Final answer:
Blood takes approximately 20 seconds to complete a full circulation in the body through the systemic and pulmonary circulations. It carries vital substances like oxygen from the heart to the body and then back to the heart through veins, with varying speeds in different parts of the circulatory system.
Step-by-step explanation:
The circulatory system ensures that blood completes a full circulation within the body, providing oxygen and nutrients to cells and removing waste products. The two main components of the circulatory system are the systemic circulation, which delivers blood to all body cells, and the pulmonary circulation, which is responsible for oxygenating the blood. It takes about 20 seconds for blood to make one complete transit through both the systemic and pulmonary circulations.
William Harvey was the first to describe the systemic circulation, detailing how blood is pumped from the heart to the brain and the rest of the body. Blood is critical for life as it carries essential substances like nutrients and oxygen to our cells. Without the oxygen in our blood, brain cells begin to die within minutes.
Systemic circulation is the specific part of the circulatory system that transports oxygenated blood from the heart to the body via the arteries, and deoxygenated blood back to the heart through the veins. As blood travels, its speed varies significantly: from about 30 cm/sec in the aorta to a much slower 0.026 cm/sec in capillary vessels. This deceleration occurs despite the narrower diameter of capillaries because the total combined diameter of all capillaries far exceeds that of the aorta.