Cardiovascular Physiology PDF

Cardiovascular physiology Cardiovascular system (CVS )consists of:  Heart : Is the pump which circulates the blood round the body.  Blood vessels: Flow blood from the heart to cells & back to the heart. Functions of Cardiovascular system: I -primary main functions of the heart:  Acts as...

Cardiovascular physiology Cardiovascular system (CVS )consists of:  Heart : Is the pump which circulates the blood round the body.  Blood vessels: Flow blood from the heart to cells & back to the heart. Functions of Cardiovascular system: I -primary main functions of the heart:  Acts as a muscular pump: In order to maintain adequate level of blood flow throughout CVS by pumping blood under pressure into vascular system.  responsible for the mass movement of fluid in body. II -Secondary functions: I – Transportation:  delivers O2 to tissues & brings back CO2 to lungs.  carries absorbed digestion products to liver & tissues.  Carries metabolic wastes to kidneys to be excreted. Distribution of body fluid. II-Regulation:  Hormonal: carries hormones to target tissues to produce their effects.  Immune: carries antibodies, leukocytes(WBC),cytokines& complement to aid body defense mechanism against pathogens.  Protection: carries platelets & clotting factors to aid protection of body in blood clotting mechanism.  Temperature: helps in regulation of body temperature by diverting blood to cool or warm the body  Anatomy of the heart  Consists of 2 separated pumps that maintain unidirectional flow of  blood: the left & right hearts  Lt heart pumps oxygenated blood from the lung to the tissues- Systemic circulation  Rt heart pumps deoxygenated blood which has returned from the tissues to the lungs- Pulmonary circulation  The heart contains 4 chambers, each pump contains 2 chambers: an atrium & a ventricle. Chambers of the heart 2 Atria: The upper two chambers of the heart (atria) are thin-walled chambers, are divided by a wall-like structure called the interatrial septum. receive blood returning back to the heart. 2 Ventricles: The lower two chambers of the heart (ventricles), are thicker, muscular walls. Pump blood from heart. Each has same capacity & pumps same volume of blood in a given period of time. Atria & ventricles are separated into 2 functional units by a sheet of fibrous connective tissue, which gives attachment to the valves.  Valves of the heart are structures which allow the blood to flow in one direction only, they do not contain any muscle tissue. Each ventricle has a valve at its inlet & valve at its outlet:  The inlet valves are termed= atrioventricular (AV)valves, allow blood to flow from atria into ventricles.  on the left side it is known as the Mitral valve.  On right side it is known as the Tricuspid valve.  The outlet valves are known as = the Semilunar valves. At origin of pulmonary artery & aorta. The valve on left side of the heart is known as aortic valve, on the right side it is also known as pulmonary valve. Two of the valves are in between the atria and the ventricles called atrioventricular valves. The other two are the semilunar valves, placed at the opening of the blood vessels arising from the ventricles, i.e. systemic aorta and pulmonary artery. The valves of the heart permit the flow of blood through the heart in only one Layers of Wall of the heart 1. Pericardium: outer covering of the heart. made up of two layers These two layers are separated by a space called pericardial cavity which contains a thin film of fluid. 2. Myocardium: is the middle layer of the wall of the heart, formed by cardiac muscle fibers. it is responsible for the pumping action of the heart. is formed by three types of cardiac muscle fibers: i. muscle Fibers which Form the Contractile Unit of the Heart: These cardiac muscle fibers are striated fibers , similar to the skeletal muscles in structure. But, unlike the skeletal muscle fibers, (involuntary in nature. The cardiac muscle fiber is covered by sarcolemma. has a centrally placed nucleus. The myofibrils are embedded in the sarcoplasm. The sarcomere of the cardiac muscle has muscle proteins namely, actin, myosin, troponin and tropomyosin. The cardiac muscle also have sarcotubular system like that of skeletal muscle. The important difference between skeletal muscle and cardiac muscle is that the cardiac muscle fiber is branched. Intercalated disk is a tough double membranous structure situated at the junction between the branches of neighboring cardiac muscle fibers. - form adherens junctions which play an important role in contraction of the muscle as a single unit. Syncytium The structure of cardiac muscle is considered as a syncytium. the adjacent muscle fibers fuse together to form gap junctions which