Developmental Biology Overview

Key Concepts

• Developmental biology involves understanding animal reproduction and development.
• Gonads are reproductive structures for gamete production: testis in males, ovaries in females.
  • Primary sex characteristics: Directly involved in reproduction.
  • Secondary sex characteristics: Indicate sexual maturity (e.g., breast development).

Female Reproductive System

• Ovary: Produces ova (eggs); each female has two.
• Oviduct (Fallopian Tube): Transfers eggs from ovary to uterus; fertilization occurs here.
• Uterus: Muscular chamber for embryo development; fertilized ovum implants on the endometrium.
• Vagina: Birth canal.

Male Reproductive System

• Testis: Produces sperm and male hormones (testosterone, androgens).
• Scrotum: Holds testes, maintains temperature for sperm production.
• Epididymis: Matures and stores sperm.
• Vas Deferens: Transports sperm to urethra.
• Seminal Vesicles, Prostate Gland, Bulbourethral Glands: Produce secretions for semen.
• Penis: Delivers sperm to the vagina.

Gametogenesis

• Oogenesis: Begins before birth; involves primary oocytes and development through meiosis during menstrual cycle.
• Spermatogenesis: Begins at puberty in seminiferous tubules; results in sperm formation.

Hormonal Control

• Female Cycle: Ovarian and menstrual cycles involve estrogen, progesterone, FSH, and LH.
• Male Cycle: Involves continuous hormone and sperm production.
• Contraception: Hormonal methods suppress ovulation or sperm production.

Embryonic Development

• Stages: Gametogenesis, fertilization, cleavage, gastrulation, organogenesis.
• Fertilization: Sperm penetrates egg, activates zygote formation.
• Cleavage: Rapid cell division without growth.
• Gastrulation: Formation of three germ layers (ectoderm, mesoderm, endoderm).
• Organogenesis: Differentiation into tissues and organs.

Extra-Embryonic Membranes

• Chorion: Gas exchange and placenta formation.
• Allantois: Waste transport, becomes umbilical cord.
• Amnion: Cushions embryo.
• Yolk Sac: Nutrient transfer and blood cell formation.

Factors Influencing Development

• Egg Cytoplasm: Influences embryonic axes and development.
• Embryonic Induction: Influence of one group of cells over another.
• Homeotic Genes: Regulate body segment development.
• Apoptosis: Programmed cell death for normal development.

Human Reproduction and Development

• Labor Stages: Uterine contractions, birth, expulsion of placenta.
• Twins: Fraternal (dizygotic) and identical (monozygotic).
• Stem Cell Types: Totipotent, pluripotent, multipotent, and unipotent.
• Differences in Development: External vs. internal fertilization, placental development.

Additional Considerations

• Placental Circulation: Exchange of gases and nutrients without direct connection.
• In Vitro vs. In Vivo Conception: IVF techniques and natural conception.
• Pregnancy Trimesters: Developmental milestones and maternal health.