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Fetus > Fetal and placental physiology > Flashcards

Fetal and placental physiology Flashcards

1
Q

What does fetal growth depend on

A

Adequate transfer of nutrients and O2 across the placenta

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2
Q

What does placental development depend on

A

Adequate maternal nutrition

Uterine perfusion

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3
Q

What is the role of fetal hormones in fetal development

A

Affect metabolic rate, growth of tissues + maturation of organs
IGFs increase growth in late gestation
Insulin + thryoxine ensure normal growth in late gestation
Fetal hyperinsulinaemia results in macrosomia due to excessive fat deposition

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4
Q

What is the main determinant of fetal growth

A

Fetal genome

IGFs are important mediator

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5
Q

How does the placenta:fetus ratio change with pregnancy

A

Placenta grows steadily
Fetus grows faster
Ratio falls

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6
Q

How does the site of red cell production change in the fetus

A

Begins in yolk sac, then liver, then bone marrow

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7
Q

What is the normal fetal heart rate and blood pressure

A

120-140bpm

BP 66/35

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8
Q

What are the effects of deficient thyroid hormone production

A

Deficiency in skeletal and cerebral maturation

Delayed surfactant production

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9
Q

What is cortisol essential for

A

Lung compliance + surfactant release
Fetal liver- induces beta receptor + glycogen deposition
Gut- villus proliferation, induction of digestive enzymes

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10
Q

What physiological characteristics can be used to predict fetal growth potential

A 
Pre-pregnancy weight, maternal booking weight
Maternal + paternal height
Maternal age + parity
Ethnic group
Fetal sex
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11
Q

How does fetal circulation differ to adult

A

Oxygenation in placenta instead of lung
Right and left ventricles in parallel rather than series
Heart, brain and upper body receive blood from left and right ventricles

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12
Q

What modifications in fetal vascularity ensure best oxygenated blood from placenta is delivered to fetal brain

A

Ductus venosus 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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13
Q

Describe fetal circulation

A

Oxygenated blood from placenta passes through umbilical vein, divided into 2 branches
One to portal vein in liver (for glucose conversion to glycogen)
Ductus venosus joins inferior vena as it enters right atrium
50% blood each way.
Ductus venosus stream passes through foramen ovale to left atrium, then to left ventricle to aorta
50% left ventricle blood to head, remainder to aorta
Minimal amount to lungs- non functional

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14
Q

How does ductus venosus prevent mixing of well oxygenated blood with desaturated blood

A

Narrow vessel, high velocity

Streaming of blood + membranous valve in right atrium

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15
Q

What changes to circulation occur at birth

A

Prostaglandin + prostacyclin drop, ductus arteriosus closes within few days
No umbilical flow so ductus venosus closes
Fall in right atrium pressure closes forament ovale
Ventilation of lungs opens pulmonary circulation, rapid fall in pulmonary vascular resistance

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16
Q

Describe peristent fetal circulation

A

Delayes closure of ductus arteriosus as pulmonary vascular resistance does not fall
Left to right shunting from aorta to lung
Baby cyanosed, hypoxia
Mostly in prematurity
Reduction in blood flow to gastrointestinal tract, necrotising enterocolitis, invtraventricular haemorrhage

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17
Q

At what gestation does the respiratory system develop

A

Full differentiation of capillary + canicular elements of lung by 20 weeks
Alveoli development after 24 weeks

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18
Q

What is the role of surfactant

A

Group of phospholipids that prevent collapse of small alveoli during expiration by lowering surface tension
Produced by type 2 alveolar cells (10% lung parenchyma)

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19
Q

What is the predominant phospholipid in surfactant

A

Phosphatidylcholine

Production enhanced by cortisol

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20
Q

What can cause progressive respiratory failure

A

Oligohydramnios and reduced intrathoracic space
Chest wall deformities
Cause pulmonary hypoplasia

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21
Q

What is respiratory distress syndrome

A

Condition of premature babies associated with surfactant deficiency
Complicated by hypoxia, intraventriculat haemorrhage, necrotising enterocolitis
Incidence/severity reduced by administration of steroids

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22
Q

Describe fetal blood production

A

Begins on surface of yolk sac 14-19 days after conception until 3rd month
Begins in liver at 5th week of embryonic life
Bone marrow production by 7-8 weeks, predominates by 26 weeks

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23
Q

Describe fetal haemoglobin

A

2 alpha 2 gamma chains compared to HbA which has 2 alpha 2 delta
80:20 HbF:HbA at term

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24
Q

What are abnormalities of blood production

A

Beta thalassemia- severe anaemia, FGR, poor muculoskeletal development, skin pigmentation
Alpha thalassaemia- severe anaemia with cardiac failure, hepatosplenomegaly + oedema, stillborn or early death

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25
Q

When does the fetus produce lymphocytes

A

From 8 weeks

26
Q

What immune elements are present by the second trimester

A

All phagocytic cells, T + B cells, complement

27
Q

Does the fetus produce immunoglobulins

A

Yes- small amount IgM + IgA
IgG from mother
Presence of IgM and IgA without IgG indicates infection

28
Q

What are the fetal immunological defences

A

Amniotic fluid- lysosyme + IgG
Placenta- lymphoid cells, phagocytes, barrier
Granulocytes from liver + bone marrow
Interferon from lymphocytes

