The Cardiovascular System

The cardiovascular systems consists of the heart and blood vessels. It is also known as the circulatory system. It's primary job is to move substance to and from cells, it also helps regulate body temperature and ph. The lymphatic system assists the cardiovascular system by gathering up exess tissue waste and returning it to the cardiovascular system. There are three different types of blood vessels. You have the arteries which pump blood from the heart. The main artery is called the dorsal aorta. That artery divides into smaller ones and branches out into different regions of your body. An artery is tough on the outside and smooth on the inside. The arterial wall has three layers an outer layer of tissue, middle layer of muscle and and inner layer of epithelial cells. The strong walls of the artery give it support when blood enters under pressure; the elastic tissues allows it to expand.

Next, you have the capillaries. Capillaries are very thin and fragile. Alot of times you will see people with broken capillaries on their face, especially on and around their nose. Capillaries are so thin that blood cells can only pass through them in single file. The blood cells in the capillary release the oxygen and the tissue release it's waste products.

Lastly, you have the veins. The vein is what carries blood to the heart. The best way to describe the vein is as a hollow tube that will collapse if empty. Most veins have valves to keep the blood from flowing backwards.

Since we are talking about the cardiovascular system we have to mention the heart.
"The heart is a cone-shaped muscular organ located between the lungs directly behind the sternum. The heart is tilted so the apex is oriented to the left." (Sylvia Mader; Human biology 10e)

The pumpling of the heart is what keeps blood flowing through the body. It is estimated that the human heart beats more than 3.5 million times in an average lifetime.