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Fetus Module > fetal and placental physiology > Flashcards

fetal and placental physiology Flashcards

1
Q

what does fetal growth depend on?

A

adequate transfer of nutrients and oxygen across the placenta
adequate maternal nutrition and uterine perfusion
hormones that affect metabolic rate, growth of tissues and maturation of individual organs

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2
Q

what do insulin growth factors do?

A

co-ordinate a precise and orderly increase in growth through late gestation

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3
Q

what do insulin and thyroxine do?

A

required through late gestation to ensure appropriate growth in normal and adverse nutritional circumstances

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4
Q

what is fetal growth determined by?

A

fetal genome - IGFs are an important mediator

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5
Q

what is fetal growth rate like?

A

slow up to week 20
accelerates to peak at week 30-36 then slows again
postnatal growth peak at week 8

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6
Q

what does amniotic fluid volume do during pregnancy?

A

increase until week 34 then declines

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7
Q

where does red cell production take place in the fetus?

A

yolk sac then liver then finally bone marrow

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8
Q

what is a normal fetal HR?

A

120-140 bpm

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9
Q

what does a lack of thyroid hormone produce?

A

skeletal and cerebral immaturation = cretinism

delayed surfactant production

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10
Q

what is cortisol essential for?

A

lung compliance and surfactant release
in the liver it induces beta-receptor and glycogen deposition to maintain a glucose supply to the neonate after delivery
in the gut it is responsible for villus proliferation and induction of digestive enzymes which enables the neonate to switch to enteral feeding after birth

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11
Q

what factors are used to predict a foetuses optimal growth potential?

A

pre-pregnancy weight and maternal booking weight
maternal height
maternal age and parity increased with mother >para2
ethnic group
fetal sex
paternal height

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12
Q

what are the 3 differences in fetal circulation?

A

oxygenation takes place in the placenta not in the lungs
right to left ventricles work in parallel rather than series
heart brain and upper body receives blood from the left V, placenta and lower body receive blood from both right and left V

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13
Q

what shunts are present in the fetus?

A

ductus venous - shunts blood away from liver
foramen ovale - shunts blood from right to left atrium
ductus arteriosus - shunts blood from pulmonary artery to aorta

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14
Q

what is the path of oxygenated blood from the placenta?

A

down the umbilical vein -> either through portal vein to liver OR the ductus venosus into the IVC -> right atrium -> foramen ovale -> left atrium -> left ventricle-> aorta -> 50% to head and arms remainder mixes with blood from DA

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15
Q

how does the DA stay open in utero?

A

production of prostaglandin E2 and prostacyclin which act as local vasodilator

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16
Q

what causes the DA to close?

A

cycle-oxygenase inhibitors (COX) = NSAIDS - ibuprofen

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17
Q

what causes the shunts to close?

A

cessation of umbilical blood flow causes cessation of ductus venosus
fall in right atrium pressure and closure of foramen ovale

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18
Q

when does persistent fetal circulation occur?

A

when there is a delayed closure of the DA after birth because the pulmonary vascular resistance fails to fall despite adequate breathing, resulting in left to right shunt of blood from aorta through DA to the lungs, baby remains cyanosed and can suffer from life threatening hypoxia, occur mostly in premature infants, results in congestion in pulmonary circulation and reduction in blood flow to GI tract and brain that lead to NEC and IV haemorrhage

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19
Q

what happens to the fluid in the lungs at birth?

A

production of fluid ceases and the present fluid is absorbed, adrenaline plays a major role in this process

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20
Q

what does surfactant do?

A

it is a group of phospholipids that prevent collapse of small alveoli during expiration by lowering surface tension, it is produced by type 2 alveolar cell, max production will be after 28 weeks

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21
Q

what is lecithin?

A

the predominant phospholipid (phosphatidylcholine, its production is enhanced by cortisol, growth retardation and prolonged rupture of membranes. its production is delayed in diabetes.
it is present in amniotic fluid and can be predictive of RDS

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22
Q

how can the incidence and severity of RDS be reduced?

A

giving steroids antenatally to mother

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23
Q

when and where are the first fetal blood cells formed?

A

surface of the yolk sac from 14-19 days after conception

haemopoiesis from yolk sac continues until the 3rd post-conceptional month

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24
Q

when does haemopoiesis begin in the liver?

A

5th week

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25
Q

when does the bone marrow start producing RBCs?

A

7-8 weeks but is the predominant source from 26 weeks

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26
Q

what haemoglobin is in the fetus?

A

fetal haemoglobin has 2 gamma chains and 2 alpha chains

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27
Q

what is the composition of adult Hb?

A 
HbA = 2 alpha and 2 beta chains 
HbA2 = 2 alpha and 2 delta chains
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28
Q

when does HbF switch to HbA occur?

A

28-34 weeks, ratio of HbF:HbA = 80:20 by 6th month of age only 1% of Hb is HbF

29
Q

what is different about HbF?

A

HbF has a higher affinity for oxygen than HbA, as in utero the fetus is exposed to lower oxygen concentrations, to enhance transfer of oxygen across the placenta, and will dissociate more easily than adult

30
Q

what does beta major thalassaemia without treatment result in?

A

severe anaemia
FGR
poor musculoskeletal development
skin pigmentation due to increased iron absorption

31
Q

what does alpha thalassaemia major result in?

A

severe fetal anaemia with cardiac failure
hepatosplenomegaly and oedema
infants are stillborn or shortly die after birth

32
Q

at what gestation do lymphocytes appear?

A

8th week

by the middle of he second trimester all phagotic cell, T B cells and complement are available

33
Q

what Ig’s are indicative of a fetal infection?

