Lecture Notes on Reproductive Systems, Fertilization, and Pregnancy

Overview of Reproductive Systems

• Male Reproductive System

  • Anatomy and sperm production in testes within seminiferous tubules.
  • Hormonal regulation by the hypothalamus-pituitary-gonadal (HPG) axis.
  • Testosterone production.

• Female Reproductive System

  • Ovarian and uterine cycles.
  • Hormonal regulation by HPG axis.
  • Estrogen and progesterone production.

Fertilization Process

• Ovulation

  • Mid-cycle event; secondary oocyte ejected into the uterine tube.
  • Viability of oocyte: 12-24 hours.
  • Sperm viability: 24-48 hours.

• Fertilization

  • Fusion of 23 chromosomes from sperm and oocyte, forming a diploid zygote.
  • Capacitation: Sperm gains energy and motility to reach the oocyte.
  • Acrosomal Reaction: Release of enzymes to penetrate oocyte.
  • Block to Polyspermy: Ensures only one sperm fertilizes the oocyte.

Early Development

• Zygote to Embryo Transition

  • Cleavage: Rapid mitotic divisions.
  • Formation of blastocyst: Inner cell mass (future embryo) and trophoblast (future placenta).

• Pregnancy Definition & Gestation Period

  • From fertilization to birth (~40 weeks from last menstrual period).
  • Zygote (fertilized ovum) -> Embryo (up to week 8) -> Fetus (week 9 to birth).

Implantation and Early Embryonic Development

• Implantation Process

  • Occurs approximately 6-12 days post-fertilization.
  • Trophoblast differentiates into cytotrophoblast and syncytiotrophoblast for uterine invasion.

• Formation of Germ Layers

  • Occurs during gastrulation, forming ectoderm, mesoderm, and endoderm.
  • Organogenesis: Formation of organs from germ layers.

Placenta and Its Functions

• Placentation
  • Formation of placenta from trophoblast and maternal tissues.
  • Exchange of nutrients, gases, and wastes between mother and fetus.
  • Hormonal functions: HCG, progesterone, estrogen, etc.

Fetal Development

• Fetal Circulation

  • Umbilical vein (oxygenated blood) and arteries (deoxygenated blood).
  • Special circulatory shunts: Ductus venosus, foramen ovale, ductus arteriosus.

• Fetal Growth Stages

  • Weeks 9 to birth: Continuous growth and organ maturation.
  • Highlight: heart, nervous system, respiratory readiness (surfactant production).

Maternal Changes During Pregnancy

• Anatomical and Metabolic Changes
  • Uterine and breast enlargement.
  • Increased nutrient requirements: 300 additional calories/day.
  • Cardiovascular adaptations: Increased blood volume and cardiac output.

Labor and Delivery

• Stages of Labor

  • Dilation: Cervix opens from 0 to 10 cm.
  • Expulsion: Delivery of baby.
  • Placental: Delivery of placenta and membranes.

• Hormonal Regulation

  • Role of oxytocin and prostaglandins in uterine contractions.
  • Progesterone's calming effect antagonized as labor approaches.

Postpartum and Lactation

• Newborn Transition

  • Establishment of independent circulation and respiration.
  • Monitoring through Apgar score (0-10 scale).

• Lactation Process

  • Initiation by prolactin and maintenance by oxytocin (letdown reflex).
  • Colostrum vs. true milk: Nutritional content and timing.

This concludes the summary of the lecture covering reproduction, fertilization, pregnancy, labor, and postpartum changes.