S6 Placental function and Dysfunction

Question 1

where does the placenta come from ?

Answer 1

begins to develop in 2nd week of development

focus developing membranes i.e the sacs supporting the foetus and the placenta

Question 2

describe the processes of implantation of the conceptus into the endometrium

Answer 2

week 2 summary
outer cell mass - syncytiotrophoblast + cytotrophoblast
inner cell mass - bilaminar disk (epiblast + hypoblast)
end of W2 conceptus implanted, amniotic cavity and yolk sac suspended by connecting stalk within the chorionic cavity
yolk sac disappears
amniotic sac enlarges (growth of embryo + amniotic fluid), chorionic sac becomes occupied by expanding amniotic sac - membranes fuse - amniochorionic membrane ( this ruptures during labour)

Question 3

what does implantation achieve?

Answer 3

establishes the basic unit of exchange
- primary, secondary and tertiary villi
anchor the placenta
establish maternal blood flow within the placenta

implantation is interstitial, the uterine epithelium is breached and the conceptus implants within the stroma

Question 4

describe the structure of the placenta and its adaptation for the exchange of materials between foetal and maternal blood

Answer 4

becomes thinner as the needs of the foetus increase

one layer of trophoblast seperates maternal blood from foetal capillary blood

Question 5

what is a chorionic villus ?

Answer 5

the placenta is a specialisation of the chorionic membrane. Chronic frondosum are finger-like projections e.g trophoblast all very good for exchange

Question 6

what is ectopic pregnancy

Answer 6

ectopic pregnancy : implantation outside uterine body, usually fallopian tube but also peritoneal or ovarian, quickly life threatening , conceptus not viable as no decidual cells outside the endometrium
RIF pain

Question 7

what is placenta praevia?

Answer 7

implantation in lower uterine segment, risk of haemorrhage, needs c section

Question 8

what is pre-eclampsia

Answer 8

failure of spiral artery remodelling. widespread endothelial dysfunction. may progress to eclampsia – seizures

Question 9

what is placental insufficiency

Answer 9

placenta doesnt develop so cant maintain pregnancy

Question 10

how is the invasive force of the trophoblast controlled

Answer 10

transformation of the endometrium to the decidua in the presence of a conceptus. the decidual reaction balances the invasive force of the trophoblast

Question 11

what is structure of the chorionic villus

Answer 11

in the first trimester, the metabolic needs of the fetus are low so we have a full cyto and syncyto
in the third trimester, cyto number decreases and barrier is at optimal thinness for metabolic transport
so through pregnancy , the placental barrier becomes thinner

Question 12

describe the role of the placenta as an endocrine organ supporting pregnancy

Answer 12

synthesises cholesterol so oestrogen and progesterone steroids can be formed, taking over from those produced by the corpus luteum by about W11
oestriol : stimulates uterine growth and mammary gland development
progesterone : maintains the pregnant state
also makes other hormones :
Human chorionic gonadotrophin
Human chorionic somatomammotropin (aka human placental lactogen) increases glucose availability to foetus , promotes breast development

Question 13

describe the hormonal basis of testing for pregnancy

Answer 13

HCG - produced during first 2 months by SCTB, supports the secretory functions of the corpus luteum, excreted in maternal urine
by W11 levels deplete to 0

Question 14

describe the capillary system within the placenta

Answer 14

the capillary system develops in core of villous stems, contracts CP and connecting stalk - extraembryonic vascular system
maternal blood – spiral arteries – placenta

Question 15

describe how the heart receives blood within the placenta

Answer 15

heart receives oxygenated blood from mother via placenta in one umbilical vein, by pass the non-functional lungs, return to placenta via the two umbilical arteries (deoxygenated). Vessels radiate to form chorionic vessels under the amnion

Question 16

describe the amnion within the placenta

Answer 16

as amniotic cavity progresss to chorionic amnion envelops connecting stalk and yolk sac forming primitive umbilical cord containing remnant of allantois. In M3 the chorionic cavity and yolk sac are obliterated due to growth of amnion. The umbilical vessels are surrounded by Wharton jelly for protection

