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MHT-CET : Biology Entrance Exam

MHT - CET : Biology - Circulation Page 1

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Types of Blood Vascular System


  • There is present an organic transporting system in the organisms which is called 'Circulatory System'.
  • 'Lymph' and 'blood' are the two liquid media through which circulatory system works.
  • The blood continuously flows from the heart to the other organs and from there back to the heart. This flow is described as 'circulation'.
  • There are two main types of circulatory system namely 'open' and 'closed'.
  • Closed Circulation: The circulation of blood in which blood flows through closed blood vessels is called 'closed circulation'. Here the blood does not come in direct contact with any open body cavity or space. It is found in most of annelids like earthworm and in all vertebrates.
  • The flow of blood in a closed circulatory system begins from heart. The heart pumps out the blood into arteries. Arteries give rise to arterial capillaries which further unite with each other to form vein capillaries. The vein capillaries unite to form veins which ultimately carry the blood back to the heart.
  • Significance of Closed Circulation:
    1. More efficient system which regulates fast flow of blood.
    2. It maintains proper pressure and unidirectional flow of blood.
    3. It prevents wastage of blood and maintains necessary blood volume.
    4. It promotes efficient and speedy distribution and exchange of metabolic products within the body.
  • Open Circulation: In this system, the blood comes out in the open spaces in body called lacunae and sinuses. It is found in leeches (annelids), arthropods like prawns, crabs, insects, spiders. Most of the molluscs except cephalopods show open circulatory system.
  • In prawns, the heart pumps out only oxygenated blood thus the heart is arterial. In cockroach, the heart is elongated, thick, tubular and 13 chambered.



Structure and Pumping Action of Human Heart


  • Position: Heart is a muscular, thick, reddish brown organ present in medistinal space present in thoracic cavity between two pleura. It is conical in shape having a size of one's closed fist.
  • The heart is protected by a sac called pericardium which is double layered. Pericardial fluid is present between the two layers which acts as a lubricant and absorbs the shocks to protect heart.
  • Internally, the heart comprises of four chambers, namely, two auricles and two ventricles. Both auricles are separated by interauricular septum which prevents mixing of pure and impure blood.
  • Right Auricle: Precaval (superior vena cava) and Postcaval (inferior vena cava) are the main veins which bring deoxygenated blood to the right auricle. Right auricle opens in the right ventricle through right auriculoventricular aperture which is guarded by tricuspid valve.
    It prevents the back flow of blood.
  • Chordae tendinae are the whitish, elastic threads which extend from tricuspid and bicuspid valve to the walls of respective ventricles. They do not allow the valves to open upwards when the ventricles contract and thus they prevent the back flow of the blood.
  • Left Auricle: It receives pure blood from lungs brought by four pulmonary veins. The left auricle opens in left ventricle by presence of an aperture guarded by bicuspid valve which is also called mitral valve. It prevents the back flow of blood with the help of chordae tendinae.
  • Ventricles are thick walled as compared to auricles. The left ventricle has much thicker wall because it pushes the pure blood to all the body parts. The ventricles are separated by interventricular septum.
  • Right Ventricle: Pulmonary aorta carries impure blood from right ventricle to the lungs for purification. A semilunar valve is present at the base of pulmonary aorta which prevents the back flow of blood.
  • Cardiac Cycle is the period between end of one heart beat to the end of next beat. It is formed of three phases, namely, atrial systole which takes 0.1 second, ventricular systole which takes about 0.3 seconds and complete cardiac diastole which takes about 0.4 seconds. Thus, cardiac cycle is completed in 0.8 seconds.
  • The auriculoventricular valves close rapidly to prevent the back flow of blood from ventricles to auricles. This closing of valves at the start of ventricular systole produces first heart sound 'Lub' which is also called systolic sound. Similarly, the rapid closing of semilunar valves at the beginning of ventricular diastole produces second heart sound called 'dup' which is also called diastolic sound.
  • Stethoscope is an instrument used to hear the heart sounds. The receiver of stethoscope is placed on the left side of chest. Any change in the nature of heart sounds due to defective valves is called murmur.
  • In mammalian heart, the blood passes twice through the heart to supply once to the body. It involves systemic circulation and pulmonary circulation.
  • In systemic circulation, blood completes its circulation from left ventricle to right auricle through body organs.
  • In pulmonary circulation, blood completes its circulation from right ventricle to left auricle through the lungs.
  • The wave of contraction which starts in the aorta travels down to the wall of the arteries and is called a pulse. The pulse rate in a normal adult person is 72 per min. It may be more in children.
  • Heart beat is the rhythmic contraction and relaxation of the heart to pump out and receive blood to and from the body parts. (Initiation of heart beat is under the control of certain nodal tissues.)
  • S. A. Node: i.e., Sinuauricular node is present in the right wall of right auricle below the opening of superior vena cava. It is called pacemaker because it is the first to originate the cardiac impulses.
  • A. V. Node: i.e., Atrioventricular node is present in the right auricle near the junction of interauricular and interventricular septum.
    It produces the cardiac impulses which are conducted to the muscles of ventricles through bundle of His and Purkinje fibres.



Arterial Blood Pressure


  • The pressure exerted by blood on the wall of artery when the blood flows through it is called 'arterial blood pressure'.
  • The heart is made up of cardiac muscles which carry out the contraction and relaxation at a regular interval.
  • The contraction of the muscle of the heart is called 'systole', while its relaxation is called 'diastole'.
  • During systolic period, the myocardial fibres undergo maximum tightening and shortening. The blood pressure occurring during the contraction of the heart is called 'systolic blood pressure' which rises during excitement and falls during sleep.
  • Normal systolic blood pressure is 120 mm Hg.
  • The blood pressure occurring during relaxation of the heart is called 'diastolic blood pressure'.
  • During diastolic blood pressure, the muscle fibres of the heart lengthen followed by its dilation and the cavities of the heart get filled with blood.
  • The normal blood pressure during diastole is about 80 mm Hg.
  • The difference between the systolic and diastolic pressures is called pulse pressure which is 40 mm Hg.
  • There are various factors which affect the arterial blood pressure such as:
    1. Age: Blood pressure increases with the increased age.
    2. Elasticity of Blood Vessels: Blood pressure is inversely proportional to the elasticity of the blood vessels. Greater the elasticity of blood vessels, lesser is the blood pressure.
    3. Cardiac Output: The blood pumped out from heart is called cardiac output. If cardiac output increases, there is increase in blood pressure.
    4. Total Peripheral Resistance: The resistance offered by the walls of blood vessels on blood affects the blood pressure. Constriction of blood vessels increases the blood pressure.
  • The blood pressure is measured by an instrument called 'Sphygmomanometer'.
  • Hypertension (High Blood Pressure): An abnormal increase in blood pressure than the normal blood pressure is called hypertension or high blood pressure.
  • Causes of Hypertension:
    1. High consumption of salts.
    2. Inelasticity of arteries
    3. Tension, emotional stress
    4. Deposition of fatty substances on the inner walls of arteries.
  • Ill Effects of Hypertension:
    1. People having high blood pressure are susceptible to stroke, heart attacks.
    2. Kidney malfunctioning.
  • Hypotension (Low Blood Pressure): An abnormal decrease in blood pressure than the normal blood pressure is called hypotension or low blood pressure.
  • The maximum and minimum blood pressure of a person suffering from hypotension are less than the normal values, i.e., 100 / 50 mm Hg.
  • Causes of Hypotension:
    1. Disorders of nervous system.
    2. Disorders of endocrine system.


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