Development of zygote and placenta

1) Development of zygote 

               

 (a) Morula

• After 30 hours of fertilization ovum(zygote) divided into 2cell by mitotic division
• these cell divide again and again by mitotic division and form cluster of cell celled "morula"
• morula remains in uterine tube for 3 day, then enter in uterine cavity  

   (b) Blastocyst-

• on 4th and 5th day's morula remains free in utreine cavity, during this time fluid secrete by zona pellucida(outermost layer of morula), forms a fluid cavity(known as blastocele) in morula.
• It seprates cell of morula and increase size, which called blastocyst(58 cell stage)
• The process from morula to the development of blastocyst is called as Blastulation
• Blastocyst consist of 2 layers 
• Outer cell mass is called Trophoblast (form plecentaand chorion)
• Inner cell mass is called Embryoblat(forms embryo,amnion,and umbilical cord
• At this stage, implantation in the endometrium occurs.

Blastocyst secrets HCG(humen chorionic gonodotropin) harmone to maintain Carpus luteum, it also secrets estrogen and progesterone for first 2 to 3 month.

Implantation 

• Implant of the developing blastocyst in the uterine mucosa occur 6 or 7 days after fertilization

Normal site of Implantation-

• Anterior or posterior wall of the body of uterus near the fundus in the endometrial wall.

Starting Time-

• On 6th day of the fertilization or 20th day of a regular menstrual period.
• Penetration of blastocyst takes place in deeply of compact layer of endometrial.

Completing time-

• On 10 and 11 day after fertilization or 24-25 days of regular cycle,deep penetration occur which called interstutial implantation.
• At this time blastocyst covers by endometrium(decidua) from all sides.
• More deep penetration, control by immunological factors of mother.

(2) Development of plecenta 

TROPHOBLAST 

• placenta and fetal membranes develop from trophoblast.
• During first 2week the trophoblast proliferates and differentiates into 2 layers 

(a) Outer layer- Cell in this layer are multinucleated which called syncytio-trophoblast (syncytium).

(b) Inner layer- Cell in this layer are mononucleated and cuboidal dividing cell which called cytotrophoblast or Langhan's cell layer.

• The outer syncytiotrophoblast invade the decidua by forming finger like projection called villi.
• Villi( contains blood vessels of embryo) begin to bfranch and make their way into the decidua and mother's blood-filled spaces called lacunae.
• Thus,villi allowing exchange between mother and embryo.