Embryonic Development in General Flashcards
What happens before implantation?
- Day 1 - sperm penetration –> then 2 nuclei fuse w/in 24 hrs
- Many divisions w/o inc size
- Blastomere up until 8 cells (totipotent)
- Morula - differentiated cells
- Blastocyst - embryoblasts, trophoblasts and inner blastocele cavity
-Must also hatch from zona pellucida
What facilitates implantation?
- Epidermal growth factor (EGF) on blastocyst binding heparin sulfate on endometrium wall
- Endometrial glands release growth factors and cytokines –> stromal cel COX2 –> prostaglandin spike
- Hormones - estrogen and progesterone
5 Main Events of Week 2
- 2 trophoblast layers (around whole border)
- Cytotrophoblasts - inner layer
- Syncytiotrophoblasts
- 2 embryoblast germ layers
- Hypoblast layer - faces into blastocele cavity
- Cytoblast - faces outer trophoblasts
- 2 cavities
- Amniotic Cavity - b/n cytoblast cells of embryoblast and outer layer of trophoblasts
- Chorionic Cavity - b/n 2 layers of extraembryonic mesoderm
- 2 extraembryonic mesoderm layers (extraembryonic mesoderm is area b/n hypoblast layer and outer trophoblast layer) - splits in 2 to form chorionic cavity
- 2 remodelings of blastocele cavity (one lined by hypoblasts)
- Primary yolk sac pinched into 2 cavities - definitive yolk sac and remnant of primary yolk sac
Process of Gastrulation
- Primitive streak w/ primitive node (gathering of cells at end of streak), primitive pit (goes down from node into layers), primitive ridges (raised cells on ea side of streak) and primitive grooves
- Cells become migratory and move thru pitt to form 3 layers (ALL 3 LAYERS COME FROM EPIBLAST)
- 1- Original epiblast layer becomes ectoderm
- 2- Middle layer of cells that migrated below becomes mesoderm
- 3- Bottom layer of cells that migrated below and pushed hypoblast away becomes endoderm
Ectoderm Derivatives
- Epidermis + nails, hair, sweat glands + tooth enamel
- Forward part of oral / nasal cavity; lens of eye; lining of internal and external ear, nose, sinuses, mouth and anus
- Pituitary gland (ant and post)
- CNS and PNS
- Mammary glands
Mesoderm Derivatives
- Skeletal muscles, skeletone, dermis
- Kidneys + reproductive system
- Heart, blood vessels, blood cells, spleen, lymph tissue
Endoderm Derivatives
- Digestive tract, tongue, lungs, liver, pancreas, tonsils
- Branchial arches –> thyroid, parathyroid, thymus
- Cloaca/allantois –> bladder, urethra
Neuralation
WEEKS 3 and 4
- 50% of cells in ectoderm become neural plate; notochord induces thickening of the ectoderm cranial to the primitive node
- Neural plate becomes wider cranially –> brain
- Neural plate stay narrow caudally –> SC
- Neural plate thickens –> neural folds/ridges –> closes to form neural tube (closes in cervical area first then cont closing both cranially and caudally) –> eventually closed off at both ends
- Failure at cranial end - anencephaly
- Failure at caudal end - spina bifida
Where do neural crest cells originate and what do they become?
Neural crest cells (at highest pt of neural ridges)
- become migratory –> peripheral ganglion, melanocytes, facial cartilage, dentin of teeth, calcitonin cells of thyroid, adrenal gland, Schwann cells, outflow septum of heart
3 Components of Mesoderm
1 - Somites
- Lateral swellings on both sides of midline in symmetrical pairs –> axial skeleton (inc vertebrae), muscles, dermis, vessel endothelium
2- Intermediate Mesoderm - urogenital
3 - Lateral Plate Mesoderm –> outer parietal and inner visceral layers which line body cavities
***B/n these 2 layers is the intraembryonic coelmic cavity which eventually becomes pleural, pericardial, abdominal and peritoneal cavities
When is the embryo most vulnerable?
Weeks 3-8 most vulnerable to to congenital anomalies
Except CNS - sensitive in wks 8-15 too
Anything in first 2 wks can be repaired by embryo or results in spontaneous miscarriage
