Embryology Flashcards
What cell do gametes begin as in men?
- Spermatogonium
What cell do gametes begin as in women?
- Oogonium
Are spermatogonium and oogonium haploid or diploid?
Diploid
What is the possible genotype of sperm produced through meiosis of a spermatogonium?
- 22 + X - 22 + Y
What is the possible genotype of ova produced through meiosis of an oogonium?
- 22 + X
What is meant by facilitation with reference to fertilisation?
- Hundreds of sperm needed to reach the ovum for one to get through into it. Without the hundreds the one won’t get through
What is the only thing the sperm passes onto the egg?
Genetic material
What is the name of the diploid fertilised cell?
Zygote
What does the zygote do as it passes through the oviduct?
- Divides to form a morula (a solid ball of cells)
What happens to the cells inside the morula as it’s size increases?
Increasingly more difficult to get nutrients to them
What develops in response to the middle cells “starving”?
Blastocystic cavity
What else forms around the blastocystic cavity and the mass of cells?
Trophoblast
When does the blastocyst reach the uterus?
Day 5
How does the blastocyst move through the oviduct?
- Has ciliated mucousal epithelium in it - These have a ciliary beat that allows the blastocyst to be transported
What happens if the blastocyst doesn’t reach the uterus in time before implantation?
- It will imbed in the oviduct - Ectopic pregnancy
Which parent is the genetics for the mitochondria and other organelles inherited?
The mother
What are examples of mitochondrial disease that come from inherited defective mitochondria?
- Leber’s optical neuropathy
What happens at the beginning of week 2?
- Blastocyst burrows into the endometrium
What part of the blastocyst do cells that form the embryo come from?
The inner cell mass
What happens to the trophoblast in week 2?
- It divides into 2 layers of cells
What is the divided trophoblast known as?
Chorion
What does the chorion develop to stick to the endometrium
Finger like villi known as chorionic villi
What does the chorion eventually become a part of?
The placenta
What hormone does the chorion secrete?
Human Chorionic Gonadatrophin
What clinical role can human chorionic gonadotrophin play?
Can be used to detect pregnancy
What effect does human chorionic gonadotrophin have on the ovary?
Inhibits it from secreting a surge of lutenising hormone that causes the endometrium to be shed
What is the endometrium now known as when the blastocyst has embedded into it?
Decidua
What is the area where the blastocyst is embedded known as?
Decidua basalis
How does the decidua basalis differ to the rest of the endometrium?
More vascular
What happens to the inner cell mass during the second week?
- Flattens - Forms two layers
What are the two layers formed by the inner cell mass called?
- Epiblast and hypoblast
What is the cavity touching the epiblast called?
Amniotic cavity
What is the cavity touching the hypoblast called?
Yolk sac
Name the coloured areas
- Yellow area = yolk sac
- Blue cavity = amniotic cavity
- Black outline = Chorion
- Brown cavity = allantoic cavity
What is the function of the allantoic cavity?
Waste cavity
What is the function of the chorion at this point?
Seperate embryionic blood and maternal blood to stop rejection
How is waste transferred out through the chorion?
Diffusion alone
What is the function of the placenta?
Provides the foetus with nutrition and allows diffusion from the allantoic cavity
How do non identical twins form?
- Di zygotic
- 2 ova released fertilised by a sperm each
How do identical twins form?
- Monozygotic
- Zygote divides two form two zygotes that each develops into an embryo with the same genetic makeup
What forms in week three?
The germ layers
When looking down on the epiblast, a small trench forms down the middle, what is this called?
Primitive Streak
What happens to the cells in the primitve streak?
They enter the space inbetween the hypoblast and the epiblast
What effect do the epiblast cells have on the hypoblast cells in the primitive streak?
They displace the hypoblast cells and a trilaminar disc forms
Which germ layer touches the amniotic cavity?
Ectoderm
Which germ layer touches the yolk sac?
Endoderm
What is the notochord?
A solid tube that sits in the mesoderm
Where do the cells of the notochord come from and how do they get there?
- Ectoderm
- Travel through the mesoderm and form a rod of cells in between the mesoderm and the endoderm
What does the notochord help form?
Neural tube
How does the notochord form the neural tube?
- Sends signals to ectoderm cells
- Ectoderm thickens to form something called the neural plate
What shape does the ectoderm take after the signals from the notochord?
A sine wave shape
How does the sine wave shape of the ectoderm form the tube like structure of the neural tube?
The peaks of the sine wave move closer together until they touch
What system is the neural tube the primitive structure of?
CNS
How many parts does the mesoderm split into?
3 major parts
What is the mesoderm part next to the neural tube (axis) known as?
Paraxial mesoderm
What is the bit of the mesoderm beside the paraxial mesoderm called?
Intermediate mesoderm
What is the most lateral part of the mesoderm called?
Lateral plate mesoderm
