7. Foetal dev. of key body systems

Question 1

why is foetal viability only possible from >24 wks

Answer 1

viable only once lungs have entered terminal sac stage of dev. - otherwise no gas exchange membrane or surfactant production

Question 2

describe the development of the resp. system during embryonic and foetal periods

Answer 2

1. embryonic period: creates broncho-pulmonary tree from a respiratory diverticulum outpouching from oesophagus and separating from this via trachea-oesophageal septum
2. foetal period: functional specialisation with dev. of gas exchange membrane:
   i) PSEUDOGLANDULAR STAGE (wks 8-16) - duct system (i.e. bronchioles) begin to form within bronchopulmonary segments created during embryonic period
   ii) CANALICULAR STAGE (wks 16-26) - formation of resp. bronchioles, budding from bronchioles of pseudoglandular stage
   iii) TERMINAL SAC STAGE (wks 26-term) - terminal sacs with squamous epithelium begin to bud from resp. bronchioles, and differentiation of Type I and Type II pneuomcytes (for gas exchange and surfactant production)

Question 3

what is neonatal respiratory distress syndrome and how can this be treated

Answer 3

• caused by insufficient surfactant production, often affects infants born prematurely (type II pneumocytes not yet developed)
• treatment = positive pressure ventilation and exogenous surfactant

Question 4

how can neonatal resp. distress syndrome be prevented if pre-term delivery is unavoidable

Answer 4

glucocorticoid treatment of the mother increases surfactant production in foetus

Question 5

when is the definitive foetal HR achieved

Answer 5

wk 15 (i.e. end of 3rd mnth)

Question 6

when can the foetal heart beat be seen via transvaginal US or heard via doppler stethoscope and plain stethoscope

Answer 6

• transvaginal US: 5-6 wks
• doppler stethoscope: <20 wks
• plain stethoscope: >20 wks

Question 7

what is foetal bradychardia a sign of

Answer 7

hypoxia (associated with foetal demise)

Question 8

when does foetal kidney function begin and why is this important

Answer 8

wk 10, important as foetal urine is major contributor to amniotic fluid volume

Question 9

what are the names of too little or too much amniotic fluid and how can these be caused

Answer 9

• OLIGOHYDRAMNIOS = too little amniotic fluid (e.g. in placental insufficiency, foetal renal impairment)
• POLYHYDRAMNIOS = too much amniotic fluid (idiopathic or caused by foetal abnormality, e.g. inability to swallow)

Question 10

what is “quickening”

Answer 10

maternal awareness of foetal movements from >17 wks

Question 11

why is the nervous system the most vulnerable to disturbances

Answer 11

1st to begin dev and last to finish

Question 12

when does voluntary foetal mov. begin and how is this possible

Answer 12

4th month (wk 16) due to cerebellar dev. and corticospinal tract formation - required for voluntary movements

Question 13

why does infant mobility increase in 1st year

Answer 13

myelination of brain only begins in 9th mnth (wk 36) so corticospinal tract myelination incomplete at birth