The Cardiovascular System

Functions

As perhaps one of the most known organ systems, the "heart-vein" system is also one of the most important. First and foremost, the system provides a network of veins, arteries, and capillary beds that can bathe every cell in blood. This is what all other functions stem from. 
1. Delivery of nutrients
Blood leaving the heart the is loaded with oxygen that is necessary for cell survival. Furthermore, nutrients and hormones and injected directly into the outward-flowing blood stream to offer a high-speed ticket to cells. The system is a circuit, however,and the same blood that carries oxygen out to cells must come back each time to be replenished with more oxygen. 
2. Removes wastes
The same circuit of blood comes back to the heart. Having dropped off it's load of nutrients to the cells, it comes back with a whole new load of nitrogenous wastes, carbon dioxide, and other harmful or unnecessary things that can then be sent out of the body.
3. Protection
The blood carries various cells for the immune system that lie in wait to detect and fight off infection. Some of these white blood cells also flow through the system waiting to be carried to an area of blood-loss, where they then proceed to clot. 
4. Regulation
The whole cardiovascular system is all over the body. Veins, arteries, and capillary beds are a system that are able to bathe the whole body with blood, meaning they are incredibly pervasive. This offers a base for self-regulation as well. By changing the pH, water content, and temperature of the blood stream, these changes go on to affect the whole body.

The Heart

As the main, and only, organ of the system, the heart is central to everything the system does; everything is carried out through the heart, through it's one simple function: it pumps. Involved in the pumping mechanism are various parts of the heart. 
1. The right ventricle is the first actual pumping mechanism in the heart. It pumps blood to the lungs to oxygenate it. 
2. The blood coming back from the lungs is then sent to the left atrium, where it collects before going to the left ventricle. 
3. The left ventricle then sends it out to the rest of the body. This gives some sense as to why the heart seems "uneven" and not symmetrical in pictures- the two ventricles differ heavily in size. The right ventricle is smaller, because it only pumps blood to a a small amount of the body. 
4. After the blood has gone to the rest of the body, it comes back in to the right atrium.
5. In the right atrium is located the sinoatrial node, or the pacemaker, which awaits an electrical signal from the brain to contract the heart, send the blood from the right atrium to right ventricle, and start the process again. 

Red Blood Cells

Also known as "erythrocytes", these are the basic cells of the blood. Most of the cell is actually hemoglobin, which is what carries oxygen. 

White Blood Cells

Leukocytes (leuko- meaning white) are primarily cells from the immune system. These cells function by binding to other cells and attempting to get rid of them.

Arteries

These are the main mode of transportation for oxygenated blood away from the heart. This gets blood to the extremities to then be distributed. 

Pulmonary Artery

The pulmonary artery is the single artery that doesn't carry blood away from the heart; it carries oxygenated blood from the lungs to the heart. 

Capillaries

Capillaries are the tubules that stem off from arteries and veins to deliver blood to all cells. They are very thin, small, and fragile. 

Plasma

This yellowish liquid contains a cocktail of essential nutrients such as salts and various proteins. This is the actual liquid component of blood. 

Blood

Blood simply refers to the whole substance that flows through the system. It consists of all the plasma, white and red blood cells, and nutrients being carried

Veins

Veins carry DEoxygenated blood through the body. As a general rule, all veins lead back to the heart into the right atrium so it can be sent to the lungs. 

Pulmonary Vein

This is the only vein that carries blood from the heart. It also carries deoxygenated blood, but takes it away from the heart into the lungs. 

Capillary Beds

This refers to the collective name for all capillaries in a specific location of the body, numerous and heavily interconnected.