A Day at the Blood Drive
1Mireille Fontaine, a sixth grader, spent a school holiday with her uncle Darius, who is 34 and gives blood twice a year at Lakemont Regional Hospital. The hospital, the people and the numbers here are made up, but they are based on real blood-donation studies. Before Darius donated, nurse Paulina Szabo pricked his finger to check his hemoglobin, a protein inside red blood cells. In the lungs, hemoglobin picks up oxygen, and the blood carries it to cells all over the body.
2Darius's body held about 5.0 L of blood. In about ten minutes, 0.5 L flowed through a tube into a collection bag, and then the nurse removed the needle. He rested and had juice and crackers. An hour later he stood up quickly and felt lightheaded, and his heart rate jumped from 72 to 90 beats per minute within a few seconds. He sat back down, and the feeling passed. Nurse Szabo explained that standing up quickly lets blood pool in the legs for a moment, so the pressure in the upper body dips. Pressure sensors in the walls of large blood vessels in the neck and chest send signals along nerves to the brain, and the brain sends signals that can speed up or slow down the heart.
3About half of blood is plasma, a liquid that is mostly water. Over the next day or two, the body refills the plasma with water that the intestines absorb from drinks and food. Water the body does not need is removed by the kidneys and leaves in urine. Replacing the lost red blood cells takes much longer. The body makes new ones all the time, but each needs hemoglobin, and building hemoglobin takes iron. Iron comes from foods such as beans, meat and leafy greens and is absorbed in the small intestine. The nurse told Darius to drink extra fluids for two days, to skip hard exercise that day and to take one iron pill a day for eight weeks, which he did.
4Mireille checked Darius's heart rate at rest and right after he climbed the same three flights of stairs at the same steady pace. He skipped the stairs on donation day. The hospital also shared a study of 120 healthy adult donors aged 25 to 45. Each gave 0.5 L of blood and got the same advice about food and drinks. Half took a daily iron pill, and half did not.