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Preksha Dhyana :
ultimately leading into tiny capillaries, that penetrate the tissues. Here, the delivery of the nutrients and chemicals, and exchange of gases take place. In time, the blood reloaded with wastes begins the return-trip draining it into successively larger veins and ultimately reaches the heart. The very name of the circulatory system implies that whatever blood goes out from the heart comes back to it, completing the circuit. The general sequence of circulation is :
heart--artery- capillary_→vein-->heart.
The exception is : Blood from the digestive tract and accessory organs follows a special pathway with an extra loop*.-from capillary veins capillary. The Heart
If a super-salesman called on you to sell a miracle pump which was designed to last three-quarters of a century and pump more than a thousand million times, circulating 400 million litres (75 to 80 million gallons) of essential liquid to keep your factory functioning, you may not believe him. But the human beart is just that miracle pump. Every day it pumps and circulates blood through about 100,000 k.m. of blood-vessels, which form a completely closed system called circulatory system.
The human heart is a strong red-brown muscle 15 centimetres long and 10 centimetres across, weighing about one-third of a kilogram. It sits on the front and centre of diaphragm which divides the chest from the abdomen. Two thirds of it lies to the left of the medium plane. It is suspended by ligaments and is surrounded by two lungs which fill the rest of the chest. A cage-like bony framework made up by the curved ribs etc, protects these three vital organs in the chest.
The heart is a hollow muscular organ. Interior of the heart is divided into a right and left side by a partition known as septum. Blood cannot pass directly from the left to the right side of the heart or vice versa. However an congenital defect-'a hole in the heart' is quite common *Also sce “Digestive System".
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