· A system that supplies oxygen, nutrients and hormones to the body cells and takes wastes to the excretory organs for the removal from the body is called the circulatory system and the transport and exchange of water, nutrients, oxygen, hormones and waste products through blood is called circulation.
· Systemic or general circulation is the circulation of blood from the left ventricle to the aorta around the body and is returned back to the right atrium by superior and inferior vena cava (Left Ventricle - Aorta - Right Atrium).
· Pulmonary circulation consists of the circulation of blood from the right ventricle to lungs through pulmonary arteries and back to the left atrium through pulmonary veins (Right Ventricle - Lungs - Left Atrium).
· In lymphatic circulation, lymph passes through lymphatic vessels and lymph nodes before returning to the blood.
· All tissues have lymphatic vessels except CNS, bone, most superficial layers of skin.
· Lymph is a clear watery fluid, similar to plasma, but does not have plasma proteins, RBCs, platelets, macromolecules in the blood and is identical in composition to interstitial fluid.
Functions of Circulatory System
· The main functions of the circulatory system are:
· Transport of respiratory gases: It transports Oxygen from lungs to tissues and Carbon dioxide from tissues to lungs.
· Transport of metabolic waste products: It transports various metabolic wastes from tissues to excretory organs (Kidney).
· Transport of digested food substances: It transports nutrients absorbed from the intestine to the liver and body tissues.
· Transport of chemical messengers: It transports hormones from the site of their origin to the target organ.
· Maintenance of temperature: It maintains temperature by distributing the heat produced in metabolically active organs to different parts of the body.
· Protection against diseases: Leucocytes produce antibodies and fight against harmful micro-organisms.
Types of the Circulatory System
· Human blood vascular system is of the closed type where blood circulates throughout the body through closed blood vessels.
· Annelids and all chordates have a closed type of circulatory system.
· In arthropods and molluscs, blood flows throughout the body through open cavities like coelom or lacunae or sinuses. It is an open type of circulatory system.
· In arthropods and molluscs, blood flows throughout the body through open cavities like coelom or lacunae or sinuses. It is an open type of circulatory system.
Type of Heart
· On the basis of mode of contraction, hearts are of two types i.e. myogenic and neurogenic.
a. Myogenic heart:
· On the basis of mode of contraction, hearts are of two types i.e. myogenic and neurogenic.
a. Myogenic heart:
· Heart in which wave of contraction starts from specialized muscle fibres of the heart is called myogenic heart.
· For example Heart of molluscs and vertebrates.
b. Neurogenic heart:
· Heart in which wave of contraction starts from specialized nerve fibres is called neurogenic heart.
· For example Heart of some annelids and most arthropods.
Type of Circulation
· It consists of single and double circulation.
1. Single circulation:
· It consists of single and double circulation.
1. Single circulation:
· In single circulation, the heart pumps out deoxygenated blood which is oxygenated by the gills and sent to the body parts from where deoxygenated blood is carried to the heart.
· It is found in fishes where blood passes once through the heart.
2. Double circulation:
· Double circulation consists of systemic and pulmonary circulations.
· In the systemic circulation, the venous blood is collected into small venules that join to form the coronary sinus which opens into the right atrium.
· In the systemic circulation, the venous blood is collected into small venules that join to form the coronary sinus which opens into the right atrium.
· The deoxygenated blood passes from different body parts to the heart (right atrium) through superior and inferior vena cava.
· It is circulated into the right ventricle and then send to the lungs for purification through pulmonary arteries.
· In pulmonary circulation, the oxygenated blood from the lungs is carried to the left atrium.
· In pulmonary circulation, the oxygenated blood from the lungs is carried to the left atrium.
· From left atrium to left ventricle and from the left ventricle to the aorta.
· From the aorta, oxygenated blood is circulated throughout the body.
THE HUMAN CIRCULATORY SYSTEM
· Human circulatory system consists of the blood vascular system and the lymphatic system.· The blood vascular system consists of the heart, blood and blood vessels.
· The lymphatic system consists of lymph, lymphatic capillaries, lymphatic vessels, lymphatic nodes and lymphatic ducts.
A. Heart
· Heart is a hollow, conical, muscular organ that pumps blood throughout the body.
Location, size and shape
· Heart is located between two lungs (called mediastinum) in the thoracic cavity.
· It’s one-third part lies in right and two-third parts on the left side.
· It is about 10-12 cm long and about the size of the owner’s fist.
· It weighs about 225 g in females and 310 g in males.
· The upper broad part of the heart is called the base and the lower narrow part is called the apex.
· The apex is slightly directed to the left.
· Heart is a hollow, conical, muscular organ that pumps blood throughout the body.
Location, size and shape
· Heart is located between two lungs (called mediastinum) in the thoracic cavity.
· It’s one-third part lies in right and two-third parts on the left side.
· It is about 10-12 cm long and about the size of the owner’s fist.
· It weighs about 225 g in females and 310 g in males.
· The upper broad part of the heart is called the base and the lower narrow part is called the apex.
· The apex is slightly directed to the left.
a. Structure of the Heart
· Histologically, the heart consists of three layers.
· Histologically, the heart consists of three layers.
· They are pericardium, myocardium and endocardium.
· Pericardium is a double-layered membrane. It has outer parietal and inner visceral layers.
· Parietal layer is made up of fibrous connective tissue that prevents overdistension of the heart as it is non-distensible.
· Visceral layer (epicardium) is made up of flattened epithelium that secretes pericardial fluid.
· The space between the parietal pericardium and visceral pericardium i.e. pericardial cavity is filled with pericardial fluid that protects the heart from shocks, external injuries and reduces the friction as it allows the free movement of the heart.
· Visceral layer (epicardium) is made up of flattened epithelium that secretes pericardial fluid.
· The space between the parietal pericardium and visceral pericardium i.e. pericardial cavity is filled with pericardial fluid that protects the heart from shocks, external injuries and reduces the friction as it allows the free movement of the heart.
· Myocardium is a thick muscular layer made up of cardiac muscle found only in the heart.
· It is involved in the contraction of the heart.
· It is involuntary in action.
