Nourishment
The lens is metabolically active and requires nourishment in order to maintain its growth and transparency. Compared to other tissues in the eye, however, the lens has considerably lower energy demands.
By nine weeks into human development, the lens is surrounded and nourished by a net of vessels, the tunica vasculosa lentis, which is derived from the hyaloid artery. Beginning in the fourth month of development, the hyaloid artery and its related vasculature begin to atrophy and completely disappear by birth. In the postnatal eye, Cloquet’s canal marks the former location of the hyaloid artery.
After regression of the hyaloid artery, the lens receives all its nourishment from the aqueous humor. Nutrients diffuse in and waste diffuses out through a constant flow of fluid from the anterior/posterior poles of the lens and out of the equatorial regions, a dynamic that is maintained by the Na+/K+ ATPase pumps located in the equatorially positioned cells of the lens epithelium.
Glucose is the primary energy source for the lens. As mature lens fibers do not have mitochondria, approximately 80% of the glucose is metabolized via anaerobic metabolism. The remaining fraction of glucose is shunted primarily down the pentose phosphate pathway. The lack of aerobic respiration means that the lens consumes very little oxygen as well.
Read more about this topic: Lens (anatomy)
Famous quotes containing the word nourishment:
“Our ancestors were savages. The story of Romulus and Remus being suckled by a wolf is not a meaningless fable. The founders of every state which has risen to eminence have drawn their nourishment and vigor from a similar wild source. It was because the children of the Empire were not suckled by the wolf that they were conquered and displaced by the children of the northern forests who were.”
—Henry David Thoreau (1817–1862)
“The point of the dragonfly’s terrible lip, the giant water bug, birdsong, or the beautiful dazzle and flash of sunlighted minnows, is not that it all fits together like clockwork--for it doesn’t ... but that it all flows so freely wild, like the creek, that it all surges in such a free, finged tangle. Freedom is the world’s water and weather, the world’s nourishment freely given, its soil and sap: and the creator loves pizzazz.”
—Annie Dillard (b. 1945)
“We can see that the baby is as much an instrument of nourishment for us as we are for him.”
—Polly Berrien Berends (20th century)