THE CARDIOVASCULAR SYSTEM

CHAMBERS

·         The walls of the heart consist of cardiac muscle called myocardium.

·         The heart consist of 4 chambers are lined with endocardium.

·         The upper chambers of the heart are right and left atria (Atrium).

·         The atria are relatively thin wall and are separated by a wall called interatrial septum.

·         The lower chambers of the heart are right and left ventricles, which have thicker walls and are separated by the interventricular septum.

Right atrium

·         The blood from the body is returned to the right atrium by the two major caval veins.

·         Blood from upper limbs is carried by superior vena cava whereas, blood from the lower body is carried by inferior vena cava.

·         From the right atrium, blood will flow through the atrioventricular valve (AV Valve) / Tricuspid valve into the right ventricle.

·         The tricuspid valve is made of three flaps (cups) of endocardium and connective tissue.

·         The main purpose of the valves is to prevent backflow of the blood.

Left atrium

·         The left atrium receive blood from the lungs by pulmonary veins.

·         This blood will then flow into the left ventricle through left atrioventricular valve / Mitral valve / Bicuspid valve.

·         It prevents backflow of blood from the left ventricle to the left atrium.

Right ventricle

·         Contraction of right ventricle, the tricuspid valve closes and the blood is pumped to the lungs through pulmonary artery.

·         The flow of blood from right ventricle to pulmonary artery is regulated by pulmonary semilunar valve.

Left ventricle

·         Thicker than the right ventricle.

·         The left ventricle pumps blood to the body through aorta, the largest artery of the body.

·         Aortic semilunar valve opened by the force of contraction of left ventricle, which also closes the mitral valve and prevent the back flow of blood.

BLOOD FLOW THROUGH THE HEART

·         The deoxygenated blood from upper limbs drains into right atrium through superior vena cava and lower limbs blood through inferior vena cava into the right atrium.

·         This blood passes into the right ventricle via right atrioventricular valve (tricuspid valve) and from there is pumped into pulmonary artery or trunk.

·         The opening of pulmonary artery is guarded by the pulmonary valve, formed by semilunar valve/cups. This valve prevents the backflow of blood into the right ventricle when ventricular muscle relaxes.

·         The pulmonary artery divided into left and right pulmonary artery, which caries venous blood to the lungs where exchange of gases takes place (CO₂ and O₂).

·         Two pulmonary veins from each lung carry oxygenated blood back to the left atrium.

·         The blood then passes through the left atrioventricular valve into the left ventricle and from there it is pumped into the aorta (the first arty of the general circulation).

·         The opening of the aorta is guarded by the aortic valve formed by three semilunar cups.

Arterial supply

·         The right and left coronary artery which split from aorta just distal to the aortic valve, supply the heart with arterial blood.

·         Coronary artery receives about 5% of blood pumped from the heart.

·         Coronary artery then forming a vast network of capillaries.

 Venous drainage

·         A number of cardiac veins that joins to form the coronary sinus, which open into the right atrium. The remainder passes directly into the heart chambers through little venous channels.

CONDUCTING SYSTEM

SA node

·         Sinoatrial node is a small mass of specialised cells lies in the wall of the right atria near opening of superior vena cava.

·         It regulates electrical impulses, maintain depolarization (60-80 beats/min) is followed by repolarization.

·         Also called pacemaker of the heart.

·         Firing of the SA node triggers atrial contraction.

AV node

·         Atrioventricular node is a small mass of neuromuscular tissue is situated in the wall of the atrial septum near the atrioventricular valves.

·         Transmit electrical current into the ventricles.

·         The action starts when the atrial finish contracting before the ventricle starts.

·         Act as secondary pacemaker function when SA node not working properly (40-60 beats/min).

Bundle of His

·         It is a mass of specialised fibre that originated from the atrioventricular node.

·         The AV bundle crosses the fibrous ring that separates atria and ventricle.

·         It is divides into right and left bundle branches.

·         Within the ventricular myocardium the branches break up into fine fibres called purkinje fibres.

·         AV bundle, Bundle branches and purkinje fibres transmit electrical impulses from A-V node to the apex of the myocardium (Ventricular contraction).