· Endocardium lines the chambers and valves of the heart. It is thin, smooth and made up of flattened epithelium. It permits the flow of blood inside the heart.
b. External structure of the Heart
· Human heart is four-chambered.
· Upper two receiving chambers are called atriums and the lower two pumping chambers are called ventricles.
· The left and right atria are separated externally by a vertical interatrial groove.
· A distinct oblique groove i.e. auriculo-ventricular sulcus divides the heart into an anterior auricular and a posterior ventricular part.
a) Atria
· Atria are thin-walled upper chambers of the heart.
· Right atrium is larger than the left atrium. The right atrium receives deoxygenated blood from the superior venacava (pre-caval vein), inferior venacava (post-caval vein) and coronary sinus.
· The left atrium receives oxygenated blood from the lungs through two pairs of pulmonary veins.
· The right and left atria to pump their blood into the right ventricle and left ventricle respectively.
· Atria are thin-walled upper chambers of the heart.
· Right atrium is larger than the left atrium. The right atrium receives deoxygenated blood from the superior venacava (pre-caval vein), inferior venacava (post-caval vein) and coronary sinus.
· The left atrium receives oxygenated blood from the lungs through two pairs of pulmonary veins.
· The right and left atria to pump their blood into the right ventricle and left ventricle respectively.
· The ventricles are thick-walled lower chambers of the heart.
· The left ventricle is longer and narrower than the right ventricle.
· The wall of the left ventricle is about three times thicker than the right ventricle because the aorta has to take the blood to organs far away from the heart.
· The ventricles are demarcated externally from each other by an oblique groove called the inter-ventricular sulcus.
c) Pulmonary trunk and aorta
· Arising from the right ventricle, the pulmonary trunk soon bifurcates into the right and left pulmonary arteries.
· Arising from the right ventricle, the pulmonary trunk soon bifurcates into the right and left pulmonary arteries.
· Pulmonary arteries carry deoxygenated blood to the lungs of the respective sides.
· Aorta emerges out from the left ventricle and gets divided into ascending aorta, arch of aorta (also called aortic arch) and descending aorta.
· Ascending aorta gives rise to the right and left coronary arteries, arch of the aorta gives rise to brachiocephalic (innominate), left common carotid and left subclavian artery.
· The descending aorta runs through the thorax and abdomen hence it is divided into thoracic and abdominal parts.
· The pulmonary trunk is connected with the aorta by the ligamentum arteriosum that represents the remnant of an embryonic connection between the pulmonary trunk and aorta.
· In an embryo, the ligamentum arteriosum is called ductus arteriosus.
· Aorta emerges out from the left ventricle and gets divided into ascending aorta, arch of aorta (also called aortic arch) and descending aorta.
· Ascending aorta gives rise to the right and left coronary arteries, arch of the aorta gives rise to brachiocephalic (innominate), left common carotid and left subclavian artery.
· The descending aorta runs through the thorax and abdomen hence it is divided into thoracic and abdominal parts.
· The pulmonary trunk is connected with the aorta by the ligamentum arteriosum that represents the remnant of an embryonic connection between the pulmonary trunk and aorta.
· In an embryo, the ligamentum arteriosum is called ductus arteriosus.
c. Internal structure of the Heart
· Internally, the heart has the following structures.
· It can be better studied by dissecting it from the ventral side.
a. Atria
· The two thin-walled atria are separated by an inter-atrial septum.
· They are separated from ventricles by the atrioventricular septum.
· Each atrium opens into its corresponding ventricle through an atrioventricular aperture.
· An oval depression, the fossa ovalis is present in the right atrium adjoining the interauricular septum. It indicates the position of an opening, the foramen ovale, between two atria in the foetus, but it persists only as a depression in the adult.
· The right atrium receives openings of superior venacava, inferior venacava and coronary sinus.
· The opening of the inferior vena cava is guarded by the eustachian valve and the coronary sinus by the coronary or Thebesian valve.
· The left atrium receives oxygenated blood from four openings of pulmonary veins.
· The two thin-walled atria are separated by an inter-atrial septum.
· They are separated from ventricles by the atrioventricular septum.
· Each atrium opens into its corresponding ventricle through an atrioventricular aperture.
· An oval depression, the fossa ovalis is present in the right atrium adjoining the interauricular septum. It indicates the position of an opening, the foramen ovale, between two atria in the foetus, but it persists only as a depression in the adult.
· The right atrium receives openings of superior venacava, inferior venacava and coronary sinus.
· The opening of the inferior vena cava is guarded by the eustachian valve and the coronary sinus by the coronary or Thebesian valve.
· The left atrium receives oxygenated blood from four openings of pulmonary veins.
Tricuspid and Biscuspid valves
· Each atrium opens into the ventricle through an atrioventricular aperture.
· Atrio-ventricular apertures are guarded by valves that prevent backflow of blood.
· Right atrioventricular aperture is guarded by a tricuspid valve (having 3 flaps) and left atrioventricular aperture is guarded by bicuspid or mitral valve (having 2 flaps).
· The term mitral refers to its resemblance to a mitre, the headdress of a church bishop.
· These valves are attached to the walls of ventricles by tendons called chordae tendineae.
· Each atrium opens into the ventricle through an atrioventricular aperture.
· Atrio-ventricular apertures are guarded by valves that prevent backflow of blood.
· Right atrioventricular aperture is guarded by a tricuspid valve (having 3 flaps) and left atrioventricular aperture is guarded by bicuspid or mitral valve (having 2 flaps).
· The term mitral refers to its resemblance to a mitre, the headdress of a church bishop.
· These valves are attached to the walls of ventricles by tendons called chordae tendineae.
· They hold the valves and prevent valves to enter the atria during ventricular contractions.
· Chordae tendineae are joined to other ends with the special muscles of the ventricular wall, the papillary muscles.
b. Ventricles
· The two thick-walled ventricles are separated by an inter-ventricular septum. The left ventricle is more muscular than the right ventricle because it has to pump blood throughout the body but the right ventricle has to pump blood only to the lungs.
· Presence of many muscular ridges (columnae caraneae) in the wall of ventricles divides the cavity of ventricles into smaller spaces, called fissures.
