One Billion Heartbeats

I have always been fascinated by the human body. And life in general. Therefore, my degrees in biology and podiatric medicine. I have decided to share some of the things I have learned which I find interesting, amazing, fascinating, etc. about the human body. I have decided to talk about each organ system separately. The first one I will talk about is the heart/circulatory system. I remember learning in school about mammals having a fixed number of heartbeats per lifetime. Here is an article I found online about this:

"Scientists have been studying living creatures for hundreds of years. One thing they noticed is that there seems to be a relation between how fast a mammal's heart beats, and how long it lives. For example, an elephant's heart beats very slowly, and they live a long time. On the other hand, a mouse's heartbeat is very fast, and mice live for only a few years.

The faster the heartbeat, the less time it lives. A relationship like this, where one quantity gets smaller as the other gets bigger, is called an inverse relationship. Scientists also made the startling discovery that most mammals live for about the time it takes their heart to beat 1 billion times, regardless of the size of the mammal. When a mouse dies after a few years, its heart will have beaten about a billion times. When an elephant dies after 70 years, its heart will have beaten about a billion times. Scientists went even further, looking for a formula which would let them predict the lifespan of a mammal, based on the speed of its heartbeat. In this case there are only two variables, the heartbeat speed (in beats per minute) and the lifespan (in years).Here's the formula they came up with:

A = 1902.6/h

... where a is the mammal's lifespan in years, and h is its heartrate in beats per minute.
Let's see how it works. Consider the common shrew, which is the tiniest mammal on earth. Its heart beats very fast, about 800 times per minute. Using this number for h in the formula ...
a= 1902.6/800 a = 2.38 years
The answer is pretty close to the expected lifespan for a shrew.
Now lets do it for an elephant. An elephant's heart is huge, and beats only 25 times per minute. Filling in 25 for the variable h and dividing gives an answer of 76.1 years. Again, the answer is typically correct for the lifetime of an elephant. People are mammals. Do you think it will work? Let's see what happens. The standard heartrate for a normal healthy human is about 60 beats per minute. When you fill this value in for h, it doesn't seem to work. The answer turns out to be 31.7 years. What went wrong? Human lifetimes are around 70-80 years, aren't they? Actually, the formula works just fine. But it will predict the lifespan of a mammal living in the wild. Humans don't live in the wild; most of us don't have to hunt for or gather our food every day, and we don't have any natural predators. Moreover, we have technology and medicines to keep us healthy and free from disease, and a plentiful diet. However, we didn't always have these life-extending amenities. Before the advent of civilization, say before about 15,000 BC, the average lifetime of a human was about 30 years! In fact, even up until New Testament biblical times (2000 years ago) or so, it still wasn't much longer than 30-40 years. So the formula works for humans too, as long as they are living in a situation where they don't have modern technology. Primitive cultures still exist today where there is little or no contact with the outside world, and the average lifetime of their members isn't much more than 30-40 years." Information obtained from worsleyschool.net

Pretty interesting isn't it? At least I thought it was, so I thought I would share this with you today. Note that the average human heart will beat 2.5 billion times in an average lifespan. (72 beats per minute for 66 years). The heart is an amazing organ. There has never been any pump manufactured that can even come close to what the human heart does. Below are listed some facts about the human heart/circulatory system. I find it fascinating.

"Amazing Heart Facts. Sure, you know how to steal hearts, win hearts, and break hearts. But how much do you really know about your heart and how it works? Read on to your heart's content!

-Put your hand on your heart. Did you place your hand on the left side of your chest? Many people do, but the heart is actually located almost in the center of the chest, between the lungs. It's tipped slightly so that a part of it sticks out and taps against the left side of the chest, which is what makes it seem as though it is located there.

-Hold out your hand and make a fist. If you're a kid, your heart is about the same size as your fist, and if you're an adult, it's about the same size as two fists.

-Your heart beats about 100,000 times in one day and about 35 million times in a year. During an average lifetime, the human heart will beat more than 2.5 billion times.

-Give a tennis ball a good, hard squeeze. You're using about the same amount of force your heart uses to pump blood out to the body. Even at rest, the muscles of the heart work hard—twice as hard as the leg muscles of a person sprinting.

-Feel your pulse by placing two fingers at pulse points on your neck or wrists. The pulse you feel is blood stopping and starting as it moves through your arteries. As a kid, your resting pulse might range from 90 to 120 beats per minute. As an adult, your pulse rate slows to an average of 72 beats per minute.

-The aorta, the largest artery in the body, is almost the diameter of a garden hose. Capillaries, on the other hand, are so small that it takes ten of them to equal the thickness of a human hair.

-Your body has about 5.6 liters (6 quarts) of blood. This 5.6 liters of blood circulates through the body three times every minute. In one day, the blood travels a total of 19,000 km (12,000 miles)—that's four times the distance across the US from coast to coast.

-The heart pumps about 1 million barrels of blood during an average lifetime—that's enough to fill more than 3 super tankers." Information obtained from PBS.org NOVA online.

Isn't the human body amazing?

That's my two cents.