Prenatal Development Flashcards
What is the first stage of development of a zygote?
Zygote undergoes mitotic cleavage to
What can be found around the outside of a zygote/morula and what is its purpose?
Zona Pellucida
Prevents the zygote/morula from expanding, so it is able to travel through the fallopian tube
What are the first two distinct cell types and their potency?
Embryonic Stem Cells
Trophoblast Stem Cells
Both pluripotent (are trophoblasts pluri??)
What cell gives rise to the placenta?
Trophoblast
What cell type within a blastocyst give rise to the embryo?
The embryonic stem cells give rise to the epiblast cells which ultimately give rise to the embryo
What purpose does the fluid within the morula serve?
It will expand once the morula has entered the uterus to burst the zona pellucida off, allowing for implantation
When does an ectopic pregnancy occur?
If the egg moves too slowly along the fallopian tube and the zona pellucida has burst off, or if the zona pellucida bursts early, implantation within the fallopian tube (or extrauterine, G.I. tract implantation) can occur
What is a blastocyst and when does it form?
It form in the first week of pregnancy when the morula cells differentiate into the inner cell mass, trophoblasts, and a blastocyst cavity forms.
What is gastrulation and when does it occur?
Gastrulation is the formation of the 3 germ layers from the bilaminar disc when invagination of the epiblast towards the primitive streak occurs, invagination of those cells give rise to the mesoderm (middle) and endoderm (bottom) layers o the disc, and the cells at the top form the ectoderm
Occurs at week 3
What cells does the trophoblast give rise to?
Syncytriotrophoblast and Cytotrophoblast
What is the purpose of the cytotrophoblast?
It gives rise to the placenta
What is the purpose of the syncytriotrophoblast?
Is is an invasive cell type that aids in implantation into endometrial lining.
What does the endometrial lining do to aid in implantation?
It undergoes decidualization where it produces molecules that will aid the trophoblast in implantation
When does decidualisation occur?
Begins at the end of week one
What is the bilaminar disc, and when/how is it formed?
A 2 layer disc formed by the differentiation of the inner cell mass into two cells types, the epiblast (superior) and the hypoblast (inferior)
Forms at week 2
When does bilaminar disc formation occur?
During week 2
When will a pregnancy test show up positive?
It tests Human Chorionic Gonadotropin excreted in mother’s urine.
It’s produced by the syncytriotrophic cells towards the end of week 2.
What can the syncytriotrophic cells do to aid in foetal development?
Form strong bond with mother allowing for O2, nutrient, and waste exchange.
What happens to the hypoblast during gastrulation?
It is pushed outwards, and will begin to form the yolk sac
What are some extra-embryonic membranes formed during embryonic development?
Yolk Sac, Amnion, Chorion, Allantois
What are the 3 stages of development and their associated weeks?
Pre-implantation (week 1), Organogenesis (week 2-8), foetal development (week 9-38)
What is the amnion?
Formed from epiblast of the bilaminar disc
Lines the amniotic cavity (filled with amniotic fluid, protects baby)
Present till birth
What is the chorion?
Double membrane encasing chorionic cavity and amnion (and all within)
Form foetal part of the placenta
Formed by the trophoblast and extra embryonic membranes
What is the chorionic cavity?
It is the space between the chorion and amnion, that slowly disappears as the foetus and amnion grow
What is the Allantios?
Forms from Yolk Sac
Forms umbilical arteries and connects to foetal bladder to yolk sac
What is the Yolk sac?
Formed from the hypoblast of the bilaminar disc
Used in nutrient transfer for weeks 2-3, disappears by week 20
Needed for blood cell and gut formation
What is the thinnest part of the fallopian tubes?
Isthmus
What is the zona pellucida composed of?
Glycoprotein
What are germ layer derivatives of the ectoderm?
Epidermis (and derivatives), epithelial lining of mouth and anus, epithelium of pineal and pituitary gland, enamel of teeth, eye cornea/lens, Nervous System, sensory receptors of epidermis, adrenal medulla
What are germ layer derivatives of the mesoderm?
Skeletal System, muscular system, muscles of stomach and intestines, excretory system, circulatory and lymphatic system, reproductive system (NOT GERM CELLS), adrenal cortex, lining of body cavities, dermis
What are germ layer derivatives of the endoderm?
Epithelial lining of digestive tract and respiratory system, lining of; urethra, urinary bladder, and reproductive system, liver, pancreas, thymus, thyroid and parathyroid glands
What is ‘hatching’ of a blastocyst, when does it happen and why does it occur? rk
Hatching is when the blastocyst bursts out of the zona pellucida (5-6 days after fertilisation)
Embryoblasts proliferate and the fluid keeps accumulating in the blastocyst cavity, expanding + eventually bursting out of the zona pellucida (breaking the glycoprotein membrane)
The blastocyst obtains all of its nutrients from the fluid in the uterine tube + uterus, which begin to run out. Hatching allows contact + adhesion of the trophoblasts with the uterus wall to allow for implantation, and consequently allows the embryo to form a connection of the blood supply of the mother
What happens to the size of the embryo and the cells within during the preimplantation stage as the zygote undergoes cellular proliferation? rk
The size of the embryo remains the same to allow for passage down the uterine tube (towards uterus), the cells become smaller as they divide
What are the 3 layers of the uterus wall? rk
Endometrium (lining inside wall)
Myometrium (thick layer of smooth muscle)
Perimetrium (peritoneal covering lining the outside wall)
Name 3 important structures formed during gastrulation rk
Primitive streak
Notochord
Neural tube
What is an ectopic pregnancy? rk
When implantation occurs outside the uterus, possibly due to slow transit of blastocyst in uterine tube or premature hatching