· The walls of ventricles are thicker than atria. The left ventricle is thicker than the right ventricle.
Semilunar valves
· The opening of the pulmonary valve in the right ventricle and the aortic valve in the left ventricle is guarded by 3 semilunar valves (half-moon shaped pockets) that prevent the backflow of blood to the ventricles once forced out.
· Blood passes from the right to the left side of the heart via the lungs by pulmonary circulation.
Working mechanism of the Heart
· In the heart, there is rhythmic contraction and relaxations of the atria and ventricles.
· The ventricles contract and force the blood into the arteries called systole.
· When the heart relaxes, the blood flows into the atria and ventricles called diastole.
· The contractions and relaxations of the atrial and ventricular parts occur in a definite order.
· The atrial systole is followed by ventricular systole and ventricular systole is followed by the ventricular diastole. The sequence of one systole followed by one diastole is termed the cardiac cycle.
· The wave of contraction in the heart originates from the sinu-auricular node (SA node), found at the point of pre-caval opening.
· At regular intervals, a wave of contraction originates at the sinu-auricular node and spreads all along with the atria.
· These waves are picked up an atrioventricular node (AV node), situated at the wall of the right atrium.
· AV node gives out a mass of specialized fibres called the Bundle of His.
· Bundle of His divides into two branches and each branch extends into the wall of each ventricle and breaks into a network of fine fibres called Purkinje fibres.
· Impulses from the bundle of His transmit throughout the wall of ventricles through Purkinje fibres and cause contraction of ventricles and ventricles to pump the blood into pulmonary artery and aorta.
Origin and Conduction of Heartbeat
· A contraction of the heart is called systole and its relaxation diastole.
· The atria and ventricles contract alternately.
· The contraction of the heart (systole) and the relaxation of the heart (diastole) constitute the heartbeat.
· A contraction of the heart is called systole and its relaxation diastole.
· The atria and ventricles contract alternately.
· The contraction of the heart (systole) and the relaxation of the heart (diastole) constitute the heartbeat.
Origin and Conduction of Heartbeat
· The heartbeat begins in a tiny island of tissues in the upper region of the right atrium, called the sinu-auricular node (SA node).
· The SA node is found at the point of pre-caval opening. This region is also called a natural pacemaker because it is the region that initiates the heartbeat.
· The heart impulses generated in this region radiate out from the heart like a wave and cause each muscle fibre to contract.
· At regular intervals, a wave of contraction originates at the sinu-auricular node and spreads all along with the atria. These waves are picked up by a similar mass of tissue, the atrioventricular node (AV node).
· atrioventricular node (AV node) is a small mass of neuromuscular tissue present in the wall of the right atrium.
· AV node gives out a mass of specialized fibres called atrioventricular bundle or AV bundle or bundle of His. The bundle of His divides into two branches and extends along the inter-ventricular septum.
· Each branch extends into the wall of each ventricle and breaks into a network of fine fibres called Purkinje fibres.
· At regular intervals, a wave of contraction originates in the SA node and spreads over the walls of the atria, causing them to contract.
· Now atrioventricular node (AV node) picks up the impulses and sends them down the middle of the ventricular septum through the bundle of His.
· Impulses from a bundle of His transmit throughout the wall of ventricles through Purkinje fibres and cause contraction of ventricles and ventricles to pump the blood into pulmonary artery and aorta.
· The heartbeat begins in a tiny island of tissues in the upper region of the right atrium, called the sinu-auricular node (SA node).
· The SA node is found at the point of pre-caval opening. This region is also called a natural pacemaker because it is the region that initiates the heartbeat.
· The heart impulses generated in this region radiate out from the heart like a wave and cause each muscle fibre to contract.
· At regular intervals, a wave of contraction originates at the sinu-auricular node and spreads all along with the atria. These waves are picked up by a similar mass of tissue, the atrioventricular node (AV node).
· atrioventricular node (AV node) is a small mass of neuromuscular tissue present in the wall of the right atrium.
· AV node gives out a mass of specialized fibres called atrioventricular bundle or AV bundle or bundle of His. The bundle of His divides into two branches and extends along the inter-ventricular septum.
· Each branch extends into the wall of each ventricle and breaks into a network of fine fibres called Purkinje fibres.
· At regular intervals, a wave of contraction originates in the SA node and spreads over the walls of the atria, causing them to contract.
· Now atrioventricular node (AV node) picks up the impulses and sends them down the middle of the ventricular septum through the bundle of His.
· Impulses from a bundle of His transmit throughout the wall of ventricles through Purkinje fibres and cause contraction of ventricles and ventricles to pump the blood into pulmonary artery and aorta.
Course of Blood circulation in the Human heart
· Human circulatory system is a closed type and consists of systemic and pulmonary circulation.
· Systemic circulation is branched to supply blood to different organs and pulmonary to lungs.
· Right and left side of the heart contains deoxygenated and oxygenated blood respectively. Normally, there is no mixing of blood.
· Human circulatory system is a closed type and consists of systemic and pulmonary circulation.
· Systemic circulation is branched to supply blood to different organs and pulmonary to lungs.
· Right and left side of the heart contains deoxygenated and oxygenated blood respectively. Normally, there is no mixing of blood.
Course of Blood circulation
· Superior venacava returns deoxygenated blood from the head, neck and upper limbs to the right atrium.
· Inferior venacava returns deoxygenated blood from the rest parts of the body to the right atrium.
· Blood from the right atrium enters the right ventricle through the tricuspid valve. This is further aided by the contraction of the right atrium.
· The right ventricle contracts and now blood flows through pulmonary arteries into the lungs.
· Oxygenated blood returns to the heart through two pairs of right and left pulmonary veins.
· Oxygenated blood from the left atrium flows into the left ventricle through the bicuspid valve. This process is aided by the contraction of the left atrium.
· Oxygenated blood is pumped into the entire body through the aorta due to the contraction of the left ventricle.
· Body tissues extract Oxygen from blood and deoxygenated blood again returns to the right atrium through vena cava.
Regulation of Heartbeat
· The rhythmic contraction and relaxation of cardiac muscles is called heartbeat.
· The rhythmic contraction and relaxation of cardiac muscles is called heartbeat.
