CIRCULATORY SYSTEM

1. CIRCULATORY SYSTEM PRESENTED BY Mr. SURESH KUMAR LECTURER IN PHYSICAL EDUCATION P.G.G.C.G. SECTOR -11, CHANDIGARH

2. CIRCULATORY SYSTEM MEANING OF CIRCULATORY SYSTEM The circulatory system means heart (cardium) and blood vessels (vascular) system, which is, the course taken by the blood through the arteries, capillaries, and veins and back to the heart. In humans the heart is made up of four chambers: the right and left auricles, or atria, and the right and left ventricles. The right side of the heart pumps oxygen-poor blood from the cells of the body back to the lungs for new oxygen and the left side of the heart receives blood rich in oxygen from the lungs that is pumped through the arteries to the different parts of the body. It is estimated that a given portion of the blood completes its course of circulation in approximately 30 seconds.

3. HEART • The heart is a wondrous pump, which powers the human body. With each heartbeat, it sends life-giving blood throughout the body. Blood carries oxygen and food to all the body cells. The heart is a large, hollow, muscular organ divided into two pumps that lie side by side. Veins transport blood from throughout the body to the right-sided pump. That pump sends the blood to the lungs, where it picks up oxygen. The oxygenated blood then flows to the left side of the heart, which is pumped through arteries to the rest of the body. Valves control the flow of blood through the heart. The left-sided pump, which delivers blood throughout the body, is larger and stronger than the right pump. • The nervous system regulates the heart and other parts of the circulatory system. The autonomic nervous system automatically • controls the heart rate, increasing or decreasing it, depending on the body's needs. For example, the heart pumps slowly while a person sleeps, providing relatively small amounts of oxygen to the body. But the heart rate can be quickly speeded up again and so increase the oxygen output enormously. This will happen when a person exercises, becomes frightened, or needs to fight or run.

5. STRUCTURE OF THE HEART • Each person's heart is about the same size as that person's fist. A newborn baby's heart weighs only about 20 grams. An adult's heart HEART CHAMBERS • The septum divides the heart lengthwise, and valves divide it crosswise. Each side of the heart thus has two chambers, one above the other. A thin membrane called the endocardium lines each chamber. The top chambers, called the right atrium and left atrium, receive and collect blood returning to the heart through the veins. After the atria • Figure 12.2 Diagram of the flow of blood through the heart. • (plural of atrium) have filled with blood, they contract and squeeze blood into the lower chambers, called the right ventricle and left ventricle. After the ventricles have filled, they contract and pump blood out of the heart

6. through the arteries. The ventricles have i-xtremeiy thick wails. The ventricles, which must squeeze blood from the heart, are much larger and stronger than the atria. • MUSCULAR WALLS • The heart: consists mainly of muscles, which are called myocardium or cardiac muscle. These cardiac muscles form the walls of the heart as well as the septum (Figure 12.3), a wall that divides the left and right sides of the heart. All the muscles contract and relax, thereby pushing blood through the heart. • A membrane called the epicardium covers the outer surface of the heart. Another membrane, the pericardium, surrounds the epicardium. It completely encloses the heart and extends above the blood vessels that emerge from the top of the heart. A slippery fluid between the epicardium and the pericardium enables the heart to contract smoothly. • Heart muscle differs from the other muscles of the body that is skeletal and smooth muscles. Heart muscle has striations like skeletal muscle but it contracts and relaxes automatically like smooth muscle addition, heart muscle cells act as one cell. When one heart muscle cell contracts or relaxes, the cells around it do the same. Because of this, the heart beats continuously and rhythmically throughout our life.

7. BLOOD VESSELS • Blood enters and leaves the heart through several major vessels. Blood from the body flows into the right atrium through the body's two largest veins i.e. the superior vena cava and the inferior vena (Figure 12.3) cava. The superior vena cava brings blood from the head and arms. The inferior vena cava carries blood from the trunk and legs. Other blood vessels transport blood between the heart and lungs. Pulmonary veins return blood from the lungs to the left atrium. The pulmonary artery carries blood from the right ventricle to the lungs. The aorta is the largest artery. It receives oxygenated blood from the left ventricle and, through numerous branches, distributes it throughout the body. The pulmonary artery and the aorta are sometimes called the great vessels. • The first arteries that branch from the aorta are the two major coronary arteries. They bring blood to the heart and so enable it to continue pumping. These two coronary arteries divide into many branches as they cover the heart. Diseases that affect the coronary arteries are among the most serious problems cardiologists treat because the arteries nourish the heart muscle itself.

