Question

How fast does blood travel through the body?

Answer 1

Blood is a fluid that is pumped out by our heart and consists of various types of cells like red blood cells, plasma, white blood cells, platelets and it also carries nutrients, oxygen and hormones from heart and organs to deliver them to their destination. Blood circulates in the circulatory system of our body and is a crucial fluid of our body.

Complete answer:
-As told before, blood is an essential fluid in the human body which helps in carrying molecules from one place of the body to another.
-The rate at which blood flows from one part to another is calculated to be around $1.3$ m/s (which is about $3$ miles per hour). The speed of blood is quite impressive enough to inject a drug into a nerve at arm so that it reaches the brain within frames of seconds.
-The average heartbeat of a person the whole lifetime is $2.5$ billion times. But this speed of heart is not at all constant.
-When aorta pumps out the oxygenated blood through the heart, the speed of blood is up to $15$ inches per second but it slows down as it reaches and interacts with various parts of our body.
The flow of blood is slowest inside narrowest capillaries.
-Flow of blood starts from the right side of the heart when inferior vena cava and superior vena cava fill the right atrium of the heart.
-From here blood goes to the right ventricle through the tricuspid valve and the valve shuts after passing blood to the right ventricle to prevent backward flow of blood.
-From lungs, oxygenated blood enters to the left atrium with the help of pulmonary vein and blood enters to the left ventricle through the mitral valve which shuts close as the blood reaches to the left ventricle to prevent the backward flow of blood.
-Now through the lungs, as the ventricles contract, the flow of oxygen and carbon dioxide through air sacs in the lungs take place.
-From the right ventricle, blood leaves from the pulmonary valve to the pulmonary artery and then to the lungs to get oxygenated.
-From the left ventricle, the blood flows from the aortic valve to the aorta and then to the whole body.

Note: It takes around $45$ seconds from heart for blood to travel around the body. The flow of blood is considered to be fastest in the middle of the vessel and slowest at the vessel wall as the value is inversely proportional to the total cross section of the blood vessel but this value also differs for different capillaries and veins. When blood travels slowly, it might be because the blood has become thicker and might lead to cardiac arrest or tumor.