· Each heartbeat includes one systole and one diastole of the heart to distribute and receive blood to and from the body.
· Adult human heart beats about 72 times/minute at rest.
· The heart of a resting human being pumps about 5 litres of blood per minute.
· Heartbeat rate is low during sleep and is high (faster) during exercise, emotion, fever, age ( in children more, adults less), gender (faster in women than in men).
· Neural control: Although the impulses are generated within the heart itself, the heartbeat rate is under the control of the autonomic nervous system. Sympathetic stimulation increases the rate and force of the heartbeat. While parasympathetic nerves decrease the rate and force of the heartbeat. Vasomotor center lies in the medulla oblongata.
· Hormonal control: Two hormones from the adrenal cortex i.e. adrenaline (epinephrine) and noradrenaline (norepinephrine) accelerate the heartbeat rate at the time of emergency. These hormones directly influence the SA node.
· The heart of a resting human being pumps about 5 litres of blood per minute.
· Heartbeat rate is low during sleep and is high (faster) during exercise, emotion, fever, age ( in children more, adults less), gender (faster in women than in men).
· Neural control: Although the impulses are generated within the heart itself, the heartbeat rate is under the control of the autonomic nervous system. Sympathetic stimulation increases the rate and force of the heartbeat. While parasympathetic nerves decrease the rate and force of the heartbeat. Vasomotor center lies in the medulla oblongata.
· Hormonal control: Two hormones from the adrenal cortex i.e. adrenaline (epinephrine) and noradrenaline (norepinephrine) accelerate the heartbeat rate at the time of emergency. These hormones directly influence the SA node.
Blood Pressure
· It is the amount of pressure exerted by the blood on the wall of blood vessels.
· In common use, by blood pressure, we mean the arterial blood pressure.
· It is the amount of pressure exerted by the blood on the wall of blood vessels.
· In common use, by blood pressure, we mean the arterial blood pressure.
· It is of 2 types:
(a) Systolic blood pressure
When the left ventricle contracts and pushes blood into the aorta, the pressure generated within the arterial system is called systolic blood pressure.
(a) Systolic blood pressure
When the left ventricle contracts and pushes blood into the aorta, the pressure generated within the arterial system is called systolic blood pressure.
· In a healthy resting adult, it is about 120 mm Hg (millimetres of mercury).
· It is called the higher limit of arterial blood pressure.
(b) Diastolic blood pressure
The pressure within the arteries at the time of complete cardiac diastole is called diastolic blood pressure.
· In a healthy resting adult, it is about 80 mm Hg.
· It is called the lower limit of arterial blood pressure.
· While writing, systolic pressure is written over diastolic pressure. E.g. 120/80 mm Hg.
· So, in each heartbeat, arterial blood pressure rises to about 120 mm Hg in the systolic phase and falls to about 80 mm Hg in the diastolic phase.
· While writing, systolic pressure is written over diastolic pressure. E.g. 120/80 mm Hg.
· So, in each heartbeat, arterial blood pressure rises to about 120 mm Hg in the systolic phase and falls to about 80 mm Hg in the diastolic phase.
· The difference between systolic and diastolic pressure is called pulse pressure which is equal to 40 mm Hg.
Measurement of Arterial Blood Pressure
· Blood pressure is measured with the help of an instrument called a sphygmomanometer.
· Sphygmomanometer was invented by Korot koff in 1905 AD.
· An inflatable Cuff (Riva-Rocci Cuff) is wrapped around the arm.
· A stethoscope is placed over the brachial artery at the elbow.
· The cuff is rapidly inflated until the pressure in it is well above the expected systolic pressure and then the pressure in the cuff is slowly lowered down.
· The pressure at which the first sound is heard is called systolic pressure.
· Again, the cuff pressure is lowered, sound becomes muffled and disappear completely i.e. diastolic pressure.
Heart Sounds
· In each heartbeat, two sounds are produced in a normal person.
· The first heart sound ‘lubb’ is produced by the closure of bicuspid and tricuspid valves. It is low pitched, less loud and of long duration. It lasts for 0.15 seconds.
· The second heart sound ‘dup’ is produced by the closure of aortic and pulmonary semilunar valves. It is higher pitched, louder and of short duration. It lasts for 0.1 seconds.
· In each heartbeat, two sounds are produced in a normal person.
· The first heart sound ‘lubb’ is produced by the closure of bicuspid and tricuspid valves. It is low pitched, less loud and of long duration. It lasts for 0.15 seconds.
· The second heart sound ‘dup’ is produced by the closure of aortic and pulmonary semilunar valves. It is higher pitched, louder and of short duration. It lasts for 0.1 seconds.
Heartbeat Rate
· It is the number of beats of the heart per minute.
· In a normal healthy person, the heart beats about 72 times per minute.
· Heartbeat rate determines the cardiac output.
· The cardiac output is directly proportional to the heartbeat rate.
· Heartbeat rate determines the cardiac output.
· The cardiac output is directly proportional to the heartbeat rate.
· Heartbeat rate increases during exercise, fever, anger and fear.
Stroke Volume
· It is the volume of blood pumped out of the heart in one heartbeat.
· It is about 70-80 ml.
Cardiac Cycle
· The rhythmic contraction (systole) and relaxation (diastole) of the heart occurs throughout the life of a person.
· The contraction and relaxation occurs in a systematic way in a definite time period and form a cardiac cycle.
· Each cycle has three phases namely atrial systole, ventricular systole and combined diastole.
· Atrial systole:
· This is the simultaneous contraction of the right and left atria to pump blood into the respective ventricles.
· It occurs due to the stimulation of the SA node and lasts about 0.1 seconds.
· Ventricular systole:
· This is the simultaneous contraction of the right and left ventricles to pump blood into the pulmonary artery and systemic circulation respectively.
· It occurs after atrial systole is over and lasts about 0.3 seconds.
· Combined (Joint) diastole:
· This is the relaxation of both atria and ventricles.
· The return of blood to the heart occurs at this stage.
· It lasts about 0.4 seconds.
· The total duration of the cardiac cycle is about 0.8 seconds in a healthy adult.
· The total duration of the cardiac cycle is about 0.8 seconds in a healthy adult.
