Salutations Monoliths of the CS art, We will begin here with the composition of the skin, or, epithelial tissues. Epithelial tissues cover all body surfaces, inside and outside. Nothing may enter the body without passing through the epithelial tissue. The digestive system is in essence a hollow tube passing through the body, and materials in the digestive system, from mouth to anus, are not in the body until they pass through the epithelial tissue. Epithelial tissues make up the outer layer of the skin, form the inner lining of body cavities, cover the organs inside these cavities, and are the major tissue of glands. It always has a free surface---one that is exposed to the outside or to an open space internally. The underside of the tissue is anchored to connective tissue by a thin nonliving layer called the basement membrane. Epithelial tissues lack blood vessels, however, epithelial cells are nourished by substances that diffuse from vessels in the underlying tissue, the lymph. Epithelial cells are tightly packed together and there is little intercellular material between them. These cells often form a protective barrier, as the skin, other epithelial functions are secretion, absorption, excretion, and reproduction. Epithelial cells are classified according to their shapes, arrangements and functions. For example there are single layers of cells called "simple", while those with many layers are called "stratified". Thin flattened cells are "squamous", cube like are called "cuboidal", and those that are elongated are referred to as "columnar". Simple squamous cells are found in the air sacs of the lungs where gas exchange takes place. Simple cuboidal cells are found in various glands, such as the salivary glands, thyroid gland, pancreas, liver, and some sweat glands. Simple columnar cells are found in sweat glands, some secrete watery fluids, and some secrete protective fluids called mucus (an oily substance). There are flasked shaped cells scattered in among the columnar cells called goblet cells which also assist with sweat production. Glandular epithelial cells are found within the columnar and cubodial epithelium and one or more cells constitute a gland. Those glands that secrete their products into a duct are called "exocrine glands", and those that secrete into tissue fluids or blood are called "endocrine glands". Although a gland may be only a single cell (unicellular gland), as in the case of goblet cells, most glands are composed of many cells (multicellular glands). For example, exocrine glands that consist of simple epithelial lined tubes opening to the surface are called "tubular" glands, while those that are composed of one or more sac like dilations connected to the surface by narrowed secretory ducts are called "alveolar" glands. Glandular secretions are classified according to whether they are a cellular product or portion of the glandular cells. Glands that secrete watery fluids (sweat) that diffuse through cell membranes are called "merocrine" glands Those that release entire cells filled with secretory products are "holocrine" glands, while those of the intermediate type that lose small portions of their glandular cell bodies during secretion are called "apocrine" glands. Now let us jump into the integumentary system, that group of tissues referred to as the skin, hair, sebaceous glands and sweat glands. The skin has three layers, the epidermis, dermis and subcutaneous layer. Hair develops in hair follicles which have "arrector pili muscle", this muscle erects the hair when you are cold or frightened or emotionally stimulated, i.e., goose bumps. Sebaceous glands are holocrine glands that are usually associated with hair follicles. They normally produce an oily secretion called sebum, which is emptied into the hair follicle and helps to keep the hairs and skin soft, pliable, and waterproof. Under the action of certain hormones the sebaceous glands may produce a less oily and more watery product. Sweat glands occur in nearly all regions of the skin, but are most numerous in the palms and soles. Each gland consists of a tiny tube that originates as a ball shaped coil in the dermis or subcutaneous layer. The ball shaped coil is in reality a long tube of tubular cells wound up in the shape of a ball. The open end exits onto the surface of the skin. The tubular cells are sweat-secreting epithelial cells. The opening at the surface is called a pore. Some sweat glands, the apocrine glands, respond to emotional stress via the action of hormones. They are responsible for the skin's becoming moist when a person is upset or suffering from stage fright. These glands are numerous in the armpits and groin and are usually associated with hair follicles. They also become active when a person is sexually stimulated. Other sweat glands, the eccrine glands, respond primarily to elevated body temperatures. These glands are common on the forehead, neck, and back, where they produce profuse sweating on hot days and during physical exercise. The fluid secreted by sweat glands is mostly water, although it contains small quantities of salts and certain wastes, such as urea and uric acid. In this way , the secretion of sweat is, to a limited degree, an excretory function also. The body regulates its temperature by radiating heat or by evaporation of water from its surface. When the body temperature is rising above normal, the nervous system also stimulates sweat glands to become active and release fluid on to the surface of the skin. As this fluid evaporates, it carries heat away from the surface. The nervous system also signals blood vessels in the dermis to dilate, bring more hot blood close to the surface, where it may be cooled by the evaporating water. In the case of extreme cold the nervous system contracts the blood vessels and stops the action of the sweat glands, shutting them off. Next we will examine the role and actions of hormones in the production of sweat.
---to be continued--- Bless you, Bob Lee -- oozing on the muggy shore of the gulf coast [email protected] -- The silver-list is a moderated forum for discussion of colloidal silver. To join or quit silver-list or silver-digest send an e-mail message to: [email protected] -or- [email protected] with the word subscribe or unsubscribe in the SUBJECT line. To post, address your message to: [email protected] Silver-list archive: http://escribe.com/health/thesilverlist/index.html List maintainer: Mike Devour <[email protected]>
