Menstruation cycle and 1st week

menstruation cycle

Ovarian Cycle: Follicular phase – Ovulation – Luteal phase

Uterine Cycle: Menstruation – Proliferation – Secretory

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1. Follicle Stimulation Hormone (FSH)

  • Produced by anterior pituitary gland
  • Stimulates primary follicles to develop

2. Estrogen

  • Produced by primary follicles
  • Endometrium to proliferate
  • Stop production of FSH so that other primary follicle don’t develop
  • Stimulate production of LH (Luteinizing Hormone)

3. Luteinizing Hormone (LH)

  • Produced by anterior pituitary gland
  • Stimulates ovulation
  • Rest of Graffian follicle forms corpus luteum – produces progesterone

4. Progesterone

  • Maintain thick endometrium (secretory phase of endometrium)


  • If fertilized, corpus luteum will form corpus luteum of pregnancy – produces progesterone and is maintained by gonadotropic hormones produced by the embryo until placenta takes over to produce progesterone
  • If not fertilized, corpus luteum will form corpus albicans which will then degenerate
  • Reduction in production of progesterone leads to menstruation
  • Reduction in production of estrogen leads to FSH production
  • Proteolytic enzymes prevent coagulation of blood during menstruation
  1. Germinal period – 2 weeks; formation of 3 germ layers
  2. Embryonic period – 3rd week to 3rd month; differentiation of the 3 germ layers into organs and systems
  3. Fetal period – growth of various organs and systems

1st week after fertilization

Zygote →Cleavage division → Morula → Blastocyst → Hatching (degeneration of zona pellucida) → Late blastocyst

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Inner cell mass forms embryoblast

Outer cell mass forms trophoblast; which has 2 poles:

  • Embryonic pole – faces site of implantation
  • Abembryonic pole – opposite pole

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Process of Implantation:

  1. Trophoblast erodes endometrium
  2. Penetration defect in endometrium
  3. Blastocyst embedded in endometrium of uterus
  4. Penetration defect closed by fibrin clot


  1. Ectopic Pregnancy – implantation can occur in the abdomen, ovarian and fallopian tube
  2. Blighted ovum – dead embryoblast
  3. Downs syndrome – Trisomy of chromosome 21
  4. Turners syndrome – monosomy of x chromosome
  5. Triple x syndrome