8 Flashcards
When does the development of the placenta begin?
- during second week of development
- very first structure that develops
- no healthy pregnancy without a healthy placenta
What tissue is the placenta made from?
- trophoblast (outer cell mass)
- specifically the synctiotrophoblast and the cytotrophoblast
What day does implantation begin?
-day 6 of pregnancy
What has happened by the end of the 2nd week?
- conceptus has implanted
- embryo has 2 cavities, amniotic cavity and yolk sac
- embryo is suspended by connecting stalk
- embryo is contained within the chorionic cavity
What is the fate of the embryonic spaces?
- yolk sac disappears
- amniotic sac enlarges as the embryo enlarges which displaces the chorionic sac
- amniotic and chorionic membrane fuse to become a single cavity
What does implantation achieve?
- establishes the basic unit of exchange
- primary villi: early finger-like projections of trophoblast
- secondary villi: invasion of mesenchyme into core
- tertiary villi: invasion of mesenchymal core by fetal vessels
- anchor the placenta
- establish maternal blood flow within the placenta
What happens to the placental membrane as the needs of the fetus increase?
- becomes progressively thinner
- in the end only one layer of trophoblast ultimately separates maternal blood from fetal capillary wall to optimize transport
- 2 circulations never mix
What is a chorionic villus?
- initial unit of exchange
- branch out like a tree
- outer layer is synctiotrophoblast and core is made of CT where fetal blood vessels develop
- maternal blood vessels surround the villi
- look at placenta slide 11
What are some implantation defects?
Implantation in the wrong place
- ectopic pregnancy
- placenta praevia
Incomplete invasion
- placental insufficiency
- pre-eclampsia
Look at placenta slide 13-14
What is decidua?
- cells of endometrium that are specialized to modulate the degree of invasion of the conceptus once it has been implanted
- happens through a decidual reaction and is balanced by promoting and inhibiting factors
- important b/c if conceptus implants into an area with no decidua then there is no inhibition of invasion, so no control of degree of invasion
- if implantation is in correct place but the decidual reaction is subpar, then pregnancy may not be maintained
- look at placenta slide 15
Describe the structure of the chorionic villus
- first trimester villus: thicker barrier
- placenta itself changes as embryo grows
- third trimester villus: barrier at optimal “thinnes”
- cytotrophoblast has basically vanished
- fetal capillaries pushed up against synctitiotrophoblast
- see placenta slides 18-20
Describe the blood vessels of the placenta
Maternal blood vessels
- endometrial arteries and veins
- bathe the outside of the villi in maternal blood for exchange to occur
Fetal blood vessels
-bring waste products to the villi through the umbilical PAIRED arteries (deoxygenated blood from fetus to placenta) and nutrients/oxygen to the fetus via the SINGULAR umbilical vein
Describe the endocrine function of the placenta
- produces steroid hormones such as progesterone and oestrogen
- responsible for maintaining the pregnant state
- produces protein hormones such as:
- human chorionic gonadatrophin (hcg)
- human chorionic somatomammotrophin
- human chorionic thyrotrophin
- human chorionic corticotrophin
What produces hcg?
Synctiotrophoblast
What hormone sustains the corpus luteum in the first trimester?
Hcg
How do placental hormones influence maternal metabolism?
Progesterone
-increased appetite to allow an increased fat deposition to help support the fetus and breastfeeding
HCS/hPL
- human placental lactose increases glucose availability to fetus by creating a diabetogenic state to cause insulin resistance in mother
- same function in HCS
Describe transport functions of the placenta
Simple diffusion
-molecules move across a concentration gradient
Eg. Water, electrolytes, gases, urea and Uric acid
Facilitated diffusion
-applies to glucose transport
Active transport
- specific “transporters” expressed by the synctiotrophoblast
- amino acids, iron, vitamins
See placenta slide 30
Describe gas exchange in the placenta
- FLOW LIMITE not diffusion limited
- simple diffusion
- fetal O2 stores are small therefore maintenance of adequate flow is essential
- need good uteroplacental circulation
- if compromised then for example, during labour the contraction can lead to compression of the blood vessels and “fetal distress”
Describe the transfer of passive immunity
- fetal immune system immature
- so antibodies are transported from placenta to fetal circulation
- specifically IgG
Describe the pathophysiology of placental transport. Give an example
- placenta is not a true “barrier”
- teratogens can access the fetus via the placenta (especially in early pregnancy since this is when the body systems develop)
- ex. Rhesus disease of the new-born can occur where maternal antigens can cross into the fetal circulation and attack fetal blood cells
- pregnancy is considered to be an immune-compromised state for the mother so infections may be prevalent
What armful substances can affect the placenta and how?
Thalidomide -limb defects Alcohol -FAS and ARND Therapeutic drugs -anti-epileptic drugs -warfarin -ACE inhibitors Drugs of abuse -dependency in the fetus and newborn Maternal smoking
Describe how teratogenesis can affect the fetus at different stages of development
Pre-embryonic -lethal effects Embryonic -super sensitive -narrow windows for some sensitive Fetal -becomes less critical apart from CNS -see placenta slide 34