Cardiac Output
· The amount of blood pumped out by each ventricle per minute is known as cardiac output.
· It can be calculated by multiplying stroke volume and heartbeat rate.
· CO = SV × HR = 70 ml × 72/minute = 5l/minute
Heart Murmur
· Heart murmur is an abnormal heart sound (lubb shhh) produced due to the damaged or defective semilunar valves.
· In this case, the blood leak back from the pulmonary trunk and aorta into the ventricles.
· It may be caused by syphilis, rheumatic fever or any other disease which injures the semilunar valves.
Electrocardiogram (ECG)
· ECG is a graphic record of the electric current produced by the excitation of the cardiac muscles.
· The instrument used to record the changes is called an electrocardiograph.
· Waller (1887 AD) first recorded the electrocardiogram but Einthoven (1903 AD) studied ECG in detail, so got a Nobel Prize for the discovery of ECG. He is also considered the ‘father of electrocardiography’ (the device used).
· A normal electrocardiogram (ECG) is composed of a P wave, a QRS wave (complex) and a T wave.
1. The P wave:
· It is a small upward wave that represents electrical excitation or the depolarization of the atria which leads to contraction of both the atria (atrial contraction).
· It is caused by the activation of the SA node.
· The impulses of contraction start from the SA node and spread throughout the atria.
2. The QRS wave (complex):
· It begins after a fraction of a second of the P wave.
· It begins as a small downward deflection (Q) and continues as a large upright (R) and triangular wave, ending as a downward wave (S) at its base.
· It represents ventricular depolarization (ventricular contraction).
· It is caused by the impulses of the contraction from the AV node through the bundle of His and Purkinje fibres and contraction of the ventricular muscles.
· Thus this wave is due to the spread of electric impulses through the ventricles.
3. The T wave:
· It is dome-shaped and represents ventricular repolarisation (ventricular relaxation).
· The potential generated by the recovery of the ventricle from the depolarization state is called the repolarisation wave.
· The end of T- wave marks the end of the systole.
· Normal P-R interval is 0.12 to 0.2 sec.
· Normal QRS complex duration is 0.10 sec.
· Normal Q-T interval is 0.42 sec.
Blood Vessels
· They are arteries, veins and capillaries.
· They are arteries, veins and capillaries.
a. Arteries
· These are the blood vessels that transport the blood away from the heart.
· These are the blood vessels that transport the blood away from the heart.
· The Wall of the artery consists of 3 layers of tissue.
a. Tunica adventitia/ externa - Outermost layer of connective tissue.
b. Tunica media - Middle layer of smooth muscle and elastic tissue.
c. Tunica intima/ interna - Innermost layer made up of two parts.
i. Elastic membrane: It is made up of elastic tissue of yellow fibres. It is thicker in the artery.
ii. Endothelium: It is made up of flattened squamous epithelial cells lining the lumen. Its cells are more elongated in the artery.
· In large arteries, tunica media consists of more elastic tissue and less smooth muscle. In small arteries, tunica media consists almost entirely of smooth muscle.
a. Tunica adventitia/ externa - Outermost layer of connective tissue.
b. Tunica media - Middle layer of smooth muscle and elastic tissue.
c. Tunica intima/ interna - Innermost layer made up of two parts.
i. Elastic membrane: It is made up of elastic tissue of yellow fibres. It is thicker in the artery.
ii. Endothelium: It is made up of flattened squamous epithelial cells lining the lumen. Its cells are more elongated in the artery.
· In large arteries, tunica media consists of more elastic tissue and less smooth muscle. In small arteries, tunica media consists almost entirely of smooth muscle.
b. Veins
· These are the blood vessels that return blood to the heart.
· They have also 3 layers as arteries but tunica media is thinner because of less muscle and elastic tissue in it.
· When cut, the veins collapse while the thicker-walled arteries remain open.
· Valves are abundant in the veins of limbs, especially the lower limbs where blood must travel considerable distance gravity when the individual is standing.
· Valves are absent in the veins of the thorax and abdomen.
· Valves are formed by the tunica intima strengthened by connective tissues.
· The valves are semilunar in shape with the concavity towards the heart.
· The smallest veins are called venules.
· These are the blood vessels that return blood to the heart.
· They have also 3 layers as arteries but tunica media is thinner because of less muscle and elastic tissue in it.
· When cut, the veins collapse while the thicker-walled arteries remain open.
· Valves are abundant in the veins of limbs, especially the lower limbs where blood must travel considerable distance gravity when the individual is standing.
· Valves are absent in the veins of the thorax and abdomen.
· Valves are formed by the tunica intima strengthened by connective tissues.
· The valves are semilunar in shape with the concavity towards the heart.
· The smallest veins are called venules.
Differences between Arteries and Veins
| Arteries | Veins |
|---|---|
| They carry blood away from the heart. | They bring blood towards the heart. |
| Except for pulmonary arteries, all arteries carry oxygenated blood. | Except for pulmonary veins, all veins carry deoxygenated blood. |
| Thick-walled, do not collapse when cut. | Thin-walled, collapse when cut. |
| Narrow lumen. | Wider lumen. |
| Present on the deep layers of the skin. | Superficial layer of skin. |
| Absence of valves. | Presence of valves. |
| Blood flows under high pressure. | Blood flows under low pressure. |
| Dark red in colour. | Pink in colour. |
c. Capillaries
· These are the smallest blood vessels connecting arteries with the veins.
· In the tissues, they form a fine network called capillary network.
· Their wall consists of only one layer i.e., the tunica intima.
· Due to the presence of very thin walls, they are involved in the exchange of oxygen, nutrients and waste products between the blood and tissues.
Arterial System of Human
· Arterial system is the circulation of blood by the arteries.· Arteries are the blood vessels that distribute the oxygenated blood throughout the body except for pulmonary arteries which carry deoxygenated blood to the lungs.
· Arterial system consists of both pulmonary and systemic circulation both.
(a) Pulmonary circulation
· This is the circulation of blood from the right ventricle to the lungs.
· The pulmonary trunk, carrying deoxygenated blood, leaves the upper part of the right ventricle of the heart. It passes upwards and divides left and right pulmonary arteries.
