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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
When does the fetus produce lymphocytes
From 8 weeks
26
What immune elements are present by the second trimester
All phagocytic cells, T + B cells, complement
27
Does the fetus produce immunoglobulins
Yes- small amount IgM + IgA IgG from mother Presence of IgM and IgA without IgG indicates infection
28
What are the fetal immunological defences
Amniotic fluid- lysosyme + IgG Placenta- lymphoid cells, phagocytes, barrier Granulocytes from liver + bone marrow Interferon from lymphocytes
29
What are the problems of prematurity with skin + homeostasis
Preterm have no vernix + thin skin, large amount of water loss Preterm babies deficient for brown fat which can produce heat
30
What are 2 methods for heat conservation in newborn
Peripheral vasoconstriction | Brown fat catabolism
31
How does the alimentary system develop
Midgut becomes herniated during 6th week as abdominal cavity is too small Re-enters abdominal vavity by 12th week after rotation
32
What happens if the midgut fails to re-enter the abdominal cavity
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
What is anencephaly
Failure of the cranial bones to form Brain not protected so broken down over time No functioning brain, not compatible with life
34
Describe liver development
Appears 18th day- diverticulum from duodenum | T shaped outgrowth by 25th day, invaded by blood vessels
35
How is the fetal liver different to adult
Reduced ability to conjugate bilirubin due to relative deficiencies in enzymes eg. glucuronyl transferase
36
Describe kidney development
Nephrogensis complete by 36 weeks | Maturation + concentrating ability gradual
37
What are the fetal behavioural states
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
Describe amniotic fluid development
By 12 weeks amnion contacts inner surface of chorion, obliterates extraembryonic space Initially secreted by amnion Volume increases progressively
39
What is the function of amniotic fluid
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
What are the main functions of the placenta
Protection, nutrition, respiration, excretion, hormone production
41
How is the placenta composed
Fetal component derived from chorion | Maternal component derived from mofidications of uterine endometrium
42
What does the placenta transport
Gases, water, minerals + vitamins, glucose + amino acids, proteins, lipids, large peptide molecules (insulin), smaller hormones (steroids), toxic substrates, bacteria + viruses
43
Describe water + nutrient exchange
Water exchange at placenta + non-placental chorion | Simple diffusion due to hydrostatic pressure difference
44
Describe electrolyte exchange
Fetus pumps Na+ into mother making fetus electronegative, creates gradient to drive other exchanges Potassium- simple diffusion Chloride- active transport Iodide- active trapping
45
Describe waste product exchange
Unconjugated bilirubin passes to mother for excretion | Gut + urinary tract opens into amniotic fluid
46
Describe iron transport
Active transport | Maternal intestinal absorption enhanced
47
What is the additional requirement of iron in pregnancy
550mg- 300 fetus, 50 placenta, 200 postpartum blood loss
48
Describe protein + amino acid transport
Maternal metabolism more efficient due to progesterone Active transport Fetal urea diffuses back into mother
49
Describe calcium transport
Actively transported for bone formation
50
What are the fetal energy substrates
Predominantly carbohydrate- 1/2 glucose, remainder amino acids + lactate
51
How does the fetus obtain glucose
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
What causes the large gradients for O2 and CO2
Placental O2 consumption Long diffusion path Pattern of blood flow
53
How does pH affect O2 transport
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
Why does HbF have higher oxygen affinity
Makes less 2,3-DPG, fewer binding sites- 2,3-DPG reduces oxygen binding
55
What are the functions of placental hormones
``` Stimulate ovarian function Maintain pregnancy Influence fetal growth Stimulate mammary function Assist in parturition ```
56
What hormones does the placenta produce
Progesterone Oestrogens (E3, Oestriol) Placental lactogen/Somatomammotropin Relaxin
57
What is the role of placental progesterone
Stimulus for elevated secretion by endometrial glands | inhibits myometrial contraction
58
What is the role of placental oestrogen
Important during last part of gestation, preparturient period
59
What is the role of placental lactogen
Growth of fetus | Stimulates mammary gland
60
What is the role of placental relaxin
Softens the connective tissue in the cervix | Promotes elasticity of pelvic ligaments
61
Describe the fetal physiology of parturition
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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