JOHN BAVOSI / SCIENCE PHOTO LIBRARY JOHN BAVOSI / SCIENCE PHOTO LIBRARY
Illustration of a single sperm penetrating mucous of the female cervix. The cervical canal connects the vagina to the uterus, and its epithelium con- tains cells which secrete mucous. This mucous is a first barrier to male sperm. However, as here, at female ovulation (egg release), cervical mucous changes structure to allow sperm to penetrate. The mucous is copious, watery, alkaline, consisting of strands which run parallel to the movement of the sperm. At infertile periods of the menstrual cycle (or when using a progesterone contraceptive pill), the mucous becomes viscous, thicker and high in albumin. These strands become tightly packed and form a trap to sperm, hindering its passage.
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