Describe, in brief, the changes the uterus undergoes
(i) to receive the zygote.
(ii) if zygote is not formed
(i) If the uterus receives the zygote, the female becomes pregnant. The embryonic development of the zygote starts immediately. The embryo moves down into the uterus forming a thick and soft lining of blood vessels around itself. This process is called implantation. After implantation, a special tissue develops between the uterine wall and the embryo called placenta, where the exchange of nutrients, oxygen and waste products takes place.
(ii) If the egg released by the ovary is not fertilized and the zygote is not formed, then the thick lining of the uterus breaks down and comes out through the vagina in the form of blood and mucous. This is called menstruation.
(i)The uterus prepares itself every month to receive a fertilised egg/zygote. The inner uterus lining (endometrium) becomes thick and is supplied with blood to nourish the embryo.
(ii) If the egg is not fertilised, then the uterus lining is not required. Hence, it breaks down and gets released in the form of blood and mucous through the vagina. This process lasts for 2–8 days. This cycle occurs every month and is known as menstruation.
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