Growth & Development of the Respiratory & Cardiovascular Systems

Be able to describe the four stages of development of the respiratory system

Lung Growth Alveolar development – last trimester, most postnatally, – 20 million at birth, – 300 million at 8 (adult) Fetal respiratory movements Lung weight: – 60-70gm at birth – increasing 20 fold to adulthood, – correlates best with height

Spirometry

Endocardial tubes form, that eventually coalesce to form the primitive heart tube at 3 weeks Heart beats soon after Nearby angiogenic cells (mesodermal) form in clusters (blood pools) and migrate to form endothelial lining of blood vessels Adjacent mesenchymal cells migrate around endothelial lining to form vessel wall Be able to describe the development of the heart

6th week - heart has developed its general definitive form 8th week - blood vessels are formed Heart tube folds and twists forming four distinct chambers

Fetal Circulation Placenta One umbilical vein - placenta to fetus Two umbilical arteries - fetus to placenta Foramen Ovale Ductus Arteriosus Result 10-15% of fetal blood goes through lungs Ductus Venosus Be able to describe the fetal and postnatal circulatory systems and the transitions that occur at birth

Fetal Circulation Umbilical vein - Oxygen saturation = 70% Fetal Periphery - Oxygen saturation = 55% After birth – Arterial = 97% – Venous = 70% fetal hemoglobin -greater affinity for Oxygen

Birth Adjustments Lungs expand, pulmonary vascular resistance decreases and systemic blood pressure rises Left atrial pressure rises - foramen ovale closes Ductus Arteriosus flows in opposite direction until vasoconstriction and eventual closure

Heart Size Left side grows faster after birth Heart growth curve same as weight (fat free mass) 40 ml at birth, ml as adult – doubles by 6 months, – quadruples by 2 years,

Heart Rate, Stroke Volume Heart rate: 140 bts/min (sd = 20) at birth Stroke Volume: – 3-4 ml at birth, 40 ml just before growth spurt, 60 ml as adult Cardiac Output: – 0.5 l/min at birth, 5 l/min as adult

Blood Pressure Reduction in pulmonary resistance, increase in peripheral resistance Systemic BP rises as Heart Rate drops

Blood Composition BloodVolume: Highly correlated with heart size and body weight, and maximum oxygen uptake Hematocrit: – Adult males 40-45%, females 38-42% – 30% at 2 months of age, – sex difference established at puberty Red blood cell count and hemoglobin concentration similar pattern