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Fetal Period (Mat of lungs (third trimester (Fetal breathing: 20 weeks, …
Fetal Period
Mat of lungs
- Type 1 and 2 pneumocytes saccular phase
- Surfactant sufficient quantities 28 weeks
- Dev throughout fetal peroid
- Liquor required
third trimester
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- 15,000 terminal bronchioli
- 100 million alveoli birth
- 300 mil after birth
Changes at birth
- Lugs inflate and fill with air pushing amniotic fluid out lungs
- Increase fetal oxygenation
- Increase O2, decrease blood flow resistance
- Surfactant reduces surafce tension alveoli aid breathing prevent alveolar collapse
Oxygenation
- Fetus does not breath, placenta does
- Fetal haemogolin:
Higher affinity oxygen
50-95% fetuses haemoglobin
- Haemoglobin level
Fetus 16-18 g/dl
Newborn 20-24 g/dl
Adult 11-15 g/dl
Fetal circ
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Bypass lungs
- High vascular resistance
- Foramen ovale
- Ductus arteriosus
Circ at birth
Conversion to adult circ
- Pulmonary oxygenation lower vascular resistance
- Foramen ovale and ductus arteriosus close
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Amniotic fluid
- Initially maternal plasma
- Then fetal urine
- Measurable on USS
- Increase to peak of 800ml 28 weeks, 400 ml 42/40
- Predominantly water
- Protective and homeostasis effects
- Decreased:
IUGR, renal pathologies, ruptured membranes
Normally reduces to term
- Increased
Diabetes, macrosomia, fetal pathologies
gyration fetal brain
- Increase size and gyration
- Fissure fomration
- Ventricular enlargment
- 4* increase cortical grey matter 20 weeks
- Nociception 21 weeks
Fetal growth
- Linear until 20 weeks
- Guesstimate
- Symphysial fundal height 25-35% accurate
- Ultrasound 40-50% accurate
- Small or large babies may have associated pathology
- Correlation of fetal size with pathology is poor
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Placental development
- Continue grow + develop
- Terminal villi formed 20 weeks
- Hormone production: hCG, hPL, progest
- Immunological Barrier: Antibody
- Respiration and excretion: Glucose, oxygen and AA exchange
Limbs and things
- Nails form
- Fingers separate
- Bones remain mostly cartilaginous and only harden slowly
- Important for delivery
- Increase fetal movements from 25 weeks
Face and head
- Enlargement of skull
- External ears form
- Sucking reflex 17 weeks
- Hair begins 20 weeks
- Face more human like
Abdominal devlopment
- Physiological herniation of gut outisde abdomen return by week 12
- Multiple rotations
- Swallowing observed 13 weeks
- Diaphragm closes
Renal and genitalia
- Kidneys begin produce urine 16 weeks
- Testicles begin descend 16 weeks
- Oocytes maximum bumber 20 weeks
- Visible external genitalia 12 weeks
Fetal movement
- Quickening 16-20 weeks
- Kicks represent large limb movements
- More active night - diurinal rhythm - opposite to children/adults
- Reduction or loss fetal movements patholgical
- No effective test/ pattern
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