Female Reproductive System and Menstrual Cycle

Overview

• Right Image: Location of the female reproductive system
• Left Image: Zoomed-in version of the system

Key Components

Ovaries

• Look like beans
• Functions:
  • Produce egg cells (female gametes)
  • Release about one egg per month post-puberty
  • Produce sex hormones: Progesterone and Estrogen
    • Help in development of secondary sexual characteristics
    • Regulate number of eggs released

Egg Release and Maturation

• Girls are born with many immature eggs
• Eggs start maturing post-puberty
• Generally, one egg is released per month
  • Eggs alternate between the two ovaries each month
  • Sometimes both ovaries may release eggs simultaneously

Oviduct (Fallopian Tube)

• Thin tube
• Role: Transport egg to the uterus

Uterus

• Elastic, bag-like structure
• Commonly known as the womb
• Role in Pregnancy:
  • Baby development site
  • Prepares lining rich in blood for potential fertilization

Cervix

• Opening to the uterus
• Needs to open during childbirth

Vagina

• Location where the penis enters during sexual intercourse

Menstrual Cycle

If No Sperm is Present

• Released egg remains unfertilized
  • Disintegrates after few days
  • Uterus sheds its lining
• Menstruation: Shedding of blood from the vagina for 2-5 days

If Sperm is Present

• Sperms travel through the vagina, cervix, and uterus
• Sperms divide into two groups, each looking for the egg
• Fertilization:
  • Sperm releases genetic material into the egg forming a zygote
  • Zygote (fused egg and sperm) starts dividing into multiple cells
  • Becomes an embryo and implants itself in the uterine wall
  • Embryo nourished by uterine blood

Development

Zygote to Embryo

• Zygote begins cell division: 1 -> 2 -> 4 -> 8 cells, etc.
• Reaches the uterus as a ball of cells called an embryo
• Embryo implants into the uterine wall & gets nourishment
• Brought to term (~9 months)

Interesting Tidbits

Twinning

• Identical Twins: Single zygote splits into two embryos
• Non-Identical Twins: Two different eggs fertilized by different sperms

Placenta Development

• Specialized tissue that meets the energy, oxygen, and nutritional needs of the growing embryo

Summary

• Ovaries produce egg cells and release one per month
• Eggs travel via fallopian tube to reach the uterus
• Uterus lining thickens to prepare for potential fertilization
• Unfertilized egg disintegrates, leading to menstruation
• Fertilized egg becomes a zygote -> embryo, implants and grows in the uterus