Integumentary Systems PDF

ANATOMY ANA 217 Integumentary Systems Auza, M I (BSc, MSc) Department of Human Anatomy Faculty of Basic Medical Sciences Bingham University, Karu  Integumentary Systems The integumentary system consists of the; Skin Accessory structures (hair and sweat...

ANATOMY ANA 217 Integumentary Systems Auza, M I (BSc, MSc) Department of Human Anatomy Faculty of Basic Medical Sciences Bingham University, Karu  Integumentary Systems The integumentary system consists of the; Skin Accessory structures (hair and sweat glands) Subcutaneous tissue below the skin. The skin is made of several different tissue types and is considered an organ. The skin covers the surface of the body The skin separates the internal environment of the body from the external environment and prevents the entry of many harmful substances. The subcutaneous tissue directly underneath the skin connects the skin to the muscles and has other functions as well.  The Skin and Its Layers The skin, the body's largest organ The skin consists of two major layers they are: Epidermis: an outer superficial cellular layer Dermis: a deep inner connective tissue layer Each of these layers is made of different tissues and has very different functions.  Epidermis The epidermis is a keratinized epithelium, made of stratified squamous keratinizing epithelial tissue It has a tough, horny superficial layer that provides a protective outer surface overlying its regenerative and pigmented deep or basal layer. The epidermis is thickest on the palms and soles. The cells that are most abundant in the epidermis are called keratinocytes.  Epidermis The epidermis has no capillaries or blood vessels or lymphatic's present between them but it is nourished by the vascularized dermis. The skin is also supplied with afferent nerve endings that are sensitive to touch, irritation (pain), and temperature. Most nerve terminals are in the dermis, but a few penetrate into the epidermis.  Epidermis The epidermis may be further subdivided into four or five sub layers. Two of these are of greatest importance: The innermost layer, the stratum germinativum, and The outermost layer, the stratum corneum The structure of the skin  Epidermis: Stratum germinativum The stratum germinativum may also be called the stratum basale. Each name tells us something about this layer. To Germinate means “to sprout” or “to grow.” Basal means the “base” or “lowest part.” The stratum germinativum is the base of the epidermis It is the innermost layer in which mitosis takes place.  Epidermis: Stratum germinativum In the SG new cells are continually being produced, pushing the older cells toward the skin surface. These cells produce the protein keratin, and as they get farther away from the capillaries in the dermis, they die. As dead cells are worn off the skin’s surface, they are replaced by cells from the lower layers. Scattered among the keratinocytes of the stratum germinativum are cells called Merkel cells (or Merkel discs) these are receptors for the sense of touch. The epidermis, showing the different kinds of cells present and the blood supply in the upper dermis.  Epidermis: Stratum germinativum The living keratinocytes are able to synthesize antimicrobial peptides called defensins The defensins and other chemicals are produced following any injury to the skin, as part of the process of inflammation. Defensins rupture the membranes of pathogens such as bacteria that may enter by way of breaks in the skin. The living portion of the epidermis also produces a vitamin; The cells have a form of cholesterol that, on exposure to ultraviolet light, is changed to vitamin D (then modified by the liver and kidneys to the most active form, called 1,25-D, or calcitriol, which is considered a hormone).  Epidermis: Stratum germinativum This is why vitamin D is sometimes referred to as the “sunshine vitamin.” Vitamin D is important for the absorption of calcium and phosphorus from food in the small intestine Vitamin D is also involved in maintaining muscle strength, especially in elderly people, Vitamin D is also involved in the functioning of insulin, and Vitamin D is also involved in some immune responses, where it may be protective for some types of cancer.  Epidermis: Stratum Corneum The stratum corneum, the outermost epidermal layer, consists of many layers of dead cells; all that is left is their keratin. The protein keratin is relatively waterproof, it does prevent most evaporation of body water. Keratin also prevents the entry of water. Without a waterproof stratum corneum, it would be impossible to swim in a pool or even take a shower without damaging our cells. The stratum corneum is also a barrier to pathogens and chemicals. Most bacteria and other microorganisms cannot penetrate unbroken skin. The flaking of dead cells from the skin surface helps remove microorganisms The fatty acids in sebum help inhibit their growth.  Epidermis: Langerhans Cells Within the epidermis are Langerhans cells, which are also called dendritic cells because of their branched appearance when they move. These cells originate in the red bone marrow, and are quite mobile. They are able to phagocytize foreign material, such as bacteria that enter the body through breaks in the skin.  Epidermis: Langerhans Cells Because they are able to phagocytize foreign material, after ingesting such pathogens, the Langerhans cells migrate to lymph nodes and present the pathogen to lymphocytes, a type of white blood cell. This triggers an immune response such as the production of antibodies (antibodies are proteins that label foreign material for destruction).  