facilitates the rapid conduction of electrical activity from one fiber to another. This makes the cardiac muscle fibers act like a single unit referred as physiological syncytium. The syncytium in human heart has two portions, atrial syncytium and ventricular syncytium which are connected by atrioventricular ring. ii.Muscle Fibers which Form the Pacemaker: Some of the muscle fibers of the heart are modified into a specialized structure known as pacemaker. The muscle fibers forming pacemaker have less striation. Pacemaker: is structure in the heart that generates the impulses for heart beat. It is formed by the pacemaker cells called P cells. Sinoatrial(SA) node forms the pacemaker in human heart. iii.Muscle Fibers which Form the Conductive System The conductive system of the heart is formed by the modified cardiac muscle fibers. The impulses from SA node are transmitted to the atria directly, the impulses are transmitted to the ventricles, through various components of conducting system 3. ENDOCARDIUM is the inner layer of the heart wall. wall. It is a thin, smooth and glistening membrane. It is formed by a single layer of endothelial cells lining the inner surface of the heart. Endocardium continues as endothelium of the blood vessels. BLOOD VESSELS The vessels of circulatory system divided into arterial and venous systems. Arterial System: comprises the aorta, arteries and arterioles The arterioles are continued as capillaries which are small, thin walled vessels having a (5 to 8 μ. ) The capillaries are functionally very important because, the exchange of materials between the blood and the tissues occurs through these vessels. VENOUS SYSTEM From the capillaries venous system starts and it includes the venules, veins and vena cavae. The venules are smaller vessels with thin muscular wall than the arterioles..  Pulmonary and Systemic Circulations--DIVISIONS OF CIRCULATION Blood flows through two divisions of circulating system: 1.Systemic circulation 2.Pulmonary circulation. Arteries include the right and left coronary arteries, marginal arteries, anterior and posterior interventricular arteries, and the circumflex artery. Pulmonary circulation: blood pumped from RV through lungs & back to the heart Systemic circulation: oxygen- rich blood pumped by the LV to all organ systems to supply nutrients. Rate of blood flow through systemic circulation= flow rate through pulmonary circulation.  Properties of Cardiac Muscle Physiology of cardiac muscle: The heart is composed of 2 major types of cardiac muscle: I.Contractile tissue (compsed of 2 types of muscles: atrial&ventricular muscles) contract when stimulated, in same way as skeletal muscles except for longer duration. II. Autorhythmic (or automatic ) tissue: specialized or modified cardiac tissues, that contract only feebly as they contain few contractile fibrils. - self stimulating with/out any external stimulation. - initiate repetitive action potentials, that exhibit ᾿᾿Pacemaker᾽᾿ potentials, rhythmicity & varying rates of conduction. - provide an excitatory system for the heart.  EXCITABILITY: is defined as the ability of a living tissue to give response to a stimulus. In all the tissues, the initial response to a stimulus is the electrical activity in the form of action potential. It is followed by mechanical activity in the form of contraction, secretion.  RHYTHMICITY is the ability of a tissue to produce its own impulses regularly. It is more appropriately named as autorhythmicity. It is also called self excitation. The property of rhythmicity is present in all the tissues of the heart. However, heart has a specialized excitatory structure from which the discharge of impulses is rapid. This specialized structure is called pacemaker. From this, the impulses spread to other parts through the specialized conductive system.   PACEMAKER: Though the SA node is the pacemaker in mammalian heart.  Contractility is ability of the tissue to shorten in length (contraction) after receiving a stimulus. Various factors affect the contractile properties of the cardiac muscle. STAIRCASE PHENOMENON When the ventricle is stimulated successively without changing the strength, the force of contraction increases gradually for the first few contractions & then it remains same. Gradual increase in the force of contraction is called staircase.  SUMMATION OF SUBLIMINAL STIMULI When a stimulus with a subliminal strength is applied, the heart does not show any response. When few stimuli with same subliminal strength are applied in succession, the heart shows response by contraction. It is due to the summation of the stimuli. REFRACTORY PERIOD is the period in which the muscle does not show any response to a stimulus. It is of two types: 1.Absolute refractory period Absolute refractory period is the period during which the muscle does not show any response at all, whatever may be the strength of the stimulus. 