Question 17

what are the placental hormones influencing maternal metabolism

Answer 17

progesterone - increased appetite

HCS - increases glucose availability to fetus

Question 18

describe the movement across placenta

Answer 18

passive diffusion : 02, C02, urea, H20, electrolytes flow linked : need good spiral artery remodelling
facilitated diffusion : glucose
Active transport : amino acids, iron, vitamins, glycine

Question 19

describe feotal immunity

Answer 19

in the placenta, feotal immunity matures as pregnancy progresses, breast feeding also helps, IgG only, greater conc in foetal plasma than maternal

Question 20

what is teratogenesis

Answer 20

placenta not a true barrier to some things e.g alcohol (lipid soluble so diffuses, can get foetal alcohol syndrome), thalidomide, smoking (also reduces placental flow and growth)
short critical periods (e.g pre-embryonic sensitivity most vulnerable, foetal least) for some structures but CNS is vulnerable throughout

Question 21

what is Rhesus blood group incompatibility

Answer 21

haemolytic disease, blood group incompatibility of mother and foetus
prophylaxis - mother can make antibodies against foetal Rh antigens, so give anti - D treatment to neutralise as the antibodies cause haemolysis when bind to foetal RBCS

Question 22

describe infection of the placenta

Answer 22

can be taken up by pinocytosis and moved across placenta e.g rubella (patent ductus arteriosus, cataracts), varicella zoster

Question 23

what are the symptoms of pre-eclampsia

Answer 23

hypertensions and proteinuria

Question 24

describe gestational diabetes

Answer 24

risk factors include age,ethincity, high BMI, smoking
can develop into T2DM. poor control can cause a macrosomic foetus (>4500g), stillbirth, increased congenital defects. Test with oral glucose tolerance test

Question 25

how does pregnancy cause anaemia ?

Answer 25

occurs more in pregnant women as the increase in blood volume outweighs increases in red cell mass, physiological anaemia. Can also get anaemia from iron and folate deficencies

Question 26

what are maternal physiological adaptations in pregnancy in CVS

Answer 26

blood volume increases
CO increases by 40%, SV increases by 35%, HR increases by 15%
afterload usually falls
preload increases as more blood volume

Question 27

what are maternal physiological adaptations in pregnancy in the urinary system

Answer 27

GFR (55%) creatinine (45%) and renal plasma flow (70%) increase
clearance increases so creatinine falls, so pregnancy range is lower than the non-pregnant range
filtration capacity remains intact so more protein excreted, urea/ bicarbonate fall

Question 28

what are maternal physiological adaptations in pregnancy in the resp system

Answer 28

diaphragm displaced, thorax diameter increases
reduced FRC, unchanged FEV1, increased alveolar ventilation,TV,02 consumption, pO2
physiological dyspnoea (progesterone-driven hyperventilation) and physiological hyperventilation (risk of respiratory alkalosis, compensated for by increased bicarbonate excretion)

Question 29

what are maternal physiological adaptations in pregnancy in carb and lipid metabolism

Answer 29

carb : increased maternal insulin resistance
lipid : in T2, lipolysis increases so more free FAs
FAs substrate for maternal metabolism, so glucose can be used by feotus

Question 30

what are maternal physiological adaptations in pregnancy affecting the thyroid

Answer 30

increased TBG, T3 and T4

HCG has a direct effect on TSH production so can be decreased in normal pregnancies

Question 31

what are maternal physiological adaptations in pregnancy in the GI system

Answer 31

progesterone relaxes smooth muscle so can get constipation, gall stones (stasis of biliary tract), pancreatitis due to stones

Question 32

what are maternal physiological adaptations in pregnancy wrt to haemotology

Answer 32

pro- thrombotic state, increased fibrinogen and clotting factors, reduced fibrinolysis

Question 33

what are maternal physiological adaptations in pregnancy wrt to immune system

Answer 33

foetus is an allograft : genetically different to mother so expresses different HLA antigens
suppression of local immune response at materno-foetal interface