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Functional Morphology of Lung Parenchyma

Ewald R. Weibel

10.1002/cphy.cp030308

Source: Supplement 12: Handbook of Physiology, The Respiratory System, Mechanics of Breathing

Originally published: 1986

Published online: January 2011

Full Article on Wiley Online Library



Abstract

The sections in this article are:

1 Elements of Lung Structure
1.1 Epithelium
1.2 Surface Lining of Air Spaces
1.3 Endothelium
1.4 Interstitial Space and Structures
2 Elements of the Fiber System
2.1 Collagen and Reticulin Fibers
2.2 Elastic Fibers
2.3 Integral Fiber Strand
3 Fiber Continuum of the Lung
3.1 Axial Fiber System
3.2 Peripheral Fiber System
3.3 Alveolar Septal Fiber System
4 Design of the Alveolar Septum
5 Alveolar Surface Lining Layer
6 Deformation of the Alveolar Septum Under the Effect of Interacting Forces
7 Geometry and Mechanics of the Acinus
8 Conclusions
Figure 1. Figure 1.

A: alveolar septum of dog lung showing delicate fiber bundle in septum and strong bundle at free edge forming the alveolar entrance ring as boundary of alveolar duct. Note collagen (CF) and elastic (EL) fibers, fibroblasts (F), and smooth muscle cell (SM). Capillaries (C) lined by endothelial cells (EN), alveolar surface lined by epithelium made of cuboidal type II (EP2) and squamous type I (EP1) cells. Scale, 2 μm. B: entrance ring at higher power. Scale, 0.5 μm.
Figure 2. Figure 2.

Fine structure of collagen (CF) and elastic (EL) fibers in perivascular sheath. Collagen fibers are bundles of banded fibrils seen in longitudinal and transverse section. Elastic fibers are made of amorphous core surrounded by microfibrils (arrows) that are partly embedded in core in thicker fibers. Scale, 0.5 μm.
Figure 3. Figure 3.

Integral fiber system seen by interference‐contrast microscopy of subcutaneous tissue of rat. Elastic fibers (EL) form network of straight fibers associated with wavy collagen fibers (CF). Scale, 50 μm.
Figure 4. Figure 4.

Section of fetal human lung showing continuity of loose peripheral mesenchymal bed from pleura (PL) to deeper parts of lung, and condensed mesenchyme (arrows) around bronchi (B) and within lobules as anlage of axial fiber system. Note location of pulmonary veins (V) and arteries (A) in loose mesenchyme. Scale, 200 μm.
Figure 5. Figure 5.

Acinar airways of perfusion‐fixed rabbit lung. Note that the wall of alveolar ducts (AD) is formed by network of coarse fiber bundles around alveolar mouths that represent the acinar extension of the axial fiber system from terminal (TB) and respiratory (RB) bronchioles. Peripheral fiber system is represented by pleura (PL) and a small septum with a branch of the pulmonary vein (arrow). Scale, 200 μm.

From Weibel 109
Figure 6. Figure 6.

Thick section of acinar airways in human lung with elastic fiber stain. Fiber strands in wall of alveolar ducts (AD, heavy arrows) decrease in thickness toward periphery. Light arrows outline peripheral fiber strands that extend from pleura (PL). Scale, 200 μm.

From Weibel 127
Figure 7. Figure 7.

Subpleural region of human lung with 2 interlobular septa (S) extending from pleura (PL). Gomori fiber stain. AD, alveolar duct. Scale, 200 μm.
Figure 8. Figure 8.

Thick slice of dried human lung showing hierarchy of interlobular septa (arrows). PL, pleura. Scale, 1 mm.
Figure 9. Figure 9.

Two‐dimensional model explaining hierarchy of interlobular septa as a sequence of shells around the branchings of a fractal airway tree.
Figure 10. Figure 10.

Septal fiber network of human lung. A: alveolar septa are extended between alveolar ducts (AD) marked by axial fibers (ax). per, Peripheral fibers. Scale, 200 μm. B: flat view at higher power of septal fibers extended between axial and peripheral fibers. Scale, 20 μm.
Figure 11. Figure 11.

Structure of human alveolar septum. A: scanning electron micrograph showing capillaries (C) in cross‐sectional and surface view; note free edge of septum toward alveolar duct (AD) and alveolar pores (P). Scale, 10 μm. B: model reconstruction of interweaving between capillaries and septal fiber meshwork.

From Weibel 109
Figure 12. Figure 12.

