(a) Explain menstrual cycl in human females
(b) How can the scientific understanding of the menstrual cycle of human females help as a contraceptive measure ?

Explanation

(a) (i) The reproductive cycle in the female primates (E.g monkey apes and human is called) menstural cycle .
(ii) The Ist mentrual cycle begins at puberty and is called menarche ltrbgt (iii) In human females menstruation is repeated at an average interval about `28//29` days and the cycle of events strarting from one menstraution till the next one is menstrual cycle.
The phase of menstural cycle are as follows :
(i) Menstrual phase : It lasts for 3-5 days .Menstrual flow results due to breakdown of endometrial lining of hte uterus and its blood vessel which form liquid that come out thorhg vagina menstruation only occurs if the releaaed ovum is not feritslied
(ii) Follicular phase: It lasts for 8-10 dyas during phase the primary follicles in the ovary grows to become f fully mature graffian folliclea and simultaneously the endometrium fof uterus regenerates through proliferation.The secreation of LH and FSH increses gradually
(iii) Obulatory phse: It lasts for 1 day .Ther is release of ovum
Luteal phase : It lasts for 13 dys .There is LH surge .These induces the remaining part of graffian if fertiliztion occurs endometriumstarts preparing for implant ation . In the absence of fertiliztion corpus luteunm degenerates
(i) Rhythm method : period absitinenerce in whinc coulples avoid coitius form day 10-17 the menestural cylce .In this method ovultion is expected occur and chancesf of fertizlaiton are very high
(ii) Pills used by females also depends on menstrual cycle .oral pills have to be taken dialy for a period of 21 days starting within the first five days menstural cycle oral pills inhibit ovulation and implanation and also modify the equality of cervical mucus to prevent / retard entry of sperms