Maternal Physiology, Pregnancy And The Placenta Flashcards
What are the broad changes that occur to maternal physiology during pregnancy?
Vasodilation, increased respiratory rate, increased insulin resistance and absorption from the gut, increased GFR, immunological sequestration, increased clotting and relaxation of muscles.
How does the immune system change to facilitate pregnancy?
Placental progesterone acts upon extravillus trophoblastic cells to cause IL10 release from TR1 cells that mediate suppressive activity of the immune system. As such, immune responses produced to the foetus are TH2 and non cytotoxic
How does ventilation increase in pregnancy?
Increase in tidal volume by 30-40%. Note that there should not be an increase in respiratory rate, and this is indicative of pathology.
Why does dyspnea occur in 65% of pegnancies?
What factors may exacerbate this?
Hyperventilation due to increased tidal volume resulting in low PaCO2.
Anaemia,
Asthma,
DVT/PE (high risk during pregnancy)
What adaptations occur in the CVS during pregnancy?
Increased cardiac output due to increased volume early in pregnancy and increased heart rate later in pregnancy.
Vasodilation aided by smooth muscle relaxing effects of progesterone.
Increased procoagulants, decreased anticoagulants and reduced fibrinolysis.
What are the (negative) consequences of the CVS adaptations of pregnancy?
Increased activation of RAAS causing peripheral oedema.
Change in plasma volume resulting in dilutational anaemia.
Hyper coagulase state - risk of DVT and thromboembolism.
How is GFR increased by 50% during pregnancy?
What other effects occur in the kidney?
Systemic vasodilation increases renal blood flow.
Decreased PCT absorption of glucose - glucosuria.
Smooth muscle relaxation - increased kidney and ureter size and decreased urine speed.
How is transit time slowed in the GI system?
What hormone mediates these changes?
Decreased motility of bowel, decreased gallbladder contractility, decreased tone of the lower oesophageal sphincter.
Progesterone.
What negative effects may result from the adaptations made to the GI system?
GORD, constipation, gallstones, aspiration.
Why may ALP levels be raised on LFTs during pregnancy?
Placental synthesis results in release of ALP.
What occurs in the thyroid during pregnancy?
Oestrogen stimulates thyroglobulin production by the liver that picks up free thyroxine. HCG has a stimulatory effect on thyroid due to similar alpha subunit to TSH. As such, it stimulates production of T4 and T3.
Note: the foetus cannot produce its own thyroid hormones.
How does pregnancy influence the function of the parathyroid gland?
Increased PTH secretion acting upon the pathway of vitamin D activation and inhibiting the Ca phosphorus resorption pathway. This results in greater amounts of calcium absorbed from the GI tract.
Which hormones found in pregnancy have effects on insulin resistance?
hPL (most prominent),
Oestrogen,
Progesterone.
What factors when alongside pregnancy may result in defective action of insulin?
Physical inactivity,
Obesity,
PCOS,
Hypertension.
What is gestational diabetes mellitus?
Onset of elevated blood sugar levels during pregnancy. Increased maternal mortality and morbidity for both mother and child.
What adaptions occur to the MSK system during pregnancy?
Change in center of gravity, increased lordosis and kyphosis, stretching of abdominal muscles,
Increased mobility of sacroiliac joints and anterior tilt of pelvis.
What negative effects may changes in the MSK system have?
Back pain, shoulder pain, tension headaches, Pelvic pain, fluid retention compression of structures eg carpal tunnel.
What features may be seen on the skin of pregnant women?
Chloasma or melasma of the face, palmar erythema, vascular spiders, linea nigra.
What is preeclampsia?
Defined as combination of new hypertension and proteinuria seen in pregnancy. thought to result due to impaired invasion of trophoblast resulting in shallow spiral arteries and higher resistance. May lead to hypoperfusion and ischaemia.
Name risk factors of preeclampsia.
Hypertension,
Diabetes,
Obesity,
First pregnancy.
What complications of preeclampsia are there?
Seizure (eclampsia), cerebral haemorrhage, pulmonary oedema, premature delivery, stillbirth, growth restriction, foetal distress.
When does the placenta begin to develop?
What aids in its hormonal role until it is formed?
Second week of development,
Corpus luteum.
What occurs during the week of twos?
Outer cell mass diverges into syncytiotrophoblast and cytotrophoblast.
Inner cell mass diverges into epiblast and hypoblast.
Syncitiotrophoblast begins secretion of hCG
What happens to each of the embryonic spaces as pregnancy continues?
Yolk sac pinches off to form part of the primitive gut.
Amniotic sac enlarges to occupy the chorionic cavity - causes chorionic sac to disappear.
Why does the placental membrane become progressively thinner as pregnancy continues?
Demand of the foetus for nutrients grows so a more efficient diffusion/transport pathway is required.
Note: maternal and foetal circulations never mix.
What is the placenta formed from?
Chorionic membrane. Forms chorion frondosum - fern shaped projections that increase surface area for exchange.
How is invasion of the embryo controlled?
The decidual layer of the endometrium exerts a resistant effect to the syncitiotrophoblasts digestive enzymes, meaning implantation occurs at a correct depth.
What is the functional unit of the placenta?
Cotyledon - contain chorionic villi within thin membranes to facilitate diffusion. Highly vascular.
What facilitates the thinning of the barrier between the chorionic villi and maternal blood supply?
Loss of the cytotrophoblastic layer.
What fetal vessels supply the placenta?
Two umbilical arteries carrying deoxygenated blood from foetus to placenta.
One umbilical vein supplying oxygenated blood from the placenta to the foetus,
What steroid hormones are produced by the placenta?
Oestrogen and progesterone.
What protein hormones are produced by the placenta?
HCG,
hPL,
Human chorionic thyrotrophin,
Human chorionic corticotrophin.
where might HCG be raised?
Molar pregnancy (tumour of the placenta leading to growth of placenta without embryo).
Choriocarcinoma.
Prostate cancer in men.
How do placental hormones influence maternal metabolism?
Progesterone - increases appetite
hCS or hPL - increases glucose availability to the fetus
Which molecules diffuse freely through the placental barrier?
Water, gases, electrolytes, urea.
What must move via facilitated transport into the fetal blood supply?
Glucose
Why is gas exchange especially important in the foetus?
When might exchange be occluded?
Fetal oxygen stores are very limited with high demand. As such gas exchange is flow limited.
May become occluded during contractions - causes foetal distress.
Which molecules are actively transported by transporters expressed in the syncitiotrophoblast?
Amino acids, iron and vitamins.
How are IgG antibodies transferred from mother to fetus?
Receptor mediated exo and endocytosis
What can cause haemolytic disease of the newborn?
What test can be done to confirm this?
Transfer of IgG antibodies to a different Rhesus group blood cell type to the fetus.
Group and save
What teratogens may cross the placenta?
Thalidomide, Alcohol, Antiepileptics, Warfarin, ACE inhibitors.
What infections can cross the placenta?
Varicella zoster (also increased risk during pregnancy), TB, cytomegalovirus, Rubella virus.