· The left pulmonary artery runs to the root of the left lung where it divides into two branches, one passing into each lobe.
· The right pulmonary artery runs to the root of the right lung and divides into two branches.
· The larger branch carries blood to the middle and lower lobes and the smaller branch to the upper lobe.
· These arteries divide and subdivide into smaller arteries, arterioles and capillaries. The exchange of gases occurs between capillary blood and air in the alveoli of the lungs.
· These arteries divide and subdivide into smaller arteries, arterioles and capillaries. The exchange of gases occurs between capillary blood and air in the alveoli of the lungs.
(b) Systemic circulation
· It is the circulation of oxygenated blood from the heart to different parts of the body.
· It is the circulation of oxygenated blood from the heart to different parts of the body.
· It consists of the aorta and its branches. Aorta emerges out from the left ventricle, ascends up, arches towards the left side and descends down behind the heart through the thoracic cavity.
· The ascending aorta gives rise to the right and left coronary arteries that supply blood to the myocardium of the heart.
· The arch of the aorta (aortic arch) gives rise to three branches- brachiocephalic, left common carotid and left subclavian artery.
· Brachiocephalic artery divides into right common carotid and right subclavian artery.
· Right common carotid arising from the brachiocephalic artery and left common carotid artery arising directly from the aortic arch, combined form carotid arteries. They have the same distribution on each side.
· Each carotid artery divides into an external and an internal carotid artery. The external carotids supply blood to the head, face and neck and internal carotids to the brain.
· The right subclavian artery arises from the brachiocephalic, left directly from the aortic arch. They pass behind the clavicles and descend down as axillary arteries.
· Before entering the axilla, each subclavian artery gives off two branches, the vertebral artery that supplies the brain and the internal thoracic artery that supplies the breast and other structures in the thoracic cavity.
· The axillary artery descends down and becomes the brachial artery. The brachial artery further at the elbow divides into radial and ulnar arteries to supply blood to the upper limb.
· The palmar-metacarpal and palmar-digital arteries arising from radial and ulnar arteries supply blood to the hand and fingers.
· The ascending aorta gives rise to the right and left coronary arteries that supply blood to the myocardium of the heart.
· The arch of the aorta (aortic arch) gives rise to three branches- brachiocephalic, left common carotid and left subclavian artery.
· Brachiocephalic artery divides into right common carotid and right subclavian artery.
· Right common carotid arising from the brachiocephalic artery and left common carotid artery arising directly from the aortic arch, combined form carotid arteries. They have the same distribution on each side.
· Each carotid artery divides into an external and an internal carotid artery. The external carotids supply blood to the head, face and neck and internal carotids to the brain.
· The right subclavian artery arises from the brachiocephalic, left directly from the aortic arch. They pass behind the clavicles and descend down as axillary arteries.
· Before entering the axilla, each subclavian artery gives off two branches, the vertebral artery that supplies the brain and the internal thoracic artery that supplies the breast and other structures in the thoracic cavity.
· The axillary artery descends down and becomes the brachial artery. The brachial artery further at the elbow divides into radial and ulnar arteries to supply blood to the upper limb.
· The palmar-metacarpal and palmar-digital arteries arising from radial and ulnar arteries supply blood to the hand and fingers.
Descending Aorta in the Thorax
· It begins at the level of the 4th thoracic vertebra.
· It begins at the level of the 4th thoracic vertebra.
· It is continuous with the aortic arch and gives off following branches.
a. Bronchial arteries: supply blood to bronchi, their branches and lungs.
b. Oesophageal arteries: supply blood to the oesophagus.
c. Intercostal arteries: supply blood to intercostal muscles, some muscles of the thorax, the ribs, the skin and its underlying connective tissues.
a. Bronchial arteries: supply blood to bronchi, their branches and lungs.
b. Oesophageal arteries: supply blood to the oesophagus.
c. Intercostal arteries: supply blood to intercostal muscles, some muscles of the thorax, the ribs, the skin and its underlying connective tissues.
Abdominal Aorta
· It is the continuation of the thoracic aorta.
· It is the continuation of the thoracic aorta.
· The name changes when the thoracic aorta enters at the level of the 12th thoracic vertebra.
· Many paired and unpaired branches arise from the abdominal aorta.
· Many paired and unpaired branches arise from the abdominal aorta.
a. Paired branches
a. Inferior phrenic arteries: supply blood to the diaphragm.
b. Renal arteries: supply blood to kidneys, give off branches, the suprarenal arteries that supply blood to the supra-renal glands. Right renal is larger and a little higher in origin.
c. Genital arteries i.e. testicular arteries: supply blood to testes (in the male) and ovarian arteries- supply blood to ovaries (in females).
a. Inferior phrenic arteries: supply blood to the diaphragm.
b. Renal arteries: supply blood to kidneys, give off branches, the suprarenal arteries that supply blood to the supra-renal glands. Right renal is larger and a little higher in origin.
c. Genital arteries i.e. testicular arteries: supply blood to testes (in the male) and ovarian arteries- supply blood to ovaries (in females).
b. Unpaired branches
· The coeliac artery arising immediately below the diaphragm divides into three branches.
a. The left gastric artery supplies blood to the stomach.
b. The splenic artery supplies blood to the pancreas and spleen.
c. The hepatic artery supplies blood to the liver, gall bladder, parts of the stomach, duodenum and pancreas.
· The superior mesenteric artery arises from the aorta and supplies blood to the whole of the small intestine and the proximal half of the large intestine.
· The inferior mesenteric artery also arises from the aorta and supplies blood to the distal half of the large intestine and the part of the rectum.
· At the level of the 4th lumbar vertebra, the abdominal aorta divides into the right and left common iliac.
· Each common iliac divides into external and internal iliac arteries.
· The internal iliac supplies blood to pelvic organs and the external iliac to the lower limbs.
· The external iliac runs downwards and becomes the femoral artery at the thigh which descends down as the popliteal artery.
· The popliteal artery divides into anterior and posterior tibial arteries of the leg.
