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Difference between RBC, WBC, and Platelets
| Features | RBC | WBC | Platelets |
| Name | Erythrocytes | Leucocytes | Thrombocytes |
| Colour | Red | Colourless | Colourless |
| Formation | Liver, spleen (embryonic life), red bone marrow (adult life) | Red bone marrow and lymphatic system | Red bone marrow |
| Size | 6-8 μm | 12 to 15 μm | Smaller than RBC |
| Shape | Biconcave | Irregular | Disc-shaped |
| Number per microlitre of blood | 5-5.5 million in males, 4-4.5 million in female | 7000 to 8000 | 150,000 – 450,000 |
| Structure | Elastic cell membrane, no nucleus | Nucleus present | Nucleus absent, membrane bounded, cytoplasmic fragment of the cell |
| Life span | 120 days | Variable | 8-9 days |
| Functions | Transport of gases | Immunity | Blood clotting |
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Coagulation process
The excessive blood flow during the injury or cut is prevented by clot formation that takes place due to platelet.
The process of coagulation is as follows:
1. The injured tissue cells and platelet release enzyme thrombokinase that converts prothrombin into thrombin (active) in presence of calcium ion.
2. Thrombin reacts with fibrinogen in presence of calcium ion to form a thread-like structure called fibrin3. Fibrin forms a mesh-like network on the wound that squeezes out the serum forming a clot thereby preventing blood loss.
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ABO system of blood grouping
The ABO blood group system was first given by Karl Landsteiner in 1901. Based on the presence of antigen A and B over the surface of RBCs blood groups are classified into four types viz. type A, type B, type AB, and type O.
Type A – In this type, there is antigen A over the surface of RBC and antibody against B in the plasma.
Type B – In this type, there is antigen B present on the surface of RBC and antibody against A in the plasma.
Type AB – In this type, there is both antigen A and B present on the surface of RBC and no antibodies are present in the plasma. Type AB is a universal acceptor, as it can accept blood from all other types but can donate only to the same group (AB).
Type O – In this type, there is no antigen present on the surface of the RBC but both antibodies A and B are present in the plasma. Type O is the Universal donor, as it can donate blood to all other groups but can accept only from the same group (O).
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Circulatory system (open and close)
- In Closed circulatory system, blood is transported to different parts with the help of the vessels. For example, vertebrates.
- In Open circulatory system, blood is pumped into the body cavity called haemocoel and diffuses back the blood to the heart. For example, invertebrates like arthropods.
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Heart
The heart is the central organ for pumping blood throughout the body. The heart is made up of strong cardiac muscles. It is located in the chest cavity with its lower part pointing towards the left. Its size is that of the person’s fist. It pumps blood rich in carbon dioxide to the lungs and oxygen-rich blood to other parts of the body. 1. The heart consists of four chambers namely the atria and ventricles.
2. The two upper chambers of the heart are known as the atrium.
3. The two lower chambers of the heart are the ventricles.
4. The left and right parts of the heart are separated by a muscular partition called a septum. The septum between the atria is called intra-atrial septum and the one between the ventricles is called intra-ventricular septum.
5. The heart has a number of valves (Mitral valve, Tricuspid valve, Pulmonary valve, and Aortic valve) that allow the blood to flow in one direction. These prevent the oxygenated blood from mixing with deoxygenated blood.
6. SA node, the natural and primary pacemaker of the heart is located in the upper wall of the right atrium in the heart.
7. AV node, the secondary pacemaker is located in the bundles of tissues on the border between the right atrium and right ventricle of the heart.
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Circulation of Blood in the Heart
The circulation of blood within the different chambers of the heart is described below:
Right atrium:
1. Deoxygenated blood enters the right atrium from the anterior region of the body via the superior vena cava and the posterior region of the body via the inferior vena cava.
2. This causes an expansion of the right atrium.
Right ventricle
1. When the right atrium contracts, the tricuspid valve is opened.
2. As a result, the blood flows from the right atrium into the right ventricle.
3. When the right ventricle contracts, the blood is forced into the pulmonary artery due to the opening of the pulmonary semilunar valves.
4. The pulmonary artery carries the blood to the lungs for oxygenation.
Left atrium
1. After oxygenation, four pulmonary veins bring the blood back from the lungs into the left atrium.
2. This makes the left atrium expand.
Left ventricle
1. When the left atrium contracts, the bicuspid valve is opened.
2. As a result, the blood flows from the left atrium into the left ventricle.
3. When the left ventricle contracts, the oxygenated blood is pushed into the aorta via the aortic semilunar valves.
4. The aorta then carries the oxygenated blood to different parts of the body.
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Double circulation
A type of circulation in which blood flows through the heart twice is called double circulation. This type of circulatory system has a separate systemic circulation and pulmonary circulation.
- Systemic circulation – The flow of oxygenated blood from the left ventricle of the heart to various parts of the body and deoxygenated blood from various parts of the body to the right atrium is called systemic circulation. The systemic arteries arising from the aorta carry oxygenated blood from the left of the ventricle to various parts of the body. The systemic veins carry deoxygenated blood from various parts of the body to the right atrium of the heart.
- Pulmonary circulation – The flow of deoxygenated blood from the right ventricle to the lungs and the return of oxygenated blood from the lungs to the left atrium is called the pulmonary circulation. The pulmonary trunk( right and left pulmonary artery) carries blood from the right ventricle to the lungs where the exchange of gases takes place. The oxygenated blood from the lungs returns to the left atrium of the heart through two pulmonary veins, one from each lung.
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Conduction of the Heart
The cardiac conduction system is a collection of nodes and specialized conduction cells that initiate and coordinate the contraction of the heart muscle. It consists of:
1. SA (Sino-Atrial) Node: – It is present in the upper wall of the right atrium, at the junction where the superior vena cava enters. It is the collection of specialised cell that generates the electrical impulses. This electrical impulse is responsible for the contraction of the cardiac muscles.
2. AV (Atrio-Ventricular) Node: – It is located within the atrioventricular septum, near the opening of the coronary sinus. The electrical impulse from the SA node converges at AV node. The AV node acts to delay the impulses by approximately 120ms, to ensure the atria have enough time to fully eject blood into the ventricles before ventricular systole.
3. Bundle of His: – The atrioventricular bundle (bundle of His) is a continuation of the specialised tissue of the AV node, and serves to transmit the electrical impulse from the AV node to the Purkinje fibres of the ventricles. The bundle of His divides into two branches – Left bundle branch and Right bundle branch.
4. Purkinje Fibre: – These fibres are a network of specialised cells that help in the transmission of the signal throughout the cardiac muscles.
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Phases of heart beat
The two main phases of the heartbeat are as follows:
Atrial Systole: – is the contraction of the heart of the left and right atria. Thus, blood is flown into the ventricles.
Ventricular Systole: – When the blood is ejected due to contraction of the ventricle, it flows down through the aorta and pulmonary artery from the left and right ventricles respectively.
Complete Cardiac Diastole: – It occurs after systole. The blood chambers of the heart relax and fill with blood once more, continuing the cycle.
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Phases of cardiac cycle
The cardiac cycle consists of one heartbeat or one cycle of contraction and relaxation of the cardiac muscle.
The successive stages of the cardiac cycle are as follows:
1. Atrial systole
2. Beginning of ventricular systole
3. Complete ventricular systole
4. Beginning of ventricular diastole
5. Complete ventricular diastole
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Waves of normal ECG
- P wave: The depolarization of the right and left atria.
- QRS complex: Right and left ventricular depolarization (normally the ventricles are activated simultaneously).
- T wave: Ventricular repolarization (ventricular relaxation).
NEET CRACKER 