Blood, Blood Group and Immunity (Antigen, Antibodies), Blood Transfusion, Immunization & Vaccination

composition and function of blood

Blood makes up about 8% of the human body weight. It contains erythrocytes, leucocytes, thrombocytes (platelets) and plasma. The volume percentage of all blood cells in the whole blood is about 45% of adults (hematocrit). The rest consists of liquid plasma (e.g. water, plasma proteins, electrolytes etc.).

The blood is composed of:


Plasma is a straw-coloured fluid in which blood cells are suspended. It is made up of approximately 90% water as well as electrolytes such as sodium and potassium and proteins.

Red Blood Cells (Erythrocytes)

The main function of red blood cells is to carry oxygen. Red blood cells contain a protein called Haemoglobin. This combines with oxygen to form Oxyhaemoglobin. Each red blood cell has a lifespan of approximately 120 days before it gets broken down by the spleen. New cells are manufactured in the bone marrow of most bones. There are approximately 4.5-5 million red cells per micro-litre of blood.

White Blood Cells (Leucocytes)

There a number of types of white blood cells, although the function of all of them is to help fight disease and infection. They typically have a lifespan of a few days and there are only 5-10 thousand WBC’s per micro-litre of blood.

Platelets (Thrombocytes)

Platelets are disc shaped cell fragments which are involved in clotting the blood to prevent the excess loss of body fluids.



Functions of blood

Messenger & waste removal: Blood is the most important transport medium in the human body. It transports gases (oxygen, carbon dioxide, nitrogen etc.) as well as nutrients (metabolism) and end products of cell metabolism. Hence the blood has the task of assuring the exchange of substances. It provides the tissues with blood gases and nutrients and in exchange transports end products (e.g. carbon dioxide, urea, uric acid, creatinine etc.) to the eliminating organs (lung, liver, kidney). Furthermore, it carries chemical messengers (hormones) to their target organs.

Acid-Base Balance: The acid-base homeostasis is regulated in the blood through the diffusion of gases between alveoli and blood in the lung (alveolar diffusion) oxygen diffuses from the alveoli into the blood due to the concentration gradient. It is taken up by the carrying protein hemoglobin (hem = iron-containing, globin = protein). Contrariwise carbon dioxide diffuses from the blood into the alveoli due to its higher blood concentration where it is breathed out.

Oxygen Supply & Carbon Dioxide Removal: The blood transports the oxygen from the alveoli to the remotest cells of the body. Because of the higher gas pressure in the plasma (relative to the cells), it diffuses to the tissues.

Carbon dioxide diffuses from the cells into the blood due to the higher gas pressure in the tissue. Here it undergoes a chemical reaction and forms carbonic acid (CO2 + H2O → H2CO3) which dissociates into hydrogen ion (H+) and bicarbonate (HCO3-). Thus the metabolism end product carbon dioxide is transported in the form of carbonic acid (or rather hydrogen ion and bicarbonate). In the lung, the above mentioned chemical reaction reverses and carbon dioxide is exhaled.

To sum it up the blood regulates the acid-base homeostasis by the gas exchange. The blood is also responsible for the homeostasis, e.g. balancing the water between the blood capillaries on the one hand and intracellular and extracellular space on the other hand. It also maintains a constant body temperature.

Coagulation: Coagulation factors (proteins) are solved in the blood and stop bleeding after a complex (cascade-like) activation of coagulation factors through damage to blood vessels finally leading to the building of thrombus (thrombogenesis). Simultaneously, fibrinogen/fibrin prevents the pathological development of blood clots in the blood vessels. Blood coagulation and fibrinolysis influence each other and maintain a sensitive equilibrium.

Coagulation of blood

Coagulation, is the process by which a blood clot is formed. The formation of a clot is often referred to as secondary hemostasis, because it forms the second stage in the process of arresting the loss of blood from a ruptured vessel. The first stage, primary hemostasis, is characterized by blood vessel constriction (vasoconstriction) and platelet aggregation at the site of vessel injury. Under abnormal circumstances, clots can also form in a vessel that has not been breached; such clots can result in the occlusion (blockage) of the vessel (see thrombosis).

