16 week fetal brain

3D Model

In the second trimester, the fetal brain begins to direct the compression of the chest muscles and movement of the diaphragm. These are kind of like practice breaths and are controlled by the brain stem. Sucking and swallowing begin around week 16, and by week 21, the fetus can swallow amniotic fluid.

References: 1. Larsen’s Human Embryology textbook ( Sixth Edition ). 2. The anatomy of human embryo electron microscope textbook ( 1st Edition ) . 3. Langman medical embryology textbook ( Fourteenth Edition ).