Embryology - Fertlisation to Trilaminar Flashcards
What happens when a single sperm enters the oocyte?
Cortical granules are released which react which react with the zona pellucida causing it to harden to prevent other sperm from entering. Slide 3
What are blastomeres?
Smaller daughter cells from the subdivided fertilised egg. Slide 4
What happens during compaction?
It maximises available space by coming into closer contact with each other and form cell junctions. Slide 5
What happens between the outer cells and the zona pelllucida?
There are formations of extensive gap junctions. Slide 5
what is in a blastocyst?
A cell lining on the zona pellucida called trophoblast, the inner cell mass, blastocyst cavity and the zona pellucida. Slide 6
What is blastocyst hatching?
When the blastocyst is at the uterine cavity and it leaves the zona pellucida. Slide 8
How does the blastocyst hatch?
The zona pellucida breaks down and the blastocyst moves out of it. Slide 8
Why does the blastocyst need to ‘hatch’?
So the embryo can interact directly with the endometrial lining of the uterus. Slide 8
Where are the normal implantation sites?
Middle or upper dorsal uterine wall. Slide 10
Where are the abnormal implantation sites?
Ovary, ampulla, uterine tube, lower part of uterus, cervix or peritoneum. Slide 10
What drives the active implantation process?
Trophoblast cells. Slide 11
The trophoblast cells divide into two types, what are they?
CYTOtrophoblast and SYNCYTIOtrophoblast. Slide 11
What are cytotrophoblasts?
Original layer of individual cells. Slide 11
What are syncytiotrophoblasts?
They are cytotrophoblasts which lose their membranes and combine together so it is one single multinucleated cell. Slide 11
The embryo organises into 2 cell layers, what are they?
The epiblast which is the dorsal surface of the embryo and hypoblast which is the ventral surface. Slide 11
How is the amniotic cavity formed?
When the epiblast divide and new cells form a new layer and secrete fluid between them. Slide 11
How is the primary yolk sac made?
When the hypoblast cells migrate out along the inner surface of the trophoblast. Slide 12
What is the extra embryonic mesoderm?
The new layer and it separates the lining of the yolk sac and the cytotrophoblast and continues to moves it will separate the amnion as well. Slide 13
When does the chorionic cavity and the secondary yolk sac begin to form?
In days 12-13. Slide 14
How does the placenta form?
The syncytiotrophoblast extends and contacts maternal blood supply. Slide 16
Where is the amniotic cavity and the definitive yolk sac situated?
Amniotic cavity I present above the bilaminar embryonic disc and the definitive yolk sac is below. Slide 16
What does the epiblast and hypoblast form?
Bilaminar embryo. Slide 17
What is the dorsal side of the embryo?
The epiblast. Slide 18
What is the ventral side of the embryo?
Hypoblast. Slide 18
What is the primitive streak?
It allows gastrulation and looks like a scratch on the surface of the embryo. Slide 18
Where is the primitive streak situated?
Midline at caudal end of epiblast and the cranial end of the primitive streak is the primitive pit and node. Slide 18
What happens during the formation of the germ layers?
The 2 layers become 3 layers; Ectoderm, mesoderm and endoderm. The cells migrate through the primitive streak to form the mesoderm. Slide 19
What happens during gastrulation in the embryo?
Movement of epiblast cells through the primitive streak to form the three primary germ layers: Hypoblast is replaces to form the definitive endoderm, the intraembryonic mesoderm layer is formed between and the epiblast becomes the ectoderm. Slide 20
What is the fate of the ectoderm?
It becomes the epidermis of the skin and the nervous system. Slide 22
What is the fate of the mesoderm?
Divides into 3 regions either side of the notochord. The three regions are paraxial, intermediate and lateral plate (somatic and visceral). Slide 23
Where is the paraxial part of the mesoderm?
paraxial means along side the axis. Slide 23`
Where is the intermediate part of the mesoderm?
Only found within the trunk. Slide 23
Where are the lateral parts of the mesoderm?
It is flattened sheets looped round with a gap at the loop, the somatic part is the top. The gap allows body cavities between the somatic and visceral parts. Slide 23
What is the fate of the paraxial mesoderm?
Axial skeleton, voluntary muscle and parts of the dermis. Slide 24
What is the fate of the intermediate mesoderm?
Urogential systems e.g. kidney, ureter, gonads. Slide 25
What is the fate of the lateral plate mesoderm (somatic)?
Lining of the body wall, most dermis an parts of limbs. Slide 26
What is the fate of the lateral plate mesoderm (visceral)?
Cardiovascular system, mesothelial covering of organs and smooth muscle. Slide 27
What is the fate of the endoderm?
Lining of the gut tube, lining of the respiratory tract and lining of the bladder and urethra. Slide 28
How is the bladder formed by the endoderm?
Expansion of the endoderm at the cloaca, splits into two parts and the anterior part forms the bladder. Slide 28
