What determines whether a substance will penetrate the skin is the molecular weight of the substance-the skin will keep out molecules of a larger molecular weight. Many toxic substances can also penetrate the skin. Thus topical skin preparations, vitamin-containing oils, Epsom salts baths and other traditional topical skin treatments work by providing nutrients via the skin rather than through the digestive tract. Substances placed on the skin can penetrate into the underlying tissue and eventually reach the blood stream. While the skin provides our bodies with a barrier, it is also absorbent. These include vasoconstriction to decrease the flow of heat to the skin cessation of sweating shivering to increase heat production in the muscles and secretion of norepinephrine, epinephrine and thyroxine to increase heat production. If the skin temperature drops below 98.6 degrees, a variety of responses are initiated to conserve the heat in the body and to increase heat production. The heat production of the body under these conditions remains almost constant as the skin temperature rises. Under control of these mechanisms, sweating begins almost precisely at a skin temperature of 98.6 degrees F and increases rapidly as the skin temperature rises above this value. The hypothalamus contains not only the control mechanisms, but also the key temperature sensors. The skin is the main organ for regulating human body temperature somewhere between 98 and 100 degrees Fahrenheit when the ambient temperature varies between approximately 68 and 130 degrees.īody temperature is fundamentally regulated by neural feedback mechanisms, which operate primarily through the hypothalamus. Its physiological functions include insulation, the storage of energy and anchoring of the skin. Sweat glands and hair follicles (roots) with their associated sebaceous glands originate in the dermis.īelow the dermis is a layer of connective and fatty tissue, sometimes referred to as the subdermis. A corrugated line of blood vessels called papillae separates the dermis from the epidermis. The dermal layer provides a site for the endings of blood vessels and nerves. These layers serve to give elasticity to the skin, allowing stretching and conferring flexibility, while also resisting distortions, wrinkling and sagging. The dermis is the middle layer of skin, composed of loose connective tissues such as collagen with elastin arranged in a diffusely bundled and woven pattern. Hair and pores allowing the release of sweat and oil pass through the epidermis from the dermis. Interspersed among the horn cells are melanocytes (pigment-containing cells), Merkel cells (associated with sensory nerve endings) and Langerhans cells (which provide immune protection). The space between the keratinocytes contains fat lamellae, that is, fat in a thin, plate-like structure. During this journey, the shape of the cells changes from rounded to flattened. The horn cells are formed at the base of the epidermis and gradually migrate to the surface, where they are sloughed off as skin dander. Most of the cells in the epidermis are keratinocytes or horn cells, so called because they produce keratin, a fibrous protein that provides waterproofing.

It is actually translucent, containing no blood vessels. The epidermis or top layer of skin provides water proof protection for the body. The skin is composed of three distinct layers, the epidermis, the dermis and a lower layer of fatty tissue, usually called the subdermis (also called the subcutis or hypodermis). As a result, humans need to use their brains to ensure adequate covering for the body and appropriate preparation of their food. The “disk space” dedicated to a complicated digestive tract and luxuriant or protective skin coverings in animals is used in humans for the development of the nervous system. Similarly, humans have a relatively simple digestive tract compared to animals. Human skin is different from that of the animals in that it lacks a covering by fur, feathers, horny plates, leathery coatings, spines, quills, horns, manes or tufts of hair-humans are naked. Thus the skin serves both neuro-sensory and metabolic functions. Our skin is also the attachment site for sensory receptors to detect pain, sensation, pressure and temperature. In humans, the skin additionally provides vitamin D synthesis. Our skin separates and informs us with regard to our surroundings, serving to waterproof, cushion and protect the deeper tissues, excrete wastes and regulate temperature. The skin is the largest organ system in the human body, accounting for 16 percent of total body weight and covering sixteen to twenty-two square feet of surface area.

Weaponization of Coronavirus by David Martin.

The skin deep