Epidermis: Melanocytes Another type of cell found in the lower epidermis is the melanocyte Melanocytes produce another protein, a pigment called melanin In dark skinned people, the melanocytes continuously produce large amounts of melanin. In light- skinned people, the melanocytes produce less amount of melanin.  Epidermis: Melanocytes The activity of melanocytes is genetically regulated; skin color is one of our hereditary characteristics. In all people, melanin production is increased by exposure of the skin to ultraviolet rays, which are part of sunlight and are damaging to living cells. As more melanin is produced, it is taken in by the epidermal cells as they are pushed toward the surface.  Epidermis: Melanocytes More production of melanin gives the skin a darker color, which prevents further exposure of the living stratum germinativum to ultraviolet rays. People with dark skin already have good protection against the damaging effects of ultraviolet rays; people with light skin do not. Melanin also gives color to hair, though its protective function is confined to the hair of the head. Two parts of the eye obtain their color from melanin: the iris and the interior choroid layer of the eyeball.  Summarized functions of the Epidermis EPIDERMIS PARTS FUNCTIONS Stratum corneum (keratin) Prevents loss or entry of water If unbroken, prevents entry of pathogens and most chemicals Stratum germinativum (stratum Continuous mitosis produces new cells to replace worn-off surface cells basale) Produces antimicrobial defensins Cholesterol is changed to vitamin D on exposure to UV rays Langerhans cells Phagocytize foreign material and stimulate an immune response by lymphocytes Merkel cells Receptors for sense of touch Melanocytes Produce melanin on exposure to UV rays Melanin Protects living skin layers from further exposure to UV rays  Dermis The dermis is made of an irregular type of fibrous connective tissue, irregular meaning that the fibers are not parallel, but run in all directions. Fibroblasts produce both collagen and elastin fibers. Collagen fibers are strong, and Elastin fibers are able to recoil after being stretched. Strength and elasticity are two characteristics of the dermis. With increasing age, however, the deterioration of the elastin fibers causes the skin to lose its elasticity. The uneven junction of the dermis with the epidermis is called the papillary layer.  Dermis Cont’d Capillaries are abundant in the dermis to nourish not only the dermis but also the stratum germinativum. The epidermis has no capillaries of its own, and the lower, living cells depend on the blood supply in the dermis for oxygen and nutrients. Within the dermis are the accessory skin structures such as: 1. Hair and Nail follicles 2. Sensory Receptors 3. Several types of glands. Some of these project through the epidermis to the skin surface, but their active portions are in the dermis.  Hair and Hair Follicles Hairs and nails are a hard type of keratin At the base of a follicle is the hair root, which contains cells called the matrix, where mitosis takes place. Each hair is formed from the hair matrix, a region of epidermal cells at the base of the hair follicle which extend deeply into the dermis and subcutaneous tissues Hair follicles are made of epidermal tissue, and the growth process of hair is very similar to growth of the epidermis.  Hair Follicles The new cells produce keratin, get their color from melanin (Melanocytes in the hair matrix impart pigment to the hair cells), then die and become incorporated into the hair shaft, which is pushed toward the surface of the skin. The change in hair pigment with age is due to decreasing melanocyte activity. Eyelashes and eyebrows help to keep dust and perspiration out of the eyes The hairs just inside the nostrils help to keep dust out of the nasal cavities. Hair of the scalp does provide insulation from cold for the head. The hair on our bodies, however, no longer serves this function, but we have the evolutionary remnants of it.  Hair Follicles Attached to each hair follicle is a small, smooth muscle called the pilomotor or arrector pili muscle. It passes obliquely to the upper part of the dermis When this smooth muscle with sympathetic innervation is stimulated by cold or emotions such as fear, these muscles 1. Pull the hair follicles upright causing the hair to stand on end 2. It may squeeze the sebaceous gland that lies between muscles and the hair follicle For an animal with fur, this would trap air and provide greater insulation. Because people do not have thick fur, all this does for us is give us “goose bumps.” Hair follicles are richly supplied by sensory nerves.  Nails and Nail Follicles Nail consist of nail plates lying on nail beds on the dorsum of the terminal segment of fingers and toes. Nail follicles are found on the ends of fingers and toes, nail follicles produce nails just as hair follicles produce hair. Mitosis takes place in the nail root at the base of the nail, and the new cells produce keratin (a stronger form of this protein than is found in hair) and then die.  Functions of the Nails Although the nail itself consists of keratinized dead cells, the flat nail bed is living epidermis and dermis. This is why cutting a nail too short can be quite painful. Nails protect the ends of the fingers and toes from mechanical injury Nails give the fingers greater ability to pick up small objects. Finger nails are also good for scratching.  