The Pre-Embryonic Period Flashcards
<p>How does once cell become a multicellular body?</p>
<p>Growth, Morphogenesis, Differentiation</p>
<p>What does morphogenesis involve?</p>
<p>Creating lots of cells in the right place at the right time</p>
<p>What is the result of morphogenesis?</p>
<p>The development of form and structure</p>
<p>Why is differentiation needed?</p>
<p>For specialisation for function</p>
<p>What does differentiation allow?</p>
<p>Certain groups of cells to specialise for a common function</p>
<p>What are the 3 stages from fertilisation to birth?</p>
<p>- Pre-embryonic
- Embryonic
- Fetal</p>
<p>When is the pre-embryonic period?</p>
<p>Weeks 1-2</p>
<p>When is the embryonic period?</p>
<p>Weeks 3-8</p>
<p>Why is the embryonic period such a critical period?</p>
<p>All structures and systems of the body are made</p>
<p>When is the foetal period?</p>
<p>Weeks 9-38</p>
<p>What happens in the foetal period?</p>
<p>The focus is on growth and physical maturation of systems</p>
<p>When are pregnancy weeks calculated from?</p>
<p>LMP, i.e. conception weeks +2</p>
<p>How long is a term pregnancy?</p>
<p>40 weeks</p>
<p>What happens in the pre-embryonic period?</p>
<ul> <li>Cleavage</li> <li>Compaction</li> <li>Implantation begins</li> </ul>
<p>What is happening in cleavage?</p>
<p>Mitotic division</p>
<p>Why is cleavage significant?</p>
<p>Because have established a new individual</p>
<p>What is formed from cleavage?</p>
<p>Morula</p>
<p>What is the morula?</p>
<p>A clump of cells</p>
<p>What happens in compaction?</p>
<p>The formation of a blastocyst</p>
<p>What is implantation?</p>
<p>The process by which the blastocyst makes contact with the endometrium of the uterus</p>
<p>What does implantation begin?</p>
<p>The establishment of the pregnancy</p>
<p>Where is the oocyte released from?</p>
<p>The ovary</p>
<p>What happens to the oocyte once it’s been released?</p>
<p>It travels along the Fallopian tubes</p>
<p>Where is the oocyte fertilised?</p>
<p>Ampulla</p>
<p>What fertilises the oocyte?</p>
<p>Sperm</p>
<p>What is the ampulla of the fallopian tubes?</p>
<p>The fan bit just above the ovary</p>
<p>What is the fertilised oocyte called?</p>
<p>The zygote</p>
<p>Where is the ideal site for implantation?</p>
<p>The posterior uterine wall</p>
<p>What does the zygote need to do before it can implant?</p>
<p>Continue to travel alone the fallopian tube to get where it needs to be to establish the pregnancy</p>
<p>How long is an oocyte viable for?</p>
<p>1 day</p>
<p>How long is sperm viable for?</p>
<p>3 days</p>
<p>What happens immediately after fertilisation?</p>
<p>Sperm is excluded due to a complex chemical reaction</p>
<p>When does cleavage begin?</p>
<p>30 hours after fertilisation</p>
<p>What does cleavage result in?</p>
<p>2 blastomeres of equal size</p>
<p>What is the zona pellucida?</p>
<p>A glycoprotein ‘shell’</p>
<p>What is the result of the presence of the zona pellucida?</p>
<p>The blastomeres are about half the size of the oocyte, as the cell prevents it from expanding</p>
<p>What has happened by day 3 post fertilisation?</p>
<p>The morula has formed</p>
<p>What feature does each cell have at the morula formation stage?</p>
<p>They are totipotent</p>
<p>What is meant by the cells being totipotent?</p>
<p>They have the capacity to become any cell type</p>
<p>What happens in assisted reproductive techniques?</p>
<p>The oocytes are fertilised in vitro, and allowed to divide to the 4- or 8- cell stage. The morula is then transferred into the uterus</p>
<p>What is PGD?</p>
<p>When a cell is removed from the morula and tested for serious heritable conditions prior to the transfer of the embryo into the mother</p>
<p>What is compaction?</p>
<p>Formation of the first cavity</p>
<p>What is the first cavity formed?</p>
<p>The blastocyst</p>
<p>How is the blastocyst formed?</p>
<p>The cells of the morula are secreting tiny amounts of tissue fluid. Together, collect a sufficient amount that it collects, and one clump of cells pushes to one side, giving a space</p>
<p>What does the formation of the blastocyst give?</p>
<p>2 groups of cells</p>
<p>What is the inner group of cells called?</p>
<p>Embryoblast</p>
<p>What is the outer group of cels called?</p>
