•The system that fulfils the transportation needs of the body is cardiovascular system.
• The cardiovascular system is composed of the heart, blood vessels, and blood.
Main functions of the cardiovascular system are:
1) Distribution of O, and nutrients to all the body.
2) Transportation of CO2 and metabolic waste cells and tissues.
3) Distribution of water, electrolytes, and hormones throughout the body.
4) Parts of the immune system.
5) Thermoregulation.
Blood is pumped through a muscular organ of the circulatory system called the heart. It is composed of very strong cardiac muscle tissue and shows rhythmic contraction and relaxation. As a result of this contraction and relaxation, a force is generated that pumps the blood to the entire body along with nutrients and oxygen.
Anatomy of Heart
Heart is a muscular organ, present in all vertebrates that pump blood to the whole body continnously.
• In humans, its size is equal to the size of a clenched fist, and average weight for females is 250-300gm, and 300-350gm or males. Average human heart beats around 70-72 times per minute.
Position
Heart is situated in the thoracic Chest
cavity, obliquely between the A Jungs in the mediastinum space,just above the diaphragm.
• Heart is present in the midline of the body, is slightly tilted towards the left It is a rounded cone shaped structure.
• The pericardial sac consists of two membranes;
1) Fibrous Pericardium: This pericardium covers the heart joining it to great vessels (vena cava, aorta, pulmonary vein and artery).
2) Serous Pericardium: This pericardium is a thin, delicate membrane.
• The outermost layer of the heart wall (known as epicardium) and large blood vessels are continuous with this membrane.
Heart Wall
The wall of the heart is composed of three layers epicardium, myocardium, and endocardium:
1) Epicardium and Visceral Pericardium: The visceral layer of partial pericardium forms the outermost layer of heart and is known as epicardium and visceral pericardium.
• This is a transparent, thin layer and consists of specialised epithelial tissues known as mesothelium Pericardial cavity is a space between the epicardial membrane of heart and the serous pericardium of pericardial sac. (Fluid present in this CAvity is known as pericardial fluid and it protects the heart from friction and erosion.
2.Myocardium:
It is the thickest layer and consists cardiac muscle tissue.
• Fibres of cardiac muscle tissue are striated, involuntary, and branched. (Heart contracts by the contraction of the myocardial membrane.)
3) Endocardium: It is the innermost and third layer of the heart wall.
• It consists of a thin layer of specialised epithelial tissues (known as endothelium) which overlies a thin layer of connective tissues. (This layer provides smooth blood flow to heart and vessels.
• Endothelium also lines inner cavities of the heart, covers valves, and forms the inner lining of blood vessels.
Cardiac chamber
Heart is a hollow chamber which is divided into four distinct chambers, i.e., two atria (right and left) and two ventricles (right and left).
• The atria are thin-walled low pressure chambers whereas ventricles are thick-walled high pressure chambers.
BLOOD CIRCULATION
• With every heart beat the blood is pumped into two closed circuits, i.e., the pulmonary and the systemic circulation.
• The arrangement of these two circuits is in the form of series, such that the output of blood from one system acts as the input for the other system.
Systemic Circulation
1) Left side of the heart participates in systemic circulation and receives
oxygenated blood from the lungs.
2) From the left ventricle blood is pumped into the aorta and the backflow is guarded by the aortic valve.
3.Aorta divides into various systemic arteries which carry blood to all organs throughout the body, except the alveoli of the lungs.
The alveoli of the lungs are supplied by pulmonary circulation.
4) The arteries then divide into small diameter arterioles which further divide into systemic capillaries.
Nutrient and gaseous exchange are seen across the thin walls of the capillaries. Oxygen is delivered and carbon dioxide is picked up via capillaries.
5) The deoxygenated blood then enters the systemic venules (smallest diameter blood vessels carrying deoxygenated blood).
The venules further unite to form large systemic veins. They carry away the deoxygenated blood (blood rich in carbon tissue .
6) Next, via the systemic veins, blood enters the superior and inferior vena cava (the largest veins carrying deoxygenated blood from the upper and lower parts of the body, respectively to the heart) and the coronary sinus (receives deoxygenated blood of the heart) and brings back the deoxygenated blood to right atrium.
BLOOD SUPPLY TO THE HEART
• To work efficiently, the heart needs a continuous supply of oxygen and other nutrients along with a means for waste removal, just Like other organ systems. •Though the blood is already present inside the chambers of the heart (carried by different circulatory systems).
• it is unable to reach the lining cells of the heart wall.
• Therefore the heart has its own system of circulation, i.e., coronary circulation, consisting of blood vessels that nourish all the cells of cardiac tissue:
1) The left and right coronary arteries originate at the base of the aorta, from where the coronary circulatory system begins.
