Sistema Tegumentario PDF

# SISTEMA TEGUMENTARIO ## 8 GENERALIDADES - The tegument is the largest organ of the human body, it is composed of skin and its appendages like sweat glands and sebaceous glands, hair and nails. - Skin (lat., *pellis, cutis* = skin, gr., *derma* = skin), constitutes a real cutaneous organ covering...

# SISTEMA TEGUMENTARIO ## 8 GENERALIDADES - The tegument is the largest organ of the human body, it is composed of skin and its appendages like sweat glands and sebaceous glands, hair and nails. - Skin (lat., *pellis, cutis* = skin, gr., *derma* = skin), constitutes a real cutaneous organ covering the whole human body and continues with the different natural orifices (digestive system mucous membranes in the lips and the anus, respiratory system in the nostrils, urogenital system in the urethra, etc.), separating the individual from the external environment and defending it from its aggressions, its total weight is approximately 17 Kg, and its surface area is from 1.80 to 2 m². - It provides special characteristics to each individual that allow their identification like fingerprints. ## 8.1 FUNCTIONS OF THE SKIN - It fulfills the following functions: - PROTECTION. It is an effective barrier against the action of physical, chemical and bacterial agents, it has antibacterial and antifungal properties because of its acidic pH, enzymes (lysozyme) and fatty acids of its secretions, it prevents dehydration and lesions, neutralizes solar radiation with the aid of its main pigment, melanin. - SENSORY. It has receptors for touch, pressure, heat, cold and pain that keep the body informed about the environment around it. - REGULATION OF TEMPERATURE. Thanks to the action of sweat glands and blood capillaries. - SUDORATION. Each square centimeter of skin also contains hundreds of sweat glands that are controlled by a heat regulation center located in the hypothalamus. These glands secrete sweat, which provides moisture that, when evaporated, cools the body surface and contributes to maintaining a normal body temperature. In this case, the skin acts as a secretory organ. - COLORATION. They provide a color to the skin, which varies depending on the amount of pigment: melanin, which is found in the melanocytes, the pigment is determined by inheritance and by exposure to sunlight, the skin may present spots (hyperpigmentation) known as freckles when they are small and isolated, chloasma when they are extensive and appear in the gestational stage and melasma due to prolonged sun exposure. There are also other types of melanodermias due to physical, chemical and biological causes. - DISPOSITION OF FANERAS. Continuous structures of the skin that include: hair, nails, sweat glands and sebaceous glands, also contribute to the skin functions mentioned. - ABSORPTION. There are substances that are absorbed by the skin, being a semipermeable barrier to water and external use medications. Ultraviolet radiation from the sun absorbed by the skin favors the synthesis of vitamin D. ## 8.2 HISTOLOGY OF THE SKIN - Under a microscope, three different well defined layers can be differentiated in the skin: epidermis, dermis and hypodermis or subcutaneous cellular tissue. ### EPIDERMIS - It is the most superficial layer, derived from the ectoderm. It is an avascular layer composed of stratified squamous keratinized epithelium and formed by four types of cells: keratinocytes, dendrite cells, melanocytes and Merkel and Langerhans cells. Keratinocytes are the ones that present intercellular bridges or desmosomes. It has between 0.07 and 0.12 mm of thickness. - The epidermis is made up of the following cell layers, from deep to superficial: - **STRATUM BASAL** or germinative, because from this layer by mitosis the cells that will make up the other layers originate. It contains cubical cells in constant division. It is in this stratum where melanocytes which contain melanin and Merkel cells are found. - **STRATUM SPINOSUM** or spongy. Above the basal layer, it is formed by eight to ten layers of polyhedral keratinocytes, closely linked by intercellular bridges called desmosomes, which represent numerous cytoplasmic protrusions that resemble spines (hence the name). It is the thickest layer of the epidermis. Langerhans cells are found in this stratum. - **STRATUM GRANULOSUM**. As they approach the epithelial surface, the squamous cells flatten. The thickness of this layer depends on the thickness of the skin, in thin areas it is formed by 2 to 3 rows and in thick areas it reaches up to 10 rows. The cells are in a state of apoptosis (process of degeneration), they present large granules stained dark in color and formed by a protein called keratohyaline. - **STRATUM LUCIDUM**. Thins layer, consists of three to five layers of transparent, flat, dead keratinocytes with a thickened plasma membrane, it is found in the skin of the palms of the hands and soles of the feet. It is rich in phospholipids bound to proteins. - **STRATUM CORNEUM**. It is formed by 25 to 30 layers of flat, dead, anucleated cells, mainly made up of a fibrous protein called keratin and eleidin. The most superficial layers experience continuous desquamation. The cells of this stratum are known as scales. - The whole desquamation process of the skin takes 20 to 30 days. ### DERMIS - Derived from the mesoderm and divided into two layers: papillary (superficial) and