Gastrulation and Trilaminar disc Flashcards
Describe monozygotic twins
Twins that are identical because they both come from the same zygote
Describe dizygotic twins
Twins that are non identical as they come from two separate zygotes
What is Sesquizygosity
Twins that are genetically identical WRT one parent but approx 50% different with the DNA from the other parent. Potentially as a result of 2 sperm penetrating Zona Pellucida
Outline the formation of the primary yolk sac
Occurs in week 2. The floor = Heuser’s membrane, the ceiling = hypoblast.
Outline the formation of the secondary yolk sac
Formed from the extra-embryonic mesoderm separates to form the extra embryonic coelom. Cells from the mesoderm pinch off an area of the yolk sac and what remains is the secondary yolk sac.
Outline the formation of the final yolk sac
Week 4 - Part of the yolk sac is surrounded by endoderm and incorporated into the embryo as the gut. The bits that remains is the final yolk sac.
Where does the amniotic cavity form?
It forms in the space between the epiblast and the cytotrophoblast
How and where does the chorionic cavity form
Extra-embryonic mesoblast cells, derived from epiblast cells grow into the extra-embryonic reticulum. Beginning of the reticular vacuole formation that with form the chorionic cavity. It forms inside the extra-embryonic mesoblast.
What is gastrulation?
Gastrulation is the formation of the three germ layers: Endoderm, Ectoderm and Mesoderm. The bilaminar disc is converted into a trilaminar disc.
When does Gastrulation occur?
Week 3
How does gastrulation begin?
It begins with the formation of the primitive streak.
What does the primitive streak include?
The Primitive groove, the Primitive Pit and the Primitive Node (AKA Hensen’s Node)
Label the diagram about the primitive streak.
on iPad.
What do the invading epiblast cells form?
The mesoblast
What replaces the hypoblast?
Endoblast.
How are the three layers generated?
The epiblast cells roll over into the Primitive Groove and migrate towards the centre. They they undergo the EMT (Epithelial - Mesenchymal Transition). The first cells through displace the hypoblast and become the endoderm. The next cells that remain in the middle become the mesoderm and the cells that remain in the epiblast become the ectoderm.
Compare and contrast Epithelial to Mesenchymal cells.
Epithelial - Cell polarity, Cell adhesion, Stationary, High levels of E-cadherin, Low levels of N-cadherin.
Mesenchymal are the complete opposite.
Give the derivatives of the endoderm.
epithelial lining of the GIT, respiratory tract bladder and urethra; thyroid and parathyroid glands, liver, pancreas.
Give the derivatives of the mesoderm.
connective tissue (cartilage, bone, blood); striated and smooth muscles; heart; blood and lymphatic vessels; kidneys; ovaries and testes; spleen; serous membranes lining the body cavities (pericardial, pleural, peritoneal).
Give the derivatives of the ectoderm
CNS (brain and spinal cord); PNS; sensory epithelia of the eye, ear, nose; epidermis and its appendages (hair and nails); mammary glands; pituitary gland.
What are formed as a result of gastrulation
The three germ layers and the creating of body axis, Anterior-Posterior, Dorsal-Ventral, and Left-Right
