HUMAN CIRCULATORY SYSTEM

CIRCULATORY SYSTEM:

The heart is one of the most important organs in the human body. It is located in the center of the chest cavity usually towards slightly left. It composed of cardiac muscles which pumps blood throughout the body. It is roughly the size of a large fist and weighs between 250-350 grams.

This diagram shows the human circulatoory system

This diagram shows the human circulatoory system

A wall of muscle called the septum separates the two sides of the heart. Each side is further divided into two chambers. The upper chamber is known as auricle and the lower chamber is known as ventricle.

THIS DIAGRAM SHOWS THE CHAMBERS OF THE HEART

THIS DIAGRAM SHOWS THE CHAMBERS OF THE HEART

In this way the heart has four chambers. Two upper chambers known as known as left and right auricle; and two lower chambers known as left and right ventricle.

The right auricle and right ventricle make up the right heart and the left auricle and the left ventricle make up the left heart.

The right auricle opens into the right ventricle through the right artio-venticular valve which is also known as tricuspid valve. It only allows the blood to flow from the right auricle to right ventricle. Similarly, the left auricle opens into left ventricle through the left autrio ventricular valve which is also known as Bicuspid valve. Bicuspid valve is smaller than Tricuspid valve but has thicker walls. Both valves allow the blood to flow from auricle to ventricle but not in the reverse direction.

THIS DIAGRAM SHOWS THE MAIN VALVES OF THE HEART

THIS DIAGRAM SHOWS THE MAIN VALVES OF THE HEART

THIS DIAGRAM SHOWS THE WORKING OF THE HEART

THIS DIAGRAM SHOWS THE WORKING OF THE HEART

The heart is covered by a double walled sac known as pericardium. The outer pericardium layer (known as the parietal pericardium) and the inner pericardium lay (known as the serous pericardium) protect the heart. A pericardial fluid runs between the both layers. This pericardial fluid lubricates the heart during contraction and movement of lungs during respiration.

THIS PICTURE SHOWS THE PERICARDIUM SAC IN HEART

THIS PICTURE SHOWS THE PERICARDIUM SAC IN HEART

THE HEART WALL:
It is made up of three layers:

THIS DIAGRAM SHOWS THE LAYERS OF HEART WALL

THIS DIAGRAM SHOWS THE LAYERS OF HEART WALL

1. EPICARDIUM: it is the outermost layer. It forms the inner wall of the pericardium. Epicardium is a thin layer of serous layer that helps to lubricate and protect the outer side of the heart.
2. MYOCARDIUM: it is the middle thicker layer. It contains the muscles which contract. In other words, it is responsible for pumping blood.
3. ENDOCARDIUM: it is the innermost smooth layer and it is responsible for keeping blood from sticking to inside of the heart and forming potentially deadly blood clots.

FUNCTION OF HEART:
The main function of heart is to pump blood into the body. The pumping of the heart is called the cardiac cycle which occurs about 72 times per minute.

WORKING OF HEART:
Deoxygenated blood returning from the body first enters into the right auricle of the heart from the superior and inferior vena cava and this deoxygenated blood is pumped through the tricuspid valve into the right ventricle.

From right ventricle, the blood is pumped into the lungs through the pulmonary artery.

THIS DIAGRAM SHOWS THE WORKING OF HEART

THIS DIAGRAM SHOWS THE WORKING OF HEART

IMPORTANT POINT TO REMEMBER:
It is the only artery which carries deoxygenated blood.

The amount of deoxygenated blood is controlled by the valve (known as the pulmonary semilunar valve) which is present at the starting point of this artery.

THIS DIAGRAM SHOWS THE PULMONARY WALL IN HEART

THIS DIAGRAM SHOWS THE PULMONARY WALL IN HEART

In the lungs, the carbon-dioxide from the blood give out to the alveoli of lungs and oxygen is taken in from the alveoli of lungs.

Now the left auricle receives oxygenated blood from the lungs via the pulmonary veins. The left auricle is smaller than the right auricle but it has thicker walls. Now blood moves from the left auricle to the left ventricle through Bicuspid valve (left atrio ventricular valve). Now oxygenated blood is pumped out throughout the body via Aorta, the largest artery in the body.

SUMMARY:
The heart is a muscular organ situated in our chest cavity between the both lungs. It is protected by double membrane known as pericardium. A pericardial fluid runs between the both layers which lubricate the heart during the contraction and movement of lungs.

CHAMBERS OF HEART:

THIS DIAGRAM SHOWS THE FOUR CHAMBERS OF HEART

THIS DIAGRAM SHOWS THE FOUR CHAMBERS OF HEART

1. THE RIGHT AURICLE:
It receives deoxygenated blood from superior and inferior vena cava and pumps it to the right ventricle through tricuspid valve.

2. THE RIGHT VENTRICLE:
It pumps the blood to the lungs via pulmonary artery.

3. THE LEFT AURICLE:
It receives oxygenated blood from the lungs and pumps it to the left ventricle through Bicuspid valve.

