There are approxiamtly five differing functions
achieved by the integumentary system: Protection, Temperature
regulation, Vitamin D production, Sensation and Excretion.
Protection is achieved in numerous ways:
These are some good examples of the great protective nature of skin. Of couse the sensory nature of skin is likewise protective in nature.
The bodies chemistry operates a an optimum temperature which, if altered, can speed or slow the numerous reactions which make us function. Enzymes, which regulate the rates of reactions, are particularly sensitive to temperature changes. Things such as fever, exercise or increased environmental temperature all increase body temperature from it's norm of 98.6 degrees F (and approximatly 100 degrees internally). Homeostasis, the maintanence of the optimum conditions, requires that heat be lost, returniong temperatures closer to the norm.
Heat is lost to the body through the dilation of arterioles that run through the dermis. This increases the flow of blood through the skin, where heat is lost through radiation (heat disapating into the air), convection (through air flow over the skin), conduction (transfer by contact with other objects), or by evaporation of heat-warmed sweat.
Should overall body temperature decline, the response is to constrict the vessels within the skin, reducing blood flow and thus reducing the amount of heat carried to, and lost by the skin. This can be a somewhat dangerous response because it reduces the temperature of the tissues in the skin, thus putting IT'S survival at risk, particularly in extreme cold. Frostbite is one such example.
This action of increased/decreased blood flow is the responsibility of a specialized region in the brain, the Hypothalamus. This region, in conjunction with temperature receptors in the skin and the various organs of the body, monitor body temperature continuously, and thus act appropriately. The hypothalamus controls the dilation/constriction of dermal arterioles and the incresed/decreased production of sweat from the eecrine glands (respectively). It should not be suprising that increased pulse rates occur when overheated, as this allows blood to flow to the skin more rapidly, and that the pulse slows when cool, reducing the speed blood flows to the skin. Likewise, respiratory rates also increase/decrease in the same manner as our breath also is a means of heat loss. Both these are also regulated by the brain.
No conscious effort is made on your part, although
if we get overheated we can seek cool areas or drink cool liquids.
Our conscious brain can upset this delicate balance. Many people
will drink alcohol when cold under the premise that it's warming.
Contrary to this myth, alcohol is a vasodilator, causing blood
flow in the skin to increase, thus reducing body temperature.
This may put a person at great risk of suffering from Hypothermia.
Vitamin D Production
Ultraviolet light from the sun stimulates the skin to produce a precursor molecule that is further altered by the kidney (especially) and liver until it is Vitamin D. This compound should rightfully be considered a hormone since it's actions are upon the intestine so that they may allow for the uptake of dietary calcium and phosphates. These two molecules are necessary for the proper development of bone. Sufficient exposure to the sun provides most people with adequate levels of Vitamin D, but many people shun the sun, live in regions where solar radiation is diminished (at high latitudes), or they wear clothing which hides the skin from these 'helpful' rays. Thus it is important for one to get dietary supplements to insure a proper level of Vitamin D in the blood. Decreased Vitamin D levels, followed by predictable calcium deficiency can easily be seen in young children who suffer from Rickets, a disease of which the newly formed bone matrix fails to calicify. This once was problematic, but today is uncommon, particularly due to the invent of Vitamin D enriched milk!
This complex series of actions is regulated
by the Parathyroid gland which, when calcium levels in
the blood diminish, produces a hormone called Parathormone.
This hormone stimulated the kidney to alter the precursor molecule
produced by the skin, increasing Vitamin D levels in the blood
(Low Ca means low Vit. D, leading to increased parathormone production.
Hi Ca means Hi Vit. D, leading to reduced parathormone production).
The skin has many nerve receptors within the epidermis and the dermis which are sensitive to pain, temperature and pressure. Hair follicles have sensory receptors around them so movements of the hair itself is detected by movements at the base of the follicle. These sensory receptors warn your body of changes to the external environment. These receptors communicate with the appropriate region of the brain suach that the body can then respond and prevent injury or maintain a stable internal environment in response to the changing external one. Many receptors are simply branched nerve endings within the epidermis. Others have elaborate structure.
Touch receptors are found near the papillae of the dermis and are sensitive to light touch and pressure, such as an insect crawling on the skin. These receptors, such as Merkel's disks and Meissner's corpuscles are formed by modified epithelial cells or coiled nerve endings. These receptors are common on the palm, soles, and lips (Merkel's) and the areas of non-hairy skin: fingertips, lips, nipples, eyelids, and genitals (Meissner's). The Root Hair Plexus surrounds the base of the hair follicle and is composed of nerve endings wrapped around such that movements of the hair can be sensed.
are buried deeper within the dermis and require a greater amount
of pressure to be applied for them to become active. The grasping
of a hand during a hand shake is one example. Somewhere between
pain and faint is the realm of the Pacinian receptor. Pain
receptors are simple nerve endings in the deep epidermis and
dermis and alarm the body to more serious actions such as cutting,
tearing or burning. Itches and tickles fall in this category
as slight pain. Free nerve ends are also sensitive to hot and
cold, with far more cold receptors being present.
The removal of wastes from the body is termed excretion, and although the skin has a role in this process, be assured it is a minor one. A small percentage of your nitrogenous waste is lost in this manner. Along with salts, urea, ammonia, and uric acid is removed from the body with the water from merocrine glands. These three nitrogen-based compounds are toxic, and thus the need for elimination. It is the combination of these plus salts which help provide an intollerable environment for bacteria on the skin.