At puberty,the female begins to undergo regular monthly cycles.These sexual cycles are controlled by the hypothalamus.Gonadotropin releasing hormon(GnRH)produced by the hypothalamus,acts on cells of the anterior pituitary gland which is turn secret gonadotropins.These hormons are follicule-stimulating hormone and luteinizing hormone,stimulate and control cyclic changes in the ovary. Ovulation:Ovulation occurs due to influence of FSH and LH.

There is an abrupt increase in LH that causes the primary oocyte to complete meiosis 1.Meiosis 2 also initiated.The surface of the ovary begins to bulge locally.LH hormone increase in high concentration,prostaglandin levels also increase in response to the LH hormone surge.and causes local muscular contraction.Those contraction extrude the oocyte which together with surrounding granulosa cells from the region of the cumulus oophorus breaks free which causes ovulation. Shortly before ovulation ,fimbriae of the uterine tube sweep over the surface of the ovary and the tube itself begins to contracts rhythmically.

In humans,the fertilized oocyte reaches the uterine lumen in approximately 3 to 4 days. Fertilization:It is the process by which male and female gamets fuse,occurs in ampulary region of the uterine tube.Only 1% of sperm deposit in the vagina enter the cervix and the cervix to uterine tube by their own propulsion.Then swim to the ampulla where fertilization usually occurs.

For fertilization spermatozoa has (a)capacitation and (b)acrosomal reaction.The phase of fertilization include phase 1,penetration of the corona radiate.phase 2,penetration of the zona pellusida and phase 3,fusion of the oocyte and sperm cell membranes. As soon as spermatozoa has entered the oocyte and formation of zygot.

Cleavage:Once the zygot has reached the two-cell stage,it undergoes a series of mitotic divisions,increasing the number of cells and become smaller with each cleavage division are known as blastomeres.Approximately 3 days after fertilization,cells of the compact embryo divide againto form a 16 cell morula.Inner cells of the morula constitute inner cell mass which form embryo proper and outer cell mass forms the trophoblast,which later contributes the placenta. Blastocyst formation:

About the time of the morula enters the uterine cavity.Gradually the intracellular space become confluent and finally a single cavity called blastocele.At this time the embryo is a blastocyst. Implantation:At the timeof implantation,the mucosa of the uterus is in the secretory phase.The human blastocele implants in the endometrium along the anterior or posterior wall of the body of the uterus.