Week 1- Embryology Flashcards
What happens between day 1-5?
Fertilisation to Blastocyst
Repeated mitotic divisions
Cells wrapped in zona pellucida
Day 3: Morula forms
Day 5: Blastocyst= x2 layers -> Trophoblast & Embryoblast
What forms on day 3?
Morula
What forms on day 5?
Blastocyst
(Trophoblast & Embryoblast= inner cell mass)
What happens on day 6?
Implantation
Blastocyst hatched out of zona pellucida to stick to uterine epithelium
What happens in Week 1 of embryology?
Fertilization
Repeated mitotic divisions
Day 3: Morula
Day 5: Blastocyst
Day 6: Implantation
What happens on Day 8?
Embryoblast —> Bilaminar disc: Epiblast & Hypoblast
Amniotic cavity forms within epiblast
Trophoblast —> Syncytiotrophoblast: Cytotrophoblast (single cell layer) & Syncytium (invasive outer later) containing digestive enzymes
Syncytiotrophoblast invades endometrium
What happens on Day 9?
KEY = Primary Yolk Sac Formation
Hypoblast forms Exocoelmoic membrane which lines the primary yolk sac
(Syncitiotrophoblast invading the uterine glands & blood vessels
(Sinusoids (maternal blood vessels) invade Lacunae (spaces in syncitiotrophoblast) –> Uteroplacentral circulation (Day 10-12) )
What happens on Day 12?
Embryo fully implanted
Extraembryonic mesoderm (cells & ECM) form layer between Bilaminar disk, yolk sac, amniotic cavity and trophoblast (Syncitio and cyto)
Extra-embryonic coelom appear (these will emerge to nearly surround the embryo forming the chorionic cavity)
Lacunae in trophoblast which communicate with maternal endometrial sinusoids deriving nutritional support
What happens on day 13?
Secondary yolk sac present (smaller than first on)
Amniotic sac present
Chorionic cavity formed by cavitation of extra embryonic mesoderm (extra-embryonic coelem)
Connecting stalk (to cytotrophoblast)= extra embryonic mesoderm & forms future umbilicus
Uterine epithelium reformed
What happens during week 2 of embryology including the important days
Day 8: Amniotic cavity formation
Syncitiotrophoblast invades endometrium
Bilaminar disc formation
Day 9: Primary Yolk sac formation
Day 12: Extra-embryonic mesoderm with coelom appearing
Trophoblastic lucunae
Day 13: Secondary Yolk sac formation
Chorionic cavity
Connecting stalk from extra-embryonic mesoderm
What happens during week 3 (brief)?
What is the significance of day 15?
Day 15 = first chance to notice mestrual cycle is late
Formation of Trilaminar disc!
Epiblast known as Ectoderm
Hypoblast known as Endoderm
Gastrulation: what happens in relation to buccopharyngeal & cloacal membrane?
Remain mesoderm free
Prochordal plate —> Buccopharyngeal membrane = membrane between mouth and pharynx
What is Gastrulation & what happens?
When does it happen?
Week 3
Formation of 3 germ cell layer
Primitive streak & node = Raised area of epiblast (rapid epipblast cell division)
Primative streak from cloaca to primitive node
Primative Groove (from streak) & Primative Pit (from node): Cells from ectoderm migrate down these and spread out laterally. Forming mesoderm.
[NOTE: Endoderm formed from migrating epiblastic cells displacing hypoblast]
Primative groove & pit = Indentations of ectoderm in centre of streak & node (cells migrating downwards)
Prochordal plate (mouth) & cloacal membrane (anus
What is the endoderm made from?
Cell that have migrated down the Primative Groove/ Pit and replaced the hypoblast
Gastrulation: How is the notochord formed?
Cells from the primitive node migrate towards buccopharyngeal membrane giving appearance of notochordal plate which folds to form solid cylinder= Notochord
What do the ectoderm, intra-embryonic mesoderm & endoderm form?
What day is this cross section showing and label the parts of the trilaminar disc
~ Day 19
Ectoderm = Skin & Neural tissue
Mesoderm:
- Paraxial:* Develop –> Somites which give rise to: Muscle, Dermis of Skin & Axial Skeleton
- Intermediate:* Genitourinary (Kidney/ Gonards)
- Lateral:* Serous membranes (peritoneum, pleura, pericardium)
Endoderm: GI & Respiratory Tract