<p>Trophoblast</p>
<p>What happens to the inner group of cells of the blastocyst?</p>
<p>It goes on to give the embryo</p>
<p>What happens to the outer cells of the blastocyst?</p>
<p>They go on to produce the supporting tissues</p>
<p>What tissues support the embryo during pregnancy?</p>
<p>#NAME?</p>
<p>Why can cells produced by the first divisions after fertilisation become inner or outer cell mass?</p>
<p>Because they are all totipotent, so they have the capacity to become any cell type</p>
<p>What are cells after compaction?</p>
<p>Pluripotent</p>
<p>What is meant by pluripotent?</p>
<p>Cells have the capacity to become one of many cell types</p>
<p>What potential are pluripotent cells said to have?</p>
<p>Multi-lineage potential</p>
<p>What do the inner cell mass cells have the capacity to do?</p>
<p>Become any cell in the human body</p>
<p>What happens at day 5 post fertilisation?</p>
<p>Hatching</p>
<p>What is meant by hatching?</p>
<p>The blastocyst hatches from the zona pellucida</p>
<p>Why must the blastocyst hatch?</p>
<p>Up until now, the zona pellucida remains in tact, meaning it becomes quite restrictive, so we must get rid of it</p>
<p>What is the result of hatching?</p>
<p>The blastocyst is no longer constrained, and so is free to enlarge</p>
<p>What can the blastocyst do once it’s hatched?</p>
<p>Interact with the uterine surface to implant</p>
<p>When does implantation begin?</p>
<p>Day 6-7</p>
<p>How long does implantation run for?</p>
<p>A very long time- not complete until the end of the first trimester (~3 months)</p>
<p>What is the conceptus?</p>
<p>All the products of conception- the embryo and all its tissues</p>
<p>How many cells does the conceptus have at implantation?</p>
<p>107</p>
<p>How many cells of the conceptus at implantation will make the embryo?</p>
<p>8</p>
<p>How many cells of the conceptus at implantation will contribute to the development of foetal membrane?</p>
<p>99</p>
<p>Why is it important that foetal membranes are established?</p>
<p>It ensures that we can establish and maintain the pregnancy</p>
<p>Where does the conceptus implant?</p>
<p>Onto the uterine epithelium, which lines the uterine stroma</p>
<p>What development has priority at the very earliest stages?</p>
<p>Placenta</p>
<p>What important process occurs in week 2?</p>
<p>Differentiation</p>
<p>Where do two distinct cell layers emerge from?</p>
<p>The outer cell mass</p>
<p>What distinct cell layers emerge from the outer cell mass?</p>
<p>- Syncytiotrophoblast
| - Cytotrophoblast</p>
<p>What is the syncytiotrophoblast good for?</p>
<p>Transporting</p>
<p>What is purpose of the cytotrophoblast?</p>
<p>Allows the syncytiotrophoblast grow and increase in SA</p>
<p>What does the inner cell mass develop into?</p>
<p>A bilaminar disc</p>
<p>What does the bilaminar disc consist of?</p>
<p>#NAME?</p>
<p>In summary, what has happened by the end of the second week?</p>
<p>#NAME?</p>
<p>What are the two cavities of the embryo by the end of week two?</p>
<p>#NAME?</p>
<p>What is the name of the sac supporting the embryo?</p>
<p>The chorionic cavity</p>
<p>What is the amniotic sac formed from?</p>
<p>Spaces within the epiblast</p>
<p>What can implantation cause?</p>
<p>A small amount of bleeding</p>
<p>Why might implantation cause a small amount of bleeding?</p>
<p>Because it’s in invasive process</p>
<p>Why is implantation an invasive process?</p>
<p>The conceptus has to break through the endothelial lining</p>
<p>What must happen once the conceptus has broken through the endothelial lining?</p>
<p>The lining must be repaired</p>
<p>How is the endothelial lining repaired?</p>
<p>Using a fibrin plug</p>
<p>What is meant my implantation being interstitial?</p>
<p>The two tissues have a very close relationship- they are embedded</p>
<p>Where does the conceptus implant?</p>
<p>Within the uterine stroma</p>
<p>Why does the conceptus implant within the uterine stroma?</p>
<p>Because then it has access to all glands</p>
<p>What does implantation establish?</p>
<p>Maternal blood flow within the placenta- the basic structural unit of materno-fetal exchange</p>
<p>What change does implantation mark?</p>
<p>The support for embryo changes from histiotrophic to haemotrophic</p>
