Placental Function and Dysfunction Flashcards
What happens in week 2 of pregnancy
- 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
Identify when implantation takes place
- Implantation begins day 6
- Interaction between trophoblast and endometrial lining
- By day 9, blastocyst becomes embedded in endometrium
Describe the structure of the conceptus at the end of week 2
- 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
What is the reason for implantation
- Establishes the basic unit of exchange
- Anchors the placenta
- Establishes maternal blood flow within the placenta
- Villi surrounded with maternal blood
Differentiate between primary, secondary and tertiary villi
- Primary villi - early finger-like projections of trophoblast
- Secondary villi - invasion of mesenchyme into core
- Tertiary villi - invasion of mesenchyme core by fetal vessels
Explain what a chorionic villus is
- 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
- Have inner connective tissue core - fetal vessels
Where in the uterine epithelium does implantation take place
- Implantation is interstitial
- The uterine epithelium is breached and the conceptus implants within the stroma
Describe the change in placental membrane as the fetus grows
- 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
Describe the change in chorionic villus structure from first to third trimester
- First trimester villus - thicker barrier
- Cytotrophoblast act as stem cell layer of syncytium
- Allow growth for transport
- Cytotrophoblast act as stem cell layer of syncytium
- Third trimester villus - barrier at optimal thickness
- Vessels pushed against syncytiotrophoblast to maximise exchange
- Only syncytiotrophoblast and fatal capillary membrane as barrier
Describe the blood vessels connecting placenta to fetus
- Two umbilical arteries - deoxygenated blood from fetus to placenta
- One umbilical vein - oxygenated blood from placenta to fetus
What molecules travel by diffusion across placenta
- Simple diffusion
- Water
- Electrolytes
- Urea and uric acid
- Gases
- Facilitated diffusion
- Applies to glucose transport
What limits gas exchange in placenta
- Simple diffusion
- Flow limited - not diffusion limited
- Fetal oxygen stores are small, therefore maintenance of adequate flow essential
What substances are actively transported across placenta
- Specific transporters expressed by the syncytiotrophoblast
- Amino acids
- Iron
- Vitamins
Explain the roles of steroid hormones produced by placenta
- 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
- Important in increasing fat stores in the mother as glucose stores mainly diverted to the fetus
State what protein hormones are produced in the placenta
- Human chorionic gonadotrophin (hCG)
- Human chorionic somatomammotrophin (hCS)
- Human chorionic thyrotrophin
- Human chorionic corticotrophin
Explain the action of hCG
- 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)
Explain the action of hCS
- 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
Explain the hormonal basis for testing for pregnancy
- hCG measured in maternal urine
- Pregnancy specific as produced by the embryo itself
- Can be reliably detected 14 days after fertilisation
Explain how fetal progress can be measured hormonally
- Oestriol used to measure fetal progress
- Only type of oestrogen directly synthesised from fetus
Explain the function of the placenta as a provider of passive maternal immunity to the neonate
- 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
Explain how the maternal CVS system adapts to pregnancy
- 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
How can the CVS system be affected in pregnancy
- 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
How are kidneys affected in pregnancy
Increases in renal blood flow and glomerular filtration rate
How are lungs affected in pregnancy
Increase tidal volume and oxygen consumption
How are breasts affected in pregnancy
- Increase breast size
- Thin watery secretion
How is the GI system affected in pregnancy
- Progesterone relaxes smooth muscle to cause acid reflux and constipation
- Prolonged transit time
Explain complications of implantation in wrong place
- 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
State complications of incomplete invasion
- Placental insufficiency
- Pre-eclampsia
Explain how control of invasion in implantation occurs in the uretrus
- 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
What are teratogens
- 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
List potential teratogens
- 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
Explain at what stage of pregnancy is teratogenesis is most dangerous
- 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
Explain clinical features of gestational diabetes
- 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
Explain clinical features of anaemia in pregnancy
- 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
- Neurological problems
Differentiate between oestrone, oestrodiol and oestriol
- 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
Describe the pathophysiology of preeclampsia
- 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
Describe the symptoms of preeclampsia
- 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
