Gastrulation Flashcards
What are monozygotic twins?
One egg for the two foetuses
What are dizygotic twins?
Two eggs for the two foetuses
What is sesquizygosity?
A third form of twinship whereby twins are genetically indentical to each other with respect to one parent but differ from each other by approx 50% with respect to the composition of DNA inherited from the other parent
Describe the time periods for implantation?
Spermatozoon penetrates into the oocyte- day 0 Two cell stage- day 1 Four cell stage - day 2 Eight cell stage - day 3 Morula (16-32 cells)- day 4 Free blastocyst- day 6
What are the different ectoptic implantation zones and what does it lead to?
Ovary Infundibulum Fallopian tube Isthmus Cervix Abdominal/pelvic cavity Abdominal peritoneum
Results in no viable zygote - usually self aborts
What is a yolk sac?
Vesicle which develops in week 2
What is the floor of the yolk sac?
Heuser’s membrane
What is the ceiling of the yolk sac?
Hypoblast
What is the function of the yolk sac?
Nourishment for the egg
How is a secondary yolk sac formed?
When the extraembryonic mesoderm separates to form the extraembryonic coelom; cells from the mesoderm pinch off an area of the yolk sac, and what remains is the secondary yolk sac
How is the final yolk sac formed?
Week 4 - part of the yolk sac is surrounded by endoderm and incorporated into the embryo as the gut - remaining part is the final yolk sac
How is the chorionic cavity formed?
Extra- embryonic mesoblast cells, derived from epiblast cells, grow into the extra-embryonic reticulum.
Beginning of the reticular vacuole formation that will form the future chorionic cavity
How is the amniotic cavity formed?
Fusion of the parts of the amniotic fold
What are the two layer of flat cells of the embyro at week 2 and what are these collectively known as?
Epiblast and hypoblast
Bilaminar disc
What happens to the bilaminar disc at week 3?
Gastrulation occurs
Bilaminar disc is converted to trilaminar disc and formation of three germ layers - Ectoderm
Mesoderm
Endoderm
What is gastrulation?
Formation of the three embyronic germ layers
The emnbryogenesis where basic organisation of the organism is established
What does gastrulation begin with?
Formation of the primitive streak
What are the three things that make up the primitive streak?
Primitive groove, primitive node and primitive pit
What happens at the primitive groove?
Immigration of epiblast cells, which form the future mesoblast, as well as the endoblast, which replaces hypoblast
What are features of epithelial cells?
Cell polarity - always sit on the basement membrane Cell ahesions- always uniform Stationary High levels of E-cadherin Low levels N- cadherin
What are features of mesenchymal cells?
No cell polarity Loss of cell adhesion Ability to migrate and invade Low levels of E- cadherein High levels of N- cadherin
What is the process whereby epithelial cells become mesenchymal cells?
Epithelial- mesenchymal transition
EMT
What is derived from the endoderm?
Epithelial lining of the GIT Respiratory tract bladder and urethra Thyroid and parathyroid glands Liver Pancreas
What is derived from the mesoderm?
CT Striated and smooth muscles Heart Blood and lymphatic vessels Kidneys Ovaries and testes Spleen Serous membranes lining the body cavities
What is derived from the ectoderm?
CNS PNS Sensory epithelia of the eye Ear Nose Epidermis and its appendages Mammary glands Pituitary gland
What are the results of gastrulation?
The primary germ layers are formed Creation of the bodies axes (Anterior posterior) (dorsal ventral) (Left right)