Receptors Receptors are chemical structures, composed of protein, that receive and transduce signals that may be integrated into biological systems The skin contains receptors that respond to touch, pressure, pain and temperature Most sensory receptors for the cutaneous senses are found in the dermis (Merkel cells are in the stratum germinativum, as are some nerve endings). The cutaneous senses are touch, pressure, heat, cold, and pain. For each sensation there is a specific type of receptor, that will detect a particular change. Information is transmitted from the receptors to the nerve fibers that are routed through the spinal cord to the brain stem, from there they are transmitted to an area of the cortex in the parietal lobe.  Receptors Cont’d For pain, heat, and cold, the receptors are free nerve endings. For touch and pressure, the receptors are called encapsulated nerve endings, which means there is a cellular structure around the sensory nerve ending The purpose of these receptors and sensations is to; Provide the central nervous system with information about the external environment and its effect on the skin. When receptors detect changes, they generate nerve impulses that are carried to the brain, which interprets the impulses as a particular sensation. Sensation, therefore, is actually a function of the brain  Glands Glands are made of epithelial tissue. The exocrine glands of the skin have their secretory portions in the dermis. Exocrine glands are glands that make substances such as sweat, saliva, milk and digestive juices, and releases them through a duct or opening to a body surface  Glands: Sebaceous Glands The ducts of sebaceous glands open into hair follicles or directly to the skin surface. Their secretion is sebum, a lipid substance that we commonly refer to as oil. Sebum inhibits the growth of bacteria on the skin surface. Another function of sebum is to prevent drying of skin and hair. skin that is dry tends to crack more easily and very small breaks in the skin are potential entryways for bacteria.  Glands: Sebaceous Glands Decreased sebum production is another consequence of getting older, and elderly people often have dry and more fragile skin. Too much sebum may trap bacteria within hair follicles and create small infections. Because sebaceous glands are more numerous around the nose and mouth, these are common sites of pimples in young people  Glands: Ceruminous Glands These glands are located in the dermis of the ear canals. Their secretion is called cerumen or ear wax (which includes the sebum secreted in the ear canals). Cerumen keeps the outer surface of the eardrum pliable and prevents drying However, if excess cerumen accumulates in the ear canal, it may become impacted against the eardrum. This might diminish the acuity of hearing by preventing the eardrum from vibrating properly.  Glands: Sweat Glands There are two types of sweat glands, apocrine and eccrine. Apocrine glands Are most numerous in the axillae (underarm) and genital areas and are most active in stressful and emotional situations. Although their secretion does have an odor, it is perceptible to other people. Animals such as dogs, however, can easily distinguish among people because of their individual scents. If the apocrine secretions are allowed to accumulate on the skin, bacteria metabolize the chemicals in the sweat and produce waste products that have distinct odors that many people find unpleasant.  Glands: Sweat Glands Eccrine glands Are found all over the body but are especially numerous on the forehead, upper lip, palms, and soles. The secretory portion of these glands is simply a coiled tube in the dermis. The duct of this tube extends to the skin’s surface, where it opens into a pore. The sweat produced by eccrine glands is important in the maintenance of normal body temperature.  Blood Vessels Besides the capillaries in the dermis, the other blood vessels of great importance are the arterioles. Arterioles are small arteries, and the smooth muscle in their walls permits them to constrict (close) or dilate (open). This is important in the maintenance of body temperature, because blood carries heat, which is a form of energy. In a warm environment the arterioles dilate (vasodilation), which increases blood flow through the dermis and brings excess heat close to the body surface to be radiated to the environment.  Blood Vessels Cont’d In a cold environment, however, body heat must be conserved if possible, so the arterioles constrict. The vasoconstriction decreases the flow of blood through the dermis and keeps heat within the core of the body. This adjusting mechanism is essential for maintaining homeostasis. Regulation of the diameter of the arterioles in response to external temperature changes is controlled by the nervous system.  DERMIS Part Function Papillary layer Contains capillaries that nourish the stratum germinativum Hair (follicles) Eyelashes and nasal hair keep dust out of eyes and nasal cavities Scalp hair provides insulation from cold for the head Nails (follicles) Protect ends of fingers and toes from mechanical injury Receptors Detect changes that are felt as the cutaneous senses: touch, pressure, heat, cold, and pain Sebaceous glands Produce sebum, which prevents drying of skin and hair and inhibits growth of bacteria Ceruminous glands Produce cerumen, which prevents drying of the eardrum Eccrine sweat glands Produce watery sweat that is evaporated by excess body heat to cool the body Arterioles Dilate in response to warmth to increase heat loss Constrict in response to cold to conserve body heat Constrict in stressful situations to shunt blood to more vital organs  Subcutaneous Tissue The subcutaneous tissue may also be called the superficial fascia, one of the connective tissue membranes. Made of Areolar connective tissue and Adipose tissue The superficial fascia connects the dermis to the underlying muscles.  