Placenta & Fetal Membranes Flashcards
What are the Fetal Membranes?
- Chorion
- Amnion
- Umbilical Vesicle
- Allantois
The placenta is the primary site for what process?
nutrient and gas exchange between mother and fetus
What are the 2 parts of the placenta?
What do they develop from?
- A fetal part = develops from the chorionic sac
- A maternal part = derived from the endometrium
What are the functions of the placenta?
- Protection
- Nutrition
- Respiration
- Excretion
- Hormone Production
- Metabolism
- Endocrine secretion (hCG)
What is the functional layer of the endometrium that separates from the rest of the uterus at birth called?
gravid endometrium
what is the process of seperating the gravid endometrium from the rest of the uterus called?
parturition
What is the decidua?
- cells of the endometrial connective tissue which swell because of the accumulation of glycogen and lipid in their cytoplasm
- (provide nutrition for the early embryo)*
What are the 3 regions of the decidua and what do they form?
- *Decidua basalis** = forms the maternal placenta.
- *Decidua capsularis** = overlies the conceptus.
- *Decidua parietalis** = all the remaining parts of the decidua
As the fetus grows, which 2 decidual layers will eventully fuse together?
What is this called?
- capsularis will eventually fuse with **parietalis **
- they form the “decidua vera”
decidual cells are large pale-staining connective tissue cells.
What do they form in response to?
increasing progesterone levels in the maternal blood
The decidual reaction, refers to ….?
cellular and vascular changes in the endometrium as the blastocyst implants
Development of the placenta is characterized by what 3 things?
- fast proliferation of the trophoblast
- development of the chorionic sac
- development of chorionic villi
By the end of week 3, what structures are established?
the anatomic structures needed for physiological exchanges between mother and embryo
What (structure) is evident by the end of week 4?
a complex vascular network
Chorionic villi cover the entire chorionic sac until the beginning of what week?
week 8
As the chorionic sac grows, what area forms?
Why/how does this occur?
the** smooth chorion** forms
As the sac grows the villi associated with the decidua capsularis are compressed, reducing the blood supply to them, causing them to degenerate
Chorionic villi associated with what decidua layer increase in number, branch profusely, and enlarge?
What area does this form?
decidua basalis
this forms the villous chorion
How many hormones are produced by the placenta?
Name at least 1 and its function.
7 - 8 hormones
relaxin = helps cervix relax during vaginal delivery
Where do the primary chorionic villi begin forming?
in syncytotrophoblast and surrounding the embryo
The placenta grows in size and thickness until week ______?
week 20
What is the weight of a fully developed placenta?
300 to 700 grams
When is the decidua basalis is replaced by the fetal part of the placenta?
By the end of the fourth month
At the time of birth, the placenta will usually detach within ___________ after the baby is delivered.
The maximun time should be up to __________.
- 20 minutes
- 1 hour
What 4 things should a physician note about the placent upon delivery?
- its weight
- its measurements
- length of umbilical cord
- implantation of umbelical cord (should be central)
What attaches the fetal part of the placenta to the maternal part?
cytotrophoblastic shell
(external layer of trophoblastic cells on the maternal surface of the placenta)
What happens as the chorionic villi invade the decidua basalis?
- decidual tissue is eroded to enlarge the intervillous space
- this erosion produces wedged-shaped areas of decidua
wedged-shaped areas of decidua are called…?
placental septa
The placental septa divide the fetal part of the placenta into **irregular convex areas **called what?
cotyledons
the decidua basalis is replaced by the cotyledons by what time?
the end of month 4
By 22 to 24 weeks the blood supply to the decidua capsularis is reduced.
What does this cause?
causes the decidua capsularis to degenerate and disappear
After the decidua capsularis is gone, what 2 structures fuse together?
the smooth part of the chorionic sac fuses with the decidua parietalis
How is the fusion between the chorionic sac and the decidua parietalis separated?
- separated when blood escapes from the intervillous space.
- collection of blood (hematoma) pushes the chorionic membrane away from the decidua parietalis.
What happens when a hematoma occurs that seperates the baby form the placenta in-utero?
