May 28, 2017

BLOOD CIRCULATION – THE HEART IN ACTION

The heart is a muscle consisting of four hollow chambers. It is a double pump: the left part works at a higher pressure, while the right part works on a lower pressure. 

The right heart pumps blood into the pulmonary circulation (i.e. the lungs). the left heart drives blood through the systemic circulation (i.e. the rest of the body). 

the right atrium (ra) receives deoxygenated blood from the body via two large veins, the superior and 

The inferior vena cava, and from the heart itself by way of the coronary sinus. the blood is transferred to the right ventricle (rV) via the tricuspid valve (tV). the right ventricle then pumps the deoxygenated blood via the pulmonary valve (pV) to the lungs where it releases excess carbon dioxide and picks up new oxygen. 

The left atrium (La) accepts the newly oxygenated blood from the lungs via the pulmonary veins and delivers it to the left ventricle (LV) through the mitral valve (MV). the oxygenated blood is pumped by the left ventricle through the aortic valve (aoV) into the aorta (ao), the largest artery in the body. 
the blood flowing into the aorta is further distributed throughout the body where it releases oxygen to the cells and collects carbon dioxide from them.

Abbreviations : Ao = aorta ; AoV = aortic valve ; LA = left atrium ; LV = left ventricle ; MV = mitral valve ; PV = pulmonary valve ; RA = right atrium ; RV = right ventricle ; TV = tricuspid valve ; IVC = inferior vena cava ; SVC = superior vena cava ; O2   = oxygen ; CO2   = carbon dioxide 

The cardiac cycle consists of two primary phases:  

1. VENTRICULAR DIASTOLE is a period of myocardial relaxation when the ventricles are filled with blood.  

2. VENTRICULAR SYSTOLE is the period of contraction when the blood is forced out of the ventricles into the arterial tree. At rest, this cycle is normally repeated at a rate of approximately 70–75 times/minute and slower during sleep.

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