Describe the structure of a Red Blood cell 2.2

Red blood cells have a unique apperance they look like doughnuts because they are thinner in the centre and thicker around the edges, they are flexible wjth the ability to twist and bend through blood vessels, red blood cells are about 1/25,000 of an inch in size, they are made in red bone marrow, in infants every bone produces red blood cells but in an adult red blood cells are produced in the thoracic bones, vertebrae, cranial bones and the ends of the femur and humerus bones, red blood cells live for approx 120 days they have a high surface area to allow maximum diffusion of gases.
Red blood cells make up 40% of the bloods volume they contain haemoglobin a protein that gives blood its red color and enables it to carry oxygen from the lungs and deliver it to all body tissues, when the number of red blood cells is to low anemia) it carries less oxygen and we feel fatigued and waek, when the red blood cells are to high (polycythemia) blood becomes too thick which causes the blod to clot and increases the risk of heart attack and strokes.