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Introduction |
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Materials formed in one part of the body have to be taken up to other parts where they are needed or to be got rid of. This is an essential requirement of most animals. This function is performed by the body fluids. |
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Functions of Circulatory System |
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The functions performed by the circulatory system in all animals are, Transport of nutrients like glucose, amino acids, vitamins, minerals. |
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Types of Circulatory System |
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In the closed type of circulatory system, the blood remains inside the blood vessels and does not come out. The blood flows from arteries to veins through small blood vessels called capillaries. The closed type of circulatory system occurs in most of the Annelids, Cephalopods and Vertebrates including man. |
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Open Circulation System in Cockroach |
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The heart of the cockroach is elongated, thick, muscular, tubular and 13-chambered. It lies in the pericardial sinus of the haemocoel. Each chamber of the heart receives oxygenated blood from the dorsal sinus through one pair of slit like openings called ostia. The heart contracts in a postero anterior direction and the blood also flows posteroanteriorly. The alary muscles are responsible for the circulation of blood. The first chamber leads into an aorta, which opens in the head sinuses which are connected to the pericardial sinus through perineural and perivisceral sinuses. |
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Closed Circulatory System in Humans |
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The organisms have a thick body wall to prevent the evaporation of water, so exchange of materials between the body cells and the environment by diffusion is not possible. |
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Components of Circulatory System |
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These are hollow, tubular vessels which conduct the blood from the heart to the tissues and from the tissues to the heart. There are 3 type of blood vessels, arteries, capillaries and veins. |
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Components of Circulatory System (Contd.) |
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The WBCs are larger in size than the RBCs but much lesser in number. They are different from the erythrocytes in the following aspects. |
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Heart - Shape and Position |
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It is a thick muscular, reddish brown, conical organ present in the mediastinal space of thoracic cavity between 2 pleura enclosing the lungs. Its broader side is called base and it is forward and upward while the pointed side called apex is backward and downward. It is 9 cm broad and 12 cm long and about 300 gms in weight. |
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Heart - Cardiac Cycle |
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This phase involves the contraction of the 2 auricles, pushing the blood into the respective ventricles. There is no back flow of blood due to the presence of the bicuspid and the tricuspid valves. The atrial systole takes 0.1 second. This is followed by the atrial diastole when both the auricles relax simultaneously. This is about 0.7 seconds. |
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Circulation of Blood Through the Mammalian Heart |
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The aorta or the great artery arising from the left ventricle takes the oxygenated blood to the body organs through a number of arteries. From these organs, the deoxygenated blood is collected by the superior and inferior vena cava and brought back to the right auricle. The right auricle pumps the deoxygenated blood into the right ventricle. |
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Nervous Regulation |
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The heart is regulated to a large extent through the central nervous system. The heart nerve branches from the vagus nerve from the medulla oblongata and the sympathetic nerve fibres from the spinal cord. |
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Rate of Heart Beat |
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Pulse is defined as the wave of distension and recoiling felt in the radial artery due to the contraction of the left ventricle which force about 70-90 ml of blood into the already full aorta. |
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Blood Pressure |
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The pressure existing in the arteries is called arterial blood pressure. The blood pressure is high during systole and is called systolic blood pressure. It is low during diastole and it is called diastolic blood pressure. The difference between these two pressures is called pulse pressure. |
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Blood Related Disorders |
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Persistently having a resting blood pressure of more than 120 / 80 mm Hg is called hypertension. In such a condition, the heart has to work harder to pump the required amount of blood to the various organs through narrowed arteries. |
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ECG - Electrocardiography |
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ECG is a graphic display or recording of the electrical variations produced by heart muscle during a cardiac cycle. The activity of the heart create an electrical field which is conducted through the surrounding body tissues to the surface of the body. |
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Lymphatic System |
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The lymphatic system is an accessory circulatory system which transports lymph, a fluid similar to plasma from the intercellular spaces of tissues to the blood. It is a one way route for the movement of interstitial fluid to blood. The lymphatic system can carry proteins and large particle matter from the tissue spaces into the blood. |
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Immunity and Immune System |
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Animals encounter many potentially dangerous microbes in air, water and food. So they have involved defense mechanisms against the disease causing germs Immunity is a defense mechanism without which we will fall a prey to all parasitic microorganisms. |
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Internal Defence |
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Second line of defence or body's internal defence is carried out by leucocytes, macrophages, inflammatory reactions, fever, interferons and natural killer cells. These operate together to check the damage to the body by the pathogens. |
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Specific Defence Mechanism |
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This mechanism provides protection against specific foreign materials and is often called the immune system. This system forms the third line of body's defence against microbes and harmful molecules. The most important characteristic of the immune system is that its cells have an ability to recognise body's own cells and macromolecules, from those which are foreign invaders or nonself. |
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Cells of the Immune System |
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Lymphocytes are the main cells of the immune system. They arise from stem cells present in the liver in the foetus and in the bone marrow in the adult. |
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Humoral Immune System |
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The plasma membrane of each B cell should be sensitised by contact with a specific antigen for the release of antibodies. The plasma cells do not migrate to the site of infection but act through the lymph. So they form the humoral immune system. The B lymphocytes are short lived and are replaced every few days from the bone marrow. |
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Cell Mediated Immune System |
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The cellular immune response is given by T - cells. There are separate T - cells for each type of antigen that invades the body. The life span of the T - cells is 4-5 years or even longer. There are four types of T - cells. |
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Immunity |
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Immunity is the ability of an organism to recognise the foreign material or chemicals that enter the body and to mobilise the cells and cell products to quickly remove the foreign material. |
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Types of Immunity |
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The type of immunity inherited by the organism from the parents and protects it from birth throughout life is known as innate or inborn immunity. |
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Summary |
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Advanced animals carry blood as the circulating fluid and a circulatory system with the heart and blood vessels to conduct the blood. In invertebrates such as insects, the blood pumped by the heart comes out from blood vessels and flows through open spaces and sinuses. This is called open system. Vertebrates possess a closed system of circulation. |
