A Brief Revision on Anatomy and Physiology of Heart:

• Heart is a hollow muscular organ located in chest region with main function to pump the blood.
• Its an organ of circulatory system and normal adult male heart weighs around 300 grams.
• It is made up of specialized muscle cells called as “Cardiac Muscles”.
• 

Anatomy of Heart:

• Upper most covering of heart is called as “Pericardium”, the cardiac muscle layer is called as “Myocardium” while innermost heart layer is “Endocardium.
• Heart has four chambers upper two are called as right and left atriums while lower two are called as right and left ventricles.
• Atriums are separated from each other by “interatrial septum”.
• Atriums are separated from ventricles by “Atrioventricular septum”.
• Ventricles are separated from each other by “Interventricular septum”.
• Blood supply to heart itself is goes through a tiny artery called as “Coronary Artery”.
• Heart is supplied with rich supply of nerves as follows,

1. Vagus Nerve: It provides “Parasympathetic Communication”  to heart and its action is to lower heart functions.
2. Nervess from Sympathetic Trunk: It provides “Sympathetic Communication” to heart and its action is to stimulate heart functions.

• The network of nerve formed in heart is called as “Cardiac Plexus”.

Valves in Hart:

• Various valves present in heart prevent the backward flow of the blood.
• The heart has total Four valves one placed between each atrium and ventricle and one valve rests at exit point of each ventricle as follows,

1. Tricuspid valve: Present between right atrium and right ventricle, also called as “Right atrioventricular Valve”.
2. Bicuspid Valve: Present between left atrium and left ventricle, also called as “left atrioventricular Valve.” and as “Mitral Valve”.
3. Pulmonary Artery: Located at base of “Pulmonary artery”.
4. Aortic Valve: Located at base of “Aorta” it is also called as “Semilunar Valve”

Physiology of Heart:

• Contractions of hart are called as “Systole” while relaxation of heart is called as “Diastole”.
• The right side of heart deals with deoxygenated blood while right side of heart deals with oxygenated blood.
• The right atrium receives deoxygenated blood from veins during diastole and then pushes it to the right ventricle through right atrioventricular valve.
• During systole the deoxygenated blood from right atrium enters the pulmonary artery and is transported to the lungs for oxygenation.
• Oxygenated blood from lungs enters the left atrium via pulmonary veins.
• Oxygenated blood from right atrium enters right ventricle through left atrioventricular valve.
• During systole the pure blood from left ventricle enters Aorta and then circulated to the entire body.

Electrical Conduction:

• The normal rhythmical heart beat, called sinus rhythm, is established by the sinoatrial node (SA Node), the heart's pacemaker.
• Here an electrical signal is created that travels through the heart, causing the heart muscle to contract.
• The sinoatrial node is found in the upper part of the right atrium near to the junction with the superior vena cava.
• The electrical signal generated by the sinoatrial node travels through the right atrium in a radial way, It travels to the left atrium via Bachmann's bundle, such that the muscles of the left and right atria contract together.
• The signal then travels to the atrioventricular node (AV Node).
• This is found at the bottom of the right atrium in the atrioventricular septum—the boundary between the right atrium and the left ventricle.
• The septum is part of the cardiac skeleton, tissue within the heart that the electrical signal cannot pass through, which forces the signal to pass through the atrioventricular node only.
• The signal then travels along the bundle of His to left and right bundle branches through to the ventricles of the heart.
• In the ventricles the signal is carried by specialized tissue called the Purkinje fibers which then transmit the electric charge to the heart muscle.

Cardiac Cycle:

• The cardiac cycle refers to the sequence of events in which the heart contracts and relaxes with every heartbeat.
• The period of time during which the ventricles contract, forcing blood out into the aorta and main pulmonary artery, is known as systole, while the period during which the ventricles relax and refill with blood is known as diastole.
• The atria and ventricles work in concert, so in systole when the ventricles are contracting, the atria are relaxed and collecting blood.
• When the ventricles are relaxed in diastole, the atria contract to pump blood to the ventricles.
• At the beginning of the cardiac cycle, the ventricles are relaxing as they do so, they are filled by blood passing through the open mitral and tricuspid valves.
• After the ventricles have completed most of their filling, the atria contract, forcing further blood into the ventricles and priming the pump.
• Next, the ventricles start to contract, as the pressure rises within the cavities of the ventricles, the mitral and tricuspid valves are forced shut.
• As the pressure within the ventricles rises further, exceeding the pressure with the aorta and pulmonary arteries, the aortic and pulmonary valves open.
• Blood is ejected from the heart, causing the pressure within the ventricles to fall.
• Simultaneously, the atria refill as blood flows into the right atrium through the superior and inferior vena cavae, and into the left atrium through the pulmonary veins.
• Finally, when the pressure within the ventricles falls below the pressure within the aorta and pulmonary arteries, the aortic and pulmonary valves close.
• The ventricles start to relax, the mitral and tricuspid valves open, and the cycle begins again.

Cardiac Output:

• Cardiac output (CO) is a measurement of the amount of blood pumped by each ventricle (stroke volume) in one minute.
• This is calculated by multiplying the stroke volume (SV) by the beats per minute of the heart rate (HR). So that: CO = SV x HR.
• The cardiac output is normalized to body size through body surface area and is called the cardiac index.
• Preload refers to the filling pressure of the atria at the end of diastole, when they are at their fullest.
• A main factor is how long it takes the ventricles to fill—if the ventricles contract faster, then there is less time to fill and the preload will be less.
• Preload can also be affected by a person's blood volume.
• The force of each contraction of the heart muscle is proportional to the preload.
• Afterload, or how much pressure the heart must generate to eject blood at systole, is influenced by vascular resistance.
• It can be influenced by narrowing of the heart valves (stenosis) or contraction or relaxation of the peripheral blood vessels.
• The strength of heart muscle contractions controls the stroke volume.
• This can be influenced positively or negatively by agents termed inotropes.
• These agents can be a result of changes within the body, or be given as drugs as part of treatment for a medical disorder.
• Inotropes that increase the force of contraction are "positive" inotropes, and include sympathetic agents such as adrenaline, noradrenaline and dopamine.
• ^“Negative" inotropes decrease the force of contraction and include calcium channel blockers.

Receptors of Autonomos Nervous system present on heart:

Receptor	Action
M2 (Muscarinic Receptor)	Decreased heart functions
B2 (Adrenergic Beta Receptors)	Increased heart functions.
B1 (Adrenergic Beta Receptors)	Increased heart functions.