Lens

The lens is a transparent tissue, with 65% of its weight consisting of water and the remainder principally of proteins. Anteriorly, the lens is in contact with the pupillary portion of the iris, and posteriorly it fits into a hollow depression of the anterior vitreous surface (Paterson and Delamere, 1992). The major components of the lens are capsule, epithelium, and lens fiber cells (Fig. 7). The lens capsule is acellular, transparent, elastic, and acts as an unusually thick basement membrane that encloses the epithelium and lens fiber cells. It is mainly composed of type IV collagen together with 10% glycosaminoglycans (GAGs). The inner portion of the anterior capsule is in immediate contact with lens epithelium, while the posterior capsule is in contact with the most superficial lens fiber cells. A single layer of epithelial cells forms a cap on the inner anterior surface of the lens, and hundreds of thousands of differentiated fiber cells form its bulk. Lens cortex or periphery is composed of fiber cells that are formed from the differentiation of epithelial cells in the equatorial zone. Young and superficial fiber cells contain cytoplasmic inclusions similar to those of epithelial cells. Since the lens does not shed any of its cellular components from embryonic development onward, the older cells of the lens will be displaced towards the center or nucleus of the lens. Most of the cells in the lens nucleus lack nuclei and particulate cytoplasmic contents. Membrane transport proteins in the lens

Figure 7 The lens. Representation of pump-leak system and cellular barriers in the movement of ions and nutrients. The fiber cells are distributed through out the lens body.

Figure 7 The lens. Representation of pump-leak system and cellular barriers in the movement of ions and nutrients. The fiber cells are distributed through out the lens body.

I.tns tiber 001

Posterior (vitreous humor)

I.tns tiber 001

play an important role in cell volume regulation, nutrient supply, and lens transparency (Goodenough, 1992, Rae, 1994). All cells of the lens are interconnected by gap junctions that form low-resistance pathways between the cytoplasm of adjacent cells.

Was this article helpful?

0 0

Post a comment