· The coeliac artery arising immediately below the diaphragm divides into three branches.
a. The left gastric artery supplies blood to the stomach.
b. The splenic artery supplies blood to the pancreas and spleen.
c. The hepatic artery supplies blood to the liver, gall bladder, parts of the stomach, duodenum and pancreas.
· The superior mesenteric artery arises from the aorta and supplies blood to the whole of the small intestine and the proximal half of the large intestine.
· The inferior mesenteric artery also arises from the aorta and supplies blood to the distal half of the large intestine and the part of the rectum.
· At the level of the 4th lumbar vertebra, the abdominal aorta divides into the right and left common iliac.
· Each common iliac divides into external and internal iliac arteries.
· The internal iliac supplies blood to pelvic organs and the external iliac to the lower limbs.
· The external iliac runs downwards and becomes the femoral artery at the thigh which descends down as the popliteal artery.
· The popliteal artery divides into anterior and posterior tibial arteries of the leg.
Venous System of Human
· Veins are the blood vessels that return blood to the heart from different parts of the body. Generally, they carry deoxygenated blood except for pulmonary veins.· Venous system comprises systemic veins (that return deoxygenated blood to the right atrium of the heart from various parts of the body) and pulmonary veins (that return oxygenated blood to the left atrium of the heart from lungs).
· So, it is divided into systemic and pulmonary venous systems.
A. Systemic Venous System
· It consists of superior and inferior venacava and their tributaries.
· Superior venacava drains all the venous blood from the head, neck and upper limbs in the right atrium of the heart. Superior venacava is formed by the union of right and left brachiocephalic veins. Each brachiocephalic vein, in turn, is formed by the union of the internal jugular and subclavian veins.
· The external jugular vein returns the venous blood from the face and scalp (the skin covering the top of the head with hair) and opens into the subclavian vein.
· The subclavian vein collects blood from axillary, cephalic, brachial, basilic, radial and ulnar veins.
· The internal jugular vein collects venous blood from the brain.
· Most of the venous blood from the thoracic region is drained into the azygous vein and hemizygous veins. Some of the main veins that join them are the bronchial, oesophageal and intercostal veins. The azygous vein is present on the right side and opens into the superior venacava. The hemizygous vein is present on the left side and opens into the left brachiocephalic vein.
· The inferior venacava is formed by the right and left common iliac.
A. Systemic Venous System
· It consists of superior and inferior venacava and their tributaries.
· Superior venacava drains all the venous blood from the head, neck and upper limbs in the right atrium of the heart. Superior venacava is formed by the union of right and left brachiocephalic veins. Each brachiocephalic vein, in turn, is formed by the union of the internal jugular and subclavian veins.
· The external jugular vein returns the venous blood from the face and scalp (the skin covering the top of the head with hair) and opens into the subclavian vein.
· The subclavian vein collects blood from axillary, cephalic, brachial, basilic, radial and ulnar veins.
· The internal jugular vein collects venous blood from the brain.
· Most of the venous blood from the thoracic region is drained into the azygous vein and hemizygous veins. Some of the main veins that join them are the bronchial, oesophageal and intercostal veins. The azygous vein is present on the right side and opens into the superior venacava. The hemizygous vein is present on the left side and opens into the left brachiocephalic vein.
· The inferior venacava is formed by the right and left common iliac.
· Inferior venacava receives the blood from:
(a Right and left renal veins: They collect blood from kidneys.
(b) Right and left adrenals: They collect blood from adrenal glands.
(c) Right and left testicular and ovarian veins: They collect blood from testes (in males) and ovaries (in females).
· Hepatic portal vein collects blood from the alimentary canal into the liver. Hepatic veins return blood from the liver to the inferior venacava.
· Hepatic portal vein is formed by the union of several veins.
· The splenic vein drains the blood from the spleen, the pancreas and part of the stomach.
· The inferior mesenteric vein returns the venous blood from the rectum, pelvic and descending colon of the large intestine. It joins the splenic vein.
· The superior mesenteric vein returns the venous blood from the small intestine and the proximal parts of the large intestine i.e. the caecum, ascending and transverse colon. It unites with the splenic vein to form the portal vein.
· The gastric veins drain venous blood from the stomach and the oesophagus and then join the portal vein.
· The cystic vein, which drains venous blood from the gall bladder, joins the portal vein.
· The right and left common iliac is formed by the union of external and internal iliac veins.
· The external iliac vein is large and is the continuation of the femoral vein. The femoral vein descends down as a popliteal vein. The popliteal vein divides into anterior and posterior tibial veins.
· The internal iliac vein is small and collects blood from the pelvis (pelvic cavity).
· The great saphenous vein is the longest vein in the body. It drains blood into the femoral vein.
· The small saphenous vein is small and drains blood from the foot and joins the popliteal vein.
(a Right and left renal veins: They collect blood from kidneys.
(b) Right and left adrenals: They collect blood from adrenal glands.
(c) Right and left testicular and ovarian veins: They collect blood from testes (in males) and ovaries (in females).
· Hepatic portal vein collects blood from the alimentary canal into the liver. Hepatic veins return blood from the liver to the inferior venacava.
· Hepatic portal vein is formed by the union of several veins.
· The splenic vein drains the blood from the spleen, the pancreas and part of the stomach.
· The inferior mesenteric vein returns the venous blood from the rectum, pelvic and descending colon of the large intestine. It joins the splenic vein.
· The superior mesenteric vein returns the venous blood from the small intestine and the proximal parts of the large intestine i.e. the caecum, ascending and transverse colon. It unites with the splenic vein to form the portal vein.
· The gastric veins drain venous blood from the stomach and the oesophagus and then join the portal vein.
· The cystic vein, which drains venous blood from the gall bladder, joins the portal vein.
· The right and left common iliac is formed by the union of external and internal iliac veins.
· The external iliac vein is large and is the continuation of the femoral vein. The femoral vein descends down as a popliteal vein. The popliteal vein divides into anterior and posterior tibial veins.
· The internal iliac vein is small and collects blood from the pelvis (pelvic cavity).
· The great saphenous vein is the longest vein in the body. It drains blood into the femoral vein.
· The small saphenous vein is small and drains blood from the foot and joins the popliteal vein.
