Embryology Flashcards
Between what weeks is the embryonic phase?
0-3 weeks
Between which weeks is the embryonic phase?
4-8 weeks
Between which weeks is the foetal phase?
9-40 weeks
What is spermatogenesis?
The formation of sperm
What is oogenesis?
The formation of the ovum
By what cellular process do gametes divide?
Meiosis
What is the spermatogonium?
The cell that produces sperm
What is the oogonium?
The cell that produces the ovum
What is the cell formed at fertilisation called?
The zygote
Does just one sperm surround the ovum?
No several
How many sperm penetrate the egg?
Just one
What part of the sperm penetrates the ovum?
The pro-nucleus
Why does mitochondrial inheritance come from the mother?
Because the sperms organelles are pushed out at fertilisation
What is the first cell in the body?
The zygote
Is the zygote diploid or haploid?
Diploid
How does the zygote divide?
By mitosis
What is the morula?
Ball of cells that have divided from the zygote
Why does a cavity develop in the morula?
To get nutrients to the central core of the cells
What is the cavity that develops in the morula known as?
Blastocystic cavity
What does the morula become?
A blastocyst
What is the outer lining of cells on the blastocyst called?
Trophoblast
How does the egg or fertilised zygote move along the oviduct?
Ciliated epithelium moves it along
How long does the first cell division take?
36 hours
If cilia function in the fallopian tubes is faulty what can occur?
An ectopic pregnancy
How many days does it take fir the blastula to have formed ready to implant in the uterine cavity?
5 or 6
Where does implantation occur?
In the endometrial layer
What is the function of the chorion?
To help the embryo burry into the endometrium
To go on and form part of the placenta
To secrete HCG
What does HCG hormone do?
Tells the body to keep producing oestrogen and progesterone to maintain the endometrium
Also is used to test for pregnancy
How does the chorion aid implantation?
By creating finger like projections (villi)
What are the 2 layers of the Bilaminar disc called?
Epiblast
Hypoblast
What cavity lies above the epiblast?
Amniotic cavity
What cavity lies below the hypoblast?
Yolk Sac
Why does the allantoic begin to get larger?
Because more and more waste products are dumped there
Why does the yolk sac get smaller?
Because the nutrients are being used up
Does maternal and foetal blood ever mix?
No
How does the transfer of nutrients and waste occur between mum and baby if there blood do not mix?
By diffusion
What are the main functions of the placenta?
Foetal nutrition
Transport of waste and gases
Immune ect
Why is the foetal part of the placenta smooth?
Because it is lined by the amniotic sac
How much does the placenta weigh?
1/6 of the foetus
By what weeks has the placenta matured?
18-20
What are fraternal twins?
2 ova
2 sperms
2 separate zygotes
Different genetic makeup
What are identical twins?
When there is 1 ovum
1 sperm
1 zygote initially
Divides into 2 and each develops into a different embryo
Which type of twins can run in families?
Fraternal
When the mother releases 2 ova
What is gastrulation?
The formation of the germ layers
What is neurulation?
Formation of the neural tube
How is the primitive streak formed?
Formed in the midline of the epiblast
By the dipping in of cells (invagination)
What are the 3 germ layers upper to lower?
Ectoderm
Mesoderm
Endoderm
Are the germ cells specialised?
Yes
Cells from which germ layer continue to divide?
Ectoderm
What is the notochord?
Solid tube of cells formed from the dividing ectoderm
What does the notochord send?
Signals that induce midline ectodermal cells to form a neural tube
How is a neural tube formed?
Signals are sent by the notochord that stimulate the midline of the ectoderm to divide and form a neural tube
What does the neural tube induce?
The mesoderm to thicken
What 3 parts does the mesoderm separate into?
Paraxial mesoderm
Intermediate plate mesoderm
Lateral plate mesoderm
What does the lateral plate mesoderm split to form?
Somatic and splanchnic mesoderm
On which day does the heart start to beat?
Day 24
What does the ectoderm go on to form?
Epidermis of skin
Neural tube
What does the endoderm go on to form?
Gut
Respiratory
What does the paraxial mesoderm go on to form?
Somites
What does the intermediate plate mesoderm go on to form?
Urogenital system
Kidneys, reproductive
What does the lateral plate mesoderm go on to form?
Peritoneum
Pleura
Body cavities
What is the peritoneum?
The membrane surrounding the heart
Where do the somites run along?
The primitive streak
What do the myotomes form?
Muscles
What do the dermatomes form?
Dermis of skin
What do the sclerotomes form?
Bones
What 3 sections do the somites divide into?
Dermatome
Myotome
Sclerotome
What is teratology?
The study of when things go wrong during foetal development
What are teratogens?
Environmental factors that cause abnormal development
What genetic factors can cause things to go wrong with foetal development?
Too many/few chromosomes
Structural changes in chromosomes
Increased maternal age
When is the highest risk of teratology?
Weeks 4-8
What drug fro? the 60s caused foetal abnormalities?
Thalidomide