|MadSci Network: Medicine|
Hello, Craig. Why is it you think that "the human body is not 100% efficient" in making blood? The key is that we are talking about a HEALTHY human body. Just ponder some of these marvels. In just one second, 8 million blood cells die every second of our lives, but the same number is born in that time. The bone marrow produces over 200 billion red blood cells a day. Your red blood cells travel some 950 miles in 4 months. More than half a ton of red blood cells are created in an average lifetime. You contain some 25 to 30 trillion red blood cells and 75 billion white blood cells. At the same time platelets are produced some 200 billion each day. All this travelling through about 62,000 miles of arteries, veins and capillaries, feeding and servicing the rest of the body's 60 trillion cells! Does this sound like an inefficient blood making machine to you? Sure, there are plenty of diseases in which there can be an underproduction or even overproduction of blood. Only in such circumstances is the body less than 100% efficient in blood making. (1.) Food provides us with energy. When we eat food, the cells take from it the components it needs to function and survive. All cells need to be nourished, including muscle cells, nerve cells and of course, blood cells. The various types of cells have different roles, but they do not act in isolation, rather, the trillions of cells that make up our body perform in concert as a unified and organized system. The point is, that you cannot extract an involuntary function, such as the manufacture of blood, and place a caloric requirement to it. These functions are interrelated and cannot be measured seperately. As well, confounding factors exist, such as, age, body size, weight, gender, metabolic differences, physiological state and activity, environmental factors and even stress levels. All of these factors would make a caloric prediction highly inaccurate, if not impossible. However, what we can do is to determine the least amount of energy required for the involuntary work of the body in order to maintain life, including respiration, maintenance of muscle tone, body temperature and circulation. We call this the B.M.R. or basal metabolic rate. It ranges from 1200 to 1400 kcals. for healthy women and 1600 to 1800 kcals. for healthy men. (2.) Calories from food can easily be determined, including food such as blood. (See my answer for calories on: www.madsci.org, using their search engine, type keywords: "measure calories nut", and click exact words or exact phrase). Blood has a long history as a food source for many societies, (other than for vampires, of course). Today, the Masai tribe, who live in Tanzania, Africa, regularly drink blood as part of their diet. (3.) The main benefit they derive from this practice is the protein content, coming from the iron rich protein called hemoglobin and the numerous proteins found in white bllod cells, such as albumin and globulins, as well as smaller proteins like platelets. Approximately 22% of blood is solids, so, factoring in the remaining carbohydrates and fat, 1 pint of blood would yield the Masai about 400 kcals. As you noted the caloric content of blood has been calculated and is available on the MadSci.org archives, which in my opinion was expertly answered by Dr. Mark Fung.) Finally, you don't have to be concerned about eating a certain number of calories to replenish a pint of blood after a donation. Within an hour or so, the blood volume has been replaced from fluid stores elsewhere in the body. Within a few weeks the body has replaced the other parts of the blood and you're as good as new! Hope that helps, Peter Bosani. References: 1. The Body Almanac - Neil McAleer. Publisher - Doubleday 2. Recommended Nutrient Intakes for Canadians. Health & Welfare Canada. 3. Food In History - Tannahill. Publisher - Crown Publishers. 4. Common Sense Medicine - Curtis H. Baylor M.D. Publishers- Gramercy Publishing Co.
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