Lecture 13 - Placenta Flashcards
Implantation
Trophoblasts interact with the endometrial lining of the uterus
Blastocyst is embedded within the endometrium, increasing its blood supply and secretory glands develop.
What day does implantation occur
Day 6
Week 2
Trophoblast differentiates into the syncytiotrophoblast and cytotrophoblast
The embryoblast becomes the hypoblast and epiblast
Conceptus implants
Amniotic cavity and yolk cavity is formed from the epiblast and hypoblast
Suspended by the connecting stalk in the chorionic cavity
Embryonic spaces
Yolk sac disappears
Amniotic sac enlarges and fuses with the chorionic membrane to form the amniotic membrane
Chorionic sac is occupied by the expanding amniotic sac
What does implantation achieve?
Placental membrane:
Primary villi - early projections of trophoblast (single layer)
Secondary villi - invasion of mesenchyme into core
Tertiary villi - invasion of foetal vessels into mesenchyme core
Placenta is anchored to maintain the pregnancy
Maternal blood flow writhing the placenta surround villi allowing exchange to occur
Placental membrane
Initially the barrier is thick with syncytiotrophoblast and trophoblasts but as the pregnancy progresses, the barrier becomes thinner as it lose the cytotrophoblast and only 1 layer of syncytiotrophoblasts remain
Short diffusion pathway for optimal exchange
2 circulations never mix - better control
Chorionic fondosum
Outer layer of the placenta with chorionic villi
Incomplete invasion
Pre-eclampsia
Placental insufficiency
Decidual reaction
Transformation of the endometrium in the presence of a conceptus to maintain the pregnancy
- inhibits invasion - balance
Chorionic villus
Finger like projection of the chorionic membrane that allows exchange with the maternal circulation
Cotyledons
When placenta is removed the cotyledons should be completely intact
If lost and remains inside the woman, can cause post partake haemorrhage
3 cellular layers for oxygen to cross
Capillary endothelium of foetus
Cytotrophoblast
Syncytiotrophoblast
Umbilical vein
Carries oxygenated blood from the placenta to foetus
umbilical arteries
2
Carry deoxygenated blood from foetus to the placenta and maternal circulation
Endometrial veins and arteries
Veins - doexygenated blood from maternal circulation
Arteries - (spiral) oxygenated blood from maternal circulation
Hormones produced by the placenta
Protein hormones:
- HCG
- human chorionic somatomammotrophin
- human chorionic thyrotrophin
- human chorionic corticotrophin
Steroid hormones: after 1st trimester
- oestrogen
- progesterone
Beta HCG
Produced during first 2 months of pregnancy then decreases
Analogous to LH - supports the corpus luteum to secrete oestrogen and progesterone
Produced by the syncytiotrophoblast - pregnancy test
Trophoblast disease
Hyatidiform mole - uterus enlarges more rapidly due to abnormal placental growth
Choriocarcinoma
Steroid hormones
Oestrogen and progesterone maintain pregnancy state
Placental production begins in the 11 th week
Progesterone
Increase appetite
Increased fat deposition which aid breast feeding
Human placental lactogen
Also called human chorionic somatomammotrophin
-increases glucose availability to foetus
- maternal insulin resistance so less glucose is absorbed into maternal cells - diabetogenic state
Simple diffusion
Water
Electrolytes
Urea
Gases
- exchange limited by circulation flow
- small foetal O2 stores - requires adequate flow
Facilitated diffusion
Glucose
Active transport
Amino acids
Iron
Vitamins
Transporters expressed on the syncytiotrophoblast
