Skin Functions PDF

SKIN 1 The skin, the largest organ in the body by weight, and its accessory structures (hair, nails, sensory receptors, and glands) make up the integumentary (in-teg-u-men′tar-e) system. The skin forms a barrier between ourselves and the outside. It is a strong and flexible covering for our...

SKIN 1 The skin, the largest organ in the body by weight, and its accessory structures (hair, nails, sensory receptors, and glands) make up the integumentary (in-teg-u-men′tar-e) system. The skin forms a barrier between ourselves and the outside. It is a strong and flexible covering for our bodies. The skin includes two distinct layers. The outer layer, called the epidermis (ep″ĭ-der′mis), is composed of stratified squamous epithelium. The thickness of the epidermis varies among different body regions. The epidermis lacks blood vessels because it is composed entirely of stratified squamous epithelium. However, the deepest layer of epidermal cells, called the stratum basale (stra′tum ba′sal), or stratum germinativum, is close to the dermis and is nourished by dermal blood vessels As the cells (basal cells) of this layer divide and grow, the older epidermal cells (keratinocytes) are pushed away from the dermis toward the skin surface. The farther the cells move away from the dermis toward the skin surface, the poorer their nutrient supply becomes, and in time they die. 2 The keratinocytes harden in a process called keratinization (ker″ah-tin″ĭ-za′shun). The cytoplasm fills with strands of tough, fibrous, waterproof keratin proteins The inner layer, or dermis (der′mis), is thicker than the epidermis. It is composed of connective tissue consisting of collagen and elastic fibers, along with smooth muscle tissue, nervous tissue, and blood. A basement membrane anchors the epidermis to the dermis and separates these two skin layers.Beneath the dermis are masses of areolar tissue and adipose tissue that bind the skin to the underlying organs, forming the subcutaneous (sub″ku-ta′ne-us) layer (hypodermis). The adipose tissue of the subcutaneous layer insulates, helping to conserve body heat. The subcutaneous layer also contains the major blood vessels that supply the skin and underlying adipose tissue 3 Skin Functions 1)The skin has many functions and is vital in maintaining homeostasis. 2)As a protective covering, the skin prevents many harmful substances, as well as microorganisms, from entering the body. 3)Skin also slows water loss by diffusion from deeper tissues, skin houses sensory receptors, 4)Skin excretes small amounts of wastes. 5) Specialized cells in the epidermis called melanocytes produce melanin (mel′ah-nin), a pigment that provides skin color, in organelles called melanosomes. The more melanin, the darker the skin. 4 Melanin also absorbs ultraviolet radiation in sunlight. Without the protection of melanin, ultraviolet radiation could cause mutations in the DNA of skin cells and other damaging effects 6) Skin helps in diagnosis of different health conditions. Environmental and physiological factors also influence skin color, in addition to the effects of genes. When blood is oxygen rich, the blood pigment hemoglobin is bright red, making the skin of light-complexioned people appear pinkish. When the blood oxygen concentration is low, hemoglobin is dark red, and the skin appears bluish—a condition called cyanosis. Diet and disease affect skin color. For example, a diet high in yellow vegetables may turn skin orange-yellow, because these foods are rich in a pigment called carotene. This pigment accumulates in the stratum corneum and adipose tissue of the dermis and subcutaneous layers. Skin color can also be affected by disease. A pathological cause of a yellowish skin tone is jaundice, which may indicate liver malfunction. 5 7)The skin plays a role in the production of vitamin D, which is necessary for normal bone and tooth development. Some skin cells produce vitamin D precursor (dehydrocholesterol), which when exposed to sunlight changes to an inactive form of vitamin D (cholecalciferol). In the liver and kidneys the inactive form is modified and becomes active vitamin D (calcitriol) 8)The skin also helps regulate body temperature. Regulation of body temperature is vitally important because even slight shifts can disrupt the rates of metabolic reactions. a. When body temperature rises above the normal set point, dermal blood vessels dilate and sweat glands secrete sweat. b. When body temperature drops below the normal set point, dermal blood vessels constrict and sweat glands become inactive. c. If body temperature continues to drop, skeletal muscles rhythmically contract. 6