Embryology 1 Flashcards
(29 cards)
Describe spermatogenesis and Oogenesis
Spermatogenesis :
Spermatogonium(46chr>Meiosis>4 Sprems ( 22 + X or 22 + Y)
-Meiosis occurs after puberty
Oogenesis:
- Oogonium(46chr)>Meiosis> 1 ovum (22 + X) and 3 polar bodies
- Meiosis l starts at early embryonic life, and Meiosis ll after puberty
Describe what happens during fertilisation
- Occurs in fallopian tube
- Only one sperm penetrates the ovum.
- (pro) Nucleus of sperm enters & will fuse with (pro) nucleus of ovum to form diploid cell= zygote
- Mitochondria and other organelles is from the mother .
Describe Week 1 of pre-embryonic phase
Zygote-Morula>Blastocyst
- Zygote divides by mitosis to form a morula(solid ball of cells)
- blastocystic cavity develops + cells accumulate to form inner cell mass + trophoblast(outer cell lining). By day 5/6 Blastocyst is now formed + reached uterine cavity and ready for implantation
- The first cell division takes 36 hours, succcessive ones will be much quicker
- The dividing blastocyst/morala/zygote requires healthy cilated epethilium in the fallopian tube to move + reach the uterine
How are mitochondrial diseases inherited?
Maternally inherited
Give an example of a mitochondrial disease
Leber’s hereditary optic neuropathy which leads to blindness
Describe what happens from Morala-blastocyst
-The dividing blastocyst/morala/zygote requires healthy cilated epethilium in the fallopian tube to move + reach the uterine cavity.
Why does ectopic pregnancy occur?
If the cillia function is abnormal (cilated epethelium in fallopian tube)
When is the blastula ready to implant in the uterine cavity?
Day 5/6 blastula has formed and reached uterine cavity and implants to uterus wall.
Describe what occurs in week 2 of pre-embryonic phase
Trophoblast>Chorion
-Implantation occurs and the blastocyst burrows into the uterine wal(endometrium) and placenta begins to develop(day 6/1st week).
-The trophoblast divides into 2 layers to form a chorion which develops finger like processes(chronionic villi)
> > > > a bilaminar disc + sacs, membranes and cord nourishes the baby as it develops.
State the function of the chorion
- involved in implantation process ( chronionic villi) +-forms part of placenta(18 weeks)
- secretes human chronionic gondatropin ( HCG) < used to detect pregnancy. This horemone helps maintain the endometrium by telling ovary to keep producing oestrogen/progesterone. After placenta formation, it is no longer produced.
What is the decidua basalis?
Decidua basalis;area of endometrium that the fertilised zygote implants to (deep in endometrium + has maternal blood vessels)
What happens to the inner cell mass?
The inner cell mass forms a 2-layered flat disc = bilaminar disc
-Eventually, 2 cavities begin to form: Amniotic cavity + Yolk sac
State the main functions of the placenta
- provides nutrition to foetus
- transports waste and gases
- immune function
When does the placenta mature? State the foetal/maternal part
- 18-20 weeks
- Foetal: smooth with foetal BV + end of umbillical cord.
- Maternal: decidua basalis of endometrium, rough + has maternal BV
How do fraternal twins occur?
- 2 ova released, 2 sperms which leads to 2 seperate zygotes
- diffferent genetic makeup and 2 seperate placenta
How do identical twins occur?
- 1 ovum, 1 sperm> 1 zygote INITIALLY. But zygote divides into 2 and each cell develops into a seperate embryo
- Same genetic makeup, shares one placenta. May/not share amnotic/chorionic sac
What processes occurs during week 3?
- GRASTULATION: formation of germ layers
- NEURULATION: formation of neural tube
- development of somites
- early CVS development
How is the axis of the embryo formed??
The primitive streak is formed in the midline of the epiblast by invagination of cells. Once primitive streak is formed, axis of embryo is formed
Describe the process of gastrulation
- cells in epiblast will migrate into space between epiblast and hypoblast layers. These cells will displace hypoblast and form 3 germ layers:ectoderm, mesoderm, endoderm.
- trilaminar disc is formed + cells are now specialised
What is the notochord a precursor of?
nucleus pulposis
Describe the process of neurulation
Some mesoderm cells will differentiate to form the notochord. The notochord stimulates ectoderm cells to thicken and form a neural plate.
-The neural plate sinks down to form a neural tube
What happens to the Chorion, embryo + umbillical cord + materna blood vessels REVIIIII
Amniotic cavity:bigger (cushions foetus + allows it to move?)
Yolk Sac:smaller ( forms remnants of RT)
Allantoic cavity: bigger (waste prod. LOOK BACK AT THIS
State the functions of the 3 germ layers
Ectoderm: formation of skin and nervous system(neural tube), muscles, bone.
Mesoderm: Urogenital system ( kidneys, Reproductive)
Endoderm: peritoneum, pleura, body cavities, gut
Describe the development of somites
The mesoderm seperated into 3 parts: Paraxial, intermediate pate, lateral plate mesoderm.
- Lateral plate mesoderm splits to form somatic, splanchnic mesoderm + intra-embryonic coelom(space formed in between)
- The paraxial intermediate plate will divide to form somites. Each somite will give rise to a dermotome, sclerotome, myotome.
