Early Embryonic Development: Day 1 - 56

Day 1: Fertilization

Feb 20, 2003

Fertilization is the fusion of haploid gametes, egg and sperm, to form the diploid zygote

Day 8: Implantation

Feb 28, 2003

A fertilized egg attaches to a woman's uterus

Day 16: Gastrulation

Mar 7, 2003

The two-layered embryo is converted into a three-layered embryo

Day 24: Beginning of Organogenesis

Mar 15, 2003

The three germ layers formed from gastrulation: the ectoderm, endoderm, and mesoderm form the internal organs of the organism

Day 32: Embryo Changing

Mar 24, 2003

Body: heart, liver, umbilical cord, mesonephric ridge visible externally as bulges
Liver: hepatic gland and its vascular channels enlarge, hematopoietic function appears
Head: 1st, 2nd and 3rd pharyngeal arch, forebrain, site of lens placode, site of otic placode, stomodeum

Day 40: Embryo Changes more

Apr 1, 2003

neural: first parasympathetic ganglia, submandibular and ciliary, are identifiable
upper limb: bud nerves median nerve, radial nerve and ulnar nerve entered into hand plate, myoblasts spindle shaped and oriented parallel to limb bud axis
heart: outflow tract elliptical configuration with four cushions, the two larger fusing at this stage. Semilunar valve leaflets form at the downstream end of the cushions

Day 56: Embyronic Events

Apr 18, 2003

Body: straightening of trunk, heart, liver, umbilical cord, intestines herniated at umbilicus
Limb: upper limbs longer and bent at elbow, hands and feet turned inward, foot with separated digits, wrist, hand with separated digits
Neural: rhombencephalon, pyramidal decussation present, nuclei and tracts similar to those present in the newborn cerebellum present as only a plate connected to midbrain and hindbrain through fibre bundles