Pulmonary and Systematic Circulation, Systole and Diastole; Arteries & Veins

The main components of human circulatory system include blood vessels (arteries, veins and capillaries), heart, blood, lymph and lymphatic system.

Human Heart

Human heart has four chambers viz. right atrium & right ventricle and left atrium & left ventricle through which blood passes.

We note that two sides of our heart are anatomically and functionally separate pumping units. The cardiovascular system is composed of these two circulatory paths.

Pulmonary Circulation

Pulmonary circulation or circuit refers to the movement of deoxygenated blood from heart to lungs, getting oxygenated in lungs and then coming back to heart.

Systematic Circulation

Systemic circulation or circuit is the movement of blood from the heart through the body to provide oxygen and nutrients, and bringing deoxygenated blood back to the heart.

Notable points about the above two circulations are as follows:

• The right side of heart pumps blood through the pulmonary circulation, while the left side of the heart pumps blood through the systemic circulation.
• Usually, arteries carry oxygen rich blood. But the pulmonary artery (which takes blood from heart to lungs) carries deoxygenated blood. Similarly, usually veins carry deoxygenated blood, but pulmonary veins carry oxygenated blood.

Systole and Diastole

Systole and diastole are the two stages into which the cardiac cycle is divided. Systole is the stage when the contraction of ventricular muscle fibers occurs and the ventricles are emptied. Diastole is the stage of the cardiac cycle when the ventricular muscle fibers expand and the ventricles are filled with blood. When ventricles contract (systole), the blood is sent to pulmonary and systemic circulation. To prevent the flow of blood backwards into the atria during systole, the atrio-ventricular valves close, creating the sound (lubb). When the ventricles finish contracting, the aortic and pulmonary valves close to prevent blood from flowing back into the ventricles. This is what creates the second sound (dubb). Then, the ventricles relax (called diastole) and fill with blood from the atria, which makes up the second phase of the cardiac cycle. This is how sounds of our heart are represented as lubb-dubb-pause-lubb-dubb-pause.

Heart Beat Rate

The normal heart beat is 70-72 per minute in males and 78-82 per minute in females. The heartbeat of a child is more than that of an adult at around 140/min.

Coronary Circulation

The coronary arteries supply blood to the heart muscle. These vessels originate from the aorta immediately after the aortic valve and branch out through the heart muscle. The coronary veins transport the deoxygenated blood from the heart muscle to the right atrium.

Arteries, Veins and Capillaries

Arteries carry blood from the heart to various body parts. All arteries carry oxygenated blood from the heart except pulmonary artery. Arteries have thick elastic muscular walls; they don’t have valves and blood in them flows under high pressure. Arteries are pulsating blood vessels. The arterial pulse can be felt during a medical examination, for instance through the palpation of the radial artery in the internal-lateral face of the wrist near the base of the thumb.

Veins carry blood from the various body parts to the heart. All veins carry deoxygenated blood from the various body parts except pulmonary vein. They have thin non elastic walls and they consist of valves to prevent back the backward flow of blood. Blood flows under low pressure in veins.

Capillaries

Capillaries are fine branching blood vessels that form a network between the arteries and veins. They help to enable the exchange of water, oxygen, carbon dioxide, and many other nutrients and waste substances between the blood and the tissue.