Clotting is a sequential process that involves the interaction of numerous blood components called coagulation factors. There are 13 principal coagulation factors in all, and each of these has been assigned a Roman numeral, I to XIII. Coagulation can be initiated through the activation of two separate pathways, designated extrinsic and intrinsic. Both pathways result in the production of factor X. The activation of this factor marks the beginning of the so-called common pathway of coagulation, which results in the formation of a clot.

The extrinsic pathway is generally the first pathway activated in the coagulation process and is stimulated in response to a protein called tissue factor, which is expressed by cells that are normally found external to blood vessels. However, when a blood vessel breaks and these cells come into contact with blood, tissue factor activates factor VII, forming factor VIIa, which triggers a cascade of reactions that result in the rapid production of factor X. In contrast, the intrinsic pathway is activated by injury that occurs within a blood vessel. This pathway begins with the activation of factor XII (Hageman factor), which occurs when blood circulates over injured internal surfaces of vessels. Components of the intrinsic pathway also may be activated by the extrinsic pathway; for example, in addition to activating factor X, factor VIIa activates factor IX, a necessary component of the intrinsic pathway. Such cross-activation serves to amplify the coagulation process.

The production of factor X results in the cleavage of prothrombin (factor II) to thrombin (factor IIa). Thrombin, in turn, catalyzes the conversion of fibrinogen (factor I)—a soluble plasma protein—into long, sticky threads of insoluble fibrin (factor Ia). The fibrin threads form a mesh that traps platelets, blood cells, and plasma. Within minutes, the fibrin meshwork begins to contract, squeezing out its fluid contents. This process, called clot retraction, is the final step in coagulation. It yields a resilient, insoluble clot that can withstand the friction of blood flow.


Blood group

Blood group is an inherited feature on the surface of the red blood cells. A series of related blood types constitutes a blood group system, such as the Rh or ABO system. The frequencies of the ABO and Rh blood types vary from population to population. In the US, the most common type is O+ (meaning O in the ABO system and positive in the Rh system), which is present in 37.4 percent of the population. The frequencies in the US (in descending order) are O+ (37.4 percent), A+ (35.7 percent), B+ (8.5 percent), O- (6.6 percent), A- (6.3 percent), AB+ (3.4 percent), B- (1.5 percent), and AB- (0.6 percent).

There are four main blood groups (types of blood) – A, B, AB and O. Your blood group is determined by the genes you inherit from your parents.

Each group can be either RhD positive or RhD negative, which means in total there are eight main blood groups.

Antibodies and antigens

Blood is made up of red blood cells, white blood cells and platelets in a liquid called plasma. Your blood group is identified by antibodies and antigens in the blood.  Antibodies are proteins found in plasma. They’re part of your body’s natural defences. They recognise foreign substances, such as germs, and alert your immune system, which destroys them.

Antigens are protein molecules found on the surface of red blood cells.

The ABO system There are four main blood groups defined by the ABO system:

blood group A: has A antigens on the red blood cells with anti-B antibodies in the plasma.

blood group B: has B antigens with anti-A antibodies in the plasma

blood group O: has no antigens, but both anti-A and anti-B antibodies in the plasma.

blood group AB:  has both A and B antigens, but no antibodies.

The Rh system

Red blood cells sometimes have another antigen, a protein known as the RhD antigen. If this is present, your blood group is RhD positive. If it’s absent, your blood group is RhD negative.

This means you can be one of eight blood groups:

  • A RhD positive (A+)
  • A RhD negative (A-)
  • B RhD positive (B+)
  • B RhD negative (B-)
  • RhD positive (O+)
  • RhD negative (O-)
  • AB RhD positive (AB+)
  • AB RhD negative (AB-)

In most cases, O RhD negative blood (O-) can safely be given to anyone. It’s often used in medical emergencies when the blood type isn’t immediately known.  It’s safe for most recipients because it doesn’t have any A, B or RhD antigens on the surface of the cells, and is compatible with every other ABO and RhD blood group.

