Blood Circulation

Circulation of blood is of 3 types- the systemic circulation which takes place between the heart and body cells, pulmonary circulation takes place between heart and lungs and lastly the coronary circulation which takes place within the heart.

Above figure is taken from resveralife.com- only for Educational purpose

Systemic and Pulmonary circulation:- The systemic circulation carries the oxygenated blood from the left ventricle to the entire body and deoxygenated blood from the tissue cells to the right atrium; While the pulmonary circulation carries the deoxygenated blood from right ventricle to the lungs and again carries the oxygenated blood back to the left atrium. Both these circulations are interrelated. The output of one circulation becomes the input of another.

The superior vena-cava, inferior vena-cava and coronary sinus drain the deoxygenated blood from the entire body into the right atrium. The two AV valves are present between the atrium and the ventricle. The AV valve present on the right side is the tricuspid valve. Through the tricuspid valve the deoxygenated blood flows from right atrium to right ventricle.

Through the pulmonary aorta, the deoxygenated blood flows from the right ventricle to the lungs. In pulmonary capillaries, the blood looses CO2 and gains O2. In this way the deoxygenated blood is converted to the oxygenated blood within the lungs. With the help of pulmonary veins, the oxygenated blood is transferred from lungs to the left atrium. The pulmonary aorta is the only artery in the body which carries the deoxygenated blood and similarly the pulmonary vein is the only vein which carries oxygenated blood.

The oxygenated blood in the left atrium then flows to the left ventricle through an AV valve known as  bicuspid valve. Now finally through aorta and systemic arteries, the oxygenated blood reaches the whole body cells. Within tissue and cells, they accepts oxygenated blood through capillaries and drain out deoxygenated blood through the veins and reaches the right atrium and the cycle continues. The systemic circulation provides oxygenated blood to the whole body except for the air sacs of lungs(alveoli); these are supplied through pulmonary circulation.

Coronary circulation:- Coronary circulation supplies the heart chambers with blood. They have specialized arteries known as coronary arteries which surrounds the entire heart muscles fibers. Coronary arteries are branched from the aorta and supply the heart. The deoxygenated blood is carried away through the coronary veins; all these veins club together and form coronary sinus which drains the deoxygenated blood into right atrium.

CONDUCTION SYSTEM

The conduction system is a network of specialized cardiac muscle fibers known as auto-rhythmic fibers which provides the rhythm of heart, or a heartbeat.

The process of cardiac excitation to progress through the heart is done in following steps-

• The cardiac excitation normally begins at the sinoatrial node (SA node) which is located in the right atrial wall, inferior to the opening of superior vena-cava. The SA node cells do not have stable resting potential that’s why they repeatedly depolarize. When the potential reaches the threshold, the action potential flows in the entire atrial muscle fibers. Following the action potential, the atria contract.
• From the SA node, the action potential reaches the AV node which is located in the interatrial septum.
• After propagating through the AV node, they conduct along the atrioventricular (AV) bundle or bundle of his. This is a site where action potential floes from atria to the ventricles.
• From AV bundle, the impulses reaches right and left bundle branches, which are present in the interventricular septum.
• Finally, the impulses reaches the large Purkinje fibers which spreads the impulses to the entire ventricular myocardium, following the impulses, the ventricles contract, which pushes the blood upwards towards the SL valves.

Multiple choice questions(MCQs)

1. How many types of blood circulation are present in the body?
A. 2 B. 3
C. 4 D. 1

2. Which type of circulation circulated blood between the heart and body cells?
A. systemic circulation B. pulmonary circulation
C. coronary circulation D. conduction system

3. Which type of muscle fibers facilitates the conduction system?
A. skeletal muscle B. cardiac muscle
C. auto-rhythmic fibers D. both B and C

4. Which of the following areas are supplied by the coronary circulation?
A. right atrium B. interventricular septum
C. left ventricle D. all of the above

5. Which of the following statement is NOT true?
A. coronary arteries are branched from systemic capillaries
B. Purkinje fibers spread impulses within the entire ventricle myocardium
c. pulmonary circulation converts deoxygenated blood into oxygenated
D. pulmonary veins carries oxygenated blood

6. which of the following valve is present between the right atrium and right ventricle?
A. tricuspid valve B. bicuspid valve
C. SL valve D. none of the above

7. Match the following-
a. SA node 1. Initiates nerve impulses
b. AV node 2. Located at the interventricular septum
C. bundle of HIS 3. Situated in the interatrial septum
d. Purkinje fibers 4. Supplies the ventricles with conduction impulses

8. At what point, the impulses flow from atria to the ventricles?
A. AV node B. SA node
C. bundle of HIS d. right and left bundle branches

9. Which of the following structure is NOT supplied by the systemic circulation?
A. bronchioles B. trachea
C. alveoli D. nose

10. Which of the following carries the oxygenated blood?
A. superior vena-cava B. inferior vena-cava
c. coronary sinus D. none of the above

ANSWERS:-

1. 3
2. systemic circulation
3. auto-rhythmic fibers
4. all of the above
5. coronary arteries are branched from systemic capillaries
6. tricuspid valve
7. a – 1 b – 3 c – 2  d – 4
8. bundle of HIS
9. alveoli
10. none of the above

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REFERENCE:-Gerard  J. Tortora -Principles of anatomy and physiology;  edition twelfth ; page no.-: .