Mammalian Development

Introduction

• Fertilization in mammals is internal.
• Processes such as zygote formation, cleavage, gastrulation, and organogenesis occur in the female reproductive tract.

Female Reproductive Tract

1. Ovaries
   • Produce the oocyte.
2. Oviduct/Fallopian Tubes
   • Site of fertilization.
3. Uterus
   • Region where the fertilized egg and embryo grow.
4. Endometrium
   • Lining of the uterus that nourishes the growing embryo.
5. Cervix and Vagina
   • Direct sperm to the oocyte and enable the embryo's exit during birth.

Embryonic Development

• Most embryonic development occurs in the uterus.
• Implantation
  • Embryo attaches to the uterine wall.
  • Uterine endometrium rich in blood vessels provides nourishment.
  • Thickness regulated by hormones like progesterone.

Menstrual Cycle

• Without implantation, hormonal changes cause shedding of the endometrial lining.
  • This can result in resorbing or shedding of the blood lining.
• Menstruation: shedding observed in humans, apes, bats, elephant shrews, spiny mouse.
• Cycle involves thickening and shedding of the endometrial lining.

Oocyte Movement

• Oocyte moves from ovary through fembrae to oviduct.
• Ovulation
  • Oocyte released from the ovary.
• Fertilization
  • Occurs in ampulla region of oviduct.
  • A sperm microRNA initiates S-phase in the zygote.
• Cleavage Stage
  • Embryo undergoes cleavage as it moves to uterus.

Summary

• Roles of different parts of female reproductive system in zygote formation and early embryonic development.
• Movement of oocyte from ovary to uterus.