B. Pulmonary Venous System
· It consists of two pulmonary veins- right and left that leave each lung.
· They return the oxygenated blood to the left atrium of the heart.
Blood Grouping and their Inheritance in Human
· There are more than 30 antigens on the surface of blood cells that give rise to different blood groups.· In a blood transfusion, the blood group of donor and recipient must be matched; otherwise the recipient’s immune system will produce antibodies that cause agglutination (clumping) of the transfused cells and block blood circulation through capillaries.
ABO Blood Groups
· Austrian scientist Karl Landsteiner discovered A, B and O blood groups in human beings in 1900 AD for which he was awarded Nobel Prize in 1931 AD while blood group AB was found out by de Castello and Steini in 1902 AD.
· ABO blood groups are determined by the gene I (isoagglutinin).
· There are three alleles of this gene-IA, IB and IO.
· Proteins produced by the IA and IB alleles are called A antigen and B antigen.
· There are four blood groups- A, B, AB and O on the basis of presence of blood antigens and antibodies.
· Antigens (agglutinogens) are the proteins on the surface of RBCs and antibodies (agglutinins) are in the plasma.
· There are four blood groups- A, B, AB and O on the basis of presence of blood antigens and antibodies.
· Antigens (agglutinogens) are the proteins on the surface of RBCs and antibodies (agglutinins) are in the plasma.
· People with blood group ‘A’ have A antigen on the surface of their RBCs and antibody b in their plasma.
· Persons with blood group B have B antigen on the surface of their RBCs and antibody in their plasma.
· Individuals with blood group AB have both A and B antigens on the surface of their RBCs and no antibodies in their plasma.
· Type O individuals are without A and B antigens on their RBCs but have both antibodies a and b in their plasma. Individuals with blood group O can donate blood to anyone so O blood group is called universal donor whereas AB blood group individuals can receive blood from all other groups so AB blood group is called universal recipient.
· Persons with blood group B have B antigen on the surface of their RBCs and antibody in their plasma.
· Individuals with blood group AB have both A and B antigens on the surface of their RBCs and no antibodies in their plasma.
· Type O individuals are without A and B antigens on their RBCs but have both antibodies a and b in their plasma. Individuals with blood group O can donate blood to anyone so O blood group is called universal donor whereas AB blood group individuals can receive blood from all other groups so AB blood group is called universal recipient.
· Hence, Universal Donor is O Negative and Universal Acceptor is AB positive.
| Blood groups | Genotype | Antigen/s (RBC) | Antibody or Antibodies (Plasma) | Can give blood or can donate to | Can receive from or / can accept from | Rh Factor Positive or negative |
|---|---|---|---|---|---|---|
| A | IAIA or IAIO | A | Anti-b | A and AB | A and O | |
| B | IBIB or IBIO | B | Anti-a | B and AB | B and O | |
| AB | IAIB | A and B | No antibody | AB | All blood groups (Universal recipient) | |
| O | IOIO | No antigen | Anti–a and Anti–b | All blood groups (Universal donor | O |
· A blood that has no Rh antigen can produce an antibody on the action of the antigen of its opposite strain.
· Antibodies are of two types- naturally occurring antibodies like Anti-a and Anti-b (which react with an antigen found in the members of the same species) and immune antibodies which are produced as a result of antigenic stimulus from another individual.
Mechanism of Inheritance of Blood Group
· Bernstein (1924 AD) discovered that the ABO blood grouping is an inherited characteristic that involves multiple-allelism.
· Three allelic genes Ia, Ib and Io control the inheritance of these blood groups in all human populations.
· There are three genes altogether, but a given individual can have only two of them.
· To belong to blood group A, a person must have either two A genes (AA) or an A gene with an O gene (AO).
· To belong to blood group B, a person must have either two B genes (BB) or a B gene with an O gene (BO).
· To belong to group AB, a person must have both the A and B genes together (AB).
· Finally to belong to blood group O, a person must have two O genes (OO).
· Neither the A nor the B genes are dominant over each other. However, both are dominant to the O gene.
· If the blood groups of the parents are known, we can predict the blood groups of their children.
· There are three genes altogether, but a given individual can have only two of them.
· To belong to blood group A, a person must have either two A genes (AA) or an A gene with an O gene (AO).
· To belong to blood group B, a person must have either two B genes (BB) or a B gene with an O gene (BO).
· To belong to group AB, a person must have both the A and B genes together (AB).
· Finally to belong to blood group O, a person must have two O genes (OO).
· Neither the A nor the B genes are dominant over each other. However, both are dominant to the O gene.
· If the blood groups of the parents are known, we can predict the blood groups of their children.
Possible Blood Groups of Children from known Blood groups of Parent
| Blood groups of parents | Possible | Impossible |
|---|---|---|
| O × O | O | A, B, AB |
| O × A A × A |
O, A | B, AB |
| O × B B × B |
O, B | A, AB |
| A × B | O, A, B, AB | – |
| O × AB | A, B | O, AB |
| A × A B × AB AB × AB |
A, B, AB | O |
· Suppose a man belonging to blood group A marries a woman belonging to blood group O, then the possible blood groups of the child depend on whether the husband’s genotype is AA or AO. If it is AA, then the child must belong to group A. On the other hand, if the husband’s genotype is AO, then there is an equal chance of the child belonging to group A or group O.
· The possible blood groups in the offspring when father’s blood group is ‘A’ and mother’s blood group is ‘B’ are O, A, B and AB.
· The possible and impossible blood groups of a father can be worked out if the blood groups of mother and child are known.
· The table below has been worked out by crossing the various possible genotypes of mother and child.
Possible Blood groups of the Father from known blood groups of mother and child:
| S.N. | Child | Mother | Possible | Impossible |
|---|---|---|---|---|
| 1 | A A A A |
A B AB O |
ALL A, AB ALL A, AB |
NIL O, B NIL O, B |
| 2 | B B B B |
A B AB O |
B, AB ALL ALL B, AB |
O, A NIL NIL O, A |
| 3 | AB AB AB |
A B AB |
B, AB A, AB A, B, AB |
O, A O, B O |
| 4 | O O O |
A B O |
A, B, O A, B, O A, B, O |
AB AB AB |