reticular (deep). It is composed of connective tissue, a network of collagen and elastic fibers, blood capillaries, nerves, fat lobules and the base of the hair follicles and sweat glands. The thickness of the dermis varies from 0.6 to 3 mm. The papilla contains either a network of blood vessels or a specialized nerve ending. ### HYPODERMIS - It is mainly composed of fatty tissue arranged in large lobules limited by septa. These elements, so arranged, confer on this layer protective properties against trauma and temperature variations, at the same time facilitating the sliding of the skin over the underlying planes. In this layer, the deep vascular network and spinal and sympathetic innervation are located. ## 8.3 FANERAS OR CUTANEOUS APPENDAGES ### SWEAT GLANDS - They have a coiled secretory tubule that is located in the dermis-hypodermis boundary and an excretory tubule that opens into the epidermis, independent of the hair follicle (eccrine), with the exception of those located in the armpits, pubis and areola of the nipple which open into the follicle (apocrine). ### SEBACEOUS GLANDS - They always open into a hair follicle, they are distributed throughout the skin surface except for the palms of the hands and soles of the feet. They are holocrine glands, their secretion is not only formed by the product of the cells but also by the cells themselves by decapitation. ### HAIR - Hair (lat. *pillus* = hair, *capilli* = hair of the head), thin filiform epidermal formation, typical of mammals, that forms the characteristic hair coat of these animals. It is derived from an invagination of the epidermis into the dermis. Each hair follicle has a sebaceous gland located in its upper third and the whole is known as pilosebaceous unit. ### HAIR FOLLICLE - It is composed of three segments: - **INFUNDIBULUM PILOSUM**: area between the hair follicle pore and the opening of the sebaceous gland. - **ISTHMUS**: area between the sebaceous duct and the insertion of the arrector pili muscle. - **BULBOPILOSUM**: lower part of the hair follicle, in the center of which there is the papilla, the area where the hair is nourished by the blood vessels present there. ### HAIR GROWTH - Hair growth has three phases: - **ANAGEN OR ACTIVE GROWTH**: It lasts for 3 to 7 years, continuously. In the scalp, approximately 80 to 85% of the hairs are in this phase and their growth capacity is so great that they can reach up to 0.35 mm per day. - **CATAGEN OR TRANSITION**: Lasts 2 weeks. During this stage, involution and fibrosis of the hair bulb occur, resulting in the retraction of the papilla. - **TELOGEN OR SHEDDING**: Lasts 3 to 4 months. This is the resting stage , where the hair remains anchored in its original site without growing, and eventually falls out. Once the hair falls out, the original morphology is restored and the cycle begins again. - Hair experiences growth and shedding as previously mentioned, approximately 50 to 100 hairs fall out every day and are replaced when the growth cycle restarts. Over a lifetime, each follicle is capable of reproducing about 20 cycles. - In humans, the growth of hair begins: - in the embryo, already in the sixth month the fetus is covered with very fine hair called **lanugo**. - during the first months of life, lanugo falls out and is replaced by coarse hair on the head (hair) and eyebrows, and fine and vellus hair on the rest of the body. - During puberty, coarse hair begins to grow in the armpits and pubis, and in men, on the upper lip and chin, giving rise to the beard. The speed of hair growth varies with the person's age and length. When it is short, it grows about 2 cm per month, but the growth rate is halved when it is long. The most hair growth occurs in women between the ages of 16 and 24. - Other characteristics related to hair growth include: - NUMBER: 100,000 to 150,000 hairs. - DENSITY: 300 to 400 per square centimeter. - DIAMETER: 40 to 100 microns. - LENGTH: 50 to 100 cm maximum. - GROWTH RATE: 1 cm per month. - HAIR SHEDDING: Between 50 and 100 per day. - SHAPE. Hair shape is one of the most important and precise hereditary characteristics. - Almost black hair of Papuans, Melanesians and Africans grows from a curved follicle that continues in a spiral shape with a flat cross-section. - Chinese, Japanese and American Indians have straight, thick, long and almost always black hair. It grows from a straight follicle with a circular cross-section, and has a clearly distinguishable medulla. - European, Indian and Semitic hair is wavy. It grows from a straight follicle but tends to curl; the cross-section is oval, and the color varies greatly from person to person, from light blonde to black. ### HAIR FUNCTION: - **THERMAL INSULATION**. The circulation of air is slowed down in hair, and in areas where there is abundant hair, the air is retained to act as an insulator. - **HEAT ELIMINATION**. Hair increases the sweat evaporation surface. - **FRICTION REDUCTION**. It protects the skin from friction between the skin, for example, in the armpit and groin area. - **SEXUAL CHARACTERISTIC**. Vellus hair identifies the sex. ### HAIR ALTERATIONS - Dysfunctions in the structure of the hair or hair follicle give rise to abnormal hair growth or premature or abnormal shedding: - The early appearance of gray hair is associated with anxiety, intense emotions, nutritional deficiencies and hereditary