DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY
Human red blood cells, T lymphocyte and activated platelets, coloured scanning electron micrograph (SEM). 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. Lymphocytes (leukocytes, white blood cells) are involved in the specific immune response. Pre-T cells circulate in the blood before migrating to the thymus where they develop into specialized cells (helper T cells and killer T cells) that are able to identify antigens and infected tissue cells. Platelets are blood cell fragments that play an essential role in blood clotting and wound repair. When an injury such as a cut is sustained, platelets change their shape (now known as activated platelets), become sticky and build up on a vessel wall to form a plug. Magnification: x1,200 when shortest axis printed at 25 millimetres.
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