Subcutaneous Tissue: Areolar connective tissue Areolar connective tissue is the type of tissue which connects and surrounds different organs in the human body. The important function of this type of tissue is that it provides nutrition to the cells and also acts as a cushion to protect the organs from various external forces. Loose connective tissue (areolar) is located directly beneath the epidermis of the skin  Subcutaneous Tissue: Areolar connective tissue Areolar connective tissue, or loose connective tissue, contains collagen and elastin fibers and many white blood cells that have left capillaries to wander around in the tissue fluid between skin and muscles. These migrating white blood cells destroy pathogens that enter the body through breaks in the skin. Mast cells are specialized connective tissue cells found in areolar tissue; they produce histamine, leukotrienes, and other chemicals that help bring about inflammation.  Subcutaneous Tissue: Adipose tissue Adipose tissue, otherwise known as body fat, is a connective tissue that extends throughout your body. It's found under your skin (subcutaneous fat), between your internal organs (visceral fat) and even in the inner cavities of bones (bone marrow adipose tissue). The cells (adipocytes) of adipose tissue are specialized to store fat. Our subcutaneous layer of fat stores excess nutrients as a potential energy source. This layer also cushions bony prominences, such as when sitting, and provides some insulation from cold.  Subcutaneous Tissue: Adipose tissue Glucose, a simple sugar, provides energy for cell functions. After food is digested, glucose is released into the bloodstream. In response to glucose released, the pancreas secretes insulin, which directs the muscle and fat cells to take in glucose. Cells obtain energy from glucose or convert the glucose to fat for long-term storage. Like a key fits into a lock, insulin binds to receptors on the cell's surface, causing GLUT4 molecules to come to the cell's surface. As their name implies, glucose transporter proteins act as vehicles to carry glucose inside the cell. Adipose tissue contributes to inflammation by producing cytokines, chemicals that activate white blood cells.  The functions of subcutaneous tissue SUBCUTANEOUS TISSUE Part Function Areolar connective tissue Connects skin to muscles Contains many WBCs to destroy pathogens that enter breaks in the skin Contains mast cells that release histamine, leukotrienes, and other chemicals involved in inflammation Adipose tissue Contains stored energy in the form of true fats Cushions bony prominences Provides some insulation from cold Contributes to appetite Contributes to use of insulin Produces cytokines that activate WBCs  Function Of The Skin Protective Function The skin protection of the body and all the organs of the body from environmental effects, such as I. Bacteria and toxic substances II. Mechanical blow III. Ultraviolet rays IV. Abrasions V. Fluid loss, VI. Harmful substances VII. Invading microorganisms.  Function Of The Skin Cont’d Sensory Function Skin is considered as the largest sense organ in the body. It has many nerve endings, which form the specialized cutaneous receptors. These receptors are stimulated by sensations of touch, pain, pressure or temperature sensation and convey these sensations to the brain via afferent nerves. At the brain level, perception of different sensations occurs.  Function Of The Skin Cont’d Storage Function Skin stores fat, water, chloride and sugar. It can also store blood by the dilatation of the cutaneous blood vessels. Synthetic Function Synthesis and storage of vitamin D. Vitamin D3 is synthesized in skin by the action of ultraviolet rays from sunlight on cholesterol.  function of the skin cont’d Regulation Of Body Temperature Heat regulation through the evaporation of sweat and/or the dilation or constriction of superficial blood vessels. Skin plays an important role in the regulation of body temperature. Excess heat is lost from the body through skin by radiation, conduction, convection and evaporation. Sweat glands of the skin play an active part in heat loss, by secreting sweat. The lipid content of sebum prevents loss of heat from the body in cold environment.  Function Of The Skin Cont’d Regulation Of Water And Electrolyte Balance Skin regulates water balance and electrolyte balance by excreting water and salts through sweat. Excretory Function Skin excretes small quantities of waste materials like urea, salts and fatty substance. Absorptive Function Skin absorbs fat-soluble substances and some ointments.  Function Of The Skin Cont’d Secretory Function Skin secretes sweat through sweat glands and sebum through sebaceous glands. By secreting sweat, skin regulates body temperature and water balance. Sebum keeps the skin smooth and moist. Containment for the body's structures Tissues and organs and vital substances (especially extracellular fluids), preventing dehydration, which may be severe when extensive skin injuries (e.g., burns) are experienced.