Question

Fibres
Natural
lence - 4​

Answer 1

Answer:

Lens fibers make up the substance of the lens and are arranged in interdigitating layers. These fibers stretch from the equatorial region toward the anterior and posterior poles of the lens. However, they do not quite reach the poles but instead meet fibers from the opposite equator and form a Y-shaped suture pattern with them. The suture pattern may become visible as a prominent upright (anterior) or inverted (posterior) Y if the lens becomes cataractous . Because new lens fibers are formed throughout life, the older fibers in the (central) lens nucleus are denser and less transparent than the younger fibers laid down around them in the cortex. This difference between nucleus and cortex becomes more pronounced as the animal ages and may result in the formation of nuclear sclerosis .

Explanation:

Answer 2

Explanation:

Lens fibres.

While each lens fibre is only a 4 × 7 µm hexagonal prismatic band in cross-section (Fig. 1-24C), it may be up to 12 mm (12 000 µm) in length. The apical portion of the elongated lens cell (or lens ‘fibre’) passes anteriorly, the basal portion posteriorly. The cell nucleus migrates anteriorly as the cell is pushed deeper in the lens, hence creating the anteriorly oriented lens bow (Fig. 1-24D). The meridionally oriented lens fibres extend the full length of the lens, meeting at the anterior and posterior sutures (Fig. 1-24A). Deeper (hence older) lens fibres are anucleate. Continual growth of the lens, by addition of superficial strips of new cells, produces a series of concentrically arranged laminae, similar to the layers of an onion (best seen by dissecting a fixed or frozen lens). In life, the outer cortex of the lens has a softer consistency than the hard central nucleus.

Lens fibres are tightly packed with little intercellular space. Neighbouring cells are linked by ball-and-socket cytoplasmic interdigitations (Fig. 1-24B,C) and numerous gap junctions. The junctions may aid maintenance of centrally positioned cells (via intercellular and molecular coupling or metabolic cooperation) some distance from the source of nutrition (aqueous humour). Superficially located lens fibres are rich in ribosomes, polysomes and rough endoplasmic reticulum, and actively synthesize unique lens proteins, lens crystallins (see Ch. 4); however, the cytoplasm of mature lens fibres appears homogeneous. Lens fibres are rich in cytoskeletal elements oriented parallel to the long axis of the cell.