Onesies are usually the article of clothing directly on the baby’s skin. So what exactly is skin, and what roles does it play for a human being?
What is the skin? The skin is the outer covering of the human body. It is considered an organ system, called the integumentary system. This system is very complex and involves many different layers. There is the epidermis, dermis, hypodermis, and underlying tissues. This is a rough diagram which encompasses the entire skin structure:
The skin covers the entire body and has a surface area of 1.2-2.2 square meters. It weighs 4-5kg and accounts for about 7% of the average adult’s body weight. It is given very little respect, but it plays essential roles in the human body, without which we could not survive (Marieb, Elaine N. and Hoehn, Katja, Human Anatomy and Physiology, 8th ed., San Francisco, Pearson Education Inc., 2010. Print).
What roles does the skin play? There are numerous functions of the skin system. I will outline the major ones:
Protection– the protective aspect of the integumentary system consists of three major types of barriers:
- Chemical Barriers- this barrier includes skin secretions and melanin. There are numerous species of bacteria on our skin. However, due to the low pH (a measure of the acidity of a substance, pH basically accounts for how many hydrogen ions are present in a substance. To fully understand pH, see any chemistry textbook) of the skin, meaning it is fairly acidic, these bacteria are unable to multiply. Sweat glands in the skin release dermicidin, which outright kills many bacteria. Skins cells secrete natural antibiotics called defensins that actually punch holes in the bacteria. Melanin, which gives the skin its pigment, protects the skin from UV light damage.
- Physical/Mechanical Barriers- The upper layer of skin, which is what we actually see, is in reality a layer of dead cells, called the keratin layer. The keratin layer is very tough. The continuity of the epidermal layer goes together with the acid mantle (the pH barrier described above) and other chemicals in skin secretion to prevent bacteria from coming into the skin. It should be noted that certain substances do penetrate the skin in limited amounts. One category is salts of heavy metals, such as lead or mercury. Another is organic solvents such as acetone. These two categories are devastating to the body and can be lethal. Absorption of lead into the body can result in anemia and neurological defects. Organic solvents which pass into the blood can cause the kidneys to shut down, as well as brain damage.
- Biological Barriers- There are many different types of cells in the skin which are active in the immune system. Epidermal dendritic cells, which are spiky looking cells, are active members of the immune system, because for an immune response to be activated, the foreign substance must be presented to lymphocytes, or specialized white blood cells. Dendritic cells, because of their numerous processes, are able to do this for the skin. Macrophages in the dermis dispose of many bacteria and viruses which penetrated the skin. Incredibly, DNA itself plays an important role, because electrons in the DNA molecules absorb UV radiation and transfer it to the nucleus of the atom, which heat up and vibrate, and the potentially destructive radiation is converted into harmless heat
Body Temperature Regulation– This role is essential to body homeostasis. Chemical reactions in the body release heat, which needs to be disposed of. As long as the external temperature is lower than body temperature, the skin loses heat to the air and to cooler objects in its environment. On a hot day or in times of intense physical exercise when body temperature rises, the nervous system stimulates the blood vessels in the dermal layer (see diagram above) to dilate and the sweat glands to secrete vigorously. Evaporation of sweat from the skin dissipates body heat and efficiently cools the body, preventing overheating. Normally, sweat is not noticeable, even though the body secretes about 500mL per day. But on a hot day, sweat can account for a loss of up to 12L of body water per day. When the weather is cold, dermal blood vessels constrict, which allows the warm blood to bypass the skin temporarily and allows skin temperature to drop to that of the external environment.
VERY IMPORTANT: According to doctor’s recommendations, an infant within the first month who has a body temperature of over 100.4 must be taken to the ER immediately to get a full workup. However, the method of taking the temperature is extremely important. The best place to take a person’s temperature is rectally. If taken in other places, it could be that the actual body temperature is higher. This is very, very important.
Cutaneous Sensation– the skin is how we feel. The sensory receptors are actually part of the nervous system. There are different types of receptors. Pacinian corpuscles in the deep dermis or the hypodermis alert us to bumps or contacts involving deep pressure. Meissner’s corpuscles in the dermal papillae and tactile disks allow us to become aware of the feel of our clothing against our skin. Hair follicle receptors relay information on wind blowing on our hair. Free nerve endings spread throughout the skin sense painful stimuli.
Metabolic Functions– Our skin is a chemical factory. This factory is fueled in part by the sun. When sunlight hits the skin, modified cholesterol molecules circulating in the blood vessels are converted to a vitamin D precursor. These molecules are transported in the blood to eventually be converted to vitamin D. Vitamin D is ESSENTIAL!! This can be seen from the following slide:
IMPORTANT: It is some doctor’s recommendation that everyone take vitamin D supplements, especially in the winter. In the winter there is a severe lack of sunlight-generated vitamin D, so supplements are necessary. Even infants should take a drop. You can get vitamin D drops (click on this link Vitamin D Drops) which contain the appropriate 400IU in each drop, so one drop per day. Speak to your pediatrician for more specifics.
Besides for vitamin D, the epidermis plays other functions. It makes chemical conversions which supplement those of the liver. For example, enzymes in the keratin layer can disarm may cancer-causing chemicals that penetrate the skin. These enzymes can also activate some steroid hormones, like transforming cortisone applied to irritated skin into hydrocortisone, which is a potent anti-inflammatory drug.
Blood Reservoir– The vascular (blood) supply of the dermis is very extensive and can hold large volumes of blood (about 5% of total blood volume). When certain organs need a greater blood supply, such as hard-working muscles, the nervous system constricts the dermal blood vessels, which pushes more blood into the general body circulation, making it available to other organs. (This concept of organs needing more blood at certain times is fascinating, and maybe one time I will explore that topic)
Excretion– Limited amounts of nitrogen-containing wastes, such as urea, uric acid, and ammonia are secreted in sweat, but most of these wastes are excreted in urine. Profuse sweating is an important mechanism for salt and water loss.
All information in this section are via this source: Marieb, Elaine N. and Hoehn, Katja, Human Anatomy and Physiology, 8th ed., San Francisco, Pearson Education Inc., 2010. Print
So next time you put a onesie, or anything on your child’s skin, look at what you are doing in a different light; you are placing protection on an incredible organ system!!