Alveolar septum of human lung in thin section. Capillary (C) bounded toward alveoli (A) by tissue barrier made of endothelium (EN) and type I epithelium (EP). On the left side the interstitium contains fibers (F) and fibroblast processes (FB); on the right side it is reduced to the fused basement membranes (minimal barrier). Note pericytes (PC). Scale, 1 μm.

From Weibel 109
Figure 13. Figure 13.

Surface lining layer (SLL) from perfusion‐fixed rat lung filling crevice in epithelial lining (EP) between 2 capillaries (C). Note osmiophilic surface film, presumably surfactant phospholipids, associated with some tubular myelin (TM). EN, endothelium; A, alveolus. Scale, 0.2 μm. Insets: fine structure of tubular myelin in transverse (A) and longitudinal (B) section. Scale, 0.1 μm.

Insets from Hassett et al. 45
Figure 14. Figure 14.

Forces interacting in molding structure of alveolar septum.

From Weibel 127
Figure 15. Figure 15.

Arrangement of alveolar septa in perfusion‐fixed rabbit lungs at 80% TLC (A, C, E) and 40% TLC (B, D, F). A, B: saline‐filled; C, D: normal air‐filled; E, F: detergent‐rinsed, air‐filled lungs. PV, pulmonary venule. Scale, 100 μm.

A, B from Gil et al. 33; C–F from Bachofen et al. 6
Figure 16. Figure 16.

Deformation of alveolar septum under the effect of surface forces counteracted by tissue force and capillary distending pressure.

From Weibel 127
Figure 17. Figure 17.

Smoothing of alveolar surface by pools of surface lining layer (SLL) and folding of barrier (arrows) in perfusion‐fixed human lung. C, capillary. Scale, 2 μm.

From Weibel 108
Figure 18. Figure 18.

Perfusion‐fixed air‐filled rabbit lung at 80% TLC after detergent rinsing. Capillaries are squashed by high surface tension (arrows). Scale, 20 μm.

From Bachofen et al. 6
Figure 19. Figure 19.

Crumpling of alveolar surface in perfusion‐fixed air‐filled rabbit lung at 40% TLC. High local curvatures (arrows) are sustained and a thin lamella of lining layer (L) spans across an alveolar pore (A). C, capillaries. Scale, 5 μm.

From Gil et al. 33
Figure 20. Figure 20.

Deformation of alveolar septum under the effect of surface forces. A: fluid‐filled lung; capillaries weave around a fiber sheet. B: air‐filled lung; capillaries appear arranged as a sheet and fibers weave across the septum. Scale, 10 μm.
Figure 21. Figure 21.

Model, reduced in length, of acinar fiber system under the effect of surface forces (arrows). Septal fibers become folded into corners.

From Weibel 127
Figure 22. Figure 22.

Surface‐to‐volume ratio of parenchymal air spaces in rabbit lungs as a function of lung volume.

Data from Bachofen et al. 6 and Gil et al. 33


Figure 1.

A: alveolar septum of dog lung showing delicate fiber bundle in septum and strong bundle at free edge forming the alveolar entrance ring as boundary of alveolar duct. Note collagen (CF) and elastic (EL) fibers, fibroblasts (F), and smooth muscle cell (SM). Capillaries (C) lined by endothelial cells (EN), alveolar surface lined by epithelium made of cuboidal type II (EP2) and squamous type I (EP1) cells. Scale, 2 μm. B: entrance ring at higher power. Scale, 0.5 μm.



Figure 2.

Fine structure of collagen (CF) and elastic (EL) fibers in perivascular sheath. Collagen fibers are bundles of banded fibrils seen in longitudinal and transverse section. Elastic fibers are made of amorphous core surrounded by microfibrils (arrows) that are partly embedded in core in thicker fibers. Scale, 0.5 μm.



Figure 3.

Integral fiber system seen by interference‐contrast microscopy of subcutaneous tissue of rat. Elastic fibers (EL) form network of straight fibers associated with wavy collagen fibers (CF). Scale, 50 μm.



Figure 4.

Section of fetal human lung showing continuity of loose peripheral mesenchymal bed from pleura (PL) to deeper parts of lung, and condensed mesenchyme (arrows) around bronchi (B) and within lobules as anlage of axial fiber system. Note location of pulmonary veins (V) and arteries (A) in loose mesenchyme. Scale, 200 μm.



Figure 5.

Acinar airways of perfusion‐fixed rabbit lung. Note that the wall of alveolar ducts (AD) is formed by network of coarse fiber bundles around alveolar mouths that represent the acinar extension of the axial fiber system from terminal (TB) and respiratory (RB) bronchioles. Peripheral fiber system is represented by pleura (PL) and a small septum with a branch of the pulmonary vein (arrow). Scale, 200 μm.

