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CHAPTER 6 STUDYGUIDE

Skin and Membranes 

This system is called the integumentary system.  Includes the skin and its appendages as an organ system. • Appendages  Hair  Nails  Skin glands

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Integument is another name for the skin The skin itself is the principal organ of the integumentary system. The skin  One of a group of anatomically simple but functionally important sheet like structures called membranes.

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Body Membranes The term membrane  Refers to a thin, sheetlike structure that has important functions in the body. Classification of membranes Epithelial membranes  Composed of epithelial tissue and an underlying layer of fibrous connective tissue Connective tissue membranes  Composed exclusively of various types of connective tissue • No epithelial cells are present in this type of membrane

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Membranes  Cover and protect the body surface  Line body cavities  Cover the inner surfaces of the hollow organs such as the digestive, reproductive, and respiratory passageways.  Some membranes anchor organs to each other or to bones  Some cover the internal organs.

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Membranes secrete lubricating fluids that reduce friction during organ movements such as the beating of the heart or lung expansion  For example • Pleural Membrane • Pericardial Membrane  Membrane lubricants also decrease friction between bones in joints.  Epithelial membranes are composed of epithelial tissue and an underlying layer of fibrous connective tissue

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Epithelial Membranes Three types of epithelial tissue membranes in the body:  Cutaneous membrane 1

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• Skin Serous membranes • Pleural membrane  Mucous membranes • Digestive tract Cutaneous membrane The cutaneous membrane, or skin, is the primary organ of the integumentary system.  One of the largest and most visible organs of the body.  The skin composes some 16% of the body weight  Considered an epithelial tissue membrane • Superficial layer of epithelial cells and an underlying layer of supportive connective tissue Serous membranes A serous membrane is a epithelial membrane composed of two distinct layers of tissue.  The epithelial sheet is a thin layer of simple squamous epithelium.  The connective tissue layer forms a very thin, glue-like basement membrane that holds and supports the epithelial cells. 

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The serous membrane that lines body cavities and covers the surfaces of organs in those cavities is a single, continuous sheet of tissue covering two different surfaces.  This arrangement results in two distinct layers of serous membranes.  The first type of serous membrane layer lines body cavities, and the second type of serous layer covers the organs in those cavities.

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Parietal layer  The serous membrane that lines the walls of a body cavity like wallpaper covers the walls of a room is called the parietal layer. Visceral Layer  The portion of the membrane that folds inward to cover the surface of organs within a body cavity is called the visceral layer.

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The two serous membranes of the thoracic and abdominal cavities  The pleura • The serous membrane around each lung in the thoracic cavity is called the pleura  Peritoneal membranes • The serous membrane covering most of the organs in the abdominal cavity is called the peritoneum

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Diseases of Serous Membranes  Pleurisy

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Inflammation of the serous membranes that line the chest cavity and cover the lungs  Peritonitis • Inflammation of the serous membranes in the abdominal cavity that line the walls and cover the abdominal organs Mucous membranes  Line body surfaces that open directly to the exterior  Produce mucus, a thick secretion that keeps the membranes soft and moist 

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Mucous membranes are epithelial membranes that contain both an epithelial layer and a fibrous connective tissue layer  These membranes line body surfaces opening directly to the exterior of the body.  For Example • Mucous membranes include those lining  Respiratory tract  Digestive tract  Urinary tract  Reproductive tracts.

The epithelial component of a mucous membrane varies depending on its location and function. The cell composition is either stratified squamous or simple columnar epithelium.  For example • The esophagus is lined with a tough, abrasion-resistant stratified squamous epithelium  Protects lining of esophagus from ingested food that is coarse and might cause injury to the esophageal wall when swallowed Stomach and small intestine  Single layer of epithelial cells lining these segments • Function for digestion, nutrient and water absorption. A thin layer of simple columnar epithelium lines the walls of the lower segments of the digestive tract. The epithelial cells of most mucous membranes secrete a thick, slimy material called mucus that keeps the membranes moist and soft The fibrous connective tissue underlying the epithelium in mucous membranes is called the lamina propria.  The term mucous identifies the type of membrane  Mucus refers to the secretion produced by that membrane. Mucocutaneous Junction The term mucocutaneous junction is used to describe the transitional area that serves as a point of “fusion” where skin and mucous membranes meet.  Such junctions lack accessory organs such as hair or sweat glands

