The circulatory system includes the heart, blood vessels, and blood, is vital to fight diseases and maintain homeostasis (adequate temperature and pH balance). The main function of the system is to transport blood, nutrients, gases, and hormones to and from the cells throughout the body.



Circulatory system facts

The circulatory system is extremely long.

If I had to place all the arteries, capillaries and veins in an adult, from end to end, they would extend around 60,000 miles (100,000 kilometers). Moreover, the capillaries, which are the smallest blood vessels, would make up approximately 80 percent of this length.


In comparison, the circumference of the Earth is approximately 25,000 miles (40,000 km). That means that a person’s blood vessels could surround the planet approximately 2.5 times!


circulatory system facts
circulatory system facts


Red blood cells must pass through blood vessels

The capillaries are small, with an average of approximately 8 microns (1/3000 inch) in diameter, or approximately one-tenth the diameter of a human hair. The red blood cells are approximately the same size as the capillaries through which they travel, so these cells must move in single file lines.

However, some capillaries have a slightly smaller diameter than blood cells, forcing cells to distort their ways to pass through.



Large bodies have a slower heart rate

Throughout the animal kingdom, the heart rate is inversely related to body size: in general, the larger the animal, the slower the resting heart rate. An adult human has an average resting heart rate of approximately 75 beats per minute, the same speed as an adult sheep.


But the heart of a blue whale is about the size of a compact car, and only beats five times per minute. A shrew, on the other hand, has a heart rate of approximately 1,000 beats per minute.



The heart does not need a body

In a particularly memorable scene in the 1984 film, “Indiana Jones and the Temple of Doom,” a man tears the still-beating heart of another man. While easily removing a person’s heart with a bare hand is a science fiction thing, the heart can still beat after being removed from the body.


This mysterious pulsation occurs because the heart generates its own electrical impulses, which make it beat. As long as the heart continues to receive oxygen, it will continue to function, even if it is separated from the rest of the body.


circulatory system facts
circulatory system facts


Red blood cells are special

Unlike most other cells in the body, red blood cells have no nuclei. Lacking this large internal structure, each red blood cell has more space to transport the oxygen that the body needs. But without a nucleus, cells cannot divide or synthesize new cellular components.


After circulating inside the body for approximately 120 days, a red blood cell will die from aging or damage. But don’t worry, your bone marrow constantly makes new red blood cells to replace those that perish.



The stress can really “break your heart”

A condition called stress cardiomyopathy involves a sudden and temporary weakening of the heart muscle (the myocardium). This results in symptoms similar to those of a heart attack, such as chest pain, shortness of breath and pain in the arms.


The disorder is also basically known as “broken heart syndrome” because it can be caused by an emotionally stressful event, such as the death of a loved one or a divorce, rupture or physical separation of a loved one.



Human blood comes in different colors, but not in blue.

The oxygen-rich blood that flows through the arteries and capillaries is bright red. After delivering your oxygen to your body tissues, your blood turns a dark red color as it runs back to your heart through your veins.


Although veins sometimes look blue through your skin, it is not because your blood is blue. The deceptive color of your veins is due to the way in which different wavelengths of light penetrate your skin, are absorbed and reflected in your eyes, that is, only high energy light (blue) can reach the veins and back.


But that does not mean that the blood is never blue. The blood of many mollusks and few arthropods lacks the hemoglobin that gives human blood its redness, and instead contains the hemocyanin protein. This causes the blood of these animals to turn dark blue when it is oxygenated.



Living in space affects the circulatory system.

Here on Earth, a person’s blood tends to accumulate in the legs due to gravity (the veins in the legs have valves that help maintain blood flow from the legs to the heart).


Things are different in space. Instead, blood builds up in the chest and head (a phenomenon called fluid change), which causes astronauts to have a congested nose, headaches and swollen faces. This change in the fluid also causes the heart to enlarge so that it can handle the increased blood flow in the area surrounding the organ.


Even though the body has the same amount of fluid as before, the brain and other body systems interpret the fluid change as a sudden increase in the general fluid. In response, the body uses several different processes to get rid of excess fluid, resulting in a general reduction in the volume of circulating blood.