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9) Foetal growth & development Flashcards

1
Q

What is the foetal period?

A

Pre-embryonic period - Fertilisation > 3 weeks
Embryonic period - 3 - 8 weeks
Foetal period - 8 - 38 weeks

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2
Q

What is crown-rump length?

A

Measurement of the length of human embryos & foetuses

Top of the head (crown) to the bottom of the buttocks (rump)

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3
Q

When does crown rump length (CRL) increase most?

A

Rapidly in pre-embryonic, embryonic, and early foetal periods

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4
Q

Describe the main changes that take place as an embryo

A

Intense morphogenesis & differentiation
Little weight gain
Placental growth most significant

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5
Q

Describe the main change that take place in the early foetus

A

Protein deposition

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6
Q

Describe the main change that take place in the late foetus

A

Adipose deposition

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7
Q

Describe the changes in body proportion during the foetal period

A

Week 9 - head approx. 1/2 CRL
Then body length & LL growth accelerates
Birth - head approx. 1/4 of CRL

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8
Q

How is the respiratory system developed in the foetus?

A

Lungs develop relatively late, not needed until birth
Embryonic development creates bronchopulmonary tree only - airways, no gas-exchanging parts
Functional specialisation occurs in foetal period
Threshold of viability - only possible after 24 weeks

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9
Q

What is the pseudoglandular stage of development of the respiratory system?

A

Weeks 8-16
Duct systems begin to form within bronchopulmonary segments created during embryonic period
Bronchioles

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10
Q

What is the canalicular stage of development of the respiratory system?

A 
Weeks 16-26
Formation of respiratory bronchioles
Budding from bronchioles (formed weeks 8-16)
May be viable at the end
More vascular
Some terminal sacs
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11
Q

What is the terminal sac stage of development of the respiratory system?

A

Week 26-term
Terminal sacs begin to bud from respiratory bronchioles
Some primitive alveoli
Differentiation of pneumocytes
- Type 1 - gas-exchange
- Type 2 - Surfactant production from week 20

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12
Q

What is the alveolar period of development of the respiratory system?

A

Late foetal-8 years

95% alveoli formed post-natally

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13
Q

How are the lungs prepared for immediate use after birth?

A

‘Breathing’ movement - conditioning of respiratory musculature
Fluid filled - Crucial for normal lung development

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14
Q

Which system begins development first and is last to finish?

A

Nervous system

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15
Q

Describe the development of the nervous system

A

Corticospinal tracts required for coordinated voluntary movements begin to form in the 4th month
Myelination of brain only begins in 9th month

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16
Q

Corticospinal myelination is incompete at birth. What is the evidence for this?

A

Increased infant mobility in the 1st year

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17
Q

When do movements of the foetus begin? (can be seen on USS)

A

Week 8
Large repertoire of movements develop
‘practising’ for post-natal life
e.g. suckling, breathing

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18
Q

The brain is the fastest developing organ in the foetus & infant. During the foetal period, what important changes occur?

A

Cerebral hemisphere becomes largest part of brain
Gyri & sulci form after 5 months, brain grows faster than head
Formation & myelination of nuclei & tracts
Relative growth of spinal cord & vertebral column

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19
Q

When do the sensory & motor systems develop?

A

Hearing & taste mature before vision
Organ of corti in inner ear well developed in foetus at 5 months
Retina is immature at birth

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20
Q

When does maternal awareness of foetal movements occur?

A

Week 17 onwards
Simple method of ante-partum surveillance
Reveals foetuses that require follow up

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21
Q

When is the definitive foetal heart rate achieved?

A

Around 15 weeks

Foetal bradycardia is associated with foetal demise

22
Q

Describe the development of the kidneys

A

Ascent of kidneys complete at week 10
Foetal kidney function begins in week 10
(functional embryonic kidney is metanephros)
Renal pelvis, calyces week 23
Histological differentiation of cortex & medulla almost complete by 8 months

23
Q

Foetal urine is a major contributor to what?

A

Amniotic fluid volume

24
Q

Foetal kidney function is not necessary for survival during pregnancy, but what happens without it?

