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SA reproductive > S6) Placental Function and Dysfunction > Flashcards

S6) Placental Function and Dysfunction Flashcards

1
Q

In week 2 of embryological development, two distinct cellular layers emerge from the outer cell mass.

Identify them

A
  • Synctiotrophoblast
  • Cytotrophoblast
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2
Q

What happens to the inner cell mass during week 2 of embryological development?

A

Inner cell mass becomes the bilaminar disk:

  • Epiblast
  • Hypoblast
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3
Q

When does implantation begin and end?

A
  • Commencement: day 6
  • Completion: day 9
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4
Q

What are the 2 cavities in the embryo?

A
  • Amniotic cavity
  • Yolk sac
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5
Q

What has happened by the end of week 2 of embryological development?

A
  • The conceptus has implanted
  • The embryo and its two cavities are suspended by the connecting stalk within a supporting sac called the chorionic cavity
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6
Q

What is the fate of the embryonic spaces after the end of week 2?

A
  • Yolk sac disappears
  • Amniotic sac enlarges as the embryo enlarges
  • Chorionic sac is occupied by the expanding amniotic sac
  • soon these two sacs will fuse and form one
  • amniochorionic membrane breaks during childbirth
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7
Q

What does implantation achieve?

A
  • Establishes the basic unit of exchange
  • Anchors the placenta
  • Establishes maternal blood flow within the placenta
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8
Q

Identify and describe the 3 forms of villi created by implantation

A
  • formed from the Childs syncytiotrophoblasts to form connections with the mother

- Primary villi: early finger-like projections of trophoblast

- Secondary villi: invasion of mesenchyme into core

- Tertiary villi: invasion of mesenchyme core by fetal vessels

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9
Q

What is meant by the statement ‘implantation is interstitial’

A

Implantation is interstitial as the the uterine epithelium is breached and the conceptus implants within the stroma

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10
Q

Briefly, how does the placenta change as the foetus develops?

A

The placental membrane becomes progressively thinner as the needs of the foetus increase = most optimised movement

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11
Q

What are chorionic villi?

A

- Chorionic villi are villi that sprout from the chorion to provide maximum contact area with maternal blood parts of cotyledons

  • placenta is a specialised form of the chorionic membrane
  • They contain foetal blood vessels
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12
Q

What is the placenta?

A

The placenta is an organ, specialised from the chorionic membrane, that connects the developing foetus to the uterine wall to allow nutrient uptake, thermo-regulation, waste elimination, and gas exchange

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13
Q

Identify 2 things that can go wrong with implantation

A
  • Implantation in the wrong place
  • Incomplete invasion
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14
Q

Identify 2 clinical conditions which can result from incomplete invasion

A
  • Placental insufficiency
  • Pre-eclampsia
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15
Q

Identify 2 clinical conditions which result from implantation at an inappropriate site

A
  • Ectopic pregnancy
  • Placentae praevia
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16
Q

Describe implantation in ectopic pregnancy and the consequences of such

A
  • Implantation at site other than uterine body (peritoneal/ ovarian)
  • Very quickly becomes life-threatening emergency
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17
Q

Describe implantation during placenta praevia and the consequences of such

A
  • Implantation in the lower uterine segment
  • Can cause haemorrhage in pregnancy
  • Requires C-section delivery
18
Q

Describe how the invasion during implantation is controlled

A
  • Transformation of the endometrium in the presence of a conceptus
  • Conceptus becomes the decidua
  • The decidual reaction provides the balancing force for the invasive force of the trophoblast
  • if you had no decidua the trophoblastic layers would grow through the fallopian tube and into the intraperitoneal region and cause haemmorage
  • so need implantation just right to allow this to occur
19
Q

What is the decidual reaction?

A
  • The decidual reaction is the set of changes in the endometrium of the uterus that prepare it for implantation of an embryo
  • These changes include swelling of stromal cells due to accumulation of glycogen and other nutrients
20
Q

What happens if the decidual reaction is sub-optimal?

A

Sub-optimal decidual reactions can lead to a range of adverse pregnancy outcomes

shallow invasion → pre eclampsia

stop in the decidual layer →fetal death

deferred implantation → placenta previa

21
Q

Describe the structure of the chorionic villus

A
  • found inside the cotyledons
  • at the far end there is thinning to allow for transportation
22
Q

Over the course of pregnancy, the ‘placental’ barrier becomes thinner.

