Figure 2316

Structure of the eyelid, a. This schematic drawing of the eyelid shows the skin, associated skin appendages, muscles, tendons, connective tissue, and conjunctiva. Note the distribution of multiple small glands associated with the eyelid and observe the reflection of the palpebral conjunctiva in the fornix of the lacrimal sac to become the bulbar conjunctiva, b. Photomicrograph of a sagittal section of the eyelid stained with picric acid for better visualization of epithelial components of the skin and the numerous glands. In this preparation, mus cle tissue (i.e., orbicularis oculi muscle) stains yellow, and the epithelial cells of skin, conjunctiva, and glandular epithelium are green. Note the presence of the numerous glands within the eyelid. The tarsal (Meibomian) gland is the largest gland, and it is located within the dense connective tissue of the tarsal plates. This sebaceous gland secretes into ducts opening onto the eyelids. x20. Inset. Higher magnification of a tarsal gland from the boxed area, showing the typical structure of a holocrine gland. x60.

cretion of the tarsal glands produces an oily layer on the surface of the tear film that retards the evaporation of the normal tear layer.

• Sebaceous glands of eyelashes (glands of Zeis), small, modified sebaceous glands that are connected with and empty their secretion into the follicles of the eyelashes

• Apocrine glands of eyelashes (glands of Moll), small sweat glands with unbranched sinuous tubules that begin as a simple spiral

• Accessory lacrimal glands, compound serous tubu-loalveolar glands that have distended lumina. They are located on the inner surface of the upper eyelids (glands of Wolfring) and in the fornix of the lacrimal sac (glands of Krause).

All glands of the human eyelid are innervated by neurons of the autonomic nerve system, and their secretion is synchronized with the lacrimal glands by a common neurotransmitter, vasoactive intestinal polypeptide (VIP).

The eyelashes emerge from the most anterior edge of the lid margin, in front of the openings of the Meibomian glands. The lashes are short, stiff, curved hairs and may occur in double or triple rows. The lashes on the same eyelid margin may have different lengths and diameters.

The lacrimal gland produces tears that moisten the cornea and pass to the nasolacrimal duct

Tears are produced by the lacrimal glands and to lesser degree by the accessory lacrimal glands. The lacrimal gland is located beneath the conjunctiva on the upper lateral side of the orbit (Fig. 23.17). The lacrimal gland consists of several separate lobules of tubuloacinar serous glands. The acini have large lumina lined with columnar

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