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These transitional areas are generally moistened by mucous glands within the body orifices or openings where these junctions are located. The eyelids, lips, nasal openings, vulva, and anus have mucocutaneous junctions that may become sites of infection or irritation

Connective tissue membranes  Do not contain epithelial components  Produce a lubricant called synovial fluid  Examples are the synovial membranes in the spaces between joints and in the lining of bursal sacs Connective tissue membranes do not contain epithelial components. The synovial membranes lining the joint capsules that surround and attach the ends of articulating bones are classified as connective tissue membranes  Membranes are smooth and slick and secrete a thick, colorless lubricating fluid called synovial fluid. The membrane helps reduce friction between the opposing surfaces of bones in movable joints.

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Synovial membranes also line the small, cushion like sacs called bursae found between many moving body parts.

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The skin The largest and one of the most important organs of the body. An architectural marvel. Consider the incredible number of structures fitting into 1 square inch of skin  500 sweat glands  Over 1000 nerve endings  Yards of tiny blood vessels  Nearly 100 oil glands  150 sensors for pressure  75 for sensors for heat  10 sensors for cold  Millions of skin cells. Structure of the skin  The skin, or cutaneous membrane, is a sheet like organ composed of two layers of distinct tissue • Epidermis • Dermis The epidermis is the outermost layer of the skin.  It is a relatively thin sheet of stratified squamous epithelium. The dermis is the deeper of the two layers.  It is thicker than the epidermis and is made up largely of connective tissue.

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Epidermis  Outermost and thinnest primary layer of skin 4

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Composed of several layers of stratified squamous epithelium • Stratum germinativum • Stratum corneum  Outermost layer of keratin-filled cells Blisters are caused by breakdown of union between cells or primary layers of skin The tightly packed epithelial cells of the epidermis are arranged in up to five distinct layers.  Stratum germinativum • The basal cells of the innermost layer undergo mitosis and reproduce themselves • As new cells are produced in the deep layer of the epidermis, they are pushed upward through additional layers, or “strata” of cells. • As they approach the surface, the epithelial cells die and their cytoplasm is replaced by a protein called keratin.  Keratin is a tough, waterproof material that provides cells in the outer layer of the skin with an abrasion-resistant protective quality  Stratum Corneum • The tough outermost layer of the epidermis

Dead cells filled with keratin “flake off” by the thousands onto our clothes, into our bath water, and onto things we handle. Millions of epithelial cells reproduce daily to replace the millions shed.

Skin pigment  The deepest cell layer of the stratum germinativum is responsible for production of pigment, which gives color to the skin • The brown pigment melanin is produced by specialized cells in this layer called melanocytes. Melanin produced and packaged in melanocytes is distributed to the surrounding epithelial cells, giving them a darker color. The higher the concentration of melanin distributed in the layers of epithelial cells, the deeper is the color of skin. The primary function of melanin is to absorb harmful ultraviolet (UV) radiation from sunlight before it reaches tissues below the outer layers of the epidermis. The amount and type of melanin in your skin depends first on the skin color genes you have inherited.  Heredity determines how dark or light or amount of pigment produced  Other factors such as sunlight exposure can modify this hereditary effect.  Prolonged exposure to sunlight in light-skinned people darkens the exposed area because it leads to increased melanin deposits in the epidermis Blood flow and oxygen quantity can produce skin color change  Increased blood flow to the skin or increased blood oxygen levels can cause a pink flush to appear. 5

