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Thyroid conditions may make getting pregnant impossible.
Human neurons are so small that they require a microscope in order to be seen. However, some neurons can be up to 3 feet long, such as those that extend from the spinal cord to the toes.
People with high total cholesterol have about two times the risk for heart disease as people with ideal levels.
Hip fractures are the most serious consequences of osteoporosis. The incidence of hip fractures increases with each decade among patients in their 60s to patients in their 90s for both women and men of all populations. Men and women older than 80 years of age show the highest incidence of hip fractures.
Adult head lice are gray, about ? inch long, and often have a tiny dot on their backs. A female can lay between 50 and 150 eggs within the several weeks that she is alive. They feed on human blood.
![Model of a longitudinal study in which 983 students were surveyed in 1984 and then again in 1985, 19](https://biology-forums.com/gallery/47/medium_6_31_05_15_8_20_42_219721459.jpeg)
![Model of a sequential study in which two cohorts were followed beginning at age 20. One cohort was f](https://biology-forums.com/gallery/47/medium_6_31_05_15_8_20_42_21974458.jpeg)