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Reproductive systems > The placenta > Flashcards

The placenta Flashcards

1
Q

Where does the placenta come from?

A
  • Begins to develop in second week of development
  • Early development there is focus on ensuring development of foetal membranes
  • Cannot have a healthy pregnancy without a healthy placenta
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2
Q

What are the foetal membranes?

A
  • The sacs supporting the embryo/foetus
  • The placenta
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3
Q

Why is week 2 known as the week of 2s?

A
  • 2 distinct layers emerge from outer cell mass (syncytiotrophoblast and cytotrophoblast)
  • And inner cell mass becomes bilaminar disc (epiblast and hypoblast)
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4
Q

What happens on day 6 of embryo development?

A
  • Implantation begins
  • Move into endometrial layer (maternal tissue)
  • Blastocoele is genetically different structure
  • Must be communication between cells of foetus and cells of mother to allow implantation
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5
Q

What happens on day 9 of embryo development?

A
  • Early embryo is fully embedded in endometrium
  • Placenta development is now vital to maintain integrity of embryo
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6
Q

What has happened by the end of the 2nd week of embryo development?

A
  • Conceptus has implanted
  • Embryo has 2 cavities: amniotic cavity and yolk sac
  • Sacs are suspended by a connecting stalk within chorionic cavity
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7
Q

What is the fate of the embryonic spaces?

A
  • Yolk sac disappears (part is pinched off to form primitive gut)
  • Amniotic sac enlarges as embryo grows bigger
  • Chorionic sac is occupied by expanding amniotic sac
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8
Q

What does implantation achieve?

A
  • Establishes basic unit of exchange (villi)
  • Anchors the placenta
  • Establishes maternal blood flow within placenta
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9
Q

What is the function of the different types of villi?

A
  • Primary villi: early finger-like projections of trophoblast
  • Secondary villi: invasion of mesenchyme into core
  • Tertiary villi: invasion of mesenchyme core by foetal vessels
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10
Q

Outline implantation

A
  • Interstitial: uterine epithelium is breached and conceptus implants within stroma
  • Placental membrane becomes progressively thinner as needs of foetus increase (large size of foetal brain requires more energy)
  • Maternal blood separated from foetal capillary wall by layer of trophoblast
  • 2 circulations never mix
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11
Q

What is a chorionic villus?

A
  • Placenta is a specialisation of chorionic membrane
  • Finger-like projections of trophoblast
  • Inner connective tissue core containing foetal vessels
  • Very good for exchange
  • Foetal vessels can actively receive nutrients across cell membranes
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12
Q

What are the different types of implantation defects?

A
  • Implantation in the wrong place (ectopic pregnancy, placenta praevia)
  • Incomplete invasion (placental insufficiency, pre-eclampsia)
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13
Q

Outline ectopic pregnancy

A
  • Implantation at site other than uterine body
  • Fallopian tube most common site
  • Can be peritoneal or ovarian
  • Quickly becomes life-threatening emergency
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14
Q

Outline placenta praevia

A
  • Implantation in lower uterine segment
  • Can cause haemorrhage in pregnancy
  • Can require C-section delivery
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15
Q

What controls how the embryo implants?

A
  • Endometrium transforms to decidua in presence of conceptus
  • Decidual reaction provides balancing force for invasive force of trophoblast
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16
Q

What happens to the decidua in ectopic pregnancy?

A
  • There is no decidua in fallopian tubes
  • Therefore no control
  • Trophoblast can invade into intraperitoneal region
  • Causes haemorrhage
17
Q

What happens if decidual reaction is suboptimal?

A
  • Can lead to a range of adverse pregnancy outcomes
  • E.g. pre-eclampsia, preterm birth
18
Q

What is a cotyledon?

A
  • Functional units containing chorionic villi
  • Allows transport
19
Q

How does the chorionic villus change with time?

A
  • First trimester villus creates thicker barrier
  • Third trimester villus - barrier at optimal thinness to meet energy requirements of larger foetus
  • Complete loss of syncytiotrophoblast
  • Marginalisation of foetal capillaries so they sit right next to villus surface
20
Q

What are the umbilical cord vessels?

A
  • 2 umbilical arteries bring deoxygenated blood from foetus to placenta
  • 1 umbilical vein brings oxygenated blood from placenta to foetus
21
Q

What is the endocrine function of the placenta?

A

Produces:
- Human chorionic gonadotrophin
- Human chorionic somatomammotropin
- Human chorionic thyrotrophin
- Human chorionic corticotrophin
- Progesterone
- Oestrogen

22
Q

Outline the production of hCG

A
  • Produced during first 2 months of pregnancy
  • Supports secretory function of corpus luteum
  • Produced by syncytiotrophoblast
  • Therefore is pregnancy specific
  • Excreted in maternal urine
23
Q

What is trophoblast disease?

A
  • Cancer derived from trophoblast
  • E.g. molar pregnancy and choriocarcinoma
  • Leads to high hCG
24
Q

What is the function of the placental steroid hormones?

A
  • Progesterone and oestrogen
  • Responsible for maintaining the pregnant state
  • Placental production takes over from corpus luteum by the 11th week
25
Q

Which placental hormones influence maternal metabolism?

A
  • Progesterone leads to increased appetite
  • hCS increases glucose availability to foetus
  • This means that you can begin to see insulin resistance in mother
  • Foetus is prioritised and gets preferential glucose for energy
26
Q

Outline the transport functions of the placenta?

A
  • Simple diffusion due to blood flow - e.g. water, electrolytes, urea, uric acid, gases
  • Facilitated diffusion (applies to glucose transport)
27
Q

Outline how gas exchange occurs over the placenta

A
  • Simple diffusion
  • Flow-limited, not diffusion-limited
  • Foetal O2 stores are small therefore maintenance of adequate flow is essential
28
Q

How does active transport occur over the placenta?

A
  • Specific transporters are expressed by the syncytiotrophoblast
  • Amino acids
  • Iron
  • Vitamins
29
Q

Outline how passive immunity is transferred from mother to foetus

A
  • Foetal and newborn immune system is immature
  • Receptor-mediated process, maturing as pregnancy process
  • Immunoglobin class-specific
  • IgG only
  • IgG concentrations in foetal plasma exceed those in maternal circulation
30
Q

Outline the pathophysiology of placental transport

A
  • Placenta is not a true barrier
  • Substances can pass across placenta out of our control
  • Teratogens can access foetus via placenta
  • Unintentional outcomes from physiological process
  • E.g. haemolytic disease of newborn secondary to Rhesus incompatibility of mother and foetus
31
Q

What substances can cross the placenta and harm the foetus?

A
  • Thalidomide - limb defects
  • Alcohol - FAS and ARND
  • Anti-epileptic drugs
  • Warfarin
  • ACE inhibitors
  • Drugs of abuse
  • Maternal smoking
32
Q

Outline teratogenesis

A
  • Timing is key
  • Pre-embryonic exposure has lethal effects
  • Embryonic period - embryo is highly sensitive
  • After embryonic period risk of structural defects is very low
  • Except CNS

Reproductive systems (20 decks)

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