From Weibel 109


Figure 6.

Thick section of acinar airways in human lung with elastic fiber stain. Fiber strands in wall of alveolar ducts (AD, heavy arrows) decrease in thickness toward periphery. Light arrows outline peripheral fiber strands that extend from pleura (PL). Scale, 200 μm.

From Weibel 127


Figure 7.

Subpleural region of human lung with 2 interlobular septa (S) extending from pleura (PL). Gomori fiber stain. AD, alveolar duct. Scale, 200 μm.



Figure 8.

Thick slice of dried human lung showing hierarchy of interlobular septa (arrows). PL, pleura. Scale, 1 mm.



Figure 9.

Two‐dimensional model explaining hierarchy of interlobular septa as a sequence of shells around the branchings of a fractal airway tree.



Figure 10.

Septal fiber network of human lung. A: alveolar septa are extended between alveolar ducts (AD) marked by axial fibers (ax). per, Peripheral fibers. Scale, 200 μm. B: flat view at higher power of septal fibers extended between axial and peripheral fibers. Scale, 20 μm.



Figure 11.

Structure of human alveolar septum. A: scanning electron micrograph showing capillaries (C) in cross‐sectional and surface view; note free edge of septum toward alveolar duct (AD) and alveolar pores (P). Scale, 10 μm. B: model reconstruction of interweaving between capillaries and septal fiber meshwork.

From Weibel 109


Figure 12.

Alveolar septum of human lung in thin section. Capillary (C) bounded toward alveoli (A) by tissue barrier made of endothelium (EN) and type I epithelium (EP). On the left side the interstitium contains fibers (F) and fibroblast processes (FB); on the right side it is reduced to the fused basement membranes (minimal barrier). Note pericytes (PC). Scale, 1 μm.

From Weibel 109


Figure 13.

Surface lining layer (SLL) from perfusion‐fixed rat lung filling crevice in epithelial lining (EP) between 2 capillaries (C). Note osmiophilic surface film, presumably surfactant phospholipids, associated with some tubular myelin (TM). EN, endothelium; A, alveolus. Scale, 0.2 μm. Insets: fine structure of tubular myelin in transverse (A) and longitudinal (B) section. Scale, 0.1 μm.

Insets from Hassett et al. 45


Figure 14.

Forces interacting in molding structure of alveolar septum.

From Weibel 127


Figure 15.

Arrangement of alveolar septa in perfusion‐fixed rabbit lungs at 80% TLC (A, C, E) and 40% TLC (B, D, F). A, B: saline‐filled; C, D: normal air‐filled; E, F: detergent‐rinsed, air‐filled lungs. PV, pulmonary venule. Scale, 100 μm.

A, B from Gil et al. 33; C–F from Bachofen et al. 6


Figure 16.

Deformation of alveolar septum under the effect of surface forces counteracted by tissue force and capillary distending pressure.

From Weibel 127


Figure 17.

Smoothing of alveolar surface by pools of surface lining layer (SLL) and folding of barrier (arrows) in perfusion‐fixed human lung. C, capillary. Scale, 2 μm.

From Weibel 108


Figure 18.

Perfusion‐fixed air‐filled rabbit lung at 80% TLC after detergent rinsing. Capillaries are squashed by high surface tension (arrows). Scale, 20 μm.

From Bachofen et al. 6


Figure 19.

Crumpling of alveolar surface in perfusion‐fixed air‐filled rabbit lung at 40% TLC. High local curvatures (arrows) are sustained and a thin lamella of lining layer (L) spans across an alveolar pore (A). C, capillaries. Scale, 5 μm.

From Gil et al. 33


Figure 20.

Deformation of alveolar septum under the effect of surface forces. A: fluid‐filled lung; capillaries weave around a fiber sheet. B: air‐filled lung; capillaries appear arranged as a sheet and fibers weave across the septum. Scale, 10 μm.



Figure 21.

Model, reduced in length, of acinar fiber system under the effect of surface forces (arrows). Septal fibers become folded into corners.

From Weibel 127


Figure 22.

Surface‐to‐volume ratio of parenchymal air spaces in rabbit lungs as a function of lung volume.

Data from Bachofen et al. 6 and Gil et al. 33
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Article Title: Functional Morphology of Lung Parenchyma
 

How to Cite

Ewald R. Weibel. Functional Morphology of Lung Parenchyma. Compr Physiol 2011, Supplement 12: Handbook of Physiology, The Respiratory System, Mechanics of Breathing: 89-111. First published in print 1986. doi: 10.1002/cphy.cp030308