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, 600 - 800 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
Thermoregulation
HEAT BALANCE & TEMPERATURE REGULATION
METABOLISM:CHEMICAL REACTIONS: HEAT & ENERGY
HEAT LOSS:– RADIATION, CONDUCTION, CONV ECT ION 70%– EVAPORATION (skin & lungs) 27%– WARMING INSPIRED Al R 2%– URINE & FAECES 1%
CONTROL:– H Y P OT H A LAM U S– PERIPHERAL RECEPTORS– Comparison of core and peripheral temperatures
CONTROL IN NEWBORNS
Mechanisms of shivering & sweating are poorly developed Sweat glands immature Large S.A./ Wt ratio Thin subcutaneous adipose tissue layer
LEADS TO INSTABILITY OF BODY TEMPERATURE
Average body temperature drops with age SD also drops, indicating better control
CONTROL IN NEWBORNS
Vasoconstriction well developedCrying increases metabolic rateRestlessness & increased
movementsBrown fat
Vulnerability of the Adolescent Athlete
There have been several deaths of adolescent athletes– Intense prolonged activity– High ambient temperature & humidity– Athletic equipment– Big (small S.A. /Weight ratio)– Lack of water
HEAT STROKE
Sweating (Sweat is hypotonic) Water leaves cells to hypertonic exterior Water leaves blood, decrease in blood volume High concentration of electrolytes in blood Excessive water loss, sweating is shut-off Temperature rises rapidly (>40ºC) Heart failure