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3 - Reproduction > Placental Function and Dysfunction > Flashcards

Placental Function and Dysfunction Flashcards

1
Q

What happens in week 2 of pregnancy

A
  • The week of 2s
  • Two distinct cellular layers emerge
  • Outer cell mass
    • Syncytiotrophoblast - transport membrane
    • Cytotrophoblast - develop into fetal membrane
  • Inner cell mass becomes the bilaminar disk
    • Epiblast and hypoblast
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2
Q

Identify when implantation takes place

A
  • Implantation begins day 6
  • Interaction between trophoblast and endometrial lining
  • By day 9, blastocyst becomes embedded in endometrium
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3
Q

Describe the structure of the conceptus at the end of week 2

A
  • The conceptus has implanted
  • The embryo and its two cavities will be suspended within a supporting sac
  • Two cavities are - amniotic cavity and yolk sac
  • Suspended by connecting stalk - lateral converted to umbilical cord
  • Supporting sac - chorionic cavity
  • Yolk sac disappears and the amniotic sac enlarges
  • The chorionic sac is occupied by the expanding amniotic sac
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4
Q

What is the reason for implantation

A
  • Establishes the basic unit of exchange
  • Anchors the placenta
  • Establishes maternal blood flow within the placenta
    - Villi surrounded with maternal blood
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5
Q

Differentiate between primary, secondary and tertiary villi

A
  • 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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6
Q

Explain what a chorionic villus is

A
  • Placental is a specialisation of the chorionic membrane (outer membrane)
  • Chorion frontosum - where villi are
  • Villi are finger like projections made of trophoblast
    • Have inner connective tissue core - fetal vessels
      • Very good for exchange
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7
Q

Where in the uterine epithelium does implantation take place

A
  • Implantation is interstitial

- The uterine epithelium is breached and the conceptus implants within the stroma

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8
Q

Describe the change in placental membrane as the fetus grows

A
  • The placental membrane becomes progressively thinner as the needs of the fetus increase
  • In the human, one layer of trophoblast ultimately separates maternal blood from fetal capillary wall
  • The two circulations never mix
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9
Q

Describe the change in chorionic villus structure from first to third trimester

A
  • First trimester villus - thicker barrier
    • Cytotrophoblast act as stem cell layer of syncytium
      • Allow growth for transport
  • Third trimester villus - barrier at optimal thickness
    • Vessels pushed against syncytiotrophoblast to maximise exchange
    • Only syncytiotrophoblast and fatal capillary membrane as barrier
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10
Q

Describe the blood vessels connecting placenta to fetus

A
  • Two umbilical arteries - deoxygenated blood from fetus to placenta
  • One umbilical vein - oxygenated blood from placenta to fetus
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11
Q

What molecules travel by diffusion across placenta

A
  • Simple diffusion
    • Water
    • Electrolytes
    • Urea and uric acid
    • Gases
  • Facilitated diffusion
    - Applies to glucose transport
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12
Q

What limits gas exchange in placenta

A
  • Simple diffusion
  • Flow limited - not diffusion limited
  • Fetal oxygen stores are small, therefore maintenance of adequate flow essential
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13
Q

What substances are actively transported across placenta

A
  • Specific transporters expressed by the syncytiotrophoblast
    • Amino acids
    • Iron
      • Vitamins
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14
Q

Explain the roles of steroid hormones produced by placenta

A
  • Progesterone and oestrogen
  • Responsible for maintaining the pregnant state
  • Placental production takes over from corpus luteum by the 11th week
  • Progesterone increases appetite
    • Important in increasing fat stores in the mother as glucose stores mainly diverted to the fetus
      • Also supports breast tissue development for lactation
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15
Q

State what protein hormones are produced in the placenta

A
  • Human chorionic gonadotrophin (hCG)
  • Human chorionic somatomammotrophin (hCS)
  • Human chorionic thyrotrophin
  • Human chorionic corticotrophin
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16
Q

Explain the action of hCG

A
  • Produced during first 2 months of pregnancy
  • Supports the secretory function of corpus luteum
  • Produced by syncytiotrophoblast therefore is pregnancy specific
  • Excreted in maternal urine therefore used as the basis for pregnancy testing
    • Can identify trophoblast disease such as molar pregnancy and choriocarcinoma (malignancy of chorion)
17
Q

Explain the action of hCS

A
  • Increases glucose availability to fetus
  • Causes insulin resistance in the mother so glucose is not stored in the mother
  • Preferentially transferred to the fetus for growth
18
Q

Explain the hormonal basis for testing for pregnancy

A
  • hCG measured in maternal urine
  • Pregnancy specific as produced by the embryo itself
  • Can be reliably detected 14 days after fertilisation
19
Q

Explain how fetal progress can be measured hormonally

A
  • Oestriol used to measure fetal progress

- Only type of oestrogen directly synthesised from fetus

20
Q

Explain the function of the placenta as a provider of passive maternal immunity to the neonate

