Growth & Development of the Respiratory & Cardiovascular Systems.

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