a) Name the hormones secreted and write their functions:
i) by corpus luteum and placenta (any two).
ii) During Follicular phase and parturition.
b) Name the stages in a human female where:
i) Corpus luteum and placenta co-exist.
ii) Corpus luteum temporarily ceases to exist.

Explanation

a) i) Luteinzing Hormone(LH) stimulates the corpus luteum to produce progestrone. This structure produces increasing level of progestrone which causes endometrial living to secretory.
Placenta: The placenta supplies oxygen and nutrients to the embryo and also does remoal of carbon dioxide and excretory/waste materials produce the embryo.
Placenta also acts as an endocrine tissue and produces several hormones like human chronic gonadotrophin(hcG), hPL (Human Placental Lactogen), estrogen and progestrone.
ii) Follicular phase: The menstrual phase is followed by the follicular phase. The primary follicles in the ovary grow to become mature Graffiani Follicle. The secretion of gonadotrophins (LH and FSH) increases gradually during the follicular phase.
Parturition: It releases oxytoxin, causes stronger uterine contraction or relaxin, secreted during later phase of pregnancy.
b) i) Corpus luteum and placenta co-exist during pregnancy.
ii) In the absence of fertilization corpus luteum is degenerated. This causes disintegration of the endometrium leading to menstruation.