causes. - **Alopecia** or baldness is mainly due to hereditary causes. Certain forms of alopecia, however, may be due to other causes: early alopecia, where the hair of a young person falls out without turning gray first; alopecia areata, where the hair falls out irregularly. This is thought to be due to inflammation, nervous disorders or local infections, especially in states of psychological stress. - Excessive hair loss, a normal phenomenon, can reach abnormal proportions after fevers exceeding 39.4°C, during diseases that cause a weakening of the organism, or after surgery or childbirth. ## NAILS - Nails (lat. *unguis* = nail, claw, gr. *onyx* = nail), laminae or protective coverings, flat, horny and translucent, that appear on the upper area of the final segment of the fingers and toes of humans. Nails are made up of dead cells containing a fibrous protein, keratin. - The nail has four edges: lateral, distal and proximal, near the latter, there is a whitish semi-circular area called the lunula. This proximal edge is in turn covered by a skin fold called the eponychium. - The nail matrix is located in the lunula and is the region from which the nail grows, as it is composed of basal polyhedral cells, just like in the epidermis, also called germinative cells. These cells contain fibrous and amorphous protein masses known as keratin. ## MAMMARY GLANDS OR BREASTS - The mammary glands are two symmetrical formations and are considered to be modified apocrine sweat glands. - **LOCATION**. Located in the anterior wall of the thorax, between the sternum and the vertical line tangent to the anteromedial or anterointernal border of the axilla. From top to bottom, it extends from the 3rd to the 7th rib. - **SHAPE AND SIZE** . They are almost spherical in shape in young people. After pregnancy they hang and are separated from the chest wall (below) by the submammary groove. - **EXTERNAL CONFIGURATION**. A conical eminence is located in the central part of its anterior surface, called the nipple or mammary papilla. The nipple is usually 1 cm high by 1 cm wide. Its free end is covered with grooves and occupied by openings (lactiferous ducts or openings), which correspond to the openings of the lactiferous ducts. The nipple is surrounded by a halo of hyperpigmented skin (4 to 5 cm in diameter) called the areola. This presents small eminences called Montgomery's tubercles or areolar glands, which are made up of sebaceous glands. - **STRUCTURE OF THE BREAST.** It is composed of: - **CUTANEOUS COVERING**. Thin and mobile skin. The areola and nipple have some smooth muscle fibers that form the areolar muscle (consisting of circular and radiating fibers). - **CIRCULAR FIBERS**. They are attached to the skin at the level of the areola and extend to the base of the nipple. - **RADIAL FIBERS**. Perpendicular to the preceding ones. They extend from the dermis of the areola to the dermis of the nipple - **MAMMARY GLAND**. The gland is covered all the way around by a fibrous membrane called the fibrous capsule. The superficial surface of the gland is smooth, almost flat, on its posterior face. The gland is located in the thickness of the adipose tissue, which has an anterior layer and a posterior layer. - **ANTERIOR OR PREGLANDULAR ADIPOSE LAYER**. It is not located in the areola region. It presents small cells called adipose pits. In this layer, the arterial plexus and a superficial venous network (developed during pregnancy and lactation) are located. - **POSTERIOR OR RETROGLANDULAR ADIPOSE LAYER**. It does not have adipose pits and is a thin layer. It also contains a network of arteries and numerous veins. Behind this layer is the cellular layer, which is located between the superficial fascia and the aponeurosis covering the pectoralis major and serratus anterior muscles. - **CONSTITUTION**. The mammary gland is composed of several independent glands (approximately 10 to 20). Each one is composed of a lobe that is divided into lobules and acini. - **LACTIFEROUS OR GALACTOPHORE DUCTS**. Each lobe has an excretory duct or galactophorous or lactiferous duct that goes towards the nipple. Before entering the nipple, it presents a dilatation of 1 to 1.5 mm in length by half a millimeter in width called a lactiferous sinus or ampulla, or lactiferous sac. Beyond that, it opens into lactiferous pores. - **ARTERIES**. The internal part of the breast is irrigated by the perforating branches of the internal mammary or thoracic artery. The main perforating artery or internal main artery or medial principal artery or medial principal branch crosses the 2nd intercostal space. The external and inferior parts are irrigated by branches of the external mammary or lateral thoracic artery, the inferior scapular or subscapular artery, the thoracoacromial or acromiothoracic artery and the superior thoracic artery (all branches of the axillary artery). - **VEINS**. The breasts have a venous network, which becomes more prominent during pregnancy and lactation. Around the areola, there is the Haller's or areolar venous circle. The deep veins end: in the external mammary or lateral thoracic veins, in the internal mammary or thoracic veins and in the intercostal veins. - **NERVES**. The cutaneous innervation comes from the supraclavicular branch (from the cervical plexus) and the 2nd, 3rd, 4th, 5th and 6th intercostal nerves (anterior and lateral perforating branches).