3.2: Main Functions for Homeostasis

Serving as a Barrier

The integumentary system must provide a barrier against several types of factors because unrestricted entry or exit of these factors can cause a deviation from homeostasis.

Microorganisms One of these factors consists of microorganisms (bacteria and viruses) that cause infections.

Chemicals A second factor is chemicals. Many chemicals, such as vitamins, are within the body because they are needed by the cells. They must not be allowed to dissipate into the external environment. By contrast, noxious and toxic substances in the external environment must not be allowed to come into contact with the body's delicate living cells.

Water Though also a chemical, water is considered a third factor because it is an especially important substance and is present in such large quantities. Its movement between the interior of the body and the external environment must be restricted. The cells of the body must have enough water to maintain their shape, size, and activities beneficial to healthy survival because it provides energy needed by the integumentary system to produce vitamin D. Still, only a small amount of light should be allowed to penetrate the body because energy from excess light damages several types of important molecules (e.g., proteins, DNA). The outcome is obvious to anyone who has had a sunburn.

Light Light is essential for healthy survival because it provides energy needed by the integumentary system to produce vitamin D. Still, only a small amount of light should be allowed to penetrate the body because the energy introduced by excess light damages several of the most important large molecules, including proteins, RNA and DNA. The outcome is obvious to anyone who has had a sunburn.

Trauma The fifth factor to which the integumentary system is a barrier is trauma. Direct contact of the cells with rough or sharp materials in the external environment immediately cuts the cells open. The result is the death of those cells and the portion of the body they constitute. Pressure or sharp blows can also injure or kill cells.

Providing Information

Gathering information about conditions in and around the body is essential for survival. It is the first step in negative feedback systems and positive feedback systems that help maintain homeostasis.

Since the integumentary system is between most cells of the body and the external environment, it can supply information about factors that might alter internal conditions of the body even before those factors have an opportunity to do so. For example, many abundant nerve cells in the integument continuously monitor the external environment and send messages to other parts of the nervous system. As a result, the person knows much about the area surrounding the body, including the location, size, shape, texture, movement, and temperature of objects and materials (e.g., clothes, furniture, water, air). Then the person can take steps to avoid or correct any threatening features, perhaps before harm is done. Information provided by nerve cells in the integumentary system can also provide pleasure that can improve the quality of life. Examples include enjoyment from physical touches (e.g., hugs, caresses) and temperatures (e.g., cool breeze, warm blanket). In later parts of this chapter, other types of cells are mentioned that monitor conditions to initiate negative feedback or helpful positive feedback activities contributing to homeostasis.

Temperature Regulation

The maintenance of a proper and relatively stable temperature within the body is essential not only for comfort and satisfactory performance but also for sustaining life. The body must be sufficiently warm that its chemical reactions proceed quickly enough. Cooling an individual's body can slow chemical reactions so much that the person will die. In contra too high, certain types of molecules (e.g., proteins) in and around the cells will be damaged or die. If it is extensive enough, this damage can result in the death of the individual.

Vitamin D Production

Vitamin D is necessary for healthy survival because it allows the intestines to absorb calcium from food. The calcium is then used in many vital ways.

Clearly, the integumentary system performs a wide variety of necessary jobs. To carry them out, it has many component structures and materials organized to operate efficiently and effectively. This chapter will examine the contributions of each of those components, paying particular attention to those known to change with the passage of time.

Where possible, changes occurring because of aging will be distinguished from those caused by environmental factors or disease. However, these distinctions cannot often be made. For one thing, the skin is subjected to many environmental influences over long periods, including sunlight and physical wear. Also, different parts of the body receive vastly different doses of these influences; perhaps the best example is differences in exposure to sunlight. Finally, there is tremendous disparity among the lifestyles of individuals. For example, the skin of a farmer or a fisher receives very different treatment from that of a person who works in an office.

Defense

The integumentary system provides defense when components assist actively in isolating, destroying or removing a harmful agent from the body (e.g., splinter, poison ivy sap, bacteria, viruses, cancer cells). Negative feedback (e.g., healing) and helpful positive feedback (e.g., inflammation, immune reactions) are used in defense activities. Defense prevents or limits damage from the harmful agent in the integumentary system and reduces the risk of damage in other body regions from agents that may spread (e.g., toxins, infection, cancer).