2) From the base of the aorta, left and right coronary arteries originate and supply to the left and right side of the heart (atrium and ventricles). respectively
3) The coronary arteries provide nutrient and oxygenated blood to cardiac cells. At the same time, cardiac veins carry the deoxygenated blood and metabolic waste, which further join into a single large vein, the coronary sinus.
4) The coronary sinus empties the deoxygenated atrium.
. NERVE SUPPLY OF HEART
• Heart has its own conduction system as the heart muscles are specialised to carry nerve impulse.
• The heart muscles are regulated by the autonomous they are innervated with sympathetic and nervous System as parasympathetic nervous system.
. CONDUCTION SYSTEM OF HEART
Conduction System of Heart The conducting system of the heart includes six components as given below:
1) Sinoatrial (SA) Node: It is located in the right atrium, near the opening of the superior vena cava. It is about 1.5cm in length and 0.5cm in width. It is also known as the pacemaker of heart.
• It comprises of the pacemaker (P) cells and some myofilaments.
• Impulse is generated by the P cells and then transmitted within the conducting system (with a speed of 0.05m/s) for the excitation and contraction of heart muscles.
2) Internodal Pathways: Three internodal pathways (figure 11.6) connect the SA node and AV node.
They are:
i) The anterior internodal pathway or tract of Bachman,
ii) The middle internodal pathway or tract of Wenckebach, and
iii) The posterior internodal pathway or tract of Thorel.
3) Atrioventricular (AV) Node: It is located in the lower part of the right atrium, close to the interatrial septum, just above the atrioventricular ringIt is 22mm long, 10mm wide, and 3 mm thick.
• The pacemaker (P) cells are also present in the AV node but normally AV node is not the pacemaker.
• It is because the impulse formation is slower in AV node than that of the SA node.
• The pacemaker cells of AV node are suppressed by the SA nodal impulses. However, when SA node stops producing impulses, AV node becomes the pacemaker of the heart.
• Sometimes it is also known as the pace-setter of heart as it controls the rate of impulse.
4) Bundle of His: A small fibre bundle arising from the AV node and terminating in the Purkinje system is known as His bundle.This is 2 located beneath the AV node and passes towards the interventricular septum.
• The bundle of His is nearly Iem in length. As it enters interventricular septum, it divides into the left bundle branch and the
right bundle branch In case of non-functioning of SA node and AV node, impulses are generated by the bundle of His.
5) Bundle Branches: The branches of bundle fibres enter the walls of the ventricle to further branch out into very small fibre bundles in the inner walls of the muscles of the ventricle, which are termed as Purkinje fibres.
• Bundle branches also have the ability to generate impulses.
• It further divided into two branches:
i) Right Bundle Branch: It supplies the right ventricle solely.
ii) Left Bundle Branch: It innervates the left ventricle.
6) Purkinje Fibres: These fibres form a network of a small bundle of conducting fibres. They are located all over the sub-endocardial regions of right and left ventricles.
PHYSIOLOGY OF HEART
Heart is a hollow, muscular organ which works by changing the tension and length of muscle fibres. The beating of heart generates a pressure that pumps the blood.
• Cardiac cells are cylindrical in shape and are arranged such that if one of the cells is stimulated, it initiates the stimulation of the adjacent cell. Two types of cardiac cells are generally seen:
1) Electrical cells, and
2) Myocardial cells.
Electrical cells are specialised myocardial cells that have essentially lost the ability to contract but at the same time possess the ability to perform a specialised conducting activity (pertaining to cardiac impulses). These cells have the following properties:
1) Conductivity: It is the cell's ability of transmission of an impulse to each other.
electrical
2) Excitability: It is the cell's ability to respond to electrical impulses, and
3) Automaticity: It is the cell's ability to generate as well as discharge an
electrical impulse spontaneously.
• An electrical impulse generated by the SA node is forwarded to rest of the conducting system of the heart. Hence a force of contraction is generated which pumps the blood to the whole body.
• The electrical impulses are the result of action potential.
CARDIAC CYCLE
• The ultimate contraction (systole) and relaxation (diastole) of auricles and ventricles, resulting in one heart beat.is known as a cardiac cycle.
• As the auricles contract (auricular systole).
• the ventricles relax (ventricular diastole); and as the ventricles contract (ventricular systole), the auricles (auricular diastole) relax, and thus it is a continuous cycle.
• Joint diastole is the term used to signify the simultaneous relaxation of both the auricles as well as the ventricles together, for a very short period of time.
• A systole signifies pumping out of blood from the cardiac chamber..
1) Atrial Systole:
• This is marked by stimulation of the SA node A wave of contraction spreads through the atria, and the bicuspid and tricuspid valves.
• thus pumping blood from the atria into the ventricles.
2) Ventricular Systole:
contraction of ventricles occurs a wave of contraction spreads through both the ventricles.
