PHTY208 Lecture Notes - Lecture 17: Hypoxemia, Thermoregulation, Subcutaneous Tissue
Paediatric pulmonary physiology
• Lung development
o Embryonic period (0-7 weeks)
• Primitive lung bud ->
▪ Lung arises as outpouching of gut
▪ Main and lobar bronchii form
▪ Conditions like TOF develop here
• Pulmonary vasculature (arteries and veins) develops and divides with lung in a
caudal direction
• Airway development
o Pseudoglandular phase (5-17 weeks)
• Airway multiplication
▪ Bronchial branching and formation completed
▪ After 16 weeks increase in length and size.
• Formation of muscle fibres, elastic, early cartilage within the bronchi, and
mucous glands
• Diaphragm develops
▪ Diaphragmatic hernias arise in this timeframe
o Cannicular phase (13-17 weeks)
• Development of and vascularisation of respiratory portion of lung.
▪ Cilia appear on epithelial cells of trachea and main bronchi, and spread
towards the periphery
▪ Formation of alveolar buds and sacculi
• Surfactant production may begin as this phase
▪ Also involves cell types which produce the phospholipid lecithin.
o Terminal sac period (24-40 weeks)
• Babies can survive in outside world from 23-24 weeks
• The phase of cilia, surfactant and alveoli development
• Terminal sacs appear as outpouchings of terminal bronchioles
• Over the next few weeks these multiply forming multiple pouches off the
alveolar chamber (alveolar duct)
• Epithelial cells differentiate
▪ Type 1 cells (95%)
• The surface epithelium thins as vascular proliferation increases
• Creatio of the future lood‐ gas arrier
▪ Type II (5%) – surfactant production
• At term primitive alveoli are detected
• Surfactant production
▪ Surface active material that reduces surface tension at air liquid
interfaces
▪ Preset fro ‐ eeks gestatio
▪ Enables the lungs to remain aerated upon expiration
▪ Preterm babies commonly suffer surfactant insufficiency
o At Birth
• Lungs are a heterogenous mix of undifferentiated and differentiated tissue
which will develop and grow
▪ Lung
▪ Nerves
▪ Lymph
▪ Blood vessels
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• Alveoli
▪ Approiatel ‐ illio terial aleoli
▪ Shallow and wider mouth in newborn
▪ Change after few months
o Postnatal lung development
• Lung development continues after birth
• Aleoli otiue to for util ‐ ears
• The number of generations of bronchi increases from 16 divisions at birth to
23 divisions at 14 years
• Anatomical Differences
o Airway diameter and length
• Narrow airways
• Smaller diameter
• Increased resistance to flow
o Heart size
• Adult 1/3 of rib cage
• Infant 1/2 of rib cage
• Less space for lungs
o Chest wall
• Soft, compliant chest wall
▪ Cartilaginous and therefore retraction
• Rib cage configuration
▪ Horizontal ribs
▪ Weak, poorly developed intercostals
o Diaphragmatic breathing
• Horizontal angle of insertion
• Combined with compliant ribs results in
▪ Less efficient ventilation
▪ Distortion of chest wall shape on inspiration
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Document Summary
Lung development: embryonic period (0-7 weeks, primitive lung bud -> Surface active material that reduces surface tension at air liquid interfaces: prese(cid:374)t fro(cid:373) (cid:1005)(cid:1012) (cid:1006)(cid:1008) (cid:449)eeks gestatio(cid:374, enables the lungs to remain aerated upon expiration, preterm babies commonly suffer surfactant insufficiency, at birth. Lungs are a heterogenous mix of undifferentiated and differentiated tissue which will develop and grow. Lymph: blood vessels, alveoli, appro(cid:454)i(cid:373)atel(cid:455) (cid:1006)(cid:1004) (cid:1011)(cid:1004) (cid:373)illio(cid:374) ter(cid:373)i(cid:374)al al(cid:448)eoli, change after few months. Shallow and wider mouth in newborn: postnatal lung development. Lung development continues after birth: al(cid:448)eoli (cid:272)o(cid:374)ti(cid:374)ue to for(cid:373) u(cid:374)til (cid:1012) (cid:1005)(cid:1005) (cid:455)ears, the number of generations of bronchi increases from 16 divisions at birth to. 23 divisions at 14 years: anatomical differences, airway diameter and length, narrow airways. Increased resistance to flow: heart size, adult 1/3 of rib cage. Soft, compliant chest wall: cartilaginous and therefore retraction, rib cage configuration, horizontal ribs, weak, poorly developed intercostals, diaphragmatic breathing, horizontal angle of insertion, combined with compliant ribs results in.