2.Relative Refractory Period The relative refractory period is the period during which the muscle shows response if the strength of stimulus is increased to maximum. It is the stage at which the muscle is in repolarizing state. Cardiac muscle has a long refractory period compared to that of skeletal muscle. The absolute refractory period extends through out contraction period of cardiac muscle CONDUCTIVITY Human heart has a specialized conductive system through which the impulses from SA node are transmitted to all other parts of the heart CONDUCTIVE SYSTEM IN HUMAN HEART The conductive system of the heart is formed by the modified cardiac muscle fibers. The conductive tissues of the heart are also called the junctional tissues. The conductive system in human heart comprises: 1. AV node 2. Bundle of His 3. Right and left bundle branches 4. Purkinje fibers. Impulse Conduction through the heart  SA node begins the action potential  Stimulus spreads to the AV node  Impulse is delayed at AV node  Impulse then travels through ventricular conducting cells  Then distributed by Purkinje fibers Atrial conducting cells are found in internodal pathways Ventricular conducting cells consist of the AV bundle, bundle branches, and Purkinje fibers. The impulses from SA node are conducted throughout right and left atria. The impulses also reach the AV node via some specialized fibers called internodal fibers. There are three types of internodal fibers, All these fibers from SA node converge on AV node and interdigitate with fibers of Av node. From AV node, the bundle of His arises. It divides into right and left bundle branches which run on either side of the interventricular septum. From each branch of Bundle of His the Purkinje fibers arise and transport electrical signals to ventricular walls. Action potential in a single cardiac muscle fiber occurs in 4 phases: 1. Initial depolarization 2. Initial repolarization 3. A plateau – final depolarization 4. Final repolarization. duration of action potential in cardiac muscle is (0.25 to 0.35 sec). Cardiac cycle & Cardiac output Arterial blood pressure  Cardiac cycle the sequence of coordinated events in heart which are repeated during every heartbeat in a cyclic manner. Each heartbeat consists of 2 major periods- systole & diastole. Systole is contraction of cardiac muscle & diastole is relaxation of cardiac muscle. The events of cardiac cycle are classified into 2 divisions: 1.Atrial events which constitute atrial systole & atrial diastole 2.Ventricular events - constitute ventricular systole&ventricular diastole. Heart sounds are the sounds produced by mechanical activities of heart during each cardiac cycle. Generally, heart sounds are produced by: 1. Flow of blood through the chambers of the heart 2. Contraction of cardiac muscle 3. Closure of valves of the heart. heart sounds are heard by placing ear over the chest or by using a stethoscope or microphone & also recorded graphically. Four heart sounds are produced during each cardiac cycle. The first & second heart sounds= called classical heart sounds. These sounds are more prominent and resemble the spoken words „LUB‟ (or LUBB) and „DUB‟ (or DUP) respectively. These two heart sounds are heard by using the stethoscope. IMPORTANCE OF HEART SOUNDS heart sounds has important diagnostic value in clinical practice because the alteration- indicates cardiac diseases involving the valves of heart. The first heart sound is a long, soft & low pitched sound. It resembles the spoken word „LUBB‟. The duration of this sound is 0.10 to 0.17 second. Its frequency is 25 to 45 cycles/second. The second heart sound is a short, sharp and high pitched sound. It resembles the spoken word „DUBB‟ (or DUP). The duration of the second heart sound is 0.10 to 0.14 seconds. Its frequency is 50 cycles/second. THIRD HEART SOUND The third heart sound is a low pitched. Usually, the third heart sound is inaudible by stethoscope and it can be heard only by using microphone. Third heart sound is a short and low pitched sound. The duration of this sound is 0.07 to 0.10 second. Its frequency is 1 to 6 cycles/second. Third heart sound can be heard by stethoscope in children and athletes. Pathological conditions when third heart sound becomes loud and audible by stethoscope are aortic regurgitation, cardiac failure and cardiomyopathy with dilated ventricles. When the third heart sound is heard by stethoscope the condition is called triple heart sound. FOURTH HEART SOUND Normally is an inaudible sound, audible only in pathological conditions. It is studied only by