Placenta Flashcards
What is the 3 structures that form the structure of the placenta and blood supply of each?
Umbilical cord
- 2 arteries (deoxygenated), 1 vein (oxygenated)
- vein is larger than arteries
Chorionic villi (tree like structure)
- fetal capillaries enclosed on trophoblast
Intervillous space
- filled with maternal blood supplied by spiral arteries from endometrium
Placental development:
What occurs at the pre-implantation stage?
- fertilisation and cleavage from blastocyst (until day 4-5 post fertalisation)
- forms an outer layer trophoblast
Placental development:
What occurs at the implantation stage?
- trophoblast proliferation, differentiation and invasion (day 8 post fertilisation)
-Trophoblast is made up of cytotrophoblast cells which differentiate into syncytiotrophoblast
- when the blastocyst implants into uterine wall the synctiotophoblast invades endometrium by secreting proteolytic enzymes
Placental development:
What occurs at the post-implantation stage?
- Lacunae formation (cavity)
- these are initially filled with tissue fluids and uterine secretions until the maternal capillaries get eroded and they fill with maternal blood
- these eventually merge to form intervillous spaces
- Villi formation
- cytotrohpblast projections invade syncytiotrophoblast and embryonic mesoderm follows
- fetal capillaries are formed in villi
- trophoblast forms above villi to close off intervillous space
- branching continues until week 20 then villi mature
- Spiral artery remodelling
- trophoblast cells invade maternal spiral arteries to break down endothelium and smooth muscle cells
- results in large, low resistance vessels which provides continuous blood supply into intervillous space
When is the placenta fully formed?
18-20 weeks
How much of the ueterus endometrium is covered by the placenta
40%
There are morphological variations in placental structure in mammals. What are the different gross shapes and distribution of chorionic villi types?
- diffuse (pig, horses, kangaroos)
- chorionic villi found all around - multicotyledonary (cows, sheep, deer)
- chorionic villi spotted across placenta - zonary (dogs, cats, bears)
- chorionic villi located in one zone of placenta - discoid (human type, rabbits, mice)
- chorionic villi in one spherical area of placenta
There are morphological variations in placental structure in mammals. What are the different tissue indigitations found?
- folded
- lamellar
- trabecular
- villous (human)
- labyrinthine
There are morphological variations in placental structure in mammals. What are the different types of tissue layers among placentas?
- epitheliochorial
- endotheliochorial
- hemochorial (humans)
- humans are known as haemo-mono-chorial
(blood does not mix between mother and fetus)
The placenta has many functions. One of its functions is to mediate the transportation of oxygen, nutrients and waste. What are the different ways transportation occurs through the placenta?
- diffusion
- transporter mediated
- endocytosis/exocytosis
Materials that can pass through the placenta to the fetus do not always stay the same. What else can happen to them?
- partial consumption by the placenta
- metabolised from one product to another by the placenta
Another function of the placenta is to protect the fetus. However it is not the perfect barrier. What can pass through the placenta that could cause damage to the fetus?
- alcohol
- steroids or arrhythmia medication
- certain infections: rubella, COVID
The placenta also has endocrine functions. How does the placenta know to release hormones?
through signalling from mother and fetus
What hormones from the fetus affect hormone synthesis of the placenta?
glucocorticoids
leptin
insulin
What hormones from the mother which affect hormone synthesis of the placenta?
glucocorticoids
mineralocorticoids
leptin/ adiponectin
insulin
angiotensin 2
The placenta has the ability to release hormones based on the hormone released by mother or fetus. What are the common hormones released by the placenta?
chorionic gonadotrophin
prolactins
placental growth hormone
prostaglandins
sex steroids
leptin
What are the common outcomes when placentation goes wrong?
pre-eclampsia
placenta accreta
placenta previa
placental abruption still birth
What goes wrong with the placenta fro pre-eclampsia to occur?
spiral arteries in the endometrium do not reshape properly due to inadequate invasion of trophoblast cells
What happens when placenta accreta occurs?
placenta does not attach to the stratum basalis of endometrium. It continue to invade and attached to myometrium
What happens when placenta previa occurs?
This is then the placenta inplants at the bottom of the uterus rather than the side results in the cervix being covered or partially covered. Natural birth cannot occur.
What happens when placental abruption occurs?
This is when the placenta detaches from endometrium. This can starve the fetus of nutrients and oxygen. Depending on how far along in pregnancy this occurs a c-section will be required
How does the abnormal placentation result in still birth?
still birth = loss of fetus after 20 weeks of gestation
all previous placental probelsm are common contributors and also long hyper-twisted umbilical cords
- restricts blood to fetus
Recent studies have began looking at the relationship between imprinted genes and placentation. What is the theory as to why imprinting genes are involved?
balance of parental resources and is important for growth of fetus.
Note: imprinting is an epigenetic phenomenon which describes the parent of origin of gene expression
