-
Fertilization occurs and the zygote begins to form
-
The morula and blastocyst form
-
The blastocyst hatches and is now free-floating. The zona pellucida is lost
-
Adplantation, the initial step of implantation, occurs
-
This is when implantation of the zygote into the uterine wall occurs
-
This is when the chorionic cavity forms
-
Gastrulation begins. The ectoderm, mesoderm, and endoderm form
-
Neural neurogenesis begins and the neural groove and folds are visible
-
Musculoskeletal somitogenesis begins and the first somites form and continue to be added in sequence. The neural crest is visible. Heart cardiogenesis begins
-
The neural crest differentiates at the spinal cord level. The neural folds begin to fuse near the junction between the brain and spinal cord. The heart begins to beat and becomes the first functioning embryonic organ
-
The thyroid begins to form. Neural rostral neuropore closes for a few hours. The ventricular optic nerve appears and the neural groove is initially filled with amniotic fluid
-
The pituitary gland forms. The liver begins its development.
-
The neural tube is completely closed and the amniotic fluid is separated from the ventricular system. The respiratory system continues to grow and the ability to hear develops
-
The upper and lower limb buds start to form. There is the first appearance of the future cerebral hemispheres.
-
Cranial nerves are now identifiable. The heart and lungs descend into the thorax
-
The eyelids start to form and the head and lips develop further. The limb buds grow and enter the hand plate
-
Smell olfactory nerves enter the brain. The heart separates and forms the aortic arch and pulmonary aorta
-
Limb bones are formed. The female uterus begins to form if the fetus is female. The liver continues to form and the bile ducts are developed
-
Eyelid folds form the eyelids. The bronchial trees in the respiratory system reconstruct. The ovaries, testes, and uterus develop.
-
The upper limbs begin to rotate ventrally. The cerebellum cell layer and the first Purkinje fibers form.
-
The anterior communicating artery forms. The upper and lower limbs rotate.
-
Fingers and toes lengthen. hCG stimulates testosterone production. The tongue and taste buds begin to develop
-
This is now the end of the organogenesis period. The fetus now had a nose, eyes, eyelids, external ears, and a rounded head. Upper limbs are longer and are bent at the elbow.