A

Oligohydramnios

25
Describe the development of the bladder
Lies in abdominal cavity in foetus & infant Urine is emptied into amniotic fluid, to be swallowed by foetus Bladder fills & empties every 40-60 minutes in foetus
26
What is the threshold of viability of a foetus?
Viability only possible once lungs have entered terminal sac stage of development After 24 weeks Viability only possible if brain is sufficiently mature to control body functions e.g. breathing
27
What is respiratory distress syndrome?
Often affects infants born prematurely Insufficient surfactant production If pre-term delivery is unavoidable or inevitable - glucocorticoid treatment (of mother) - increases surfactant production in foetus
28
What techniques can be used to assess foetal development?
USS Doppler ultrasound Non-Stress test (monitors heart rate changes associated with foetal movement) Biophysical profiles (5 measured variables) Foetal movements kick chart
29
What are the type of foetal growth restrictions?
'growth restriction' if weight below 10th percentile for gestational age Symmetrical: Growth restriction is generalised & proportional Asymmetrical: Abdominal growth lags, Relative sparing of head growth, Tends to occur with deprivation of nutritional & oxygen supply to foetus
30
Foetus' born prematurely must be distinguished from those born at full term but are small. How can foetal age be estimated?
Duration of pregnancy - fertilisation age, age since last menstrual period Developmental criteria - CRL, Foot length, Biparietal diameter of head, weight/appearance after delivery Symphysis-Fundal height
31
What are the problems with measuring symphysis-fundal height?
Measured with tape measure: - Number of foetuses can cause variation - Volume of amniotic fluid can cause variation - The lie of the foetus can cause variation
32
What daily rhythms does a foetus have?
Daily rhythms of HR, breathing & activity
33
What is oligohydramnios?
Too little amniotic fluid Placental insufficiency Foetal renal impairment Pre-eclampsia
34
What is polyhydramnios?
``` Too much amniotic fluid Foetal abnormailty e.g inability to swallow, structural - blind-ended oesophagus, neurological - unable to coordinate swallowing movements ```
35
Which tests can be carried out to examine foetal body systems?
Foetal movement - Nervous, MSK Foetal breathing movement - Respiratory, MSK, Nervous Foetal tone - Nervous, MSK Amniotic fluid volume - Urinary, GI, Utero-placental Non-stress tests - CVS, Autonomic nervous
36
Describe the classification of birth weights
4.5kg = Macrosomia (maternal diabetes)
37
What may happen to the foetus is there is poor nutrition in early and late pregnancy?
Early pregnancy - Neural tube defects e.g. DiGeorge syndrome | Late pregnancy - Asymmetrical growth restriction, oligohydramnios
38
Describe the foetal circulation before birth
Oxygenated blood enters foetus via the umbilical vein from the placenta Oxygenated blood bypasses the liver via the ductus venosus Oxygenated blood passes from RA>LA via foramen ovale Blood passes from pulmonary artery > aorta via ductus arteriosus Deoxygenated blood returns to placenta via the 2 umbilical arteries
39
Why is resistance in the lungs extremely high before birth?
Hypoxic pulmonary vasoconstriction (pulmonary arteries constrict in presence of hypoxia without hypercapnia, redirect blood flow to alveoli with higher O2 content)
40
Describe the foetal circulation after birth
First breath, removal of hypoxic pulmonary vasoconstriction, greatly reduced resistance of lungs - Greater venous return to LA, LA pressure > RA, closure of foramen ovale (mins) - Increased O2 sat of blood & decreased [prostaglandins], constriction of ductus arteriosus & umbilical artery (hrs) - Stasis of blood in umbilical vein & ductus venosus, clotting of blood, closure due to fibrosis (days)
41
What is the function of amniotic fluid?
``` Surrounds foetus Mechanical protection (shock absorber) Moist environment so foetus doesn't dehydrate ~10ml at 8 weeks ~1l at 38 weeks Falls to ~300ml at 42 weeks ```
42
Amniotic fluid is turned over constantly, how is this achieved in early & late pregnancy?
Early - Amniotic fluid formed from maternal fluids Foetal extracellular fluid by diffusion across non-keratinised skin Later - Turnover via foetus
43
What does amniotic fluid contain?
Cells from foetus & amnion Variety of proteins Sampled by amniocentesis, diagnostically useful
44
What is the function of the foetal kidneys?
Metanephros - produces foetal urine 25 weeks ~100ml hypotonic urine a day Term ~500ml urine a day Adult! ~1 litre a day
45
The foetus swallows amniotic fluid constantly, why?
Absorbs water & electrolytes Debris accumulates in foetal gut Together with gut debris forms meconium
46
How is bilirubin eliminated from a foetus?
``` Bilirubin formed as result of Hb breakdown in foetus & mother Mother excretes bilirubin via bile Must be conjugated first Foetus cannot conjugate bilirubin Bilirubin accumulates, crosses placenta Excreted by mother ```
47
What happens if conjugation of bilirubin does not establish quickly in the neonate?
Neonate may become jaundiced Liver never had to conjugate bilirubin before during pregancy Takes time for liver to kick in Exposure to light (phototherapy) stimulates liver to begin conjugation
48
Describe O2 transport in foetal blood
O2 diffuses across placenta (haemomonochorial) Gradient of partial pressures Placenta - large s.a. low resistance to diffusion Maternal pO2 increased Umbilical venous pO2 must be lower O2 transport determined by umbilical artery pO2
49
Describe foetal O2 stores
Very low (~2mins worth) Can be problematic in labour Contraction of myometrium can compress placental blood vessels Foetal HR good indicator of foetus O2 saturation
50
How is the O2 content of foetal blood increased?
Foetal pO2 is 4kPa Normal arterial pO2 in adults is 13.3kPa Foetal Hb different, without beta chains, better at lower pO2 Higher affinity of foetal Hb 'sucks' O2 across Foetal Hb 70% saturated at 4kPa Adult Hb 45% saturated at 4kPa 4kPa foetal blood then contains ~7.5mmol of O2 per litre, similar to normal adult
51
What is the double Bohr effect?
Increase in pCO2 of [H+] results in Hb losing affinity for & releasing more O2 (Bohr effect) Happens in maternal & foetal blood (Double Bohr effect)
52
What is CO2 transfer between mother & foetus dependant on?
Partial pressure gradients Foetus cannot tolerate higher pCO2 than mother due to acid base problems Placental CO2 needs to be facilitated by lowering maternal pCO2 Achieved by hyperventilation, stimulated by progesterone

Reproduction (13 decks)

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