-
Jan 1, 1111
Day 1: Fertilization
The sperm fertilizes the egg to form a zygote in the falopian tube; begins 1st trimester -
Jan 1, 1112
Day 1: Cleavage
A mitotic cell division occurs in the zygote multiple times as the zygote becomes a pre-embryo and develops into a multicelular blastocyst; eventually ends when uterine wall is contracted -
Jan 1, 1113
Day 2: Morula
A solid ball of blastomere cells forms from cleavage phase; reaches uterus on 4th day -
Jan 1, 1114
Day 5: Blastocyst/blastocoele
The morula develops inner cavities and an inner cell mass; formed by many blastomeres as division continues -
Jan 1, 1115
Day 7: Implantation
The blastocyst adheres to the uterine lining as the trophoblast cells rapidly divide to create several layers -
Jan 1, 1116
Day 16: Gastrulation
The 3rd layer of cells begin to form (mesoderm) as others move towards the central line; the primitive streak begins to form -
Jan 1, 1117
Day 18: neural neurogenesis
The neural grooves and folds of the developing brain are first seen -
Jan 1, 1118
Day 20: Musculoskeletal somitogenesis
1-3 somite pairs appear in the neural groove and can now be added to sequence to develop the musculoskeletal system in the embryo -
Jan 1, 1118
Days 21-25: Organ generation and development continues
Heart cardiogenesis occurs on day 21 as paired tubes; laryngotracheal groove (precursor to lungs) forms on day 22 to begin respiratory development; Thyroid development begins on day 24; Liver formation begins on day 25 -
Jan 1, 1118
Day 27: Beginning of Vascular Dev.
The hindbrain is supplied by 2 arteries to begin the development of the circulatory system and bloodflow -
Jan 1, 1119
Day 31: Sense Appearance and Visibility of Organs
Sensory receptors and sight and smell structures become prominent in the embryo while the 4th brain ventricle also appears; The heart, liver, and umbilical cord become externally visible as bulges protruding from the embryo -
Jan 1, 1120
Days 35-36: Further Organ Development
The pituitary gland becomes defined and independent in the proper location; Parathyroid glands generate in the thyroid; Adrenal glands begin to form; Heart and lungs descend into thorax; tongue begins to become defined -
Jan 1, 1121
Day 41: Sense Organs Distinguish Structure
Olfactory nerve fibers enter the brain to provide the early parts of the smell sense; Eyelid sulcus deepen as eyelid folds develop -
Jan 1, 1123
Day 43: Middle Organs Perform Important Roles
The pancreas secretes insulin at an increasing rate; Liver enlargement stops the movement of the heart and lungs, keeping them at the desired location -
Jan 1, 1125
Days 51-52: Structure and Digestion Established
The abdominal cavity becomes defined to provide structure with the presence of muscle arising along with connective tissue presence; The gastrointestinal tract seperates from the anal membrane -
Jan 1, 1126
Day 55: Sex Hormone Secretion Begins
Testosterone production begins in the embryo -
Jan 1, 1127
Day 56: End of Embryonic Development and Beginning of Fetal Phase
Body trunk straightens; Rounded head; Abdominal wall forms 3 layers; G cells in stomach begin to appear; Fetal development begins
