Blood Read Online Free

acquires a different colour, blood in any human body is bright red when freshly oxygenated and travelling via the arteries to deliver oxygen to the body’s tissues. But it is a darker red in the veins, when it is on its way back to the heart for another infusion of oxygen.
    When I think of hemoglobin, I imagine millions of miniature versions of Sisyphus. As a punishment for deceitfulness, Sisyphus, a king in Greek mythology, is sentenced to the interminable task of hauling a boulder up a hill, only for it to roll down again so that he has to push it right back up. Unlike Sisyphus, hemoglobin isn’t always struggling against gravity. For hemoglobin, the struggle is the laps that it must run around the body — laps that accelerate as the body works harder. The endless task of hemoglobin is to bind itself to oxygen and haul the oxygen to tissues throughout the body.
    It takes blood about a minute to circulate through the resting body. When you get to work — chopping logs, hauling laundry, chasing toddlers, or trying to win a dragon boat race — you oblige your blood to work harder. As your arms and legs speed up, your blood is like a stagehand, supplying props at a furious pace as the play unfolds.
    The best endurance athletes — especially in the ultimate cardiovascular tests, such as running 42.2 kilometres or racing a bike for three weeks through both the Alps and the Pyrenees — are the ones who transfer oxygen most effectively from their red blood cells to cells in their muscles. After refuelling in the lungs and being pumped back out by the heart, hemoglobin, in its oxygen-rich state, is called oxyhemoglobin. But once it unloads the oxygen at its destination points, it becomes hemoglobin again and scrambles through the veins back toward the lungs for another hit of oxygen, only to recommence its endless trucking route. Pity the hemoglobin of an elite runner in the Boston Marathon, or of a cyclist in the Tour de France. All work and no glory. No wonder Lance Armstrong and a legion of other cyclists opted for blood doping, withdrawing and later re-transfusing their own blood to deliver oxygen more effectively to their overworked muscles.
    An average adult has about five litres of blood, representing about 7 percent of their body weight. Blood, like just a few other body parts, such as hair, fingernails, and toenails, is always replenishing itself. Dying and growing back. And like hair and nails, blood will regenerate if you lose it intentionally or accidentally. The bone marrow constantly produces red blood cells, white blood cells, and platelets. And the body can replace donated plasma within hours. But beware: not too many body parts work this way. Lose ’em once, and — like an arm or a leg — they’re gone forever. But you can afford to lose up to about 40 percent of your blood and still survive, if you don’t lose it too quickly.
    There are various types of blood. One common grouping is A, B, AB, and O. And then you can be Rhesus (Rh)-positive or Rh-negative. You have a certain blood type, and that blood type matters. Most blood types cannot be mixed with other blood types. If they are, the person receiving mismatched blood could die.
    It is humbling to contemplate all that blood does. In addition to lugging oxygen to all bodily tissues, blood delivers nutrients such as amino acids, fatty acids, and glucose. It carries away waste such as carbon dioxide and lactic acid, detects and attacks foreign invaders, coagulates to stop bleeding, regulates body temperature, transports hormones, detects tissue damage, and is responsible for hydraulic functions — an oddly formal term for the task of blood during sexual activity. I imagine blood as a happy workaholic, humming away and in a state of constant calisthenics as it nourishes us, lifts us into arousal, does battle with invaders, and replenishes itself.
    Blood, like human identity, is ever shifting. Just when it has