Fertilization and Early Development + Extraembryonic tissue

How does the body prevent polyspermy

Zona pellucida closes as soon as one sperm enters

What happens in the blastula stage

Blastocyst forms into trophoblast and inner cell mass

What does trophoblast and inner cell mass form into

Trophoblast → extraembryonic tissue; inner cell mass → embryo and extraembryonic tissue

What happens in bilaminar stage

Development of epiblast and hypoblast at embryonic pole and formation of embryonic cavities

What are the embryonic cavities

Amniotic and chorionic cavities, yolk sac

What happens in implantation phase

STB implant into the endometrium and spread → STB forms into villi and connect to the trophoblast lacuna (where maternal blood is)

Common sites of ectopic pregnancy

Ampulla > Isthmic > Fimbrial > Interstitial > rectouterine pouch > ovarian > cervical > abdominal

What happens in gastrulation

Forms into epiblast (into bilaminar into 3 germ cell layers), hypoblast (cavity) and primitive streak

What does each germ cell layer make

Ectoderm → Outside of body + neural tube; mesoderm → Most soft tissue; endoderm → GI

What is hydatidiform moles

Caused by loss of maternal pronucleus → only paternal cell

What is the difference between fraternal and identical twins

Dizygotic = fraternal where there is 2 egg and 2 sperm; monozygotic = identical where there is 1 egg and 1 sperm that duplicate

Which parent gives child the mitochondria

Mother only

What week (conceptual age) does fertilization, implantation and gastrulation happen

1st = fertilization, cleavage, blastocyst; 2nd = implantation; 3rd = gastrulation

How does the amniotic cavity form

Forms first; in week 2 fluids collects between epiblast and trophoblast → Amnioblast expand and enclose embryo by week 8

How does yolk sac form

Hypoblast proliferation + cell migration form yolk sac → First wave form primary yolk sac → Mesoderm fill blastocyst cavity → second wave form secondary yolk

How does chorionic cavity form

Mesoderm forms two layers → Chorionic cavity splits the embryo (with amnion and yolk sac) from blastocyst (chorion)

What is yolk sac made of

Extraembryonic ENDOderm and mesoderm

What is amnion and chorion made of

Extraembryonic ECTOderm and mesoderm

Connecting stalk function

Suspend dorsal amnion and central yolk sac to chorionic cavity at day 13

How does allantois form

Week 4 → neural tube overgrow caudal yolk sac → connecting stalk merge with yolk sac neck → Root of connecting stalk contains allantois

How does amniotic sac form

Folding separate embryo from extraembryonic membrane → Amnion expand and cover everything but umbilical area → Fuses with chorion

What happens when chorion merge with amniotic sac

Stem villi grow → Has blood vessel that bring blood from mother to fetus

What is chorion frondosum and laeve

Frondosum becomes placenta; remaining part is laeve

How does umbilical vesicle develop

Yolk sac becomes smaller as pregnancy does on → Has no effect if it persist unless it is omphaloenteric duct

What is Meckel’s diverticulum

Caused by omphaloenteric duct that does not detach from midgut at week 6

Allantois function

Blood cell formation, blood vss persist at umbilical artery and vein, part of it becomes urachus

How does placenta form

Decidual reaction where endometrial stroma accumulate lipid and glycogen and thickens = decidua

Parts of placenta

Fetal: has chorion frondosum and intervillous space (with maternal blood); maternal: made of decidua basalis

What tissue layers must blood pass through to get from mother to fetus

Endothelium of villus capillary, loose CT at villus core, CTB layer, STB layer

What is amniochorionic membrane

Amnion + chorion → fuse with decidua capsularis

hCG, hCS and hCT function

hCG = maintain CL to keep pregancy; hCS = lower glucose utilization and increase FFA use; hCT = similar to TSH

What diseases can and CANNOT be given immunity through maternal Ab

CAN: diphtheria, smallpox and measles; CANNOT: Pertussis, varicella;

How does umbilical cord develop

vitelline duct and connecting stalk + amnion → Grows into umbilical cord

What is amniocentesis

Aspirate amniotic fluid at 14-16 weeks; look for alpha fetoprotein → If high = neural tube defect

What is chorionic villi sampling

If CVS is ambiguous = chromosomal mosaicism

Fetal circulatory shunts

Ductus venosus (bypass liver), foramen ovale (RA to LA without lung), ductus arteriosus (PA to aorta)