Embryos - Implantation Flashcards
Where does fertilisation occur
What does it begin with
Begins with contact of sperm with secondary oocyte
ends with formation of zygote (1 cell embryo)
Occurs in ampulla of fallopian tube
Average volume of semen
2.5-3.5 ml after 3 days abstinence (2-6ml)
What is the fertility index
At least 20 million sperm/ml
40% sperm show vigorous swimming
60% normal shape
pH 7.35-7.5
Seminal vesicles (2/3) releases
Water
Fructose
Fibrinogen
Vit C
Prostaglandins
Prostate releases
Water buffers
Fibrinoginase (clotting)
Fibrinolytic enzyme (liquification)
Citric acid
Prostaglandins
Bulbourethral gland releases
Water
Buffers
Mucus
Epididymis releases
Water
Nutrients
1 min after ejaculation
Semen coagulation - fibrinogenase
20 min after ejaculation
semen liquifaction by the fibrinolytic enzyme in seminal plasma
How does the female prevent sperm entry
How is this overcome
Thick mucous prevents entry (keeps micro-organisms out)
Preovulatory rise in oestrogen makes the mucus thin and watery
(Sperm swim through 1.2-3mm/min)
Life span of sperm
3-6 days
process of fertilisation
- Secondary oocyte - 1st polar body
surrounded by granulosa cells and Zona Pellucida
- Acrosome rxn
- Hyaluronidase - loss of corona (derived from golgi apparatus)
- Acrosin and neuminidase facilitate passage through ZP
- On contact with plasmallema of oocyte zona rxn prevents polyspermy - release of cortical granules
- contact induces secondary oocyte to divide to become ootid (ovum) and 2nd polar body - nucleus known as female pronucleus
- Tail of sperm degenerates
- Head and centriole enter
- Head forms male pronucleus
- Pronuclei fuse to form zygote
What are the results of fertilisation
- Restoration of diploid number - 46
- Determination of chromosomal sex of embryo
- Variation of human species - new combination of chromosomes
- Intitiation of cleavage - mitotic division of zygote into blastomeres
What happens to the zygote as it passes along the fallopian tube
Undergoes cleavage to daughter cells - blastomeres
New cells are smaller after each division
Describe the formations within the 1st week of human life
16 cell embryo - morula
Blastocyst with blastocyst cavity - 4 days
Outer flattened cells - trophoblast
Inner cells - inner cell mass
Trophoblast
Embryonic part of the placenta
Inner cell mass
Primordium of the embryo
When does the ZP disappear
What does this signal the beginning of
5-6 days after fertilisation
Process of implantation begins
Process of fertilisation
What do the polar body and oocyte have in common
Contain same amount of genetic info
Microscopic view of fertilisation
Stages prior to formation of morula
Relations between embryoblast, blastocyst and trophoblast
What happens at implantation
Trophoblast differentiates into outer syncytiotrophoblast & inner cytotrophoblast
Uterine stroma decidual response
What does success of implantation require
Trophoblast penetration of several tissue components to reach maternal blood supply
- Epithelial lining of the uterus
- Basal lamina
- Underlying stroma
sequence of events resembles invasion of malignant tumours
MOA in order to achieve implantation
- Invasive cells must attach to ECM proteins
- Secrete proteases capable of degrading these proteins and migrate through the degraded ECM
- During implantation and subsequent placentation in the human, populations of trophoblast cells invade the endometrium and maternal vasculature within the uterus
- Once reaching spiral arteries within the myometrium, trophoblast invasiveness ceases
How does trophoblast invasion differ from tumour cells
Tumour cells exhibit uncontrolled invasion
Trophoblast invasion is tightly regulated
Events leading to pre-eclampsia and intrauterine growth retardation
Sub-optimal trophoblast invasion
Overview of menstrual cycle
How does the corpus luteum protect itself
HCG (human chorionic gonadotrophin) - 1st text to mother
after that placenta produces progesterone
Structure formed at day 7.5
What has formed at the end of the 2nd week
Uteroplacental circulation
Structure at day 9
Structure at day 12
What is significant about this day
Embryo makes contact with mother’s blood supply
Structure at day 13
Primary villi are sticking into trophoblast
Where might hatching occur
What are ectopic pregnancies
Structure at the end of the 3rd week
Getting set up for embryonic circulatory system
Some of the cytotrophoblast extends all the way out to provide anchorage
What constitutes the major foetal component of the placenta
Describe its composition
Chorionic villi
Consist of a mesenchymal core containing matrix, cells and foetal BVs
Describe the chorionic villi during the first trimester
Villi are covered by the 2 layered epithelium of trophoblast - cyncytiotrophoblast (multi-nucleated, bathed in maternal blood) and cytotrophoblast (cellular, non-invasive, villous)
Describe the cytotrophoblast
Cellular, non-invasive, villous
Describe the syncytiotrophoblast
Multinucleated, bathed in maternal blood
OUTER layer
How does the haemochorial placenta change as gestation continues
Cytotrophoblast becomes discontinuous and syncytiotrophoblast becomes thinner
Nutrients from maternal blood are transported across compartments to reach foetal vessels
What are anchoring villi
Some chorionic villi FREE others attached to decidua at the site of invasion - respiratory and absorptive - lungs & gut
At these sites villous cytotrophoblast cells proliferate and break through the syncytiotrophoblast to form cytotrophoblast columns and invade the decidua basalis
What cells augment vessel walls
Some extravillous cytotrophoblast cells also invade uterine spiral arteries becoming endovascular trophoblast
Decidua basalis
Decidualised endometrial cells and several kinds of immune cells including macrophages and large granular lymphocytes
Structure of haemochorial placenta
Placental blood supply
Changes in blood supply between 4 weeks and 4 months
Structures seen during gestation
What lies beneath the decidua basalis
