Corticoid

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Corticoid, also corticosteroid, any steroid hormone that derives from the outer layer, or cortex, of the adrenal gland. Among the corticoids are the glucocorticoids, such as cortisone and cortisol (see Hydrocortisone), essential to metabolism and the body's reaction to stress; and the mineralocorticoids, which have other important regulatory functions, such as maintaining ion balance. The adrenal cortex also secretes sex hormones, although these are produced in much greater quantities by the testes and ovaries. See Endocrine System; Steroids.

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The Human Eye

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Structure of the Eye The amount of light entering the eye (right) is controlled by the pupil, which dilates and contracts accordingly. The cornea and lens, whose shape is adjusted by the ciliary body, focus the light on the retina, where receptors convert it into nerve signals that pass to the brain. A mesh of blood vessels, the choroid, supplies the retina with oxygen and sugar. Lacrimal glands (left) secrete tears that wash foreign bodies out of the eye and keep the cornea from drying out. Blinking compresses and releases the lacrimal sac, creating a suction that pulls excess moisture from the eye’s surface. The entire eye , often called the eyeball, is a spherical structure approximately 2.5 cm (about 1 in) in diameter with a pronounced bulge on its forward surface. The outer part of the eye is composed of three layers of tissue. The outside layer is the sclera, a protective coating. It covers about five-sixths of the surface of the eye. At the front of the eyeball, it is continuo
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Respiratory System

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