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.
Placenta formation
The placenta begins to develop upon implantation of the blastocyst into the maternal endometrium.
The placenta matures by 18-29 weeks
placeta main functions
- Foetal nutrition
- Transport of waste and gases
- Immune
parts of the placenta?
- Foetal part and surface:
o Smooth with foetal blood vessels and end of umbilical cord. - Maternal part:
o Rough and has maternal blood vessels
o Decidua basalis of endometrium
Summary so far:
concept and where
CONCEPT:
Morula reaches uterine cavity blastocyst implants outer cells form chorionic villi which help implantation decidua basalis formed placental formation begins
WHERE:
Morula reaches uterine cavity blastocyst implants outer cells form chorionic villi which help implantation decidua basalis formed placental formation begins
twins formation
Fraternal/Dizygotic twins:
- 2 ova released, 2 sperms
- -> 2 separate zygotes
- Has different genetic makeups and 2 placenta
- Can run in families
Identical/monozygotic:
- 1 ovum, 1 sperm,
- -> 1 zygote initially
- Divides into 2 zygotes and each cell develops into a different embryo
- Has the same genetic makeup and shares one placenta.
- Might not share amniotic and chorionic sac
