Types of circulation

Circulation is the movement of blood through the vessels of the body induced by the pumping action of the heart. The types of circulation in the human body is described as a part of the physiological study.

1. PHYSIOLOGY OF CIRCULATION (Types)

2. WHAT IS CIRCULATORY SYSTEM ? The circulatory system, also called cardiovascular system or blood vascular system consists of BLOOD, THE HEART and BLOOD VESSELS . In general it maintains appropriate environment in all the tissue fluids of the body for optimal survival and functions of the cells.

3. Transport of nutrients to the body tissues To transport waste products away Transport of the hormones Functions of Circulation

4. Role of each part of the Circulation BLOOD VESSEL FUNCTIONS CHARACTERISTICS Arteries Transport of oxygenated blood under high pressure to the tissues Strong vascular walls Blood flow at high velocity Arterioles Control conduits for blood release into capillaries Strong muscular walls Capillaries Exchange of fluids, nutrients, electrolytes, hormones etc Very thin walls Have numerous pores Venules Collect blood from capillaries and coalesce into larger veins Elastic tissues and fibrous connective tissues are present Veins Transport of blood from venules to the heart Have thin walls Blood flows under low pressure

5. TYPES OF CIRCULATORY ROUTES (1) Systemic Circulation (2) Pulmonary Circulation (3) Portal Circulation (4) Collateral Circulation

6. Systemic Circulation This includes the arteries and arterioles that carry oxygenated blood from the left ventricle to systemic capillaries. It also includes veins and venules that return deoxygenated blood to the right atrium. Because it supplies blood flow to all the tissues of the body except lungs, it is also called as the greater circulation or peripheral circulation .

7. Pulmonary Circulation The pulmonary circulation carries deoxygenated blood from the right ventricle to the air sacs (alveoli) within the lungs and returns oxygenated blood from the air sacs to the left atrium. The pulmonary trunk emerges from the right ventricle and then divides into the right pulmonary artery to the right lung and the left pulmonary artery to the left lung. The pulmonary arteries are the only arteries that carry deoxygenated blood. On entering the lungs the branches divide until they form capillaries around the alveoli within the lungs. The pulmonary capillaries unite to form venules and eventually pulmonary veins ( only veins that carry oxygenated blood ).

8. Portal Circulation In some parts of the body, however, blood passes from one capillary network into another through a vein called a portal vein. Such a circulation of blood is called a portal system. The portal systems are associated with the following locations –

9. (1) Hypophyseal Portal System (associated with the pituitary gland)

10. (2) Hepatic Portal System (associated with the liver)

11. Collateral Circulation Collateral circulation  is the alternate  circulation around a blocked artery or vein  via another path, such as nearby minor vessels. Its formation may be provoked by pathological conditions such as high vascular resistance or ischaemia.

12. An example in humans and some other animals is after an acute myocardial infarction (heart attack). Collateral circulation in the heart tissue will sometimes bypass the blockage in the main artery and supply enough oxygenated blood to enable the cardiac tissue to survive and recover.

13. OXYGEN TRANSPORT Oxygen does not dissolve easily in water, so only 1.5% of inhaled oxygen is dissolved in blood plasma, which is mostly water. About 98.5% of blood oxygen is bound to hemoglobin in RBCs. Oxygen and hemoglobin bind in an easily reversible reaction to form Oxyhemoglobin. Partial pressure of oxygen is the most important factor that determines how much oxygen binds to hemoglobin. Factors affecting hemoglobin’s affinity for oxygen are pH, partial pressure of carbon dioxide, temperature etc.

14. Carbon Dioxide Transport When arterial blood flows through the tissue capillaries, CO 2 diffuses down its partial pressure gradient from the tissue cells into the blood. The transport to the lungs takes place in three ways -

15. References - Guyton and Hall (2011) Textbook of Medical Physiology 12 th ed. Philadelphia : Saunders, Elsevier Pranav Kumar and Usha Mina (2018) Life sciences fundamentals and practice 6 th ed. New Delhi, India : Pathfinder https://socratic.org/questions/what-is-the-difference-between-pulmonary-and-systemic-circulation https://socratic.org/questions/what-is-a-portal-system-what-is-the-purpose-of-the-hepatic-portal https://www.easynotecards.com/notecard_set/84284

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