DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY
Light micrograph (LM) of Progesterone crystals. Progesterone is a steroid hormone involved in the female menstrual cycle, pregnancy and embryogenesis of humans and other species. Progesterone is secreted in the second half of the menstrual cycle (after ovulation) by granulosa cells of the corpus luteum. Progesterone levels vary during the menstrual cycle and it is an ingredient of most birth control pills where it acts by arresting the cycle. It has a number of physiological effects, usually to normalize or restore changes to the body caused by oestrogen. These effects include normalizing blood clotting and use of fat stores for energy. Progesterone also assists in thyroid function and bone building by osteoblasts, and appears to prevent endometrial cancer and breast cancer. Magnification: x40 when shortest axis printed at 25 millimetres.
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