8. HEART VALVES Valves regulate the flow of blood through the heart. The valves have flaps that open as blood pours from a chamber. When the flaps close, they prevent blood from flowing back into the chamber. Two valves separate the atria and the ventricles. They are called the atrioventricular valves or AV valves (Figure 13.3). The AV valve between the right atrium and right ventricle has three flaps and is called the tricuspid valve. The atrio-ventricular (AV) valve on the left side of the heart has two flaps and is called the bicuspid or mitral

9. three flaps shaped like half moons. When the right ventricle contract! it delivers blood to the pulmonary artery. The semilunar valve thul controls the blood flow to the pulmonary artery is known as the valve The heart also has a valve, called a semilunar valve, between ea< h ventricle and its great vessel (the pulmonary artery or the aorta). Each semilunar valve has pulmonary valve. The left ventricle squeeze. blood into the aorta. The semilunar valve on the left side is called tin aortic valve.

10. FUNCTIONS OF THE HEART The main functions of the heart are as under: Pumping blood to the lungs. Pumping blood throughout the body. Regulating Blood Pressure. Regulating the heart Rate. Pumping blood to the lungs: • Blood from the body that enters the right side of the heart contains carbon dioxide, a gaseous waste the cells produce in creating energy. • Blood enters the right atrium through the superior vena cava and infeiliil vena cava. The atrium fills with blood and then contracts, forcing. till blood through the tricuspid valve into the right ventricle. After thi ventricle is filled, pressure pushes the tricuspid valve to close and Hi. pulmonary valve, leading to the pulmonary artery, to open. Tin ventricle contracts, and the blood gush through the pulmonary arterj and into the lungs. In the lungs, carbon dioxide is removed from I In blood and oxygen is added. The oxygenated blood then flows through the pulmonary veins to the left side of the heart

11. PUMPING BLOOD THROUGHOUT THE BODY: • Oxygenated blood from the lungs enters and fills the left atrium, The atrium then contracts which squeezes the blood through the mitral/ bicuspid valve into the left ventricle. After blood fills the ventricle, the mitral (bicuspid) valve closes and the aortic valve opens. Blood pours into the aorta and flows through arteries to the body tissues. • REGULATING BLOOD PRESSURE: • Blood in the circulatory system, like water in the pipes of a water system, is always under pressure. Blood pressure refers to the force with which the blood pushes against the walls of the arteries. That force drives blood from the heart to ail parts of the body. Each person's blood pressure reflects the amount of blood in the body, the strength and rate of the heart's contractions, and the elasticity of the arteries. As the heart pumps in cycles, pressure in the arteries rises and falls during systole and diastole. Contraction of the heart produces systolic blood pressure, and relaxation produces diastolic blood pressure. The heart helps regulate blood pressure by producing a hormone that helps the kidneys in eliminating salt from the body. Excess salt may contribute to high blood pressure, which is called hypertension. Hypertension (high blood pressure) can injure the heart, brain, and kidneys.

12. REGULATING THE HEART RATE: • Both sides of the heart pump blood at the same time. As the right ventricle contracts and sends blood to the lungs, the left ventricle contracts and squeezes blood out to the body. The heart's cycle of activity has two periods, systole and diastole. Systole occurs when the ventricles contract, and diastole when they relax. One complete contraction and relaxation of the heart muscle makes up one heartbeat. • The contraction and relaxation of the ventricles also open and lose the heart valves. Closing of the valves produces the "lub-dupp'' sound of the heartbeat, which can be heard with an instrument called stethoscope. As the ventricles contract, the mitral (bicuspid) and ncuspid valves close, causing the first sound (SI) of a heartbeat: immediately after the valves close, pressure in the ventricles forces the idiotic and pulmonary valves to open. After the contraction ends, pressure in the ventricle drops then the aortic and pulmonary valves close, making the second heart sound (S2). The pressure in the atria is then greater than in the ventricles, and so the tricuspid and mitral (bicuspid) valves open and blood begins to fill the ventricles again. SI is louder and longer, while S2 is softer and sharper.

