Question

Describe how blood is pumped through the heart from the entry of deoxygenated blood through the venae cavae to the exit of deoxygenated blood out of the aortae, taking into account the roles of the heart valves and cardiac conductance in the flow of blood.

Answer 1

FLOW OF BLOOD AND VALVES

The flow of blood via a normal heart is always unidirectional.this is ensured by presence of valves.

The deoxygenated blood from the body enters right atrium via the venae cavae (superior and inferior). The sinuatrial node then fires and causes contraction of the atria ( both right and left ). The right atrium contracts and then the deoxygenated blood from the body (collected in the right atrium) enters the right ventricle via the tricuspid atrio-ventricular valve . This blood then goes from the right ventricle to the lungs via the pulmonary artery. And this junction between the ventricle and the pulmonary artery is guarded by the semilunar valve . The blood then goes to lungs to get oxygenated and comes back to the left atrium via the pulmonary veins . The oxygenated blood enters the left atrium and then goes to the left ventricle when the atrium contracts. The valve at this atrioventricular junction is a bicuspid valve and is called the mitral valve. the blood then goes to the aorta and is supplied to the entire body. this movent is guarded by a semilunar valve present between right ventricle and aorta.

ELECTRICAL ACTIVITY OF THE HEART

The sinu atrial node acts as the pacemaker of the heart and when it fires, it causes contraction of both the atria simultaneously and this contraction is know as atrial systole. The electrical signal is then conducted to the AV node via the AV bundle. this signal then goes to the Right and Left Bundle oh His which supply the ventricles via the Purkinje Fibres. this causes contraction of the ventricles known as Ventricular systole . the atrial systole lasts for 0.1 seconds and the ventricular systole for 0.3 seconds. When the atria contract, the ventricles relax to collect the blood (ventricular diastole -0.5 secs) .