8 - Embryology Weeks 1-4 Flashcards
Where are erythrocytes produced?
In fetus yolk sac, then liver and spleen, then bone marrow
What is the annulus fibrosus and nucleus pulposus?
AF - Cartilage in intervertebral disc. Great tensile and torsional strength
NP - Discs core of gel like material. Produced by notochord
What are the three developmental stages of pregnancy?
Preembryonic –> Embryonic –> Fetal
How long is pregnancy?
38 weeks + 2 (date of last period)
What are the risks to pregnancy and what is the effect on the fetus if these risks are presented at each stage of embryonic development?
- Ionising radiation
- Mother’s drugs
- Viruses
What happens during fertilisation?
- Capacitation (maturation of sperm)
- Acrosome reaction
- Cortical reaction (prevent polyspermy)
- Meiosis II of ovum
What happens in week 1 of the preembryonic period?
What is the first cavity formed in the conceptus?
In the blastocyst, called the blastocoele
What happens during week 2 of the pre-embryonic period and draw a diagram of what the embryo looks like?
- Week of 2’s, differentiation
- Embryo has two cavities, amniotic and yolk sac, and is suspended in chorionic cavity by connecting stalk
Why might women bleed but still be pregnant?
- Implantation bleeding (late fibrin plug)
- 50% of zygotes lots in first 3 weeks
- 15% of all pregnancies will miscarry
Where should implantation occur and what are some disorders caused by an error in implantation?
- Superior posterior uterine lining
- Ectopic pregnancy (anywhere but uterus, dangerous due to invasive)
- Placenta previa (risk of haemorraghe so dangerous)
Where are the following structures formed from?
What happens first after week 2 of embryonic development and explain the proccess of this stage?
Gastrulation - Formation of the trilaminar disc
- Lack of mesoderm where mouth and anus will be
What tissues originate from each germ layer?
Ecto: Organs that maintain contact with outside, e.g skin and CNS
Meso: Supporting tissues like heart, muscle, bone
Endo: Lining open internal structures, e.g GI and respiratory
What happens when identical twins are formed?
- Two primitive streaks
- Not allowed to study embryos anymore as gastrulation has started
What is situs invertus and what is it caused by?
All of the main organs are on the wrong side of the body
What happens after gastrulation and what is the steps of this process?
- Neuralation
(paraxial mesoderm either side of neural tube becomes somites)
(intermediate makes genital tract)
What happens in the embryo after neuralation and differentiation of the mesoderm?
Segmentation
What happens after neuralation and segmentation in the embryo?
- Cephalocaudal folding: Head to toe, pulls primitive heart in and pulls connective stalk ventrally. Divides up gut
- Lateral folding: Forms belly, suspends embryo in amniotic sac and forms the gut tube
What does the embryo look like at the end of the fourth week?