A

IgA and IgM

34
Q

what are some general immunological defences of the fetus?

A

amniotic fluid (lysosomes, IgG)
placenta (lymphoid cells, phagocytes, barrier)
granulocytes from liver and bone marrow
interferon from lymphocytes

35
Q

what is vernix?

A

consisting of desequemated skin cells, cholesterol and glycogen covering the skin of fetus in last wks
preterm infants have no vernix and thin skin, allows proportionately large amounts of insensible water loss

36
Q

when does the gut reenter the abdomen cavity?

A

12th week
failure to re-enter results in defects like omphalocele or gastroschisis
(primitive forgot and hind gut are present by end of 4th week as straight tube

37
Q

what can a failure in a foetuses swallowing mechanism cause?

A

polyhydraminos

38
Q

what causes defects in swallowing mechanisms?

A

neurological abnormalities = anencephaly

obstruction of gut = atresia of oesophagus

39
Q

what does the primitive liver appear out of?

A

diverticulum arising from the duodenum

40
Q

how does the fetal liver differ from adult?

A

reduced ability to conjugate bilirubin because of enzyme deficiencies = glucuronyl transferase (placenta is performing the normal metabolic function of liver)

41
Q

what does the metanephros form?

A

renal collecting system = uerters, pelvis, calyces, collecting duct

42
Q

when is nephrogeneiss complete?

A

week 36

43
Q

what does renal agencies result in?

A

severe oligohydraminos

44
Q

when can fetal movements be 1st perceived?

A

18-20weeks

45
Q

what are the 4 defined behavioural states in he fetus?

A

1F = quit sleep, absence of eye and body movements
2F = periodic body and eye movements are present
3F = quiet wakefulness when there are eye but no body movements
4F = body in active ongoing body and eye movement
>80% time in 1F and 2F state

46
Q

what is amniotic fluid initially secreted by?

A

amnion
10th week = transudate of fetal serum via skin and umbilical cord
16th week = kidney and lung fluids removed by swallowing

47
Q

how does amniotic fluid increase?

A 
10wk = 30ml 
20wk = 300ml 
30wk = 600ml 
38wk = 1000ml 
40wk = 800ml 
42wk = 350ml
48
Q

what is the function of amniotic fluid?

A

protect fetus from mechanical injury
permit fetal movement and preventing limbs contracture
prevents adhesions between the fetus and amnion
permits fetal lung development, if there is absence of the fluid especially in the 2nd trimester this will lead to pulmonary hypoplasia

49
Q

what is the function of the placenta?

A 
protection 
nutrition 
respiration
excretion 
hormone production
50
Q

what are the two parts of the placenta?

A

fetal component from chorion

maternal component derived from modifications of uterine endometrium

51
Q

what does the placenta transport?

A 
gases
water
minerals and vitamins 
glucose and AA
proteins 
lipids 
large peptide hormones = TSH, ACTH, GH, insulin, glucagon 
smaller molecular weight hormones = T3 and T4 and catecholamines 
toxic substances 
bacteria and viruses
52
Q

how does water cross the placenta?

A

simple diffusion across the amnion and chorion - hydrostatic pressure from maternal blood

53
Q

what electrolytes are transported across the placenta?

A

sodium is pumped from fetus to mother making fetus electronegative,
potassium simply diffuses down an electrochemical gradient
chloride - active transport
iodide - trapped in placenta

54
Q

what waste products cross the placenta?

A

bilirubin, unconjugated and crosses by diffusion to mother to excrete.
gut and urinary tract open into amniotic fluid

55
Q

what energy sources does the fetus use?

A

carbohydrates
glucose
amino acids
lactate

56
Q

how is glucose transported?

A

facilitated diffusion - fetal glucose is directly related to the maternal glucose as fetal mechanisms for regulating glucose are immature

57
Q

why do pregnant mothers not need to eat more protein?

A

urea excretion falls so the amino acids are used more efficiently due to progesterone
AA use active transport into the fetus

58
Q

how is iron transported?

A

actively across placenta

maternal intestinal absorption is enhanced

59
Q

what vitamins are needed in pregnancy?

A

folic acid and vitamins B12
calcium
KADE

60
Q

how does gas exchange take place?

A

across the placenta
oxygen diffuses readily across the placenta and CO2 diffuses even more readily fall in pH of maternal blood as it passes through the placenta causes release of O2
rise in pH of fetal blood increases uptake of O2
flow is not the limiting factor - level of fetal oxygenation is regulated by feta requirement for oxygen

61
Q

what are the 2 main types of hormones produced by the placenta?

A

protein hormones

steroid hormones

62
Q

what do the placenta hormones affect?

A 
stimulate ovarian function 
maintain pregnancy 
influence fetal growth 
stimulate mammary function 
assist in parturition
63
Q

when does the placenta start producing progesterone?

A

2 and half months gestation

previously produced by corpus luteum

64
Q

what action does progesterone have on the myometrium?

A

inhibits contractions

65
Q

what type of oestrogen does the placenta produce?

A

oestriol - E3

66
Q

what are the 2 major effects of lactogen/somatomammotropin?

A

promoting growth of uterus

stimulating the mammary glands

67
Q

what are the effects of relaxin?

A

softening of connective tissue in the cervix

promotes elasticity of pelvic ligaments (can cause pelvic girdle pain or symphysis pubis dysfunction)

68
Q

what is the physiology of parturition?

A

limited space for fetus -> fetus hypothalamus -> fetus ACTH -> fetus cortisol -> placental estrogen -> uterus PGF2alpha -> progesterone -> induction of parturition

Fetus Module (18 decks)

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