Basement membranes structural functions

In biology, extracellular matrix (ECM) is the extracellular part of animal tissue that usually provides structural support to the cells in addition to performing various other important functions. ECM is the defining feature of connective tissue in animals. ECM includes the interstitial matrix and the basement membrane. 

Microscopically, the cornea shows a rather simple and multilayered structure that can be divided into six layers the epithelium, basement membrane, Bowman s layer, stroma, Descemet s membrane, and endothelium. The corneal tissue consists of three different cell types epithelial cells, keratocytes (corneal fibroblasts), and endothelial cells. The outermost corneal surface is covered with the preocular tear film, which is functionally associated with the cornea. The epithelial surface must be kept moist and smooth, a role played by the tear film in conjunction with a spreading function of the eyelids during blinking motions. Furthermore, the tear film provides a protection against infectious agents that may gain access into the eye. 

Network-forming collagens Types IV and VII form a three-dimensional mesh, rather than distinct fibrils (Figure 4.4). For example, type IV molecules assemble into a sheet or meshwork that constitutes a major part of basement membranes. [Note Basement membranes are thin, sheet-like structures that provide mechanical support for adjacent cells, and function as a semipermeable filtration barrier for macromolecules in organs such as the kidney and the lung.]... 

BASEMENT MEMBRANE PROTEINS MOLECULAR STRUCTURE AND FUNCTION... 

Figure 4.1. Tlie vasculai blood-brain barrier tliree levels of complexity. The upper panel illustrates tlie brain endotlielial cell. Tliis is tlie functional and anatomical site of botli banier function and of saturable and non-saturable mechanisms of passage. The major modifications allowing botli banier function and selective penetration of substances ai e indicated. Tlie middle panel illustrates otlier cell types and sti uc-tures important in BBB function. Pericytes are embedded in a basement membrane and asti ocytes foim a net-like structure over tlie capillary bed. Botli cell types are in paracellular communication witli tlie brain endotlielial cells. Pericytes and asti ocytes to some extent oppose each o tilers effects on BBB functions. Tlie lower panel illusti ates tlie neurovasculai unit, a concept, tliat emphasizes inlegration of peripheral, BBB, and centi al inleractions.

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