Lecture notes from BIOL2018 Adaptive physiology respiratory changes. Covering: changes in heart-lungs-blood in relation to birth, surfactant, drivers for surfactant synthesis, ion pump action, blood flow, pulmonary resistance, diseases and alveoli
Respiratory changes
Changes in heart-lungs-blood in relation to birth
At birth – major changes occur in heart due to altered resistance in vascular system
and by altered demands
Oxygen expenditure by neonate is approx. twice the rate of the adult/kg body mass
Cardiac output/kg body mass is approx. 4 times that of the adult
Heart muscle development at birth
Conversion from right to left-sided domination
Needs major remodelling up to and after birth
Circulatory redistribution
Body energy needs change
Energy needs – thermogenesis, behaviours, growth
Heart – before birth – growth, mainly hyperplasia – after birth – growth, mainly
hypertrophy
The heart post-natally must change and increase its output – left side must now
dominate
Mitochondrial increase in cardimyocytes before birth
During Foetal Life
Both haemodynamic forces and circulating factors regulate cardiomyocyte
proliferation
Factors that stimulate proliferation include – increased arteriol load, angiotensin II,
cortisol and insulin-like growth factor 1 – all tend to increase blood pressure
Those that suppress cardiac cell proliferation are – tri-iodo-L-thyronine (T3), reduced
cardiac systolic load and atrial natriuretic peptide – last two tend to decrease blood
pressure
Summary
Cardiac mass is dependant upon hyperplasia (cell division) prenatally
Late Prenatally and Postnatally the cardiomyocyte matures - Becomes binucleate -
Leaves the cell cycle
This maturation is caused primarily by - Thyroid hormones (T3) andANF
Postnatally heart growth is dependent on hypertrophy - Size increases but not cell
number
Clinical correlate- if maturation occurs early, eg stress-(hypoxia/ placental
insufficiency)
or preterm birth … a premature T3 surge, heart maybe hypocellular
increased compensatory hypertrophy is needed to produce sufficient cardiac muscle
strength - if this is insufficient the heart may show cardiac failure later in life - too
large cells and or lowered capillary density
Lung changes leading to birth
Changes needed for lung function at birth
Surface for gaseous exchange – inflatable – low surface tension – not fluid filled
Suitable blood supply (now 50% of cardiac output)
Protection – infectious agents – oxygen radicals
Perinatal lung development
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