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The Skin as Our Integument Help (page 2)

By — McGraw-Hill Professional
Updated on Aug 30, 2011

The Dermis As Our Tough Main “skin”

True to its name, the epidermis literally lies “upon” ( epi -) the dermis ( DER -mis). The dermis is the main, fiber-rich, connective tissue portion of the skin. The dermis is especially rich in a dense network of collagen ( CALL -uh-jen) fibers . The word collagen translates to mean “glue” ( coll ) “producer” (- gen ). Collagen fibers are thick, tough, unbranched fibers that have a high tensile ( TEN -sil) strength ; that is, they have a great ability to resist pulling or “tension” ( tens ) forces. [ Study suggestion: Place two fingers on the skin of your forearm. Now, gently try to stretch your skin between your fingertips. Feel the resistance to stretching, the tensile strength, that is being exerted? This glue-like function is mainly the result of the thousands of collagen fibers running like a tough, woven basket throughout your dermis.]

One important type of structure found within the dermis is the hair follicle ( FAHL -uh-kul). As evident from Figure 13.1, the hair follicle is a “little bag” lined by a membrane, and containing a hair. The base of the hair follicle lies in the dermis. The hair, itself, is basically a flexible rod of tightly packed, keratin-stuffed squamae. Arranged around the base of the hair follicle is a sensory nerve basket . [ Study suggestion: Without touching your skin, gently stroke the hairs on your forearm. What do you feel – a tickling, tingling sensation? This reveals the main function of hairs: touch sensations.]

There are many other types of sensory receptors located within the dermis. Besides receptors for the sense of touch, there are those for pressure, pain, cold, heat, and vibration.

One of the most critical functions of the dermis is its role in thermoregulation ( THER -moh-reg-you- LAY -shun). By thermoregulation, we mean the “regulation” or control of “heat” (therm): specifically, the control of internal body temperature. Way back in Chapter 1, we talked about the homeostasis or relative constancy of oral body temperature, measured in units of degrees Fahrenheit. This homeostasis (relative constancy) of oral body temperature is another term for thermoregulation. It was represented symbolically by an S-shaped curve shown back in Figure 1.2 (A):

Skins and Skeletons “Ain’t We Just Peachy?”: The Skin as Our Integument The Dermis As Our Tough Main “skin”

Figure 13.2 reveals what happens when the oral body temperature of a human or other homeothermic animal rises towards the upper limit of its normal range. (This temperature boost often occurs during heavy exercising.) In the dermis, two critical events kick in. The sweat glands increase their secretion of sweat into the sweat ducts, which then moves up and out onto the surface of the skin through sweat pores. The excess body heat essentially boils the watery sweat from the skin surface, causing it to evaporate into the air. This net heat loss helps to lower the oral body temperature.

A second chain of physiological events involve vasodilation ( vase -oh-die- LAY -shun) – the “process of” (-tion) blood “vessel” (vas) “widening” (dilat). As the body gets hotter, the blood vessels in the dermis vasodilate ( vase -oh- DIE -late), becoming wider. This allows more hot blood to circulate from the deep core of the body, and flow more freely into the vessels of the skin. Much more heat is then lost by radiation, the movement of heat waves or rays from the hot blood in the skin out into the cooler air surrounding the body.

By both of these means combined (increased evaporation from sweat + increased heat loss by radiation from the blood), oral body temperature is eventually brought back down to its average, long-term level (about 98.6 degrees Fahrenheit in most human beings). And thermoregulation, or homeostasis of oral body temperature, is thereby achieved.

Skins and Skeletons “Ain’t We Just Peachy?”: The Skin as Our Integument The Dermis As Our Tough Main “skin”

Fig. 13.2 Thermoregulation: Keeping our body heat within range.

 

Practice problems for these concepts can be found at:  Skins And Skeletons Test

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