The construction and function of the skin
How skin function?
Human body is covered by skin. Adult has skin 1,5 to 2 square meters and skin thickness varies from 0,1 to 4 mm. The skin is thin on eyelids and on external auditory canal, but thick on palms and on feet. Human skin with subcutaneous fat accounts for 16 to 17,7% of total body weight. On human scalp there is 150 000 hairs and on the whole body there is 5n million of follicles. Daily hair grow about 0,1 to 0,5 mm. With sweat glands is excreted 300 to 800 sweat, sometimes 1500 ml and more.
- subcutaneous fat
The epidermis is composed of four layers : stratum corneum, stratum granulosum, stratum spinosum, stratum basalt. The epidermis is renew in about 30 days. The layer of stratum corneum is formed by containing nuclei of keratin cells. This layer of skin is thicker on sloes of the feet and palms of the hands, is thinner on eyebrows and genitals. In the bottom layer distinguished between the cylindrical cells and dendritic cells. Cylindrical cells multiply and produce new epidermis. Dendritic cells produce skin pigment. There are no blood vessels in the epidermis but there range endings of nerve.
The dermis is composed of two layers. Below epidermis is stratum papillary and then stratum reticulare. In dermis there is located network of blood vessels-capillaries and small arterioles and venous as draining system. Epidermis pass threw lymph, here are located hair follicles, sweat glands, sebaceous glands. In the palms and soles there are not sebaceous glands. Sweat glands are divided into apocrine and eccrine. Eccrine sweat glands are located in the skin, but not on lips, genital head, and on small labia. There are a lot of eccrine sweat glands on the palms, soles of the feet, forehead, chest, abdomen and shoulders.
Apocrine sweat glands are located under arm, around the anus, on the nipples, female external genitals, groin and around the navel. Apocrine sweat glands are located deep in the adipose and begin to function until sexual maturity period.
The skin has very important function to perform because it separates external environment and the human body needs to ensure body defenses. The skin defenses tissues and organs from mechanical factors (hits, friction, oppression) thanks to the collagenous dermis and adipose tissue and elastic fibers.
Stratum carenum is poor conductor of heat, which protects the deeper layers of drying. Melanin pigment absorbs ultraviolet light, protecting the body from radiation damage. The surface of the skin has a PH of 5.0 to 6.0, which helps to neutralize chemical substances and destroy germs. The same effect in on the sebum and sweat glands, therefore excessive washing weakens the skins protective functions.
Skin has a sense of human body, which is known through the pain sensation, touch, oppression, vibration, heat and cold. Furthermore, skin performs secretory and excretory function. Human sweat chemical composition varies depending on the person’s general condition and the excretion of sweat form. For an example in case of illness, if the perturbation of metabolism, the composition of sweat appear there usually not occurring substances (in case of diabetes-sugar). Sweating helps the body to get rid of arsenic, iodine, bromine, quinine. The sweat and the fat on the skin surface miscible and form so called wat-fat emulsion, a thin layer, which helps maintain the normal physiology of the skin surface. Sweat and sebaceous glands are regulated by the nervous system, sex hormones, adrenal cortex and thymus. Person also breathes threw the skin. Compared to lungs it is small, 1/180 consumes oxygen and 1/90 secretions of carbon dioxide. Skin excretes daily 800 grams of water vapor, which is 2 to 3 times greater than water vapor excreted through the lungs.
The skin is not able to absorb water, but sucks in fat-soluble substances. Significant is the part of the skin in the metabolism. For an example in the skin formats keratin, melanin and d-vitamin. Skin takes and active part in the water, minerals, fat, protein, carbohydrates, hormones, enzymes, vitamins and elements of metabolism. The skin of our body has a function equivalent to all the other organs of the human body! Let’s cherish skin the body’s state of the mirror for better or for worse.