span of these cells is only about 120 days.
Functions of RBC’s: 
  • It helps in exchange of gases, and is called respiratory pigments.
  • They maintains the viscosity of blood, acid-base and ionic balance.
  • The disintegration of haemoglobin leads to formation of many other pigments like bilirubin, biliverdin, etc. in liver.

 White blood corpuscles(WBC’s):

  • They are also called Leucocytes.
  • Hey lack haemoglobin and are therefore colorless.
  • They are nucleated and amoeboid.
  • The amoeboid nature of the leucocytes helps them to squeeze through the walls of the blood vessels in order to engulf bacteria.
  • WBC s are commonly known as POLICE OF THE BODY; because they protects the body by killing germs.
  • They number 5000 to 9000 per cubic mm .
  • The ratio of WBC to RBC is 1:7.
Functions of WBC's/ Leucocytes:
  • Defense against diseases : They have the ability to differentiate between their own body cells and foreign cells .WBC's destroy bacteria and protect the body. 
  • Production of Anti bodies: The WBC's are involved in the production of antitoxins and antibodies that neutralize, kill or poison the germs.
  • WBC's can be induced to produce anti bodies with the help of vaccinations thus prepairing the body for an attack.

Blood Platelets/Thrombocytes:

  • Blood contains fragments of larger bone marrow cells known as platelets.
  • They are small, round, biconvex cells that do not have a distinct nucleus.
  • They are also called Thrombocytes.
  • They number 250,000 to 400,000 per cubic mm of blood.
  • Their life span is 8 to 14 days .
  • They are destroyed in the spleen.
Functions of platelets:
  • Helps in blood clotting.
  • Help in the repair of damaged Endothelium.
  • The clot forms is made denser smaller by the action of platelets, called clot Retraction.