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Sembulingam K & Sembulingam P.(2012). Essential Medical Physiology. (6th ed.). new Delhi: Jaypee Brothers medical Publishers (P) Ltd
MODULE 4
Heart and Circulatory Physiology108
2.0 Objectives 3.0 Main Content
3.1 The Concept of Haemodynamics 3.2 The Functional Parts of the Circulation 3.3 The Functional Divisions of the Circulation 4.0 Conclusion
5.0 Summary
6.0 Tutor- Marked Assignment 7.0 References/ Further Reading
1.0 INTRODUCTION
There is a mechanism of fluid movement through the body that allows for change of required nutrients and exchange of different types of wastes. This unit covers the coordinated circulation of blood to different parts of the body.
2.0 OBJECTIVES
At the end of this unit, you should be able to:
explain the concept of haemodynamics
explain the functional parts of the circulation
explain the functional divisions of the circulation.
3.0 MAIN CONTENT
3.1 Systemic and Pulmonary Circulation: Haemodynamics
The function of the circulation is to service the needs of the body tissues—to transport nutrients to the body tissues, waste products from the tissue to the excretory organs, hormones from one part of the body to another, and in general, to maintain an appropriate environment in all the tissue fluids of the body for optimal survival and function of the cells. The rate of blood flow through most tissues is controlled in response to tissues need for nutrients. The heart and circulation in turn are controlled to provide the necessary cardiac output and arterial pressure that are required for tissue blood flow.The circulation is divided into the systemic circulation and the pulmonary circulation. The systemic circulation supplies blood to all the tissues of the body except the lungs, so it is also called the greater circulation or peripheral circulation.
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3.2 Functional Parts of the Circulation
Arteries: Are blood vessels that carry blood away from the heart to the lungs and tissues. The arterioles are the last small branches of the arterial system; they act as control conduits through which blood is released into the capillaries and because of their small diameter, they play a key role in vasoconstriction and vasodilatation. Most arteries and arterioles carry oxygenated blood, except the pulmonary artery which transports deoxygenated blood from right ventricle to the lungs.
Capillaries: They are microscopic blood vessels that allow the exchange of fluid, nutrients, electrolytes, hormones, and other substances between the blood and the tissue. To serve this role, the capillary walls are very thin and have numerous minute capillary pores permeable to water and other small molecular substances.
Veins: These are blood vessels that carry blood to the heart, from the lungs and tissues. They serve as a major reservoir of extra blood. Blood pressure in veins is extremely low as a result, valves formed by the tunica internal layer are necessary to prevent backflow. Most veins carry deoxygenated blood, except the pulmonary vein which transports oxygenated blood from the lungs to the left atrium. The venules collect blood from the capillaries, and they gradually coalesce into progressively larger veins.
3.3 Functional Divisions of the Circulation
Systemic CirculationSystemic circulation is a part of the cardiovascular system which is responsible for carrying oxygenated blood away from the heart to the body, and return deoxygenated blood back to the heart. Oxygen-rich blood from the lungs leaves the pulmonary circulation when it enters the left atrium through the pulmonary veins. The blood is then pumped through the mitral valve into the left ventricle. From the left ventricle, blood is pumped through the aortic valve and into the aorta, the body's largest artery. The aorta arches and branches into major arteries to the upper part of the body before passing through the diaphragm, where it branches further into arteries which supply the lower parts of the body.
The arteries branch into smaller arteries, arterioles, and finally capillaries. Waste and carbon dioxide diffuse out of the cell into the blood, while oxygen and nutrients diffuses out of the blood into the interstitial fluid and then into the cell. The deoxygenated blood continues through the capillaries which merge into venules, then veins, and finally the venae cavae, which drain into the right atrium of the heart. From the right atrium, the blood travels through the pulmonary
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circulation to be oxygenated before returning again to the system circulation. Coronary circulation, blood supply to the heart muscle itself, is also part of the systemic circulation.
Pulmonary Circulation
Pulmonary circulation is a part of the cardiovascular system which is responsible for carrying de-oxygenated from the heart to the lungs and then back to the heart for it to transfer the oxygenated blood to the rest of the body. Oxygen-depleted blood from the body leaves the systemic circulation when it enters the right atrium through the superior and inferior vena cavae. The blood is then pumped through the tricuspid valve into the right ventricle. From the right ventricle, blood is pumped through the pulmonary valve and into the pulmonary artery. The pulmonary artery splits into the right and left pulmonary arteries and travel to each lung. In the lungs, the blood travels through capillary beds on the alveoli where gaseous exchange occurs, removing carbon dioxide and adding oxygen to the blood. The alveoli are air sacs in the lungs that provide the surface for gas exchange during respiration. The oxygenated blood then leaves the lungs through pulmonary veins, which returns it to the left atrium, completing the pulmonary circuit.
After entering the left heart, the blood flows through the bicuspid valve into the left ventricle. From the left ventricle, the blood is pumped through the aortic valve into the aorta to travel through systemic circulation, delivering oxygenated blood to the body before returning again to the pulmonary circulation.
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Fig.1.1: The Human Heart
SAE
Explain what happens in pulmonary and systemic circulation.
4.0 CONCLUSION
With blood circulation through the arteries, veins and capillaries, circulation is divided into the systemic circulation and the pulmonary circulation. The systemic or greater circulation supplies blood to all the tissues of the body except the lungs, while the pulmonary circulation covers the movement of de-oxygenated blood from the heart to the lungs and then back to the heart for it to transfer the oxygenated blood to the rest of the body.
5.0 SUMMARY
In this unit, you have learnt about the concept of Haemodynamics, the functional parts of the circulation and the functional divisions of the circulation.
6.0 TUTOR -MARKED ASSIGNMENT
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Activity – Laboratory assignment Answer the following questions:
1. Explain the concept of Haemodynamics 2. Describe the functional parts of the circulation 3.
7.0 REFERENCES/ FURTHER READING
Fox, S.I. (2012). Human Physiology. (12th ed.). New York: Mc Graw Hill,.
Ganong, W.F. (2019). Review of Medical Physiology. (26th ed.). New York: Mc Graw Hill.
Guyton, A.C. & Hall, J.E. (2021). Textbook of Medical Physiology.
(14th ed.). Philadelphia: Harcourt International Edition, W.B.
Saunders.
Sembulingam K & Sembulingam P.(2012). Essential Medical Physiology. (6th ed.). new Delhi: Jaypee Brothers medical Publishers (P) Ltd