fetus to neonate Flashcards
describe the in-utero environment
- Foetus surrounded by amniotic fluid
- Warm, cushioned, quiet
- Fluid filled lungs
- Foetal circulation
- Relative hypoxia – O2 and CO2 exchange via placenta
- Nutrient acquisition and waste elimination via placenta
what mediates the filling of the lungs with fluid before birth?
active chloride secretion
when does surfactant secretion start?
24 weeks gestation
what increases surfactant secretion?
glucocorticoids
thyroid hormones
when does the foetus make breathing efforts before birth?
during sleep
describe the gasping reflex?
will gasp if O2 supply is removed
describe what pulmonary changes happen at birth?
- physical pressure of labour squeezes some of the fluid out
- initial breath causes -ve thoracic pressure –> opens the airways
- active absorption of alveolar fluid via Na+ transport
- Establishes a functional residual volume
- Onset of regular respirations
how does active absorption of alveolar fluid occur?
via sodium transport stimulated by cortisol, catecholamines and thyroid hormones
what forms surfactants?
type II pneumocytes in the alveoli
what is surfactant?
lipoprotein complex consisting of;
- phospholipids
- surfactant proteins A, B, C and D
- other lipids e.g. cholesterol and trace substances
what are the lipoproteins and what are their functions?
B + C = structural
A + D = immune
what is the function of surfactant and how does the occur?
it reduces surface tension by:
o Increasing pulmonary compliance
o Preventing atelectasis
also has some innate immunity function
what is atelectasis?
collapse/closure of the lung, resulting in reduced/absent gas exchange
where does most oxygenated blood in a fetus come from?
placenta
where does most oxygenated blood in the fetus go?
heart and brain
what changes happen to the cardiovascular system at birth?
- Blood flow in umbilical vessels ceases –> systemic vascular resistance rises
- Increase in pulmonary blood flow –> pulmonary vascular resistance drops
- RA pressure drops, LA pressure rises, reducing flow through foramen ovale
- Flow preferentially goes to RV and pulmonary artery
- Flow through ductus arteriosus changes
what cardiovascular follow on changes happen?
- ductus arteriosus closes functionally and anatomically
- foramen ovale functionally closes soon after birth
- umbilical vein forms the round ligament of the liver
- umbilical artery partly obliterates to become the medial umbilical ligament
what causes the closure of the ductus arteriosus?
increasing pO2 and decreased prostaglandins
why cant pregnant mothers have ibuprofen
contains prostaglandins –> causes ductus arteriosus to close
when does the ductus arteriosus close functionally?
12-15 hours after birth
when does the ductus arteriosus close anatomically?
4-6 days anatomically
how does the ductus arteriosus change anatomically?
forms ligamentum arteriosum
how does the umbilical artery change after birth?
o Partly obliterates to become the medial umbilical ligament
o A part remains open as a branch of the anterior division of the internal iliac artery
what happens to foetal cortisol levels during the third trimester?
increase
what does an increase in cortisol levels do?
o Stimulates surfactant production
o Activates thyroid hormone
o Matures hepatic glucose and gut digestive enzymes
o Increase in beta-adrenergic receptors
what does the surge of catecholamines during delivery do?
o Raises blood pressure
o Supports energy metabolism
o Aids thermogenesis via brown fat - releasing energy as heat rather than ATP (important to combine with skin-to-skin)
describe the metabolism of the new baby?
• Nutritional supply from placenta stops at birth and blood glucose levels fall
• Reduction in insulin, rise in glucagon and catecholamines
- lower blood glucose
- glucose –> fatty acids and ketone bodies
- increase in intestinal motility
what energy supply to newborns use in utero?
glucose
what energy supply do newborns use after birth?
fatty acids and ketone bodies
what is the initial feeding supply of a child?
colostrum, the energy rich first milk
what is meconium?
dark green first faeces of an infant
when should the passage of meconium be?
within the first 48 hours
how does the fetus overcome the low oxygen levels in utero?
- Foetus and neonate have higher red blood cell levels
- Foetal haemoglobin has higher affinity for O2
where does haemopoiesis transition from after birth?
liver to bone marrow
why is clotting variable in babies/
clotting factors dont cross the placenta so neonates have a lower value than adults
what vitamin are neonates deficient in?
Vitamin K
why is neonatal jaundice common?
- Breakdown of foetal red cells results in high levels of bilirubin
- Poor activity of hepatic glucuronyl transferase leads low levels of conjugation and biliary excretion
when is urine produced in a fetus?
16 weeks of gestation
when does nephrogenesis finish?
34 weeks
what does an increase in renal blood flow lead to?
increase in GFR
when should babies pass their first urine?
first 24 hours
when does diuresis establish?
within the first few days, with increase in urine output and loss of water
why is it okay that the fetus is immunosuppressed in utero?
sterile environment
what does immunity rely on postnatally?
o innate immune system - although has less capability to mount neutrophil response
o maternally-derived IgG
- gains immune benefit from breastmilk - IgA, complement, lactoferrin, lysozyme
name causes of difficult transition?
o Prematurity
o Other disease states in baby, e.g. congenital abnormalities, infection, asphyxia
o Non-labour deliveries, e.g. elective caesareans
o Complicated deliveries
o Maternal health and medications (including anaesthesia)
