Placental Function and Dysfunction Flashcards
Why is development of the placenta so important and given precedence?
In very early embryonic development establishment of the placenta takes precedence this ensures support for the pregnancy.
What happens to the yolk sac, chorion and the amniotic sac by the end of the 2nd week?
By the end of the 2nd week the yolk sac disappeared, the amniotic sac enlarges to encompass the embryo and occupy the chorionic sac which is enclosed by the smooth chorion. On the chorionic membrane are specialised structures called chorionic villi.
Describe how implantation is described and why a woman might think she isn’t pregnancy at about 7 days after fertilisation?
Implantation is interstitial this means that the conceptus is embedded within the endometrium. The uterine epithelium is breached and the conceptus implants within the stroma (can be small amount of bleeding here that is confused with a period.
What happens to the placental membrane throughout the pregnancy and how is the placenta described?
The placental membrane becomes progressively thinner as the needs of the foetus increase. The human placenta is haemomonochorial – one layer of trophoblast ultimately separates maternal blood from foetal capillary wall.
What are the 3 main aims of implantation?
- Establish the basic unit of exchange – primary villi: early finger-like projections of trophoblast – secondary villi: invasion of mesenchyme into core – tertiary villi: invasion of mesenchyme core by foetal vessels.
- Anchor the placenta – establishment of the outermost cytotrophoblast shell.
- Establish maternal blood flow within the placenta – high flow low resistance.
What is an ectopic pregnancy and placenta praevia?
Ectopic Pregnancy
Implantation at site other than uterine body (most commonly Fallopian tube), can be peritoneal or ovarian and can very quickly become life threatening emergency.
Placenta Praevia
Implantation in the lower uterine segment this can cause haemorrhage in pregnancy and requires C-section delivery.
How is the endometrium prepared for implantation?
The endometrium is prepared for implantation by pre-decidual cells and the elaboration of spiral arterial blood supply.
Decidualisation – the decidual reaction provides the balancing force for the invasive force of the trophoblast. In fallopian tube these cells aren’t present and so ectopic pregnancy is characterised by excessive invasion.
Remodelling of the spiral arteries elaborates these arteries this creates a vascular bed of low resistance vascular and high flow required to meet foetal demand – particularly late in gestation.
What are the two most common implantation defects?
Implantation defects - Invasion incomplete:
Pre-eclampsia – normal remodelling doesn’t take place and so invasion isn’t enough.
Placental insufficiency
How does the 1st trimester placenta differ from the term placenta?
1st trimester placenta
Placenta established and placental “barrier” is still relatively thick. There is a complete cytotrophoblast layer beneath syncytiotrophoblast.
Term placenta
Surface area for exchange dramatically increased. Placental “barrier” is now thin and cytotrophoblast layer beneath syncytiotrophoblast is lost.
What blood vessels travel through the umbilical cord?
Umbilical cord vessels & the foetal circulation
Two umbilical arteries – Deoxygenated blood from foetus to placenta. One umbilical vein – Oxygenated blood from placenta to foetus
What metabolite functions does the placenta have?
Metabolism – placental synthesis of: glycogen, cholesterol (for hormones) and fatty acids.
Progesterone – increased appetite and hCS / hPL (human placental lactogen) – increases glucose availability to foetus.
What endocrine functions does the placenta have
Protein hormones: human gonadatrophin, human somatomammotrophin, human chorionic thyrotrophin and human chorionic corticotrophin. Steroid hormones include only progesterone and oestrogen.
Describe the importance of hCG produced by the placenta and what is trophoblast disease?
Produced during the first 2 months of pregnancy it supports the secretory function of corpus luteum and is produced by syncytiotrophoblast therefore is pregnancy specific. It is excreted in maternal urine therefore used as the basis for pregnancy testing. Trophoblast disease – abnormal growth of placental tissue without an embryo called molar pregnancy (hydatidiform mole) or choriocarcinoma which is the malignant variant.
What are the roles of oestrogen and progesterone in pregnancy?
Progesterone and oestrogen. These are responsible for maintaining the pregnant state because high levels of both will shut down the HPG axis. Placental production takes over from corpus luteum by 11th week.
Which molecules are moved by simple diffusion vs facilitated and active transport?
Simple diffusion – molecules moving down a concentration gradient: water, electrolytes, urea & uric acid, gases. Facilitated diffusion – applies to glucose transport.
Gas exchange
Simple diffusion, flow-limited, not diffusion-limited. Foetal O2 stores are small therefore maintenance of adequate flow essential. As a result, adequate uteroplacental circulation is essential.
Active transport – specific “transporters” expressed by the syncytiotrophoblast: amino acids, iron and vitamins.
