Because human anatomy does not change (except over long periods of

Because human anatomy does not change (except over long periods of time), knowledge acquired a century ago is still accurate today. Broad functions of any part of the body, such as the skin, are duplicated in different ways by other organs. One can eventually understand the entire body as a larger system made up of smaller, interdependent systems.

A cross-section of the skin reveals a top layer of epidermis, or cuticle, followed by derma, and finally, subcutaneous cellular tissue. Sprouting through all three layers are hairs, with hair follicles and erector pili muscles embedded deep within the subcutaneous tissue. Sweat (sudoriferous) glands, fat cells, and sebaceous glands are scattered throughout, while papillae, which are conical and extremely sensitive, can be found directly beneath the superficial layer. The skin is the primary organ of the sense of touch. It can excrete substances as well as absorb them, and it plays a vital role in regulating body temperature and in protecting the tissues that lie beneath it. The epidermis has no veins or arteries and varies considerably both in thickness and in depth or fineness of its furrows. On the palm, for example, the skin is quite thick, or horny, and is marked by deep furrows or lines. On the back of the hand, however, the skin is less thick, and has only a faint network of lines crisscrossing it. The pigment found in the epidermis gives whatever color there is to the skin; this pigment is similar to that found in the retina of the eye. One layer down, in the derma, there is similar variation in thickness, mostly to protect underlying tissue.

In the derma lies the vascular system, which includes nerves, blood vessels, and lymphatics. The derma is divided into two sub-layers: the reticular layer and the papillary layer, which is closer to the epidermis. The less sensitive the skin, the fewer papillae reside there; in the most sensitive places, such as the fingertips and the nipples, the papillae are long, large, and grouped closely together to form parallel arcs with ducts to sweat glands lying in between. Under the papillary layer, and conforming to it, is the reticular layer, composed of fibrous bands and elastic tissue, and interlaced by fat and sudoriferous glands.

The basic functions of muscular contraction, vascular transport, nerve communication, and protection all take place in the various layers of the skin, so that understanding the components of the skin and how they work together is a helpful step in understanding the complex anatomy of the human body.

1. The author implies that

A. there is a relationship between the thickness of the skin and the number and depth of the skin's furrows
B. the reticular layer is the only layer that contains fibrous bands
C. the skin is the only part of the body that has a sense of touch
D. areas of the skin with sudoriferous glands are extremely sensitive
E both hair and the reticular layer are made up of the same kind of tissue


2. The passage suggests that if the skin were damaged in some way, and unable to perform some of its functions, which of the following might happen?

A. The pigmentation would no longer be similar to that found in the retina
B. The deep furrows found on some parts of the skin would disappear.
C. The body would regulate its temperature less effectively.
D. The fingertips would no longer be characterized by an abundance of papillae.
E. The body would lose its sense of touch


3. The passage states that all the following are found in the skin EXCEPT

A. fat cells
B. lymphatics
C. veins
D. pigmentation
E. ligaments