Describe this in terms of the chorionic villi

A
  • First trimester villus: thicker barrier (blue) as metabolic requirements are not as high
  • Third trimester villus: barrier at optimal “thinness” (pink) meets energy requirement, you can see complete loss of synctiotrophoblast later
23
Q

Identify the 2 classes of hormone produced by the placenta

A
  • Protein
  • Steroid
24
Q

Identify 2 steroid hormones produced by the placenta

A
  • Progesterone
  • Oestrogen

takes over the corpus luteum

25
Q

Identify 4 protein hormones produced by the placenta

A
  • Human chorionic gonadotrophin (hCG)
  • Human chorionic somatomammotrophin (hPL/hCS)
  • Human chorionic thyrotrophin
  • Human chorionic corticotrophin
26
Q

Describe the production, excretion and function of hCG

A
  • Production: produced during first 2 months of pregnancy by synctiotrophoblast (so pregnancy specific)
  • Excretion: excreted in maternal urine
  • Function: mimics the action of LH and supports the secretory function of corpus luteum
27
Q

What do the placental steroid hormones do?

A
  • Responsible for maintaining the pregnant state
  • Placental production takes over from corpus luteum by the 11th week around first trimester
28
Q

Explain how placental hormones influence maternal metabolism

A
  • Progesterone increases appetite, foetal brain requires lots of glucose
  • hCS increases glucose availability to foetus
  • fetus will take most of the glucose so must monitor mother to ensure she is getting enough of th =e key material
29
Q

Identify and describe the transport functions of the placenta

A
  • Simple diffusion: H2O, electrolytes, gases, urea & uric acid
  • Facilitated diffusion: glucose
  • need rapid strong blood flow to maintain high diffusion
30
Q

Describe gas exchange in the placenta

A
  • Simple diffusion
  • Flow-limited, not diffusion-limited
31
Q

Why is it important to maintain adequate uteroplacental circulation?

A

Foetal O2 stores are small therefore maintenance of adequate uteroplacental circulation is essential

fetus in a hypoxic state

32
Q

There are specific “transporters” expressed by the syncytiotrophoblast.

Identify 3 substances which are transported

A
  • Amino acids
  • Iron
  • Vitamins
33
Q

The foetal (and newborn) immune system is immature and thus needs the transfer of passive immunity.

Describe this

A
  • Passive immunity is a receptor-mediated and immunoglobulin class-specific process involving the transfer of the IgG antibody only through endo/exocytosis
  • IgG concentrations in foetal plasma exceed those in maternal circulation → very effective process
34
Q

Identify 5 substances which can cross the placenta and their effects

A
  • Thalidomide: limb defects
  • Alcohol: FAS and ARND
  • Therapeutic drugs e.g. warfarin, ace inhibitors, anti-epileptic drugs
  • Drugs of abuse: dependency in the fetus and newborn
  • Maternal smoking: smaller placenta, smaller babies
35
Q

Teratogens can access the foetus by crossing the placenta.

Briefly highlight the effects of teratogenesis in the following period of development:

  • Pre-embryonic
  • Embryonic
  • Foetal
A
  • Pre-embryonic – lethal effects
  • Embryonic – extremely sensitive (narrow windows for some systems)
  • Fetal – ± sensitive
36
Q

morphology

A
  • surface of placenta interacting with the maternal layers
  • exchange of oxygen and nutrients
  • cotyledons → contain chorionic villi
  • during delivery you must check all the cotyledons have come out along with placenta and child.
37
Q

what is the blood supply to the foetus

A
  • two umbilical arteries → deoxygenated blood for fetus to mother
  • one umbilical vein → oxygenated blood from placenta to the fetus
  • both not only provide transport but provide anchoring
  • speed and flow of blood is important for diffusion
38
Q

which cells express active transport

A
  • syncytiotrophoblasts
  • amino acids
  • iron
  • vitamins
39
Q

what are teratogens

A
  • anything that disturbs the fetal development
  • can occur from physiological processes
  • some antibodies may be able to get across → rhesus incompatibility
  • therefore the placenta is not a true “barrier”
40
Q

what are some harmful substances to the placenta

A
  • limb defect as baby can’t form proper vascular structures
  • fetal alcohol syndrome, alcohol related neurological disease → alcohol is a small molecules so can pass through easily and effect the brain
    *
41
Q

teratogenesis

A
  • timing is key
  • pre-embryonic → lethal effects
  • embryonic → quite sensitive
  • fetal → not as sensitive
  • after embryonic period there is a low risk of defects except CNS

SA reproductive (22 decks)

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