graphical recording that is by phonocardiography. Fourth heart sound is a short and low pitched sound. The duration of this sound is 0.02 to 0.04 second. And its frequency is 1 to 4 cycles/second. Ventricular stiffness occurs in conditions like ventricular hypertrophy, long standing hypertension & aortic stenosis. To overcome the ventricular stiffness, the atria contract forcefully producing audible fourth heart sound. METHODS OF STUDY OF HEART SOUNDS Heart sounds are studied by three methods: 1. By using stethoscope 2. By using microphone 3. By phonocardiogram. CARDIAC MURMUR is the abnormal or unusual heart sound heard by stethoscope along with normal heart sounds-- also called abnormal heart sound or cardiac bruit. The abnormal sound is produced because of the change in the pattern of blood flow. cardiac murmur is heard by placing the chest piece of the stethoscope over the auscultatory areas. The murmur due to disease of a particular valve is heard well over the auscultatory area of that valve. Sometimes, the murmur is felt by palpation as “thrills”. In some patients, the murmur is heard without any aid even at a distance of few feet away from the patient. Valvular diseases are of two types: 1.Stenosis or narrowing of the heart valve: The blood flows rapidly with turbulence through the narrow orifice of the valve resulting in murmur. 2.Incompetence or weakening of the heart valve: When the valve becomes weak, it cannot close properly. It causes back flow of blood resulting in turbulence. This disease is also called regurgitation or valvular insufficiency. CLASSIFICATION OF MURMUR Cardiac murmur is classified into three types: 1. Systolic murmur produced during systole of the heart 2. Diastolic murmur produced during diastole of the heart 3. Continuous murmur produced continuously.  Cardiac output is the amount of blood pumped from each ventricle. Usually, refers to the left ventricular output through aorta. is most important factor in cardiovascular system, because, the rate of blood flow through different parts of body depends upon the cardiac output. cardiac output is expressed in three ways: 1. STROKE VOLUME It is the amount of blood pumped out by each ventricle during each beat. Normal value: 70 mL (60 to 80 mL) when the heart rate is normal (72/minute). 2.MINUTE VOLUME is the amount of blood pumped out by each ventricle in one minute. It is the product of stroke volume and heart rate: Minute volume = Stroke volume × Heart rate Normal value: 5 liters/ ventricle/ minute.  3.CARDIAC INDEX is the minute volume expressed in relation to square meter of body surface area. It is defined as the amount of blood pumped out per ventricle/minute/ square meter of the body surface area. Normal value: Cardiac index = 2.8 ± 0.3 liters/ square meter of body surface area/ minute. (In an adult, the average body surface area is 1.734 square meter and normal minute volume is 5 liters/minute). MEASUREMENT OF CARDIAC OUTPUT The methods used to measure cardiac output are: 1.By using Fick‟s principle 2.Indicator (dye) dilution technique 3.Thermodilution technique 4.Ultrasonic Doppler transducer technique 5.Doppler echocardiography 6.Ballistocardiography. HEART RATE Normal heart rate is 72/minute. It ranges = 60 & 80 per minute. TACHYCARDIA is the increase in the heart rate above 100/minute.  Physiological conditions when tachycardia occurs are: 1. Childhood 2. Exercise 3. Pregnancy 4. Emotional conditions such as anxiety.  Pathological conditions when tachycardia occurs are: 1. Fever 2. Anemia 3. Hypoxia 4. Hyperthyroidism 5. Hypersecretion of catecholamines 6. Cardiomyopathy 7. Valvular heart diseases. BRADYCARDIA is the decrease in the heart rate below 60/minute. Physiological conditions when bradycardia occurs are: 1. Sleep 2. Athletic heart. Pathological conditions when bradycardia occurs are: 1. Hypothermia 2. Hypothyroidism 3. Heart attack 4. Congenital heart disease 5. Degenerative process of aging 6. Obstructive jaundice 7. Increased intracranial pressure. Arterial blood pressure is the lateral pressure exerted by the column of blood on the wall of arteries. is expressed in four different terms: 1. Systolic blood pressure 2. Diastolic blood pressure 3. Pulse pressure 4. Mean arterial blood pressure. Systolic blood pressure (systolic pressure) is the maximum pressure exerted in the arteries during systole of the heart. The normal systolic pressure is 120 mm Hg. It ranges = 110 & 140 mm Hg. Diastolic blood pressure (diastolic pressure) is the minimum pressure in the arteries during diastole of the heart. The normal diastolic pressure is 80 mm Hg. It varies between 60 and 80 mm Hg. Pulse pressure is the difference between systolic pressure and diastolic pressure. Normally, it is 40 mm Hg (120 to 80). PHYSIOLOGICAL VARIATIONS 1. Age 2. Sex In females, up to the period of menopause, the arterial pressure is about 5 mm Hg less than in males of same age. After menopause, the pressure in females becomes equal to that in males of same age. 3. Body Built The pressure is more in obese persons than in lean persons. 