circulatory system library

The heart is a hollow, muscular organ that maintains blood circulation throughout the body. Learn how the circulatory system - your heart, blood vessels and blood - bring nutrients to the body.

Featured Article: Blood Flow

This detailed medical animation explains the movement of blood between the heart and the body's organs and tissues. See more »

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Blood Flow

This detailed medical animation explains the movement of blood between the heart and the body's organs and tissues.

A vampire is headed straight for you. "I vant to drink your blood," he hisses. To prevent him from sucking the life force straight out of you, you decide to distract him with your amazing knowledge of blood. Take the quiz and prove yourself.

How and why does the heart pump blood to itself?

Every second of the day, blood bustles through your body, bound for your brain, toes and everything in between. How does your heart receive its fair share of the good stuff?

How Blood Works

When you cut yourself accidentally, do you ever wonder what makes up this thing we call blood? It's pretty amazing stuff, considering how it wards off infections while supplying nutrients to every cell in the human body.

How Cholesterol Works

Medical research shows that high levels of cholesterol are associated with heart disease, the nation's number one killer. One in five Americans has high cholesterol -- find out if you're at risk.

How does the body make electricity -- and how does it use it?

Everything we do is controlled and enabled by electrical signals running through our bodies. But how are those signals produced, and what happens when your electrical system breaks down?

How Natriuretic Peptides Work

The natriuretic peptides are sometimes called the body's "natural diuretics" because they lower the concentration of sodium in the blood.

How Your Heart Works

The heart is a vital organ that basically serves as a pump. Learn about heart chambers and valves, blood flow, the heart's electrical system and blood supply. Read more about how this amazing organ works.

What causes the sound of a heartbeat?

Lub-dub, lub-dub, lub-dub, that's usually the sound of a happy heart. But what's responsible for that steady, comforting beat, and what if your heart doesn't sound like that?

What determines the rhythm of your heart?

When it comes to the heart, timing is critical. An irregular heartbeat is inefficient and deprives the body of blood. So what sets your ticker's rhythm?

What's the difference between LDL and HDL cholesterol?

Unless you've been hiding under a giant cheeseburger for the past decade, you probably know that having high cholesterol is bad for you. But it's not all created equal, and knowing the difference will help you to make sense of your cholesterol test.

8 Most Common Blood Types

Did you know there are eight common blood types? Read our list of blood types to find out which are the most common and which types are compatible.

How the Body Uses Cholesterol

Cholesterol produces a wealth of highly valuable substances in the body. It makes its mark in digestion, absorption of vitamins, and even reproduction. Find out why your body needs cholesterol.

Cholesterol Levels

We�ve all heard of �good� and �bad� cholesterol, and you may even know which is LDL and which is HDL. It�s important for doctors to know the levels of each. Find out how each type affects your heart and what the levels tell you.

Arrhythmia

Arrhythmia is the medical term for an irregular heartbeat. In this animation, learn what causes it and how it affects the health of the body.

Artery Problems in Smokers and Non-Smokers

Smokers are at greater risk of developing artery complications. This animation illustrates the difference between an artery in a smoker and a non-smoker.

Atherosclerosis

Atherosclerosis is caused by fatty material is deposited on the wall of a damaged artery. Watch this animation to learn how it can cause an artery to become blocked.

Blood Clots

A blood clot can lodge in an artery in the brain blocking an artery in the brain. This animation illustrates how this happens.

Blood Clotting Process

Clotting is the process by which the body heals cut blood vessels. This animation explains how blood clots develop from platelets, clotting factor and fibrin.

Blood Pressure

One of the heart's most important functions is maintaining normal blood pressure in the body. This animation describes the factors that affect blood pressure and how the heart keeps it steady.