• This is stimulated by AV node stimulates The bicuspid and tricuspid valves close and produce the first heart sound.
• As the ventricles contract, blood flows into the dorsal aorta from the left ventricle and into the pulmonary artery from the right ventricle.
3) Ventricular Diastole:
• As ventricles relax bath semi-lunar valves close with a sound of dub At this time, pressure within the ventricles decreases continuously, When the pressure falls below the pressure of the atrium (atrial pressure), both the bicuspid and tricuspid valves open and the blood again flows into the ventricles.
HEART BEAT
Rhythmic contraction and relaxation of the heart is known as heartbeat. It may either originate neurogenically (origin within a nerve tissue) or myogenically (origin other than the nervous stimulation).
Heartbeat can be regulated by the following two mechanisms:
1) Nervous Regulation: Sympathetic 'nervous system increases the heartbeat by secreting adrenaline hormone. Parasympathetic nervous system -supplying vagus nerve decreases the heartbeat by secreting Acetylcholine (Ach).
2) Hormonal Regulation:
• Thyroxine, epinephrine, and nor-epinephrine affect the heartbeat
• Thyroxine is secreted by the thyroid gland and increases the heartbeat indirectly by increasing Basal Metabolic Rate (BMR).
• Epinephrine and nor-epinephrine are secreted by the adrenal medulla. In case of emergency, epinephrine increases the heartbeat: while under normal conditions, nor-epinephrine increases the heartbeat.
. CARDIAC OUTPUT
• Cardiac output is defined as the amount of blood flowing from the heart (Ge., from the left ventricle into aorta) over a given period of time (or in one heartbeat).
• Cardiac Output Stroke Volume x Heart Rate = 70ml x 72/min = 5040ml/min = about 5 litre/min
Where, Stroke volume = Volume of blood pumped by heart heartbeat).
Heart rate Ventricular systole/min.
PULSE
Pulse is defined as a wave of distension felt in the arteries with each heartbeat.
• It is counted from radial artery of the wrist.
• The pulse rate normally is the same as the heart rate.
• Tachycardia is a rapid resting heart or pulse rate over 100 beats/min.
• Bradycardia is a slow 5 resting heart or pulse rate under 50 beats/min.
• Endurance-trained athletes normally exhibit bradycardia.
• Normal pulse rate ranges 70-90 per minute which may vary under the
following conditions:
1) Pulse rate in man is 72/min and in woman 80/min.
2) Pulse rate in children is more rapid than an adult.
3) Pulse rate is increased under strong emotions, e.g., anger. excitement, etc, 4) Exercise increases the rate of pulse.
Pulse per minute is known as heart rate, which is increased by:
1) Increasing blood pressure in the vena cava,
2) Increasing blood CO concentration,
3) Decreasing blood pH,
4) Increasing body temperature (core temperature),
5) Increasing hormone adrenaline.
ELECTROCARDIOGRAPH (ECG)
• Electrical currents generated in the heart by potential can be detected on the surface of the body as electrical signals.
• These changing signals are recorded by an instrument known as an electrocardiogram (ECG).
• Hence ECG is a composite record of action potentials produced by all the muscle fibres of the heart with cach electrocardiograph.
• The recordings obtained are known as heartbeat.
• Clinically, the recording of ECG in humans is done by positioning four electrodes on the limbs (limb leads) and six electrodes in different positions on the chest (chest leads).
• These electrodes detect the electrical changes of heart.
• The electrical signals recorded from each electrode differ slightly from each other due to the difference in its position relative
to the heart.
• Comparison of these records with each other and with the normal one helps in determining the complications like:
1) Any abnormality in the conducting pathway.
2) Any enlargement in the heart,
3) Damage to any region of the heart, or
4) Any type of pain occurring in the chest
Blood Pressure
• Blood pressure is the hydraulic pressure exerted by the blood on the blood vessels. Normal blood pressure has high systolic value and low diastole value, i.e., 120mm Hg/80mm Hg in arteries.
• The blood pressure is measured by sphygmomanometer.
Types of Blood Pressure
Arterial blood pressure may be of four types:
1) Systolic Pressure:
• It is the maximum pressure or peak pressure (120 mmHg in a healthy adult) exerted in the arteries during the systole of the heart.
• It occurs at the beginning of the cardiac cycle when the left ventricle contracts and pumps blood to the aorta.
2) Diastolic Pressure: It is the minimum pressure (80 mmHg in a healthy. adult) on the arteries.
• It occurs at the end of the cardiac cycle when the ventricles are in resting phase after pumping the blood.
3) Pulse Pressure: It is the differential pressure of systolic and diastolic pressure. It is about 40 mmHg in a healthy adult.
4) Mean Arterial Pressure: It is the average pressure on the arteries.
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