Ultrastructure, basement membranes

Carlson EC, Audette JL, Veitenheimer NJ, Risan JA, Latumus DI, Epstein PN. Ultrastructural morphometry of capillary basement membrane thickness in normal and transgenic diabetic mice. Anatomical Record Part A Discoveries in Molecular, Cellular, and Evolutionary Biology 2003, 271, 332-341. 

In summary, both collagen IV and laminin show the ability to self-assemble. In addition, the various components of basement membrane have an affinity for one another that involves binding to specific sites. These interactions generate rather defined aggregates in solution and lead to the deposition of the components in a gel-like form whose ultrastructure resembles in some details authentic basement membranes. Such multiple interactions would be expected to be stronger than single interactions and may account for the codistributions of these components in basement membranes. 

Ultrastructural changes include abnormalities in the epithelial basement membrane, defective or absent hemidesmosomes, and decreased anchoring fibrils. The condition may occur after superficial corneal trauma, in conjunction with ABMD, or may be idiopathic. 

Figure 1 Diagrammatic representation of the ultrastructure of the respiratory membrane. Arrows indicate the passage of drugs (horizontal heavy lines) through the respiratory membrane after alveolar or capillary exposure, or of metabolites (horizontal broken lines) generated in the epithelial or endothelial layers. Key (1) monomolecular surfactant layers, (2) thin fluid film, (3) interstitial space, (4) endothelial capillary basement membrane, (5) drug transport from the alveoli, (6) absorption of drug into endothelial cells from the circulation, (7) transport of drug from the circulation to alveolar epithelium, (8) transport of drug from the circulation to the alveoli. (From Ref. 102. Reproduced by permission, CRC Press, Inc.)...

Ultrastructurally, the basement membrane is composed of three distinct zones the lamina lucida (or rara), the lamina densa and the lamina fibroreticularis (see Figure 2). 

The authors concluded that sulphur mustard injury to human skin commences at the level of the basal keratinocyte and thus confirmed the original theories of McAdams (1956). They also drew some parallels with thermal injury, which is also thought to act by disrupting the basal epidermal layer (Cullumbine, 1947). These ultrastructural observations and the belief that blistering results from dermo-epidermal separation at the level of the epidermal basement membrane have now been confirmed by im-munohistochemical studies (Lindsay and Rice, 1995). 

Leakage of fibrin and inflammatory cells through perforations within the GBM may be present on electron micrographs (83). Other ultrastructural findings include loss of podocytes, thickening of the basement membrane, and endothelial cell and capillary disruption (58,84). 

Alveolar septa may show some degree of expansion due to capillaritis, edema, and/or interstitial fibrosis (84,85). Capillaritis, characterized by neutrophils within the septa, is usually focal and of mild to moderate intensity. Diffuse or prominent capillaritis, or vasculitis of larger blood vessels is atypical, and if present, suggests another disease process. When interstitial fibrosis is present, it too is usually patchy and mild. Type II pneumocytes may show hyperplasia and reactive atypia in response to alveolar damage. In some cases, hyaline membranes are seen focally (85). Ultrastructural studies have shown fragmentation of alveolar septal basement membranes and wide gaps between endothelial cells (90). 

Familial essential benign haematuria (FEBH) is characterised by the familial occurrence of persistent, usually microscopic haematuria without progression to renal failure and extrarenal manifestations (Gauthier et al. 1989). Diffuse attenuation of the GBM (thin basement membrane nephropathy) is the typical ultrastructural finding, but renal biopsy is mostly unnecessary. 

MiosgeN, 2001. The ultrastructural composition of basement membranes in vivo. Histol Histopathol. 16(4) 1239. 

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