-
Day 1
The early human zygote where the male and female pronuclei have not yet combined to form the single zygote nucleus. -
Day 2
First cell mitotic divisions of the zygote forming initially 2 blastomeres that continue to divide to form the morula, a solid mass of cells -
Day 4
The free-floating blastocyst has reached the uterine body still enclosed in the zone pellucida and hatches from this surrounding extracellular matrix -
Day 6
Sees the attached blastocyst begin implantation into the maternal uterine lining epithelium and underlying stroma -
Day 7
Implantation completed inner cell mass, bilaminar embryo, trophoblast development, no villous development. -
Day 13
he bilaminar (epiblast and hypoblast) embryo is now about 0.2 mm diameter in size. The three extra embryonic spaces (amniotic, primitive yolk sac and chorionic) are present -
Day 16
Gastrulation is continuing as cells migrate from the epiblast, continuing to form mesoderm. -
Day 18
Gastrulation is continuing as cells migrate from the epiblast, continuing to form mesoderm -
Day 20
The embryo is now 1.5 to 2.5 mm in size and somites have begun to form and number between 1 to 3 somite pairs during this stage -
Day 22
Somite Number 4 - 12, rostral neuropore, neural folds in region of developing brain, neural tube, somites, caudal neuropore, neural fold fuses, remnant of amniotic sac -
Day 24
This early week 4 embryonic stage shows key features of heart tube and neural plate to tube development. The embryo is still transparent enough to view the underlying somite and transverse septum development. -
Day 25
Ectoderm, Mesoderm, head and body come in. -
Day 28
The embryos have a crown rump length (CRL) of 4 - 6 mm and somite number 30 pairs. -
Day 32
Ectoderm: sensory placodes, lens pit, otocyst, nasal placode, primary/secondary vesicles, fourth ventricle of the brain,
Mesoderm: continued segmentation of paraxial mesoderm (more than 30 somite pairs), heart prominence
Head: 1st, 2nd and 3rd pharyngeal arch, forebrain, site of lens placode, site of the otic placode, stomodeum
Body: heart, liver, umbilical cord, mesonephric ridge
Limb: upper and lower limb buds -
Day 33
Identify: midbrain region, nasal pit, lens pit, 1st, 2nd and 3rd pharyngeal arches, 1st pharyngeal groove, maxillary and mandibular components of 1st pharyngeal arch, fourth ventricle of brain, heart prominence, cervical sinus, upper limb bud, mesonephric ridge, lower limb bud, umbilical cord Labelled Stage 15 -
Day 37
Eye showing retinal pigment, nasolacrimal groove, nasal pit, fourth ventricle of brain, umbilical cord, 1st and 2nd pharyngeal arches, cervical sinus, heart, developing arm with hand plate, foot plate -
Day 41
Ectoderm: sensory placodes, lens pit, otocyst,nasal pits moved ventrally, fourth ventricle of brain
Mesoderm: heart prominence
Head: 1st, 2nd and 3rd pharyngeal arch, forebrain, eye, auricular hillocks
Body: heart, liver, umbilical cord, mesonephric ridge
Limb: upper and lower limb buds, hand digital rays -
Day 44
Development indices: number of semicircular ducts (1-3) and length of the paramesonephric duct.
Identify: pigmented eye, eyelid, nasolacrimal groove, external acoustic meatus, heart, digital rays, liver prominance, thigh, ankle, foot plate, umbilical cord -
Day 48
eyelid, eye, external acoustic meatus, auricle of external ear, digital ray, wrist, liver prominence
Identify: straightening of trunk, pigmented eye, eyelid, external acoustic meatus, digital rays, liver prominance, thigh, ankle, foot plate, umbilical cord -
Day 50
scalp vascular plexus, eylid, eye, nose, external acoustic meatus, auricle of external ear, arm, elbow, wrist, liver prominence, digital rays
Identify: straightening of trunk, pigmented eye, eyelid, nose, external acoustic meatus, scalp vascular plexus, digital rays, liver prominance, thigh, ankle, foot plate, umbilical cord -
Day 52
scalp vascular plexus, eylid, eye, nose, auricle of external ear, arm, elbow, wrist, knee, notch between digital rays, umbilical cord
Identify: straightening of trunk, pigmented eye, eyelid, nose, external acoustic meatus, scalp vascular plexus, webbed digits, liver prominance, thigh, ankle, foot plate, umbilical cord -
Day 54
Identify: straightening of trunk, pigmented eye, eyelid, nose, external acoustic meatus, ear auricle, scalp vascular plexus, separated digits (fingers), thigh, ankle, umbilical cord
hearing - cochlea continues spiral growth. -
Day 56
Mesoderm: ossification continues
Head: eyelids, external ears, rounded head
Body: straightening of trunk, intestines herniated at umbilicus
Limbs: hands and feet turned inward