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Decrease in blood flow or oxygen content may produce cyanosis • The skin turns a blue-gray color Structure  Dermal-epidermal junction • Specialized area between two skin layers  Dermis • Deeper and thicker of the two primary skin layers and composed largely of connective tissue • Upper papillary layer of dermis characterized by parallel rows of tiny bumps called dermal papillae • Ridges and grooves in dermis form pattern unique to each individual  Basis of fingerprinting  Improves grip for tool use and walking  Dermal-epidermal junction  The junction that exists between the thin epidermal layer of skin above and the dermal layer below forms a type of basement membrane called the dermalepidermal junction.  The deeper cells of the epidermis are packed tightly together.  Cells are held firmly to one another and to the dermis below by cellular junctions between the membranes of adjacent cells, sometimes described as “spot welds,”  Cells also by a type of gel that serves to “glue” the two layers of the skin together and provide support for the epidermis attached to its upper surface  Small nipplelike bumps that project upward from the dermis into the epidermis, called dermal papillae play an important role in stabilizing the dermal-epidermal junction 

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The skin falls apart if the junction is weakened or destroyed and blisters may result.  Causes include burns, friction injuries, or exposure to irritants  Widespread detachment of a large area of epidermis from the dermis is an extremely serious condition that may result in overwhelming infection and death.

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Dermis Composed largely of connective tissue Cells are scattered far apart, with many fibers in between. Some of the fibers are tough and strong like collagen or white fibers Some fibers are stretchable and elastic like elastic or yellow fibers

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The dermis is the deeper of the two primary skin layers and is much thicker than the epidermis. The mechanical strength of the skin is in the dermis.  Deeper reticular layer of dermis filled with network of tough, interlacing, collagenous and stretchable elastic fibers • Number of elastic fibers decreases with age and contributes to wrinkle formation

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Dermis also contains  Nerve endings  Muscle fibers  Hair follicles  Sweat and sebaceous glands  Blood vessels

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Papillary layer  The upper region of the dermis  Characterized by parallel rows of tiny bumps called dermal papillae  Composed essentially of loose connective tissue elements within a fine network of thin collagenous and elastic fibers  The dermal papillae increase the surface area of the glue like dermalepidermal junction that helps bind the skin layers to each other.     

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The ridges on the tips of the fingers and on the skin covering the palms of your hands result from the parallel arrangement of dermal papillae under the epidermis. The biological function of skin ridges is to improve our grip when making or using tools Friction ridges help us to walk upright without slipping These ridges also help us sense textures on surfaces in our environment. Friction ridges develop sometime before birth  Their pattern unique in each individual but also it never changes except to grow larger  Fingerprints or footprints can provide positive biological identification

Reticular layer  The deeper area of the dermis is filled with a dense network of interlacing fibers  Mostly collagen fibers that gives toughness to the skin.  Elastic fibers also present • These make the skin stretchable and elastic • The number of elastic fibers in the dermis decreases as we age • The amount of fat stored in the subcutaneous tissue is reduced. • Wrinkles develop as the skin loses elasticity. • The skin sags and becomes less soft and pliant. 

The dermis contains an extensive network of nerves and nerve endings to detect sensory information  Pain  Pressure  Touch  Temperature. 7

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Dermis contains  Muscle fibers  Hair follicles  Sweat and oil glands  Blood vessels.

Subcutaneous tissue  The subcutaneous tissue is often called the superficial fascia or hypodermis by anatomists.  It is not a part or layer of the skin.  Located deep to the dermis and forms a connection between the skin and underlying structures of the body such as muscle and bone.  The layers of the skin are supported by this thick layer of loose connective tissue and fat called the subcutaneous tissue or the hypodermis.  Fat in the subcutaneous layer insulates the body from extremes of heat and cold.  Serves as a stored source of energy for the body  Acts as a shock-absorbing pad that helps protect underlying tissues from injury caused by bumps and blows  The spongy nature of subcutaneous tissue determines the relative mobility of the skin.  Loose fibrous and adipose tissue are prominent in subcutaneous tissue  Obese individuals the fat content may exceed 10 cm or more in thickness.  A surgical procedure called liposuction involves inserting a hollow tube into the subcutaneous tissue and removing fat with a vacuum aspirator.  CLINICAL APPLICATION  SUBCUTANEOUS INJECTION  The subcutaneous layer carries the major blood vessels and nerves that supply the skin  Make it an ideal site for the rapid and relatively pain-free absorption of injected material.  Liquid medicines such as insulin and synthetic hormones are often administered by subcutaneous injection  Needles used to inject materials into the hypodermis are called hypodermic needles.  Accessory Organs of The Skin  Hair, nails, and skin receptors  Hair • Soft hair of fetus and newborn is called lanugo • Hair growth requires epidermal tubelike structure called hair follicle • Hair growth begins from hair papilla • Hair root lies hidden in follicle and visible part of hair called shaft • Arrector pili is specialized smooth muscle that produces “goose bumps” and causes hair to stand up straight  Nails 

