Birth Story

Blood is actually connective tissue, the only liquid type in the human body.

How much blood we have depends on how big we are — blood accounts for about 8 percent of body weight, on average about five quarts (roughly five liters). More than half of blood is plasma, a yellowish fluid that itself is mostly water.

Plasma carries all the things the cells need when it begins its journey out from the heart. The bulk of its cargo is the 25 trillion red blood cells filled with oxygen, but it also carries infection-fighting white blood cells and platelets that will clot the blood when needed, as well as vitamins, electrolytes, hormones and other materials.

Animals that use a protein called hemoglobin to store oxygen have bright red blood when it's fully oxygenated, because hemoglobin contains iron. (Spider blood, for example, contains copper-rich hemocyanin, and is blue when oxygenated.)

Red blood cells are manufactured in bone marrow, and circulate in the blood for about four months. They look like fat plates, flat but curved, a shape that allows them to squeeze into capillaries. They have no nucleus, devoting as much space as they can to hemoglobin.

One entire circulation of the blood through the body of the average resting adult, given that five quarts of blood, takes about one minute. Without the life-giving oxygen it carries, the most vulnerable cells, including those in the brain, would begin to die within about five minutes, and organs would start shutting down just a few minutes later.

Image from Wikimedia Commons

The circulatory system is all about distributing oxygen around the body. The mighty heart — which never rests as long as we live — the 60,000 miles worth of blood vessels, and blood itself, all come down to this: Every cell in our bodies needs a fresh supply of oxygen every few minutes, or it will die. And so will we.

The human heart

The heart is at the center of the circulatory system, a hollow organ composed of muscle and connective tissue. In humans, the heart has four chambers — two atria or "entrances," and two ventricles or "bellies" — and weighs less than a pound.

The heart beats optimally about 70 times a minute throughout our lives, beginning within three weeks after conception, for a total of about 3 billion pulses in a lifetime of  80 years.

The heart pumps blood to the lungs, where it picks up its cargo of oxygen, and then on to the rest of the body.  Valves in the heart and the blood vessels ensure that blood travels in one direction only, away from the heart in the arteries, and toward the heart in the veins.

Red blood cells travel single-file through the capillaries, the fine vessels that connect the arteries and the veins, to deliver oxygen and other nutrients to the cells. Here the blood takes on waste, especially carbon dioxide, which it will deposit in the lungs for expulsion into the air.

A septum in the middle of heart keeps waste-filled blood returning from its journey through the body separate from oxygenated blood fresh the lungs.

Here in the heart, over and over, the journey begins again.

Image from http://commons.wikimedia.org

Countless American schoolchildren learned about the circulatory system from Bell Labs’ 1957 educational film, Hemo the Magnificent, written and directed by Frank Capra (It’s a Wonderful Life). Here is the first 10 minutes of the hour-long film, which is available for purchase.

In the early 17th century, before the scientific method began its ascendancy in the Western world, the Englishman William Harvey described how the blood circulates through the human body, solving a mystery that had stumped scientists for centuries.

Some other scientists — Galen, the ancient Greek; Ibn al-Nafis, who worked in Egypt in the 13th century; and Michael Servetus, a 16th-century Spaniard — had got a chunk of the story right.

William Harvey

Only Harvey, who assiduously tested his theories on living animals, figured out that blood circulates throughout the entire body.

He published his thesis in 1628, as On the Motion of the Heart and Blood in Animals. His discovery is considered one of the most important achievements in medical history.

Harvey introduced the "experimental and observational approach" to scientific inquiry, the British medical historian P.M. Dunn writes in an article for the Archives of Disease in Childhood.

In addition to his revolutionary work on blood, Harvey also advanced our understanding of human reproduction. His practice extended to obstetrics, and he was interested in and knowledgeable about birth.

Harvey's 1651 book On the Generation of Animals, published with the stunning essay "On Parturition," debunked the idea that embryos were fully formed at conception, and advanced the theory of epigenesis, which held correctly that a chick, for example, grew all its various parts from a single cell.

Harvey also addressed labor, advising birth attendants to let nature take its course rather than to intervene unnecessarily. Harvey's tract was the first original work on obstetrics written by an Englishman. Aside from these famous works, the rest of his prodigious writing has been lost.

What remains is "truly remarkable when judged against the ignorance of the times and the prevalent reliance on ancient authority," Dunn writes of Harvey.

I'm embarking on a series of posts about blood. I can't help it. I'm fascinated with blood.

The final classic symptom of amniotic fluid embolism is disseminated intravascular coagulation (DIC). When I suffered an AFE during the birth of my younger daughter, I was nothing but classic.

I hemorrhaged to the point where all the blood ran out of my body three times over. I didn't die from this event because I received a total of 87 units of blood and blood products — whole blood, plasma, cryoprecipitate and extra clotting factor.

I am alive to tell our birth story because thoughtful strangers had donated their blood, a large stockpile of blood was five minutes away when I needed it, and because a whole raft of people had done the work over centuries to figure out how to make someone else's blood work in my body.

And, by 1997, the blood supply had been made safe again, after a horrific tainting with the HIV/AIDS virus.

The bill for my daughter's birth, including two surgeries (a Caesarean section and separate hysterectomy performed to stop the bleeding), a stint for the baby in the high-risk nursery, a night for me in the intensive-care unit and an additional four days in the hospital, was $100,000 all those years ago.

Blood accounted for $13,000, more than 10 percent of the total.

Blood was a major factor in giving our birth story a happy ending. Fascinating!