xi Chapter 4 Membranes and the Integumentary System 91 Copyright Goodheart-Willcox Co., Inc. to affect individuals with light skin. Sunburn is also less likely once a light-skinned person has a tan. An inherited condition called albinism (AL-bi-nizm) prevents the normal production of melanin. Albinism is characterized by very little pigment in the skin, hair, and eyes. Individuals with albinism have extremely pale skin and white hair. The epidermis also contains specialized cells associated with the immune and nervous systems. Epidermal dendritic cells respond to the presence of foreign bacteria or viruses by initiating an immune system response, which brings in other cells to attack the foreign invaders. The skin contains as many as 800 dendritic cells per square millimeter to help ward off infections. Merkel cells (also called Merkel-Ranvier cells), located in the stratum basale, function as touch receptors. These cells form junctions with sensory nerve endings that relay information about touch to the brain. flatter and more filled with keratin, which makes them tough and water resistant. The stratum lucidum is a clear layer of thick skin found only on the palms of the hands, the fingers, the soles of the feet, and the toes. The outer layer of the epidermis, the stratum corneum, consists of dead cells that are completely filled with keratin and are continually shedding. You might be surprised to learn that the epidermis completely replaces itself every 25 to 45 days. Over the course of an average life, the epidermis sheds approximately 18 kg (40 lb) of skin cells. As described earlier, the melanocytes in the stratum basale produce the pigment melanin. Melanin, which ranges in color from reddish-yellow to brown and black, is primarily responsible for human skin Exposure to sunlight causes melanocytes to produce more melanin. As melanin granules are pushed out into neighboring skin cells, the skin becomes tanned.. The presence of extra melanin in the skin functions as a sunscreen, which is why sunburn is more likely Clues to Health in Skin Color Alterations in the color of the skin can serve as indicators of underlying changes in body function or patterns of food consumption. Among Caucasians, changes in coloration are relatively apparent. In people with darker skin coloration, the same color changes are masked but can be observed to some extent in the mucous membranes and nail beds. Capillaries in the dermis carry oxygenated hemoglobin, which is bright red. In people who have less melanin and lighter complexions, the hemoglobin in the blood gives the skin a pinkish tone. Conditions that cause dilation of the blood vessels, such as elevated blood pressure or infl ammation, can produce fl ushing, or reddening, of the skin. The blood vessels are dilated during vigorous exercise and exposure to hot conditions, which can result in reddening, especially of the face. Alternatively, any condition that causes constriction of the blood vessels can result in paleness or pallor of the skin. Cold conditions and certain emotional responses, such as fear or anger, can also cause this constriction. Low blood hemoglobin content, known as anemia, and low blood pressure can also cause paleness of the skin. Poor oxygenation of the blood causes hemoglobin to lose its red color and turn bluish. This condition is known as cyanosis. Breathing disorders such as asthma, chronic obstructive pulmonary disease (COPD), and lung cancer can cause cyanosis. Different forms of heart failure can also cause this condition. A yellowish hue in the skin and eyes is an indication of jaundice, a condition in which excess bile from the liver is deposited throughout the body. Jaundice is a symptom of disease or damage to the liver. Diet can also infl uence skin color, especially a person has eaten a large amount of beta-carotene. Beta-carotene is the orange-colored pigment that gives carrots, sweet potatoes, and acorn squash their color. The pigment is also found in leafy green vegetables. Beta-carotene is deposited in the stratum corneum. Diets excessively rich in beta-carotene can produce an orange-yellow coloration of the skin, especially in the palms of the hands and soles of the Clinical Application John Radcliff e Hospital/Science Source This premature infant is experiencing cyanosis due to poor oxygenation of the blood supply. Notice the bluish color of the soles of the infant’s feet. , r eceptors. Th ese ce ll s f orm junctions wit h sensory nerve ending s that relay infor mation about touch to m o t ra y m pll o m ra w n ccolor. o ed out n ne d cti ons , m o t a m o m r w n c o d out 186 Anatomy & Copyright Goodheart-Willcox Co., Inc. dancing—particularly running on a hard surface or uphill. The cause of the pain is believed to be micro- damage to the muscle tendons that attach to the tibia or inflammation of the periosteum of the tibia. The muscles potentially involved include the soleus, tibialis anterior, and extensor digitorum. Whiplash Injuries Whiplash injuries to the neck are fairly common, often resulting from automobile accidents in which the victim’s car is rear-ended. Such injuries result Understanding Medical The suffi x means ammation.” Numerous medical conditions involve infl ammation of a part of the body. The names for all of those conditions contain the -itis suffi x. Shin Splintss The term shin is often used to describe pain localized to the medial The condition is an overuse injury that typically arises running or Tennis Elbow Focus On Maxisport/Shutt erstock.com Melodia plus photos/Shutt erstock.com Cause Tennis elbow is the common name for lateral epicondylitis, or infl ammation of the tendons on the lateral side of the elbow. A common cause of this condition is repeated twisting motions of the arm, as when hitting a backhand with poor technique in racquet