4. Diurnal Variation In early morning, the pressure is slightly low. It gradually increases and reaches the maximum at noon. It becomes low in evening. 5. After Meals The arterial blood pressure is increased for few hours after meals due to increase in cardiac output. 6. During Sleep Usually, the pressure is reduced up to 15 to 20 mm Hg during deep sleep. However, it increases slightly during sleep associated with dreams. 7. Emotional Conditions During excitement or anxiety, the blood pressure is increased due to release of adrenaline. 8. After Exercise After moderate exercise, systolic pressure increases by 20 to 30 mm Hg above the basal level due to increase in force of contraction and stroke volume. Normally, diastolic pressure is not affected by moderate exercise. It is because the diastolic pressure depends upon peripheral resistance, which is not altered by moderate exercise. After severe muscular exercise, the systolic pressure rises by 40 to 50 mm Hg above the basal level. But, the diastolic pressure reduces because the peripheral resistance decreases in severe muscular exercise. DETERMINANTS OF ARTERIAL BLOOD PRESSURE – FACTORS MAINTAINING ARTERIAL BLOOD PRESSURE Some factors are necessary for maintenance of normal blood pressure, which are called local factors, mechanical factors or determinants of blood pressure. These factors are divided into 2 types: I. Central factors -pertaining to the heart:(Cardiac output& Heart rate). II. Peripheral factors-- pertaining to blood and blood vessels: 1. Peripheral resistance 2. Blood volume 3. Venous return 4. Elasticity of blood vessels 5. Velocity of blood flow 6. Diameter of blood vessels 7. Viscosity of blood. REGULATION OF ARTERIAL BLOOD PRESSURE Arterial blood pressure varies even under physiological conditions. However, immediately it is brought back to normal level because of the presence of well organized regulatory mechanisms in the body. Body has four such regulatory mechanisms. The nervous regulation is rapid among all the mechanisms involved in regulation of ABP. When BP alters, nervous system brings the pressure back to normal within few minutes. Although nervous mechanism is quick in action, it operates only for a short period & then it adapts to the new pressure= called short-term regulation. The nervous mechanism regulating ABPoperates through the vasomotor system. The vasomotor system includes three components: 1. Vasomotor center 2. Vasoconstrictor fibers 3. Vasodilator fibers. The vasomotor center regulates ABP by causing vasoconstriction or vasodilatation, its actions depend upon the impulses it receives from other structures such as baroreceptors, chemoreceptors, higher centers and respiratory centers. --baroreceptors and chemoreceptors play a major role in the short-term regulation of blood pressure. Regulation of blood pressure by baroreceptor mechanism 2. Chemoreceptor Mechanism Chemoreceptors are receptors giving response to change in chemical constituents of blood. Peripheral chemoreceptors influence thevasomotor center. Peripheral chemoreceptors are sensitive to lack of oxygen, excess of carbon dioxide and hydrogen ion concentration in blood. Whenever blood pressure decreases, the blood flow decreases resulting in decreased oxygen content and excess of carbon dioxide and hydrogen ion. These factors stimulate the chemoreceptors, which send impulses to stimulate the vasoconstrictor center. The blood pressure rises and blood flow increases. Chemoreceptors play a major role in maintaining respiration rather than blood pressure. Sinoaortic mechanism Mechanism of action of baroreceptors and chemoreceptors in carotid and aortic region. The nerves from the baroreceptors and chemoreceptors are called buffer nerves because these nerves regulate the heart rate, blood pressure and respiration.  