13. CONTROL OF THE HEART RATE • The autonomic nervous system controls the heart rate. Special cells send electrical impulses (nerve signals) through the heart, causing it to contract and relax rhythmically. The impulse begins in a small bundle of muscle fibres called the sinoatrial node, or S-A node. The Sino-atrial (S-A) node is usually called the pacemaker of the heart as it sets the pace of the heartbeat and it sends out rhythmic signals. The S-A node lies in the right atrium near where the superior vena cava enters the heart (Figure 12.7). The S-A node sends impulses along certain pathways, causing the atria to contract when the electrical signal reaches them. The impulse then arrives at another node, called lli«s atrioventricular node, or A-V node. The A-V node lies between the atria and ventricles. It delays the nerve signal briefly, allowing (lis ventricles enough time to fill with blood. As the impulse continues, the ventricles contract.

14. The nerves of the autonomic nervous system control the S-A and A-V nodes. Stimulation of those nerves can quicken or slow the heartbeat. When the body needs more blood, as during vigorous exercise, the nervous system stimulates the S-A node, which increase', the rate of its impulses. The impulses keep the heart chambers contracting at a faster speed. • A person's size largely determines a person's resting heart rate, The bigger a person is, the slower the heart rate. A newborn baby'a heart beats about 120 times per minute. The typical rate for adults is 72 beats per minute. But doctors consider resting rates from 60 to 100 beats per minute within the normal range. Sports/Aerobic training enlarges the heart and slows the heartbeat. Many well-trained athletes/ sportspersons have resting rates from 40 to 60 beats per minute even less than 40 beats per minute too

15. BLOOD VESSELS • The blood vessels form a branching network of about 97,000 kilometers. They are divided into the following three types: • Arteries carry blood from the heart. • Capillaries connect the arteries and veins. • Veins carry blood to the heart. • Blood leaves the left side of the heart through the aorta. This vessel is the largest artery in the body. Several major arteries branch off the aorta. These arteries, in turn, divide into smaller and smaller vessels. Finally, the smallest arteries empty into the tiny capillaries. Through the thin walls of the capillaries, food and oxygen in the blood are exchanged for carbon dioxide and other wastes from individual cells. • From the capillaries, the blood enters small veins, which join larger and larger veins. Finally, the blood enters the right side of the heart through the superior vena cava and inferior vena cava, the body's two largest veins. The right side of the heart then pumps the blood through the pulmonary arteries to the capillaries surrounding the air sacs in the lungs. The blood returns from the lungs to the left side of the heart through four pulmonary veins. The left side of the heart then pumps the blood out through the arota, and the blood’s journey begins once more.

16. ARTERY • Artery is the tube or blood vessel through which blood is pumped away from the heart to the different parts of the body. The blood Carried by most arteries is bright red because it has picked up oxygen while passing through the lungs. However, the blood that flows through the arteries connecting the right side of the heart with the lungs has not yet picked up oxygen. This blood has a brownish color. If an artery is cut, blood gushes out in a series of spurts timed with the heartbeats. • Veins differ from arteries because they carry the blood bail in heart instead of away from it. If a vein is cut, blood flows from in an even stream. • When a large blood vessel has been cut by accident, the differencein the colour and flow of the blood from the vessel makes it possibleto tell whether an artery or a vein has been injured. • The walls of arteries are made up of three layers (Figure I2.9). The outer layer consists of elastic tissue, and the middle layer is muscle.The inner layer, or lining, of the arteries is made of thin, smooth edit of the same kind that line the other blood vessels and the heart, Each time the heart beats, the elastic walls of the arteries swell to make room for the blood pushed into them. Then their muscular tissues slowly contract again. This squeezes the blood farther along the length of the arteries and toward the capillaries. In this way, the arteries do a considerable share of the work that keeps the blood circulating through the body. If the arteries had rigid instead of elastic walls, the he-nil would have to pump all the blood without the arteries' assistance. Al a result, the heart would work much harder than it does

