The ovum released in the ovulatory phase may or
may not be fertilized. If the ovum is fertilized, it becomes
embedded in the endometrium (implantation). In this case
the corpus luteum remains to secrete progesterone which help the
embryo to grow within the uterus. If the ovum is not fertilized,
the corpus luteum disintegrates and the progesterone level falls
sharply. Fourteen days after ovulation, unless fertilization occurs,
menstruation begins again.
ESTROUS CYCLE
The cyclic changes in the female reproductive system
of non-primate mammals is called estrous cycle. It differs
from the menstrual cycle in two respects: (1) there is no
menstruation or blood flow at the end of estrous cycle; (2)
there is a strong sex urge in the female animal, and the animal
is said to be in ’heat’ and ready to receive the male only
during the short period of estrous or heat. This part of the season
is called breeding period, the rest part of the cycle forms
the non-breeding period. The estrous period may extend from
few hours to few days in different animals. The animals may be monoestrous
(e.g., deer, sheep) or polyestrous (e.g., cat, dog). The
hormonal regulation of the estrous cycle is similar to that of the
menstrual cycle.
Hormonal Control of Menstrual Cycle
The following hormones regulate the menstrual cycle.
(Figure 24.7)These hormones have profound effects on the ovaries
and the uterus.
(1) The anterior pituitary gland produces
two gonadotrophic hormones: the follicle stimulating hormone
(FSH) and the luteinizing hormone (LH). FSH stimulates
the ovarian follicle to mature and secondly, it stimulates the follicle
to produce estrogen. The estrogen brings about healing and repair
of uterine wall (endometrium) following menstruation.
Click here for enlargement
Figure 24.7 Hormonal Control of menstrual cycle
