Blood is a substance of profound biological, historical, and even cosmic significance. Far more than just a simple red fluid, blood connects us to the universe itself: the iron that gives our blood its life-sustaining properties originated from the catastrophic death of supernovas. Furthermore, its composition of salt and water echoes the ancient oceans from which life emerged.
The Body's Vast Highway System
The human circulatory network is staggering in scale. The system of veins, arteries, and capillaries spans approximately 100,000 kilometers, which is twice the circumference of the Earth. The majority of this length is composed of capillaries, tiny blood vessels that extend to nearly every single cell in the body to deliver essential oxygen and nutrients.
In a resting human, the heart is a powerful pump, circulating a liter of blood about every 10 seconds and beating an average of 75 times per minute. The amount of blood in the average human body ranges from eight to twelve pints, and an individual can typically survive losing up to 40% of this volume before organs begin to fail due to a lack of oxygen.
A Substance of Constant Renewal
Unlike a fixed supply, our blood is in a constant state of decay and renewal. A red blood cell has a lifespan of approximately 143 days inside the body. Once collected for medical use, a bag of blood has a shelf life between 35 and 49 days—longer than milk, but not as long as cheese.
While most people are familiar with the common A, B, O, and AB blood groups, there are many other lesser-known types, including Duffy, Kid, and the uniquely named Landsteiner-Wiener. Even animals have distinct blood types, such as the eight types found in dogs and three in cats.
Life-Saving and Mythic Power
The power of blood has been recognized throughout history. Ancient Greek mythology, for instance, spoke of Medusa, whose blood from the right side of her body was fatal, while blood from the left could restore life. This mythic force is embedded in modern language through phrases like "blood brothers," "blood feud," and "bloodlines."
In modern medicine, the power is real: a blood transfusion is performed every three seconds worldwide. Though scientists can now grow red blood cells in a laboratory setting, the process remains extremely expensive. For now, the most reliable and affordable source of this life-saving and life-enhancing liquid continues to be the simple act of human donation.
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