DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY
Human red blood cells on a blood vessel wall, coloured scanning electron micrograph (SEM). Endothelial cells make up the inner lining of blood vessels in the body, as well as the capillary beds where the blood delivers its nutrients and oxygen to other cells. Red blood cells (RBCs), or erythrocytes, are the most common type of blood cell in vertebrates. They are involved in delivering oxygen to the body tissue. RBCs take up oxygen in the lungs or gills and release it into tissues while squeezing through the body's capillaries. The cytoplasm of RBCs is rich in haemoglobin, an iron-containing biomolecule that can bind oxygen and is responsible for the red color of the cells. In humans, mature RBCs are flexible and oval biconcave disks. Capillaries are the small blood vessels that make up the microcirculation of the human body. Magnification: x1,635 when shortest axis printed at 25 millimetres.
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