A
  • Fetal immune system is immature
  • Immunoglobulin transported to fetus through receptor mediated endocytosis
    • Maturing as pregnancy progresses
  • Immunoglobulin class-specific
  • Only IgG transported across placenta
    - IgG concentrations in fetal plasma exceed those in maternal circulation
21
Q

Explain how the maternal CVS system adapts to pregnancy

A
  • Increases in plasma volume, cardiac output, heart rate
  • Decrease in peripheral resistance - progesterone causes relaxation of smooth muscle
  • Overall decrease in blood pressure early on, but gradually increases
  • Increases in coagulation factors and fibrinogen
22
Q

How can the CVS system be affected in pregnancy

A
  • Venous distension and engorgement may occur in late pregnancy
    • Increase in stroke volume
    • Uterus compresses against IVC and causes blood stasis - venous distension
    • May lead to varicose veins and haemorrhoids
23
Q

How are kidneys affected in pregnancy

A

Increases in renal blood flow and glomerular filtration rate

24
Q

How are lungs affected in pregnancy

A

Increase tidal volume and oxygen consumption

25
Q

How are breasts affected in pregnancy

A
  • Increase breast size

- Thin watery secretion

26
Q

How is the GI system affected in pregnancy

A
  • Progesterone relaxes smooth muscle to cause acid reflux and constipation
  • Prolonged transit time
27
Q

Explain complications of implantation in wrong place

A
  • Ectopic pregnancy
    • Most commonly in the ampulla
    • Can be peritoneal or ovarian
    • Can very quickly become life-threatening
      • Development into pelvic cavity can affect blood vessels and cause bleeding into peritoneum
  • Placenta praevia
    • Implantation in the lower uterine segment
    • Can cause haemorrhage in pregnancy
      • Can require C-section delivery
28
Q

State complications of incomplete invasion

A
  • Placental insufficiency

- Pre-eclampsia

29
Q

Explain how control of invasion in implantation occurs in the uretrus

A
  • Transformation of the endometrium in the presence of a conceptus
    • Becomes the decidua
  • The decidual reaction provides the balancing force for the invasive force of trophoblast
    • Ectopic pregnancy - no decidua therefore no control
  • If the decidual reaction is sub-optimal
    - Can lead to a range of adverse pregnancy outcomes
30
Q

What are teratogens

A
  • Agent that can disrupt development of embryo/fetus
  • Can access fetus via the placenta
  • Eg, unintentional outcomes from physiological process
    • Haemolytic disease of the newborn secondary to Rhesus incompatibility of mother and fetus
31
Q

List potential teratogens

A
  • Thalidomide - used in treatment of cancers
    • Limb defects
  • Alcohol
    • Fetal alcohol syndrome
    • Alcohol related neurodevelopmental disorder
  • Therapeutic drugs
    • Anti-epileptic drugs
    • Warfarin
    • ACE inhibitors
  • Drugs of abuse
    • Dependency in the fetus and newborn
  • Maternal smoking
    - Fetus smaller - calcification
32
Q

Explain at what stage of pregnancy is teratogenesis is most dangerous

A
  • Pre-embryonic - lethal effects
  • Embryonic - high sensitivity
    • Each organ has a period of peak sensitivity
  • Fetal - decreasing sensitivity
  • After embryonic period, risk of structural defects very low - except CNS
33
Q

Explain clinical features of gestational diabetes

A
  • Hyperglycaemia in mother will increase glucose transfer to fetus
  • Increase insulin produced in fetus
  • Leads to increased growth of fetus - larger baby more difficult to give birth
  • May cause congenital abnormalities - heart and nervous system development interrupted
  • Baby has too much insulin after birth - hypoglycaemia
    - Brain damage from hypoglycaemia as it does not have glycogen storage
34
Q

Explain clinical features of anaemia in pregnancy

A
  • Mother needs more iron as oxygen given to fetus so more haemoglobin production needed
  • Iron supplements given to mother
  • Consequences of poor fetal-placental perfusion associated with anaemia
    • Neurological problems
      • Fetal retardation
35
Q

Differentiate between oestrone, oestrodiol and oestriol

A
  • Oestrone - maintains healthy thin uterine lining during menopause
  • Oestrodiol - maintains healthy uterine lining for possible pregnancy during reproductive years
  • Oestriol - maintains healthy thick uterine lining providing blood to the placenta during pregnancy
36
Q

Describe the pathophysiology of preeclampsia

A
  • Hypertension and proteinuria important diagnostic features
  • Narrowing of utero-placental arteries due to fibrosis reduces blood flow to placenta
    • Lead to intra-uterine growth restriction or death
    • Pre-inflammatory proteins released into mother’s vessels, causing vasoconstriction and retention of salt
      • Both cause hypertension
      • Low blood to kidney can damage glomerulus, leading to proteinuria
37
Q

Describe the symptoms of preeclampsia

A
  • Oedema may be present
  • Seizures/fits in the mother - eclampsia
    • Headaches, blurred vision, vomiting, oedema
    • Stroke, impaired liver and kidney function, blood clotting problems, pulmonary oedema
  • Baby - impaired development, premature birth, born small

3 - Reproduction (17 decks)

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