<p>What is meant by histiotrophic?</p>
<p>Support for tissues based on simple diffusion</p>
<p>Why must support for the embryo change from histiotrophic?</p>
<p>Because staying with this would drastically limit the size that it could grow</p>
<p>What is meant by haemotrophic?</p>
<p>Relying on support from maternal circulatory system</p>
<p>Why does the basic structural unit for materno-fetal exchange have to be within the placenta?</p>
<p>To allow for gas exchange, absorption of nutrients and removal of waste products from the foetus</p>
<p>Give 4 conditions linked to implantation defects</p>
<p>- Interuterine growth restriction (IUGR)
- Pre-eclampsaia
- Ectopic pregnancy
- Placenta praevia</p>
<p>What kind of defect causes ectopic pregnancy and placenta praevia?</p>
<p>When the conceptus implants at the wrong site</p>
<p>Where does the conceptus implant in an ectopic pregnancy?</p>
<p>At a site other than the uterine body, most commonly the Fallopian tubes</p>
<p>What are the two types of ectopic pregnancy?</p>
<p>#NAME?</p>
<p>What is the problem with ectopic pregnancy?</p>
<p>It can very quickly become a life threatening emergency, as it can cause haemorrhage</p>
<p>Where does the conceptus implant in placenta praevia?</p>
<p>In the lower uterine segment</p>
<p>What is the problem with placenta praevia?</p>
<p>It can cause haemorrhage in pregnancy</p>
<p>Why can placenta praevia cause haemorrhage?</p>
<p>If implantation occurs very near the point of exit, the placenta can grow across, causing the mother to bleed out</p>
<p>What does placenta praevia necessitate?</p>
<p>C-section delivery</p>
<p>What happens on day 9 post fertilisation?</p>
<p>- Embryonic pole develops
| - Abembryonic pole develops</p>
<p>What causes the development of the embryonic pole?</p>
<p>The rapid development of the syncytiotrophoblast</p>
<p>What happens once the abembryonic pole has been formed?</p>
<p>The primitive yolk sac is formed</p>
<p>What is the significance of the formation of the primitive yolk sac?</p>
<p>You then have an embryo with two cavities</p>
<p>What is the yolk sac membrane in contact with?</p>
<p>The cytotrophoblast layer</p>
<p>What are present in the syncytiotrophoblast?</p>
<p>Lacunae</p>
<p>What are lacunae?</p>
<p>Spaces opening up</p>
<p>What is the purpose of lacunae?</p>
<p>They allow for rapid increasing SA</p>
<p>What happens on day 11 post fertilisation?</p>
<p>Primitive yolk sac membrane pushed away from the cytotrophoblast layer</p>
<p>What pushes the cytotrophoblast layer away from the primitive yolk sac membrane?</p>
<p>An acellular extraembryonic reticulum</p>
<p>What later happens to the acellular extraembryonic reticulum?</p>
<p>Its converted into extraembryonic mesoderm by cellular migration</p>
<p>What happens on day 12 post fertilisation?</p>
<p>Maternal sinusoids are invaded by syncytiotrophoblast</p>
<p>What happens once the maternal sinusoids have been invaded by the syncytiotrophoblast?</p>
<p>The lacunae become continuous with the sinusoids</p>
<p>What does maternal sinusoids being invaded by syncytiotrophoblast begin?</p>
<p>Uteroplacental circulation</p>
<p>What is the uterine stroma preparing for when the maternal sinusoids are invaded by syncytiotrophoblast?</p>
<p>Support of the embryo</p>
<p>What happens day 13 post fertilisation?</p>
<p>Formation of the secondary yolk sac</p>
<p>Where does the secondary yolk sac come from?</p>
<p>Pinches off from the primitive yolk sac</p>
<p>What happens day 14 post fertilisation?</p>
<p>Spaces within the extra-embryonic mesoderm merge</p>
<p>What is formed when spaces within the extra-embryonic mesoderm merge?</p>
<p>The chorionic cavity</p>
<p>What suspends the embryo and its cavities?</p>
<p>The connecting stalk</p>
<p>What is the connective stalk made up of?</p>
<p>A column of mesoderm and future umbilical cord</p>
<p>What can bleeding be confused for at day 14?</p>
<p>Menstrual bleeding</p>
<p>What % of zygotes are lost within the first 2-3 weeks?</p>
<p>~50%</p>
<p>What % of diagnosed pregnancies miscarry?</p>
<p>15%</p>
<p>What % of women suffer from recurrent miscarriages?</p>
<p>1%</p>
<p>What is meant by recurrent miscarriages?</p>
<p>Miscarriages in 3 consecutive pregnancies</p>