29
Q

What are the problems of prematurity with skin + homeostasis

A

Preterm have no vernix + thin skin, large amount of water loss
Preterm babies deficient for brown fat which can produce heat

30
Q

What are 2 methods for heat conservation in newborn

A

Peripheral vasoconstriction

Brown fat catabolism

31
Q

How does the alimentary system develop

A

Midgut becomes herniated during 6th week as abdominal cavity is too small
Re-enters abdominal vavity by 12th week after rotation

32
Q

What happens if the midgut fails to re-enter the abdominal cavity

A

Gastroshisis- can be delivered normally at full term, gut can be returned and stitched
Omphalocoele- more serious, indicative of chromosomal abnormality, associated with other problems

33
Q

What is anencephaly

A

Failure of the cranial bones to form
Brain not protected so broken down over time
No functioning brain, not compatible with life

34
Q

Describe liver development

A

Appears 18th day- diverticulum from duodenum

T shaped outgrowth by 25th day, invaded by blood vessels

35
Q

How is the fetal liver different to adult

A

Reduced ability to conjugate bilirubin due to relative deficiencies in enzymes eg. glucuronyl transferase

36
Q

Describe kidney development

A

Nephrogensis complete by 36 weeks

Maturation + concentrating ability gradual

37
Q

What are the fetal behavioural states

A

1F- quiet sleep, absence of eye + body movements
2F- REM sleep, periodic eye + body movements
3F- quiet wakefulness, eye but no body movements
4F- active ongoing eye + body movements

38
Q

Describe amniotic fluid development

A

By 12 weeks amnion contacts inner surface of chorion, obliterates extraembryonic space
Initially secreted by amnion
Volume increases progressively

39
Q

What is the function of amniotic fluid

A

Protects fetus from mechnical injury
Permits fetal movements, prevents limb contracture
Prevents adhesion between fetus and amnion
Permits fetal lung development- absence leads to pulmonary hypoplasia

40
Q

What are the main functions of the placenta

A

Protection, nutrition, respiration, excretion, hormone production

41
Q

How is the placenta composed

A

Fetal component derived from chorion

Maternal component derived from mofidications of uterine endometrium

42
Q

What does the placenta transport

A

Gases, water, minerals + vitamins, glucose + amino acids, proteins, lipids, large peptide molecules (insulin), smaller hormones (steroids), toxic substrates, bacteria + viruses

43
Q

Describe water + nutrient exchange

A

Water exchange at placenta + non-placental chorion

Simple diffusion due to hydrostatic pressure difference

44
Q

Describe electrolyte exchange

A

Fetus pumps Na+ into mother making fetus electronegative, creates gradient to drive other exchanges
Potassium- simple diffusion
Chloride- active transport
Iodide- active trapping

45
Q

Describe waste product exchange

A

Unconjugated bilirubin passes to mother for excretion

Gut + urinary tract opens into amniotic fluid

46
Q

Describe iron transport

A

Active transport

Maternal intestinal absorption enhanced

47
Q

What is the additional requirement of iron in pregnancy

A

550mg- 300 fetus, 50 placenta, 200 postpartum blood loss

48
Q

Describe protein + amino acid transport

A

Maternal metabolism more efficient due to progesterone
Active transport
Fetal urea diffuses back into mother

49
Q

Describe calcium transport

A

Actively transported for bone formation

50
Q

What are the fetal energy substrates

A

Predominantly carbohydrate- 1/2 glucose, remainder amino acids + lactate

51
Q

How does the fetus obtain glucose

A

Progesterone stimulates maternal apetite
Maternal metabolism switched via GH-like actions, mobilises fatty acid stores, maternal tissues less sensitive to insulin
Rise in maternal glucose fetus can capture
Transport by facilitated diffusion

52
Q

What causes the large gradients for O2 and CO2

A

Placental O2 consumption
Long diffusion path
Pattern of blood flow

53
Q

How does pH affect O2 transport

A

Fall in pH of maternal blood through placenta causes release of O2
Rise in pH of fetal blood through placenta causes uptake of O2

54
Q

Why does HbF have higher oxygen affinity

A

Makes less 2,3-DPG, fewer binding sites- 2,3-DPG reduces oxygen binding

55
Q

What are the functions of placental hormones

A 
Stimulate ovarian function
Maintain pregnancy
Influence fetal growth
Stimulate mammary function
Assist in parturition
56
Q

What hormones does the placenta produce

A

Progesterone
Oestrogens (E3, Oestriol)
Placental lactogen/Somatomammotropin
Relaxin

57
Q

What is the role of placental progesterone

A

Stimulus for elevated secretion by endometrial glands

inhibits myometrial contraction

58
Q

What is the role of placental oestrogen

A

Important during last part of gestation, preparturient period

59
Q

What is the role of placental lactogen

A

Growth of fetus

Stimulates mammary gland

60
Q

What is the role of placental relaxin

A

Softens the connective tissue in the cervix

Promotes elasticity of pelvic ligaments

61
Q

Describe the fetal physiology of parturition

A

Limited space for fetus alerts fetal hypothalamus which produces ACTH which stimulates cortisol, which stimulates placental oestrogen, which stimulates uterine PGF2a + progesterone which induces parturition

Fetus (18 decks)

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