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Name the components of the formed elements in the blood and mention one major function of each of them.

The components of formed elements are Erythrocytes, Leucocytes and platelets. Its functions are :

(a) Erythrocytes or RBC
These play a significant role in transport of respiratory gases.

(b) Leucocytes or white blood cells (WBC)
There are two types of WBC granulocytes and agranulocytes. The granulocytes include neutrophils, eosinophils and basophils and the agranulocytes include lymphocytes and neutrophils. Each of these cells help the body in fighting against the invading pathogen and protect the body.

Neutrophil and Monocyte
These cells are phagocytic. They engulf and destroy the foreign organism entering the body.
It secrets histamine, serotonin, heparin etc. which are involved in inflammatory reaction.
It helps in resisting infection and also helps in allergic reaction.
Lymphocytes: These are of two types ‘B’ and ‘T’ forms which are responsible for immune responses of the body.

(c) Platelets or thrombocytes
They are mainly involved in coagulation or clotting of blood.


What is the importance of plasma proteins?

The plasma protein include fibrinogen, globulins, and albumins. Fibrinogen is essential for clotting or coagulation of blood.
Globulins are mainly involved in the defense mechanism of the body.

Albumins maintain the osmotic balance of the body.


Why do we consider blood as a connective tissue?

Blood is a special connective tissue as it plays a major role in providing all the cells in the body with nutrients, O2 and essential substance. It also removes the harmful substances continuously from the different cells where it is produced. Since blood circulates and connects to all the parts of the body to perform the above function it is called as a special connective tissue.


What is the difference between lymph and blood?




1. Lymph is colourless fluid. 1. Blood is red in colour.
2. It contains specialized lymphocytes responsible for immune response. 2. Blood consist of fluid matrix, plasma and formed elements.
3. Lymph moves out into spaces between the cells of the tissues and are collected by lymphatic capillaries which join to form larger vessels from where it passes into lymph nodes. 3. Blood supply O2 & nutrients to the tissues and collect the waste from the tissue by diffusion and passes from the capillaries into the venules which join to form the large veins and open into the heart.



What is meant by double circulation? What is its significance?

In man as in all mammals two circulations of blood takes place one is systemic circulation or body circulation and the other is pulmonary circulation or lung circulation.

In systemic circulation the oxygenated blood received by the left atrium is forced into the left ventricle, when the ventricles contract the blood leaves the heart through the aorta. Through successive branchings the aorta gives rise to hundred of arteries which again branch to arterioles and capillaries. These carry blood to different parts of the body where exchange of nutrients and gases take place. From the organs similar number of venules converges to form veins which reunite to form two large veins, the superior and inferior venacava and open into the right atrium. This course of blood from the left ventricle to the right atrium is one type of circulation, which is the systemic circulation.

The second type of circulation is the pulmonary circulation. In this circulation the venous blood from the right atrium is pushed into the right ventricle, which is carried by the pulmonary artery to the lungs. In the lungs the deoxygenated blood exchanges the gases, becomes oxygenated and is carried by the pulmonary vein back to the heart. This course of the blood from right ventricle to the left atrium is pulmonary circulation.

Significance of double circulation is

1. Systemic circulation provides nutrients, O2 and other essential substances to the tissues and collects CO2 and other harmful substances for elimination.

2. The pulmonary circulation helps in carrying deoxygenated blood to the alveoli which are site for exchange of gases. It carries the oxygenated blood from the alveoli back to the heart.

3. There is no mixing of oxygenated and deoxygenated blood.


Write the differences between:


(a) Blood and Lymph

(b) Open and Closed system of circulation

(c) Systole and Diastole

(d) P-wave and T-wave







1. Blood is red in colour due to presence of haemoglobin Lymph is colourless due to absence of haemoglobin.
2. Blood consist of fluid matrix, plasma, and formed elements. Lymph consists of specialised lymphocytes.

Open System of Circulation

Closed System of Circulation

1. The blood pumped by the heart passes through the large vessels into the open spaces of the body cavity. The blood pumped by the heart passes through a closed network of blood vessels called arteries veins and capillaries.
2. Open system of circulation is seen in arthropods and molluscus. Closed system of circulation is seen in Annelids and Chordates.



The contraction of ventricles is called systole The relaxation of the atria is called diastole.

P- wave

T- Wave

This represents the electrical excitation of the atria leading to the contraction of both the atria. This wave represents the return of the ventricles from excited state to normal state.


Describe the evolutionary change in the pattern of heart among the vertebrates.

A comparative study of the structure of heart of vertebrates reveals that there is a gradual development in the structure of heart in the evolutionary line. Among the vertebrates the lowest forms include the fishes which possess 2 chambered heart with an atrium and a ventricle. The next higher form, which is amphibians, possess 3 chambered heart with two atria and a single ventricle. The same structure is seen in reptiles also. In these two groups both the pure blood and impure blood gets mixed in the ventricle. The remaining higher forms which include the aves, the reptiles and the mammals possess 4 chambered heart - two atrium and two ventricle. All these groups exhibit double circulation and hence there is no mixing of oxygenated and deoxygenated blood.


Why do we call our heart myogenic?

Heart is called myogenic because all the normal activities of the heart are regulated intrinsically or the activities are auto regulated by specialised muscles known as nodal tissues. The nodal tissues are SA node and AV node which are present in the heart.


Sino-atrial node is called the pacemaker of our heart. Why?

The Sino – artrial node is a patch of nodal tissue present in the right upper corner of the right atrium. These nodal tissues have the ability to generate action potential without any external stimuli. The maximum action potential can be generated by SAN which is around 70-75 mm – and this action potential is responsible for initiating and maintaining the rhythmic contraction of the heart. Due to this ability of the SAN, it is called as the pace maker of the heart.


What is the significance of atrio-ventricular node and atrio-ventricular bundle in the functioning of heart?

The atrio- ventricular node is a mass of tissue seen in the lower left corner of the right atrium close to the antrio- ventricular septum and the atrio ventricular bundle is the continuation of AVN which passes through the atrio ventricular septa and it divides immediately into right and left bundle. Both AVN and AN have the ability to generate action potential and their main function is to get excited by the action potential initiated by the Sino- atrial node and conduct the stimulus to the remaining part of the heart through which they branch thus helping in the rhythmic contraction and relaxation of the heart.


Define a cardiac cycle and the cardiac output.

The sequential events taking place in the heart which is the contraction or systole and relaxation or diastole of both the atria and ventricles is called cardiac cycle. The amount of blood pumped by the ventricle during this cardiac cycle is approximately 70 ml which is called as the stroke volume. The stroke volume multiplied by the heart rate gives the cardiac output.

Cardiac output can be defined as the volume of blood pumped out by each ventricle per minute which is around 5000 ml or 5 litres in a healthy individual.


Explain heart sounds.

There are two prominent sounds produced during each cardiac cycle, the first sound is ‘lub’ associated with the closure of the tricuspid and bicuspid valves whereas the second sound is ‘dub’ associated with the closure of the semilunar valves. These sounds can be heard through the stethoscopes.


Draw a standard ECG and explain the different segments in it.


In the above diagram each peak is given letters for P to T. the first peak 'P' represents the electrical excitation of the atria. This leads to the contraction of both the atria. The next part QRS complex represents the depolarisation of the ventricles, which initiates the ventricular contraction. The last 'T' wave represents the return of the ventricles from excited state to normal state.

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