Stages of Embryonic Development

Stages of Embryonic Development

• Morula (days 3-4): A compact, spherical cluster of cells formed through several divisions of the zygote.
• Blastula (days 4-5): A fluid-filled cavity called a blastocoel forms, surrounded by an outer layer of cells (trophectoderm) and an inner cell mass (embryoblast).
• Gastrula (days 5-7): The embryo undergoes gastrulation, where the blastula invaginates to form three primary germ layers:
  1. Ectoderm: Gives rise to skin, nervous system, and sensory organs.
  2. Mesoderm: Forms muscles, bones, cartilage, and connective tissue.
  3. Endoderm: Develops into lining of digestive system, respiratory tract, and other internal organs.

Organogenesis

• Neurulation (weeks 3-4): The neural tube forms from the ectoderm, eventually giving rise to the central nervous system (brain and spinal cord).
• Somitogenesis (weeks 3-4): The paraxial mesoderm differentiates into somites, which will form muscles, bones, and connective tissue.
• Organ formation (weeks 4-8): The three primary germ layers differentiate into specific organs and organ systems.

Fetal Development

• Fetal period (weeks 9-38): The embryo is now called a fetus, and rapid growth and organ maturation occur.
• Fetal circulation: The fetus receives oxygen and nutrients from the placenta, and waste products are removed through the umbilical cord.

Embryonic Development Abnormalities

• Teratogens: External factors (e.g., chemicals, radiation, viruses) that can cause birth defects.
• Congenital anomalies: Abnormalities present at birth, such as neural tube defects or limb deformities.