The eye is located in the orbit of the skull and has several external features. Above the eye is the eyebrow. The corners of the eye have either a lateral commissure or a medial commissure. Next to the medial commissure is the caruncle, a small thickened tissue in the medial corner of the eye. The outer surface of the eye is protected by the upper and lower eyelids. The blink reflex rapidly closes the eyelids to keep dust from hitting the outer surface of the eye. Label and color the sclera (the white of the eye), iris (the colored part of the eye), pupil (the opening that lets light into the back of the eye), and the eyelids. There is a transparent extension of the sclera called the cornea and it covers the iris and pupil.
The eyes are kept moist and are subject to potential bacterial infection. Tears have antimicrobial properties and are formed by the lacrimal gland. They contain digestive enzymes and wash microbes from the surface of the eye. Tears drain from the eye into the lacrimal canals. These canals lead into the nasolacrimal duct and then into the nasal cavity.
Answer Key: a. Lacrimal gland, b. Upper eyelid, c. Sclera, d. Lacrimal canal, e. Medial commissure f. Nasal cavity, g. Lateral commissure, h. Pupil, i. Iris, j. Lower eyelid, k. Caruncle, I. Nasolacrimal duct
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.