Physiology of Heart

Circulatory System of Class 11

The heart pumps blood to all parts of the body. The deoxygenated blood is drained into right auricle through superior and inferior venae cavae and coronary sinus whereas the pulmonary veins carry oxygenated blood from lungs to the left auricle. This is called as Auricular circulation. About 70% of the auricular blood passes into the ventricles during diastole. This phase is called diastasis. The rest of 30% of blood passes into the ventricles due to auricular systole (contraction). In this way, blood reaches the ventricles and is called ventricular filling. During ventricular systole (which starts first in left ventricle than in right ventricle), the pressure increases in the ventricles, thus, forcing the oxygenated blood from left ventricle into systemic aorta and deoxygenated blood from right ventricle into pulmonary aorta. The systemic arch distributes the oxygenated blood to all the body parts except lungs while pulmonary aorta carries the deoxygenated blood to lungs for oxygenation.

During foetal life, heart receives and pumps mixed blood and hence, it can be compared with transitional heart, the eustachian flap, in the foetus directs the blood of right atrium towards left atrium through foramen ovalis. From left atrium, blood reaches left ventricle from which the systemic aorta arise. An iliac artery arise from this aorta from the internal branches of illiac artery, two umbilical arteries arise which come out of body through naval and reach placenta where exchange of gases takes place. A single umbilical vein arises from placenta and enters the foetal body through naval and reaches the liver to give some blood to it and some blood to inferior vena cava. Inferior vena cava already possess impure blood. So, there is mixing of blood. In foetus, pure blood is there only in umbilical vein (allantoic vein). Umbilical cord is a tube possessing a jelly like connective tissue (Wharton jelly) along with two umbilical arteries and one umbilical vein.

Coronary circulation : It involves blood supply to the heart wall and also drainage of the heart wall.

Coronary arteries : One pair, arising from the aortic arch just above the semilunar valves. They break up into capillaries to supply oxygenated blood to the heart wall.

Coronary veins : Numerous, collecting deoxygenated blood from the heart wall and drains it into right auricle through coronary sinus which is formed by joining of most of the coronary veins. But some very fine coronary veins, called venae cordis minimae open directly in the right auricle by small sized openings called foramina of Thebesius.

(a) Heart beat : The spontaneous and rhythmic contraction and relaxation of the heart to pump out and receive blood to and from the body is called Heart beat. Depending upon the nature of control of the heart beat, hearts are of 2 types –

Neurogenic and Myogenic or autorhythmic.

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