RENAL MECHANISM FOR REGULATION OF B P – LONG-TERM REGULATION kidneys play an important role in the long term regulation of ABP. by 2 ways: 1. By regulation of ECF volume 2. Through renin-angiotensin mechanism. BY REGULATION OF EXTRACELLULAR FLUID VOLUME When the BP increases, kidneys excrete large amounts of water & salt, particularly sodium by means of pressure diuresis & pressure natriuresis. Pressure diuresis is the excretion of large quantity of water in urine because of increased BP Even a slight increase in BP doubles the water excretion. Pressure natriuresis is the excretion of large quantity of sodium in urine. Because of diuresis & natriuresis, there is decrease in the ECF volume &blood volume, which in turn brings the ABP back to normal level. When blood pressure decreases, the reabsorption of water from renal tubules is increased. This in turn, increases ECF volume, blood volume & cardiac output resulting in restoration of BP. Actions of Angiotensin II When BP & ECF volume decrease, renin secretion from kidneys is increased. It converts angiotensinogen into angiotensin I. This is converted into angiotensin II by ACE (angiotensin converting enzyme). Angiotensin II acts in 2 ways to restore the BP: i.It causes constriction of arterioles in body so that the peripheral resistance is increased, & BP rises. In addition, angiotensin II causes constriction of afferent arterioles in kidneys so that the glomerular filtration reduces. This results in retention of water & salts. This increases ECF volume to normal level. This in turn increases the BP to normal level. ii.Simultaneously, angiotensin II stimulates the adrenal cortex to secrete aldosterone. This hormone increases reabsorption of sodium from renal tubules. Sodium reabsorption is followed by water reabsorption resulting in increased ECF volume & blood volume. It increases the BP to normal level. Regulation of blood pressure by renin-angiotensin mechanism. ACE = Angiotensin converting enzyme HORMONAL MECHANISM FOR REGULATION Of BP Hormones which Increase the Blood Pressure 1. Adrenaline 2. Noradrenaline 3. Thyroxine 4. Aldosterone 5. Vasopressin 6. Angiotensin 7. Serotonin. Hormones which Decrease the Blood Pressure 1. Vasoactive intestinal polypeptide (VIP) 2. Bradykinin 3. Prostaglandin 4. Histamine 5. Acetylcholine 6. Atrial natriuretic peptide 7. Brain natriuretic peptide 8. C-type natriuretic peptide. LOCAL MECHANISM FOR REGULATION OF BP some local substances also regulate the BP. The local substances regulate the blood pressure by vasoconstriction or vasodilatation. LOCAL VASOCONSTRICTORS The local vasoconstrictor substances are of vascular endothelial origin and are known as endothelins (ET). Endothelins are produced by stretching of blood vessels. These peptides act by activating phospholipase, which in turn activates the prostacyclin and thromboxane A2. These two substances cause constriction of blood vessels and increase in blood pressure. LOCAL VASODILATORS The local vasodilators are of two types: 1.Vasodilators of metabolic origin such as carbon dioxide, lactate, hydrogen ions and adenosine 2. Vasodilators of endothelial origin such as nitric oxide (NO). HYPERTENSION the persistent high blood pressure. Clinically, systolic pressure remains elevated above 150 mm Hg & diastolic pressure remains elevated above 90 mm Hg, it is considered as hypertension. If there is increase only in systolic pressure, it is called systolic hypertension. Types of Hypertension 1. Primary hypertension or essential hypertension Primary hypertension is the elevated blood pressure in the absence of any underlying disease- called essential hypertension. The arterial blood pressure is increased because of increased peripheral resistance, which occurs due to some unknown cause. 2. Secondary hypertension Secondary hypertension is the high blood pressure due to some underlying disorders. The different forms of secondary hypertension are: i.Cardiovascular hypertension that is produced due to the cardiovascular disorders such as atherosclerosis(hardening of blood vessels by fat deposition) and coarctation (narrowing) of aorta ii.Endocrine hypertension which is due to hyperactivity of some endocrine glands such as pheochromocytoma, hyperaldosteronism and Cushing‟s syndrome iii.Renal hypertension that is caused by renal diseases like glomerulonephritis and stenosis of renal arteries iv.Neurogenic hypertension which is developed by nervous disorders such as increased intracranial pressure and lesion in tractus solitarius v. Hypertension during pregnancy which is due to toxemia of pregnancy. HYPOTENSION is the low BP. When the systolic pressure is less than 90 mm Hg, considered as hypotension. Types 1. Primary hypotension is the low BP that develops in the absence of any underlying disease and develops due to some unknown cause. It is also called essential hypotension. Frequent fatigue and weakness are the common symptoms of this condition. However, the persons with primary hypotension are not easily susceptible to heart or renal disorders. 2. Secondary hypotension It is the hypotension that occurs due to some underlying diseases. The diseases which cause hypotension are: i. Myocardial infarction ii. Hypoactivity of pituitary gland iii. Hypoactivity of adrenal glands iv. Tuberculosis v. Nervous disorders. Thank you for listening