sports. Other repetitive motions in activities such as painting, carpentry, plumbing, and yard work can also lead to lateral epicondylitis. A direct blow to the lateral elbow or a fall on an outstretched arm can also cause the condition. Treatment The key to successful treatment is cessation of the activity that caused the irritation. Rest! Depending on the severity of the microtears in the tendons, weeks or months of rest may be needed. Applying ice packs for 10–15 minutes at a time several times a day can help relieve pain. Over-the-counter pain medications can also be used judiciously. Severe cases may require surgery. Elbow splints and sleeves have not been shown to help. Symptoms The onset of symptoms is usually gradual, with soreness or a dull ache around the lateral elbow that disappears within 24 hours following activity. With repeated occurrences, the pain may persist longer as the tendons are further damaged. In serious cases, any use of the arm during daily activities can cause pain. The pain may also spread to the hand, wrist, and other parts of the arm, shoulder, or neck. Sometimes the pain increases later in the day, making sleep diffi cult. Extensor muscles Humerus Lateral epicondyle Injured common extensor tendon Tennis elbow Right arm, lateral (outside) side Alila Medical Media/Shutt erstock.com 186 186 A & A natomy & Ph i l E ssent ials dancing— up h ill. Th d amage to ti b ia or inf The mu sc tibia lis ant Whiipla p p l a a a as Whiplash of ten resu th i ti U nderstanding Medical Terminology The suffi x --itiss iti means ““infl infl amma tion.” N umerous m edical conditions involve infl ammation o f a p art of the bod y. The names f or all o f those conditions c onta in the -i t is suffi x. S hin Sp lint T he te rm s hin ssplintt plint is often used to describe pain localized to t h e me d ial llower ower lleg. eg. T h e condition is an h ll ffrom Chapter 2 Molecules and Cells 39 Copyright Goodheart-Willcox Co., Inc. Functions of ProteinsEssentialsliEygoloiysPhPhysiology Among their many functions in the body, proteins act as structural elements, enzymes, and carriers. Terminology Collagen, which gives strength to ligaments and tendons, is an example of a protein with a structural function. For proteins made of multiple polypeptides, there is one step beyond the tertiary structure. The arrangement of these subunits into a whole, known as the quaternary structure, is the final step in determining the protein’s shape. Glycogen Storage Diseases Glycogen storage diseases are a class of disorders in which either the formation or the breakdown of glycogen does not work properly. In healthy individuals, the liver and muscles perform two different processes involving glycogen and glucose. They synthesize glycogen from glucose, and they break down glycogen to release glucose. Glucose from the liver is released into the bloodstream. Glucose in muscle is used to make ATP for energy. In hepatic (hepat/o means “liver”) glycogen storage diseases, the liver does not release glucose into the blood as it should. The liver is often enlarged due to an abnormal accumulation of glycogen in its cells. In myopathic (my/o means “muscle” and path/o means “disease”) glycogen storage diseases, the storage or breakdown of glycogen in muscles does not work properly. Glycogen storage diseases are usually inherited. They are caused by genetic mutations that affect enzymes (proteins) that catalyze biochemical reactions involving glycogen. There is no cure, but in many cases, symptoms can be lessened by dietary changes, medications, or a liver transplant. Research Notes Blood glucose to various tissues Muscle Glycolysis Energy Glycogen Glucose Glycogen Glucose Glycolysis Glycogen Glucose Glycogen Glucose Liver Blood glucose to muscle Low energy output Low blood glucose to various tissues A Normal formation and breakdown of glycogen B Hepatic form of glycogen storage disease C Myopathic form of glycogen storage disease © Body Scientifi c International Glycogen storage disease. col or, espe cially wwhen hen oun t o f beta-carotene. ored pigment that gives c orn sq uas h th e ir co l or. af y green vegetables. h e stratum corneum. arotene can produce an s kin, especially in the of the ffeet. eet. Understanding Medical Terminology The word cortical (coming from cortex) pertains to the outer layer of something. For example, the outer layer of the brain is known as the cerebral cortex. The outer layer of many structures and objects, including a plant stem or even a rock, is also known as its cortex. The type of bone tissue forming the outer layer of bone is therefore called cortical bone. Features Multiple features address topics of interest to students studying anatomy and physiology. In addition to the Clinical Case Study at the beginning of each chapter, Clinical Applications throughout the textbook provide insights about how concepts relate to healthcare practices. Research Notes highlight recent and ongoing scientifi c studies related to human anatomy and physiology. Focus On… features introduce chapter-related topics of interest to today’s students. Throughout every chapter, Understanding Medical Terminology boxes explain the meaning of medical terms, provide insights about why certain structures and medical conditions are named as they are, and provide helpful hints for remembering the terms. In addition, a Medical Terminology section at the end of each chapter helps students practice medical word-building skills. The Self Check questions at the end of each section help students determine how well they understand the concepts. Review, critical thinking, and research questions at the end of each chapter assess student knowledge and retention, and questions related to the Clinical Case Study help students tie together the chapter concepts in a meaningful way.