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• Produced by epidermal cells over terminal ends of fingers and toes • Visible part is called nail body • Root lies in a groove and is hidden by cuticle • Crescent-shaped area nearest root is called lunula • Nail bed may change color with change in blood flow Skin receptors  Specialized nerve endings that make it possible for skin to act as a sense organ • Lamellar corpuscle or Pacini corpuscle  Capable of detecting pressure  Tactile corpuscle or Meissner corpuscle • Capable of detecting light touch

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Skin glands  Types • Sweat or sudoriferous • Sebaceous  Sweat or sudoriferous glands • Types  Eccrine Sweat Glands  Apocrine sweat glands

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Eccrine sweat glands  Most numerous, important, and widespread of the sweat glands  Produce perspiration or sweat, which flows out through pores on skin surface  Function throughout life and assist in body heat regulation

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Apocrine sweat glands  Found primarily in the skin in the axilla (armpit)  Larger than eccrine glands  Thicker secretion

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Sebaceous glands  Secrete oil for the hair and skin  Grow where hairs grow  Tiny ducts open into hair follicles  Sebum secretion increases during adolescence

Functions of the Skin  Protection; first line of defense against: • Infection by microbes • Ultraviolet rays from sun • Harmful chemicals • Cuts and tears • The most important functions of the skin

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CHAPTER 6 STUDYGUIDE

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Protection Temperature regulation Sense organ activity Excretion Synthesis of vitamin D.

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Temperature regulation  Skin can release almost 3000 calories of body heat per day • Mechanisms of temperature regulation  Regulation of sweat secretion  Regulation of flow of blood close to the body surface

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Sense organ activity  Skin functions as an enormous sense organ  Receptors serve as receivers for the body, keeping it informed of changes in its environment

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Excretion  Body rids itself of wastes  Excess vitamins, drugs, and hormones can be excreted onto the skin by sweat

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Synthesis of vitamin D  Occurs when skin is exposed to ultraviolet light  Vitamin D is critically important to good health

• The skin’s millions of nerve endings serve as antennas or receivers for the body. • Excretion can influence amounts of certain ions and waste products present in blood. • Recent research has shown how important vitamin D is, which emphasizes the importance of this skin function. • Skin reddens when blood supply increases  

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Skin Cancer Most common types  Squamous cell carcinoma  Basal cell carcinoma  Malignant melanoma Causes  Genetic predisposition  Sun's ultraviolet (UV) radiation damages skin cell deoxyribonucleic acid (DNA), causing mistakes during mitosis Kaposi sarcoma (KS)  First appears as purple papules  Kaposi sarcoma is also known as human herpes virus 8 (HHV8). 10

CHAPTER 6 STUDYGUIDE

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Squamous cell carcinoma  Common type of skin cancer  Slow growing  Lesions begin as painless, hard, raised nodules  Will metastasize Basal cell carcinoma  Most common type of skin cancer  Originates in cells at base of epidermis, often on upper face  Lesions begin as small raised areas that erode in center, bleed, and crust over  Less likely to metastasize than other skin cancer types Malignant melanoma  Most serious form of skin cancer  May develop from benign, pigmented moles or excess UV radiation  Incidence in th...