4. THE LEFT VENTRICLE:
It pumps this oxygen rich blood to the rest of the body. The left ventricle is the strongest chamber of the heart. The left ventricle’s vigorous contraction creates our blood pressure.

The coronary arteries run along the surface of heart and it provides oxygen rich blood to the heart muscles.

BLOOD PRESSURE:
It is the force of blood pushing against the walls of the arteries. Each time, the heart beats (about 60-70 times a minute at rest); it pumps out the blood into the arteries.

• Our blood pressure is at its highest when the heart beats, pumping the blood. This is called systolic pressure.
• When the heart is at rest between the beats, our blood pressure falls. This is the diastolic pressure.
• Blood pressure is always given as these two numbers, the systolic and diastolic pressures. Both are important usually they are written one above the other such as 120/80. The top number is systolic and the bottom number is diastolic.
• Blood pressure changes during the day. It is the lowest during sleep and the highest during exercise. It is measured by sphygmomanometer.

E.C.G.:-
An electrocardiogram is a test that checks for problems with the electrical activity of your heart. An E.C.G. translates the heart’s electrical activity into line tracing on paper. The spikes and dips in the line tracings are called wave. It is done to check the heart’s electrical cavity and also for the checking of any heart disease.

THIS DIAGRAM SHOWS THE E.C.G. OF HEART

THIS DIAGRAM SHOWS THE E.C.G. OF HEART

ARTERIES:
All blood vessels which carry blood from the heart to the various body organs are called arteries. All the arteries carry oxygenated blood except pulmonary artery which carries deoxygenated blood. Arteries have thick elastic muscular walls. Valves are absent. Blood flows under high pressure. These vessels have narrow lumen.

VEINS:
The blood vessels which carry blood from various body organs to the heart are known as veins. All the veins carry deoxygenated blood except pulmonary vein which carries oxygenated blood. Veins have thin, non-elastic walls. Valves are present to prevent the backward flow of blood. Blood flows under low pressure. These vessels have large lumen.

Arteries are the main blood vessels which carries oxygenated blood from the heart into arterioles branches.

THIS DIAGRAM SHOWS THE ARTERIOLES BRANCHES

THIS DIAGRAM SHOWS THE ARTERIOLES BRANCHES

ARTERIOLES:
Arterioles are the tiny branches of arteries. It transports blood from arteries to capillaries. Arterioles are the main regulators of blood flow and pressure. These are also under the control of the sympathetic nervous system.

CAPILLARIES:
Each arteriole is further branched into extremely narrow, tiny vessels approximately 5-20 micro-meters. There are networks of capillaries in most of the organ s and tissues of the body.
These capillaries are supplied with blood by arterioles and drained by venules. Capillary walls are so thin and permeable which easily permits exchanges of material between the content of the capillary and the surrounding tissue.
It supplies oxygen and food to the tissues and take out carbon-dioxide and the other waste material from the tissue.

VENULES:
Venules are minute vessels that drain blood from the capillaries into the vein.

VEIN:
Vein are the main blood vessels which carry deoxygenated blood from the body to the heart.

FUNCTION OF BLOOD:
1. TRANSPORTATION:
1) Blood transports nutrients and materials to and from the cells and molecules that make up our body.
2) It transports oxygen from the lung to all the cells of our body and then collects carbon-dioxide from the cells and delivers it to the lungs.
3) It collects metabolic waste up and down the body and takes them to the kidney for excretion.
4) Blood also has to carry out the transportation of hormones produced by the endocrine glands.

2. PROTECTION:
1) The white blood cells found in the blood, play an important role to protect the body from the threat of infection and disease causing it under bacteria. These white blood cells protect body organs by producing antibodies and proteins which are capable of fighting off and killing the germs and virus.
2) The blood platelets (present in the blood) make blood clot during an injury. Blood clotting prevent loss of blood from the body.

3. REGULATION:
1) It regulates the body temperature.
2) It controls the ion concentrations in the body.
3) It controls the blood pressure and restricts it under a normal range.

BLOOD CLOTTING:
It is the body’s way of stopping injured blood vessels from bleeding. Too much clotting can block the blood vessels that are not bleeding. But when the clotting is poor, even a slight injury to a blood vessel may lead to severe blood loss.

Blood clotting involves three main processes:
1) Narrowing of the blood vessels.
2) Activity of the cell that helps in blood clotting (platelets).
3) Activity of proteins found in blood that work with platelets to help the blood clot.

An injured blood constricts so that blood flows out more slowly and clotting can start. As soon as a blood vessel wall is damaged a series of reactions activates platelets so that they stick to the injured area. A protein is produced by the cells of the vessel wall. The protein collagen and thrombin act at the site of the injury to induce platelets stick together.as platelets accumulate at the site, they form a mesh that plugs the injury. The platelets change shape from round to spiny and they release proteins and other substances that entrap more platelets and clotting proteins in the enlarging plug that becomes a blood clot. The blood clotting factor thrombin converts fibrinogen (which is normally dissolved in blood) into long strands of fibrin. The fibrin strands add bulk to the developing clot and help hold it in place to keep the vessel wall plugged.

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