Embryology 1 Flashcards
Describe the formation of the gametes and fertilisation
sperm
Sperm:
- Spermatogenesis
- Spermatogonium oogonium (parent cells with 46 chromosomes) which undergo meiosis.
- Stage 1 and stage 2 -> 4 sperms. (22 + X or 22+Y)
Describe the formation of the gametes and fertilisation
ovum
Ovum:
- Follicles are nothing but Spermatogonium oogonium (parent cells with 46 chromosomes)
- 1 ovum (22+X only. And 3 polar bodies)
- When the baby is born part 1 of meiosis has already occurred pre-utero.
- When puberty occurs then stage 2 of meiosis occurs.
Describe the formation of the gametes and fertilisation
fertilasion
- Several sperm surround the ovum but only one penetrates. ONLY the (Pro) nucleus (has the genetic information) of sperm enters and fuses with the (pro) nucleus of ovum to give a diploid cell called the Zygote.
• _Define the stages of embryology
Pre-embryonic phase= 0-3 weeks
Embryonic phase= 4-8 weeks
Foetal phase= 9-40 weeks
• _Define the stages of embryology
week 1 overview.
Week 1 of pre-embryonic phase: ZYGOTE to BLASTOCYST
- Diploid Zygote is formed, is the 1st cell in the body; divides to form a blastocyst.
- Moves through the uterine tube to reach uterine capacity.
• _Define the stages of embryology
genetic detail and mitochondrial disease.
- zygote is genetically unique because it has 23 of mum’s and 23 of dad’s chromosome.
- Mitochondria and cell organelles are from the mum. So, mitochondrial diseases are inherited from the mother. (e.g. Leigh Syndrome)
• _Define the stages of embryology
zygote-morula
zygote divides by mitosis forming 2 cells, then 4, then 8
- A solid ball of cells (MORULA) is formed.
• _Define the stages of embryology
morula-blastocyst
- As the solid ball of cells (morula) increase in size and number of cells, getting nutrition to the central core of cells starts becoming difficult.
- Morula and develops into an inner cell mass and outer cell mass.
- Hence why a cavity develops called the blastocystic cavity and nutrition diffuse into this cavity.
- Cells accumulate at one end to form an inner cell mass.
- The outer lining of cells is called the trophoblast.
^ THIS is the blastocyst
• _Define the stages of embryology
when does first cell division occur?
- First cell division takes 36 hours and successive cell divisions take lesser and lesser time.
- By day 5 or 6, the blastula has formed and this has reached the uterine cavity ready to implant into it.
- The fertilised ovum/dividing zygote/morula/blastocyst requires healthy ciliated epithelium to move it through the fallopian tube and reach the uterine cavity.
- (If cilia function is abnormal it could result in an ectopic pregnancy.)
Week 2 of pre-embryonic phase:
where implantation occurs and development of placater
- Implantation occurs in the uterine wall/endometrium
- The placenta begins to develop (this may start by day 6 of first week).
- –> Inner cell mass of blastocyst, that later form the embryo form a bilaminar disc (two layer disc)
- Sacs, membrane and cord to nourish the human conceptus (baby) start to form
Week 2 of pre-embryonic phase:
Trophoblast -> chorion
- Outer cell mass is initially called the trophoblast.
Initial outer cell mass Trophoblast will Divides to form 2 layer which ultimately forms CHORION - Develops finger like processes chorionic villi.
Week 2 of pre-embryonic phase
What does chorion do?
- Helps Implantation process (chorionic villi)
- Forms part of the placenta in due course
- Secretes human chorionic gonadotropin (HCG) which is going to help maintain the endometrium after implantation has occured
- HCG travels throughout the body, causes morning sickness. Used to detect pregnancy.
Week 2 of pre-embryonic phase:
when implantation occurs
- At around 7 days the blastocyst begins to burrow into the uterine wall/endometrium.
summary so far:
- Zygote- first cell. Diploid
- Blastocyst- inner cell mass and outer cell mass.
- Inner cell mass will form the embryo.
- Outer cell mass trophoblast will form chorion.
- Chorion will form the placenta.
What happens to the inner cell mass?
- Flattens itself to form a 2 layered flat disc called the bilaminar disc
- 2 cavities begin to form:
o Amniotic cavity (A) –
Above epiblast
On top all on the outside
o Yolk sac (Y)
Below Hypoblast
Bottom tube on the inside.