17. MAIN ARTERIES • The aorta is the largest artery,which is directly connected with a chamber of the heart (See Gigure 12.2). The heart pumps oxygenated blood (blood carrying oxygen) through the aorta and its many branches hi nearly all parts of the body. Two small but important branches of Mit' norta are the coronary arteries. They supply the blood by which the ppiirl muscle itself is nourished. The right and left carotid arteries carry Blond to the two sides of the head and neck. Blood flows through the Might and left subclavian arteries to the shoulders and arms. Numerous jpllicr branches of the aorta furnish (Provide) blood to the internal ■ruans. In the abdominal region the aorta divides into two large Itiiinches, the right and left iliac arteries. These arteries have branches (lint supply the organs located in the pelvis. The iliac arteries then Continue downward into the legs, where they become known as the temoral arteries. • After the arterial blood has passed through the body and has picked up impurities, the veins collect it and return it to another chamber of Hie heart. The heart pumps this blood through the pulmonary artery to the lungs. Here the blood takes on a new store of oxygen. It then returns to the heart, where it is once more pumped out through the aorta.

18. CAPILLARY • Capillary is the smallest blood vessel in the body having thin walls, which can be seen only under the microscope. Most capillaries are so small that only one blood cell can pass through them at a time. Capillaries connect the smallest arteries with the smallest veins. They make up a network of blood vessels throughout the body. The largest capillaries are in the bone marrow and skin. The smallest are in the brain and lining of the intestine. • Foods, which are carried in the blood stream, are able to pass through thin walls of capillaries into the tissues. Waste materials from the tissues also pass into the blood stream through capillary walls. In the capillaries of the lungs, oxygen goes through the walls into the blood and carbon dioxide goes out. Other waste products pass through tiny capillary walls into the kidneys, intestine and skin.

19. VEIN • Vein is a blood vessel, which carries blood toward the heart. Most veins return blood to the heart after it has given out nourishment to the tissues and taken up waste products. Blood in veins is called venous blood. The blood returning from the body cells has lost much oxygen, and is dull, brownish-red. It circulates through the right of the heart and then goes to the lungs. Here it gives off its \ carbon dioxide and takes on a new supply of oxygen. Bright red b from the lungs returns to the heart through the pulmonary veins, it begins its trip through the body. • The veins begin at the capillaries. At first they are very tiny, are called venules. Small veins join to form larger ones. Final I the venous blood of the body pours into two very large veins that into the heart. One of these, the superior vena cava, carries b from the head and arms. The other, the inferior vena cava, carri from the trunk and legs. • Veins, like arteries, have walls made of three layers. But the v walls are thinner, less elastic, and less muscular than those of arteries. The lining membrane of the veins is the intima. In many the larger veins, the intima has folds that serve as valves. These fol lie against the wall when the blood is flowing freely. Several thi can cause the blood to slow down or stop—the weight of blood abo the vessel, effects of gravity, pressure on a vein, or low fluid pressu Then the valves open out, and stop the blood from flowing backward The valves are usually just above the place where two veins join. Then are no valves in (lie veins of the abdomen, brain, and lungs, or in tlfl smaller veins.

20. CARDIAC CYCLE • The cardiac cycle consists of one complete cycle of contraction and relaxation. Its major events, in order of occurrence, are: atrial systole, atrial diastole, ventricular systole, ventricular diastole, and a passive or inactive period. (Quiescent Period). • Cardiac Cycle Phases: The following are the phases of cardiac cycle: • The cardiac cycle begins with the passive/inactive period in which the heart is at rest, blood is flowing into the atria, and AV valves are open, allowing blood to passively flow through to the ventricles. • The SA nodes fire, and resulted in atrial systole. • Is volumetric contraction of the ventricles occurs after the ventricles depolarize. The AV valves close as ventricular blood suddenly rush back against the cusps. This phase is called is volumetric because the ventricles do not yet eject blood and there is no change in their volume even though they are contracting. • Next comes ventricular ejection, in which the amount known as stroke volume passes into the major vessels on top of the heat. • Is volumetric relaxation and ventricular filling follow, completing one cardiac cycle.

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