THE HEART

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Our heart is an amazing organ which pumps blood around the body, non-stop, 70 times every minute, throughout our lifespan.

What is even more stunning is how the human heart is constructed in the mother’s womb. With so many staggeringly complicated steps involved in the formation of our heart, it is awe-inspiring that almost all us are born with a normal heart. The heart is the first organ to emerge and function in the human embryo. It forms from the cells located in the cardiogenic region of the newly developing embryo. These cells form two tubes called the endocardial tubes which appear in the chest of the embryo, 18-19 days after gestation. By the 3rd week these 2 tubes merge to form a single tube, our primitive tubular heart, which starts beating and pumping ‘blood’ to the cells which form the heart. Needless to say, this supply of nourishment is essential for the development of the embryonic heart.

The heart undergoes rapid remodeling and by week 9 our embryonic heart has valves and 4 chambers. The process of remodeling continues right up to birth, and even after birth.

At the same time, another separate complex process is in motion, to form the coronary arteries, so vital for the heart to function. The coronary arteries are produced by cells which are completely different from the cells which form the heart:  a grape-like bunch of epithelial cells from the chest wall migrate to the embryonic heart and spread over it like a film. Some these cells convert to mesenchymal cells, which eventually form the coronary arteries. Formation of the coronary arteries is complete by the 9th week, and  shortly after, the ends of the right and left coronary arteries penetrate the aorta at two separate points. This establishes blood flow from the aorta to the coronary arteries.

When the heart starts beating at week 3, the rate is about 80 beats per minute. This gradually increases to 170 at week 8 and then settles to 120-160 by week 12, a rate that persists till birth. By week 22, the heart beat can be heard with a stethoscope.

In a healthy foetus, blood flow can be detected by doppler sonography in the coronary arteries from 31 weeks. In baby’s who suffer from poor fetal development, this flow can be detected much earlier, by week 26: this is not good news and indicates high risk of death for the baby either during the pregnancy or after delivery.

Having developed in such an intricately spectacular manner in the embryo, our heart serves us well till our death. Indeed, our life is totally dependent on our heart, when it ceases to function, death ensues.

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