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There are major differences in the metabolism of morphine and the illegal drug heroin. Morphine mostly produces its CNS effects through m-receptors, and at k- and d-receptors. Heroin has a slight affinity for opiate receptors. Most of its actions are due to metabolism to active metabolites (6-acetylmorphine, morphine, and morphine-6-glucuronide).
An identified risk factor for osteoporosis is the intake of excessive amounts of vitamin A. Dietary intake of approximately double the recommended daily amount of vitamin A, by women, has been shown to reduce bone mineral density and increase the chances for hip fractures compared with women who consumed the recommended daily amount (or less) of vitamin A.
After a vasectomy, it takes about 12 ejaculations to clear out sperm that were already beyond the blocked area.
A good example of polar molecules can be understood when trying to make a cake. If water and oil are required, they will not mix together. If you put them into a measuring cup, the oil will rise to the top while the water remains on the bottom.
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
![The respiratory system. (a) Sagittal section of the head and neck, revealing the organs of the upper](https://biology-forums.com/gallery/47/medium_14755_11_11_12_7_23_09_100491445.jpeg)
![A typical distillation curve. Heavier molecules evaporate at higher temperatures and contain more ...](https://biology-forums.com/gallery/29/medium_548020_25_05_17_1_36_19_29366542.png)