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Embryology week 1-3
| Question | Answer |
|---|---|
| Ovarian cycle When? | Regular monthly cycle from puberty |
| Follicular phase | During follicular phase the follicle grows and releases oestrogen. Oestrogen causes an increase in LH and FSH release from pituitary LH initiates ovulation (±day 14 of cycle) |
| Duration of ovarian cycle | +_ 28 days |
| Difference between ovarian cycle and menstrual cycle | the ovarian cycle relates to changes taking place at the ovary, while the menstrual cycle refers more to the changes taking place at the uterus. |
| 3 Phases of the ovarian cycle | Follicular, Ovulation and luteal phase |
| What happens during follicular phase | This phase (day 1-12) FOLLICULAR CELLS SURROUNDING OOCYTES BEGIN TO DEVELOP- CONVERTING PRIMARY FOLLICLE TO SECONDARY FOLLICLE |
| What happens as the follicle grows | Follicular growth>stimulates oestrogen in body>stimulates release of LH and FSH from pituitary in brain. FSH enables last bit of development of secondary follicle while LH initiates the process of ovulation to happen at approx 14 days of ovarian cycle |
| Ovulation (part 1) | release of the egg cell from the ovary. Ovulation initiated> LH surge. Follicle bulges on side of ovary (stigma). Meiosis I completed, follicle ruptures, secondary oocyte released (arrests in meiosis II) |
| Ovarian cycle When? | Regular monthly cycle from puberty |
| Follicular phase | During follicular phase the follicle grows and releases oestrogen. Oestrogen causes an increase in LH and FSH release from pituitary LH initiates ovulation (±day 14 of cycle) |
| Duration of ovarian cycle | +_ 28 days |
| Difference between ovarian cycle and menstrual cycle | the ovarian cycle relates to changes taking place at the ovary, while the menstrual cycle refers more to the changes taking place at the uterus. |
| 3 Phases of the ovarian cycle | Follicular, Ovulation and luteal phase |
| What happens during follicular phase | This phase (day 1-12) FOLLICULAR CELLS SURROUNDING OOCYTES BEGIN TO DEVELOP- CONVERTING PRIMARY FOLLICLE TO SECONDARY FOLLICLE |
| What happens as the follicle grows | Follicular growth>stimulates oestrogen in body>stimulates release of LH and FSH from pituitary in brain. FSH enables last bit of development of secondary follicle while LH initiates the process of ovulation to happen at approx 14 days of ovarian cycle |
| Ovulation | release of the egg cell from the ovary. Ovulation initiated> LH surge. Follicle bulges on side of ovary (stigma). Meiosis I completed, follicle ruptures, secondary oocyte released (arrests in meiosis II). Follicular cells released with oocyte – corona rad |
| Ovulation part 2 | Follicular cells released with oocyte – corona radiata around zona pellucida Remaining follicular cells differentiate into corpus luteum (luteal phase), secrete oestrogen & progesterone (causes thickening of endometrium) |
| What happens if fertilisation does not occur | Corpus luteum degenerates (luteolysis) Forms fibrous tissue – corpus albicans Progesterone decreases, menstrual bleeding starts |
| What happens if fertilisation occurs | degeneration prevented by human chorionic gonadotropin (hCG) secreted by embryo Corpus luteum continues to grow – corpus luteum graviditas |
| Fertilisation (sperm transport) | Cervix to uterine tube via uterine muscular contractions Swim rest of way to ampulla where fertilization occurs |
| Fertilisation (fertilisation of the ovum) | Capacitation: tube mucosa removes membrane over acrosomal cap of sperm, can now pass through corona radiata Acrosome reaction: sperm binds to zona pellucida, release enzymes to penetrate it |
| Phase 1 of fertilisation | Penetration of the corona radiata. Only one sperm can pass, others aid in the breakdown of the barrier |
| Phase 2 of fertilisation | Penetration of the zona pellucida. Sperm binds to zona, acrosomal reaction enzymes break it down Sperm moves to oocyte plasma membrane Granulosa releases lysosomal enzymes to prevent polyspermy |
| Phase 3 of fertilisation | fusion of oocyte & sperm cell membranes Plasma membrane over acrosome disappears, rest fuses to oocyte membrane |
| Fertilisation (ovum reactions) | Cortical & zona reactions:lysosomal enzymes (prevent polyspermy)Meiosis II completed, female pronucleus forms.Male pronucleus forms (head of sperm)fuses to female one Both replicate DNA, cell undergoes mitotic division creating 2 diploid cells of zygote |
| When is the genetic sex of the baby established | As soon as the sperm enters the oocyte |
| XX Zygote | Female offspring |
| XY Zygote | Male Offspring |
| Blastocytes formation | Morula splits into 2 cell masses Inner embryoblast Outer trophoblast (later placenta) Also forms blastocele cavity forms – blastocyst Zona pellucida disappears (blastocyst “hatches”) Ready for implantation |
| Which layer of uterine muscle is responsible for muscle contractions | Myometrium |
| Where does implantation normally occur | On the anterior or posterior wall of the uterus Sometimes at the opening of the cervix or on the fundus |
| Ectopic implantations | Anywhere from ovary to end of uterine tubes. Can be abdominal (retrouterine pouch) |
| True or false: The embryo is naturally aborted without a trace | True |
| One cause of ectopic implantations | May cause rapture of the area |
| When and at which structure does implantation occur | 6-7 days after fertilisation at the endometrium |
| Completion of implantation | Blastocyst partially embedded in endometrium Trophoblast differentiates into 2 layers: Inner layer – cytotrophoblast (mononuclear) Outer layer – syncytiotrophoblast (multinuclear) Formed by cytotrophoblasts migrating into endometrium & fusing together |
| Two layers of the embryoblasts | 1)Hypoblast – adjacent to blastocyst cavity 2)Epiblast – adjacent to developing amniotic cavity Amnioblasts – epiblasts adjacent to cytotrophoblast Together form bilaminar disc |
| Edematous | Fluid filled |
| Displaced hypoblast cells | Endoderm |
| Invaginating epiblast cells | mesoderm |
| Remaining epiblast cells | Ectoderm |
| Primitive streak (start of third week) | Appears on epiblast side of bilaminar disc |
| Gastrulation | Process starts with formation of primitive streak on epiblast side of the bilaminar disc. Streak starts on caudal side and extends one third of the way to the cephalic side (primitive node with pit through it) Epiblast cells move through streak |
| Trilaminar disc | Endoderm, ectoderm, mesoderm |
| Formation of notochord | prenotochordal epiblast cells migrate through the primitive pit, into the space between the ectoderm and endoderm layers. In this space, these cells will migrate along the midline of the trilaminar disc towards the cranial end of the disc |
| Formation of notochord (part 2) | Cells then form notochordal process which extends from primitive pit to prechordal plate |
| Prechordal plate | Ectoderm and endoderm are in direct contact without mesoderm in between |
| Anterior | head side |
| Posterior | Tail side |
| Dorsal | back/spine |
| Ventral | Belly |
| What causes mesoderm ventralization | BMP4 and FGF |
Created by:
Brenty
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