Human Anatomy - Circulatory System

This 360 degree gallery contains 4 illustrations of a heart; each one presents distinct features of the organ such as its layered construction and the locations of the vital veins and arteries. 

The pumping action of the heart sends oxygenated blood from the lungs to the body for use while simultaneously moving returning, deoxygenated blood from the body, and pumping it to the lungs for oxygenation.

The workings of the heart are mostly hidden from view by the pericardium, the outermost layer which secures and protects the heart. The pericardium holds the heart in place while still allowing it enough room to beat and reducing friction between it and surrounding structures.

With the pericardium out of the way, we can see the heart’s myocardium, or middle layer. The myocardium is the heart muscle; it contracts to pump blood out and then relaxes and refills with returning blood.

The innermost layer of tissue that lines the chambers of the heart is called the endocardium. The heart is divided into 4 chambers: 2 atria, which receive blood, and 2 ventricles that pump blood.

Underneath the cardiac tissue are blood vessels known as the coronary arteries and cardiac veins. These supply the heart tissue with blood. The larger, dark-red tunnels shown are the routes through which the heart pumps blood to and from the lungs and the body.

Blood is not all the same and every human belongs to one of 4 main blood groups: Type A, Type B, Type AB, and Type O. These groups differ due to antigens on the surface of red blood cells. 

Antigens, carbohydrates that cause an immune system to produce antibodies against it, are named, A, B, and D. Type A blood has A antigens, type B has B antigens, AB blood has both, and O blood has no antigens. Presence of D antigen indicates a positive blood type. 

Blood group O carries 2 opposing blood type antibodies (against Type A and Type B) and no antigens. Type O is the universal blood donor as all blood groups can accept it. AB blood, containing both A and B antigens, is called the universal recipient. 

Type A blood can only receive from A and O blood types. Every blood group further divides into positive and negative types. Positive signifies evidence of D antigen. 

Positive types can receive from either positive or negative, but negative types must only receive from negative. 

Plasma, the pale yellow liquid part of blood, contains proteins that allow the blood to clot. Plasma makes up 55% of the body’s total blood and a plasma transfusion is needed if someone has a blood clotting disorder or has suffered excessive bleeding. 

Plasma blood transfusions almost act in the opposite way to red blood cell transfusion. AB plasma is the universal donor and O plasma is the universal recipient. This is because AB plasma does not have antibodies that may cross-react with recipient antigens. 

Damage to the endothelium can be caused by smoking, high blood pressure, or high cholesterol. Plaque may form and restrict blood flow. Plaque buildup can cause a rupture in the artery and the blood clot that forms over the rupture can cause a heart attack.

Plaque is a mix of cholesterol, cells, and debris that create a bump in the artery wall. As more cholesterol gets near the damaged endothelium, white blood cells stream in to digest the bad cholesterol, which causes the arterial bump to grow bigger. 

Blocked arteries completely restrict blood flow to the heart. This doesn’t just happen in the arteries that carry blood from the heart, but all over your body. When blood can no longer flow through the arteries it causes a heart attack or stroke.