- the baby will die
- must remove the placents/conceptus to stop the bleeding
- focus is to save mother
How much blood loss is normal after a full delivery (birth)?
approximately 1 Litre, or 1 pad every 3-4 hours
What happens if the membranes remain inside the mother after delivery?
- heavy bleeding can continue
- hemmoraging can occur
- potential maternal death if bleeding isn’t stopped
What do the Intervillous spaces of the placenta contain?
When were these formed?
- maternal blood derived from the lacunae
- formed in the syncytiotrophoblast during week 2
How/where does the maternal blood enter the intervillous space?
through spiral endometrial arteries in the decidua basalis
(spiral arteries pass through gaps in the cytotrophoblastic shell and discharge blood into the intervillous space)
Endometrial veins…
… help drain the intervillous space
(penetrate through the cytotrophoblastic shell)
branched chorionic villi…
… are showered with maternal blood
(circulates through the intervillous space)
The maternal blood contains…
- oxygen and nutritional materials
(important for fetal growth and development)
** - fetal waste products**
(i.e. carbon dioxide, salts, and products of protein metabolism)
Primary chorionic villus
- time of development
- structures
- surrounded by…
- during week 2
- consists of a core of cytotrophoblastic cells
- surrounded by syncytiotrophoblast
Secondary chorionic villus
- time of development
- structures
- surrounded by…
- during the start of week 3
- Consists of a core of extraembryonic mesoderm
- surrounded by cytotrophoblastic cells and syncytiotrophoblast
Tertiary chorionic villus
- time of development
- structures
- surrounded by…
- end of week 3
- Consists of a core of villous (fetal) capillaries
- surrounded by cytotrophoblastic cells and syncytiotrophoblast
Chorionic Villi Classifications
Primary, Secondary, Tertiary
Which 2 structures fuse to form the amniochorionic membrane?
What happens to this during labor?
amnion and smooth chorion fuse
- membrane ruptures during labour -
“water breaking”
Preterm rupture of the amniochorionic membrane (amniotic cavity) is the most common cause of what?
premature labor
(amniotic fluid escapes through the cervix and vagina0
What is the usual dialation present at the normal rupture of the amniotic cavity?
“water breaking”
9 cm dialated
What position should the mother be in after her water breaks?
Why?
Supine (laying down)
to avoid trauma from the baby’s head hitting the pelvic bone
How does poorly oxygenated blood leave the fetus?
passes through the umbilical arteries to the placenta
(when the umbilical cord joins the placenta, these arteries divide into several chorionic arteries that branch in the chorionic plate before entering the chorionic villi)
What side of the fetal heart has a higher pressure?
When does this change?
right side
- changes to left side after birth
(once baby breathes on its own)
Describe the maternal blood flow into the intervillous space from the spiral arteries.
- very fast
- pulsatile
- propelled in jetlike fountains
- spurts toward the chorionic plate
- flows **slowly over the branch villi **(metabolic gas exchange)
- return to the maternal circulation through the endometrial veins
What is caused by a reduction in uteroplacental circulation?
- fetal hypoxia** **
- intrauterine growth restriction (IUGR)
Placental Metabolism:
What is synthesized here?
nutrients for the embryo/fetus
- glycogen
- cholesterol
- fatty acids
How are most materials transported across the placental membrane?
- Simple diffusion
- Facilitated diffusion
- Active Transport
- Pinocytosis
What are Substances That Do Not Cross The Placental Membrane?
- Maternally-derived cholesterol, triglycerides, and phospholipids
- Protein hormones (e.g., insulin)
- Drugs (e.g., succinylcholine, curare, heparin, methyldopa, drugs similar to amino acids)
- IgD, IgE, IgM
- Bacteria in general
Each branched chorionic villi has ____________?
- a venous and artery pair
What happens to the baby’s heart rate suring vaginal delivery?
- during uterine contractions blood vessels in placents collapse/constrict
- baby’s HR changes (increases or decreases)
need to monitor this
What happens to the baby when the mother is Rh negative and the father is Rh positive?
1st pregnancy: Rh positive baby; nothing abnormal
2nd pregnancy: Rh positive baby; maternal immune system attacks fetus
