CIRCULATORY SYSTEM

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.
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What makes your heart beat?

What makes your heart beat is not a simple as you think. Take a look into what makes this crucial organ tick with the help of the information inside this article.

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  • Are all blood types needed for for donation?

    Are all blood types needed for for donation?

    When you donate blood, your blood type is an important factor in how useful your donation may be. Just what are blood types? See more »

  • Do you know what's flowing through your veins?

    Do you know what's flowing through your veins?

    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. See more »

  • How and why does the heart pump blood to itself?

    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? See more »

  • How Blood Works

    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. See more »

  • How Your Heart Works

    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. See more »

  • Natriuretic Peptide

    Natriuretic Peptide

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

  • Serum Creatinine Overview

    Serum Creatinine Overview

    Creatinine is a chemical molecule that is present in the serum (liquid portion) of the blood. The amount of creatinine produced depends on a person's muscle mass. But how is it measured? See more »

  • What causes the sound of a heartbeat?

    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? See more »

  • What determines the rhythm of your heart?

    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? See more »

  • Why do you have two lungs but only one heart?

    Why do you have two lungs but only one heart?

    Why don't you have two hearts? Here's a hint: It's the same reason why you have one liver, but two eyes. Would a second heart help you live better? See more »

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