Embryonic Development Process: Key Stages & Growth Factors

Embryonic development occurs in a step-by-step manner, beginning at fertilization and continuing until birth. The process is divided into five key stages:

1️⃣ Fertilization (Day 0)

• The process begins when a sperm cell fuses with an egg (oocyte) in the fallopian tube.
• This forms a zygote, a single cell containing genetic material from both parents.
• The zygote starts dividing through mitosis to create multiple cells.

2️⃣ Cleavage (Day 1-4)

• The zygote undergoes rapid cell division without increasing in size.
• It forms a morula, a solid ball of cells.
• Cells continue dividing until they form a blastocyst, a hollow structure ready for implantation.

3️⃣ Implantation (Day 5-9)

• The blastocyst travels to the uterus and attaches to the uterine lining (endometrium).
• The outer layer of the blastocyst develops into the placenta, which supports the growing embryo.
• The inner cells form the embryonic disc, which will develop into the baby.

4️⃣ Gastrulation (Week 2-3)

• The embryo forms three distinct layers:
  🔹 Ectoderm – Becomes the nervous system, skin, and hair.
  🔹 Mesoderm – Forms muscles, bones, and the circulatory system.
  🔹 Endoderm – Develops into the digestive system, liver, and lungs.
• These layers give rise to all major organs.

5️⃣ Organogenesis (Week 3-8)

• Major organs begin forming, including the heart, brain, and limbs.
• The neural tube closes, becoming the spinal cord and brain.
• The heart starts beating around Week 4.
• By Week 8, the embryo transitions into a fetus with fully developed basic structures.