What are the stages of the pre-embryonic period? And when is that?
- The first two weeks
- Stages: Zygote, Morula, Blastocyst (which after implantation differentiates into epiblast and hypoblast)
What is the Zygote and what does it do?
- It is one diploid cell that forms in the uterine tube
- undergoes 4-5 mitotic divisions called cleavage divisions (to form morula)
What is the Morula and what does it do?
- is in the fallopian tube
- solid ball of 16-32 cells (but same size as ovum/zygote)
after cells continue to divide and begin to differentiate into diff cell types with specific form and fcn
What are the features Blastocyst pre-implantation?
- blastocoel/blastocyst cavity (fluid-filled)
- the embryoblast (inner cell mass), which will later divide and differentiate to form the embryo
- trophoblast (made of trophoblast cells) which will divide and differentiate to form chorion (which provides nutrients to the embryo)
What does the blastocyst do?
Travels from fallopian tube to uterus where it implants itself to the endometrium of the uterine wall. Then develops further (another flashcard).
What development does the blastocyst do after implantation?
1. the embryoblast differentiates into a bilayered (2 cell layers) embryonic disc
made of:
- epiblast (which undergoes mitosis to form amnion (fluid-filled amniotic cavity) and 3 germ layers of the embryo)
- hypoblast, which undergoes mitosis to form the yolk sac
2. extraembryonic membranes start to form
What stage of the pre-embryonic period is this?
Pre-implantation blastocyst
What stage are the labeled items in picture formed?
Post-implantation blastocyst
What stage are the labeled items in picture formed?
Post cell differentiation and mitosis of the epiblast cells formed after implantation of the blastocyst
After undergoing mitosis, what does the labeled cell layer form?
The yolk sac
When is the embryonic period and what happens in it?
- 3rd to 8th week of pregnancy
- the 3 germ layers formed in mitosis of the epiblast cells,ectoderm, mesoderm, and endoderm, are now forming the embryo
What does the ectoderm layer develop?
Forms the nervous system and epidermis of the skin
*dev in time, not all in this period*
What does the mesoderm layer develop?
forms muscles, cardiovascular system, dermis, and most bones
*dev in time, not all in this period*
What does the endoderm layer develop?
will form the epithelial linings of the digestive, respiratory, urinary and reproductive systems and their associated glands
*dev in time, not all in this period*
What are milestones the embryo hits in the embryonic period?
- major organ systems almost completely formed (but will need to grow)
- heart begins to beat
- limb buds differentiate (some fingers by end of period)
What are the 4 extraembryonic membranes?
Chorion, amnion, yolk sac, and allantois
Where does amnion come from and what does it do?
- derived from epiblast
- forms amniotic cavity which surrounds embryo/fetus with amniotic fluid (fluid works as shock absorption and temp regulation)
What does the yolk sac come from and what does it do?
- derived from hypoblast
- forms part of digestive track
- source of reproductive germ cells & embryonic blood cells
What is the allantois and what does it do?
- a projection off the yolk sac
- forms umbilical cord and urinary bladder
What is chorion and what does it do?
- derived from trophoblast cells
- surrounds all embryonic membranes
- projections of the chorion are chorionic villi (another flashcard)
When is the fetal period and what happens in it?
- 9th to end of 40th week
- growth and maturation of organs occurs
What is the chorionic villi and what does it do?
- projection of chorion that contains blood vessels that will form fetal part of the placenta (where nutrients, wastes, oxygen/carbon dioxide move between fetal and maternal blood)
What is this?
Chorionic Villi, a projection of the chorion.
Redraw early human development chart
