57.3 Placenta Flashcards
Describe placental blood flow.
Fetal circulation:
- Umbilical arteries (from the internal iliac) take blood to the placenta, where it picks up oxygen
- Oxygenated blood returns to the fetus’ liver via the umbilical vein and from there to the right atrium
Mother’s circulation:
- Uterine arteries (branches of the internal iliac) take blood to the uterus
- Spiral arteries supply the intervillous spaces
- Uterine veins drain the uterus
Uterine contractions allow blood to spurt in from the arteries, but close venous outflow, causing the low pressure in the intervillous space to rise. When the myometrium relaxes, veins reopen and intervillous pressure falls.
Summarise the function of the endometrium.
Thin inner layer which contains many glands and arteries to nourish the developing conceptus which implants in this layer.
Functional layer of the endometrium is sloughed off once a month during menstruation
What is the function of the myometrium?
Smooth muscle layer which contracts during labour to delivery the foetus
What are the amnion and chorion.
- Amnion -> A membrane that covers the embryo when it is first formed. It contains the amniotic fluid, used for protection.
- Chorion -> The outermost fetal membrane. It contains chorionic fluid, usd for protection. Chorionic villi (a.k.a. placental villi) are used for exchange with the mother.
What is the function of the amnion?
Contains a fluid (amnionic fluid) which serves as a mechanical buffer and helps remove waste products (turned over every day)
What is the chorion made up of?
Cytotrophoblasts, syncitiotrophoblasts and extraembryonic mesoderm
What is the decidua basalis? Summarise the function.
- The term given to the uterine endometrium at the site of implantation where signaling transforms the uterine stromal cells (fibroblast-like) into decidual cells.
- Functions:
- Exchanges of nutrition, gas, and waste with the gestation
- Protects the pregnancy from the maternal immune system
- Hormone production
What are cotyledons?
- They are divisions of the placenta, separated by septa, only visible from the maternal side.
- Each cotyledon consists of a main stem of a chorionic villus as well as its branches and subbranches.
Summarise the function of uterine glands.
- Uterine glands tubular glands of the endometrium
- Provide the foetus with nourishment
Summarise the function of Wharton’s jelly.
- A gelatinous substance within the umbilical cord, largely made up of mucopolysaccharides (hyaluronic acid and chondroitin sulfate).
- It acts as a mucous connective tissue, important in the protection of the vessels in the umbilical cord.
Summarise the function of the intervillous spaces in the placenta.
expansive vascular space lined by villous syncitiotrophoblasts between the chorionic (placental) villi
Supplied by open end maternal arterioles which supply nutrients for exhange with the cotyledons
Drained by maternal endometrial veins
What is the function of cytotrophoblasts?
line the inside of the syncytiotrophoblast and will eventually form the foetal portion of the placenta
What is the function of syncitiotrophoblasts?
initially invade the endometrium, drawing the blastocyst into the uterine wall -> Ruptures capillaries so creating an interface between maternal blood and embryonic fluid for passive transfer. Also secretes a lot of hCG to maintain corpus luteum
What are the different stages of nutrition of the foetus?
In order, the fetus obtains nutrition from:
- The small amount of yolk proteins in the oocyte
- Secretions of the uterus and oviduct (before implantation)
- Digestion of the uterine decidua (endometrium that is specialised for implantation)
- Maternal blood (via placenta)
What are the three layers of the uterine wall?
Endometrium
Myometrium
Perimetrium
What is A?
Fetal ARTERY (heading to placenta to become oxygenated)
What is B?
foetal vein
What is D?
Chorionic villus
What is E?
Maternal Vein
What is F?
Intervillous space (lacunae)
Describe the structure of the placenta?
Disc shaped structure formed by the trophoblast upon implantation
Separated into cotyledons to give a lobar arrangement which are supplied by maternal arteries
Contains open ended spiral arterioles which empty into intervillous spaces. These fill up with maternal blood and leave via endometrial veins
Slow movement of blood allows for sufficient time for gas exchange with chorionic villi
Chorionic villi extend into pools of blood
What is the function of the spiral arteries?
Supply the endometrium and the intervillous spaces in cotyledons where gas exchange occurs
What are placental cotyledons? What is their function?
Structure in the placenta consiting of a main stem chorionic villus and its branches
They are surrounded by maternal blood and separated by placenta septa
SITE OF EXCHANGE OF OXYGEN AND NUTRIENTS
What are the umbilical arteries contained within?
Wharton’s jelly
What is G?
Maternal artery
