Thump-thump, thump-thump, thump-thump. What's that sound? Three weeks after fertilization, Baby Chris has reached a significant developmental milestone: his or her heart is beating! The embryonic heart is currently tube-shaped, but already performing the critical function of delivering nutrients throughout the body to allow continued growth. Baby Chris's heart will beat 54 million times before he or she is born.
Khan Academy has a nice summary of what has happened in Baby Chris's life so far:
Last week, we mentioned that Baby Chris's body was beginning to divide into three sections known as germ layers: the endoderm, mesoderm, and ectoderm. That process, known as gastrulation, is now complete. The endoderm will become the liver, pancreas, bladder, digestive tract, and respiratory tract. The mesoderm is home to the heart, kidneys, bones, cartilage, muscles, and blood vessels. The ectoderm will become the brain, spinal cord, nerves, skin, nails, and hair.
|Illustration of an 18-day-old human embryo|
Don't forget: you can learn more about Baby Chris's 9-month journey by downloading the See Baby app on your smartphone!