Respiratory System - Postnatal
From Embryology
Introduction
This site mainly focuses on prenatal development, but the respiratory system is one of those that continues to grow and change postnatally. This page includes some topics related to this postnatal development.
Some Recent Findings
References | Recent References
Alveolar Stage
- The postnatal lung, with alveoli forming.
- Expansion of gas exchange alveoli, vascular beds (capillaries), lymphatics and innervation.
- Very premature infants will still be at the earlier Saccular stage.
Preterm Saccular Stage
- week 24 to near term.
- most peripheral airways form widened "airspaces", termed saccules.
- saccules widen and lengthen the airspace (by the addition of new generations).
- future gas exchange region expands significantly.
- Fibroblastic cells also undergo differentiation, they produce extracellular matrix, collagen, and elastin.
- May have a role in epithelial differentiation and control of surfactant secretion.
- Alveolar Cells Type II (Type II pneumocytes)
- begin to secrete surfactant, levels of secretion gradually increase to term.
- allows alveoli to remain inflated
- Vascular tree - also grows in length and diameter during this time.
Alveoli Number
- At birth about 15% of adult alveoli number have formed
- 20 - 50 million to in the adult about 300 million.
- remaining subdivisions develop in the first few postnatal years
Age (months) | Alveoli (million) | Respiratory Airways (million) | Generations of Airways |
Birth | 24 | 1.5 | |
3 | 86 | 1.8 | |
3 | 77 | 2.5 | 21 |
3 | 73 | 2.0 | |
7 | 112 | 3.7 | |
13 | 129 | 4.5 | 22 |
16 | 127 | 4.7 | |
22 | 160 | 7.1 | |
48 | 257 | 7.9 | |
98 | 280 | 14.0 | 23 |
Adult | 296 | 14.0 | 23 |
Dunnill MS. Postnatal growth of the lung. Thorax 1962;17:329–333. PDF
<pubmed>139844</pubmed>| PDF
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Respiratory Rate
- neonatal rate is higher (30-60 breaths/minute) than adult (12-20 breaths/minute).
- tachypnea - (Greek, rapid breathing) an increased respiratory rate of greater than 60 breaths/minute in a quiet resting baby
Age | Rate (breaths/minute) |
Infant (birth - 1 year) | 30 - 60 |
Toddler (1 - 3 years) | 24 - 40 |
Preschool (3 - 6 years) | 22 - 34 |
School age (6 - 12 years) | 18 - 30 |
Adolescent (12 - 18 years) | 12 - 16 |
Rib Orientation
Infant Rib
- lies virtually horizontal
- allowing diaphragmatic breathing only.
Adult Rib
- lies oblique (both anterior and lateral views)
- allows for both pump-handle and bucket handle types of inspiration.
References
Reviews
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Articles
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Search PubMed
Search Pubmed: PostnatalTract Development |
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Cite this page: Hill, M.A. (2024, April 26) Embryology Respiratory System - Postnatal. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Respiratory_System_-_Postnatal
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G