Blood transfusion

A blood transfusion is a routine medical procedure in which donated blood is provided to you through a narrow tube placed within a vein in your arm.

This potentially life-saving procedure can help replace blood lost due to surgery or injury. A blood transfusion also can help if an illness prevents your body from making blood or some of your blood’s components correctly.

blood is made up of several different parts including red and white cells, plasma, and platelets. “Whole blood” refers to blood that has all of them. In some cases, you may need to have a transfusion that uses whole blood, but it’s more likely that you’ll need a specific component.

Risks and Complications

In general, blood transfusions are considered safe, but there are risks. Sometimes complications show up immediately, others take some time.

Fever: It’s usually not considered serious if you get a fever 1 to 6 hours after your transfusion. But if you also feel nauseated or have chest pain, it could be something more serious. See your doctor right away.

Allergic reactions: It’s possible to experience an allergic reaction to the blood you receive, even if it’s the correct blood type. If this happens, you’ll likely feel itchy and develop hives. If you have an allergic reaction, it’s likely to happen during the transfusion or very shortly after.

Acute immune hemolytic reaction : This complication is rare, but is a medical emergency. It happens if your body attacks the red blood cells in the blood you’ve received. This normally takes place during or right after your transfusion, and you’ll experience symptoms like fever, chills, nausea, or pain in your chest or lower back. Your urine might also come out dark.

Delayed hemolytic reaction: This is similar to an acute immune hemolytic reaction, but it happens more gradually.

Anaphylactic reaction: This happens within minutes of starting a transfusion and may be life-threatening. You may experience swelling of the face and throat, shortness of breath, and low blood pressure.

Immunity is disease resistance and is of following two types:-

  1. Natural or Innate Immunity:- It is present from birth and is inherited from birth by the offspring from the mother.In this form of immunity the response from the organism against the pathogen is immediate in the form of non-specific immune response without the need of recognizing the pathogens.
  2. Acquired or Adaptive Immunity:- It is non- Inherited and is acquired as an enhanced response to a disease during the lifetime of an organism. It takes time to develop and can be more effective in the next encounter with the said Pathogen.The Process of adaptive immunity is the basis of vaccination.


Vaccination or immunization:-

  • Vaccination or immunization is based on the property of the memory of the immune system. In vaccination an inactivated on weaknd pathogen is introduced into the body. Vaccine helps in generating the primary immune response whereby immunological memory is established in the body. Vaccine generate memory cell that quickly identifies the pathogen on subsequent exposure and produces a robust secondary immunity response quickly including mass production of antibodies during the actual infection of pathogen.
  • Immune memory formation of antibodies occur on 1st exposure to a specific antigen and secondary response occur after the second exposure to the same antigen. It began very quickly.

Active immunity :-it is immunity which is developed by the person own body either in the form of antibodies or memory cells in response to exposure to living or dead microorganisms. While when preformed antibodies are directly inducted into the body to obtain temporary immunity is called passive immunity.

For example:-The yellow fluid colostrol secreted by mother during the initial days of lactation has abundant antibodies to protect the infant.

Examples of antimicrobial resistance

  1. Increase number of cases of the hospital acquired infection
  2. Multidrug resistant tuberculosis

It was launched in India in collaboration with World Health Organisation to directly observed treatment short course for the complete services monitoring diagnosis and provision of the second line anti TB drugs under the supervision of dedicated health circles


Types of Vaccines:-

Conventional Vaccines- These vaccines use live attenuated(Ex SABIN) or killed Pathogen(IPV) in Vaccine

Recombination Vaccines:-They use Antigen,Dna or Part of genetic material of pathogen as vaccine like hepatitis B vaccine.