Skin and Membranes Chapter 6

Learning Objectives Lesson 6.1: Skin and Membranes Classify, compare the structure of, and give examples of each type of body membrane. Describe the structure and function of the epidermis and dermis. List and briefly describe each accessory organ of the skin. List and discuss the five primary functions of the integumentary system.

Learning Objectives Lesson 6.1: Skin and Membranes (Cont.) List and briefly describe the three most common types of skin cancer. Classify burns and describe how to estimate the extent of a burn injury.

Body Membranes Classification of body membranes (Figure 6-1) Epithelial membranes Composed of epithelial tissue and an underlying layer of connective tissue Connective tissue membranes Composed largely of various types of connective tissue The term membrane refers to a thin, sheetlike structure that may have many important functions in the body.

Types of Body Membranes Figure 6-1, A: Epithelial membranes include cutaneous membrane (skin), serous membranes, and mucous membranes. Figure 6-1, B: Connective tissue membranes include synovial membranes.

Body Membranes (Cont.) Epithelial membranes Cutaneous membrane: Skin Serous membranes: Simple squamous epithelium on a connective tissue basement membrane Types Parietal layer: Line walls of body cavities Visceral layer: Cover organs found in body cavities Examples Pleura: Parietal and visceral layers line walls of thoracic cavity and cover the lungs Peritoneum: Parietal and visceral layers line walls of abdominal cavity and cover the organs in that cavity Three types of epithelial tissue membranes: cutaneous, serous, and mucous. Cutaneous membrane is primary organ of integumentary system.

Body Membranes (Cont.) Epithelial membranes Serous membranes Diseases Pleurisy: 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 A serous membrane is composed of two distinct layers of tissue.

Body Membranes (Cont.) Epithelial membranes Mucous membranes Line body surfaces that open directly to the exterior Produce mucus, a thick secretion that keeps the membranes soft and moist Mucous membranes contain an epithelial layer and a fibrous connective tissue layer. The term mucocutaneous junction is used to describe the area where the skin and mucous membranes meet.

Body Membranes (Cont.) 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 are smooth and slick. Connective tissue membranes reduce friction between opposing surfaces of bones in movable joints.

The Skin Structure (Figure 6-3): Two primary layers called epidermis and dermis Epidermis Outermost and thinnest primary layer of skin Composed of several layers of stratified squamous epithelium Stratum germinativum: Innermost layer of cells that continually reproduce; new cells move toward the surface (Figure 6-4) As cells approach the surface, they are filled with a tough, waterproof protein called keratin; eventually cells flake off Stratum corneum: Outermost layer of keratin-filled cells The skin is the largest organ of the body. The skin is one of the most important organs of the body. The skin is also known as the cutaneous membrane and is composed of the epidermis and dermis.

The Skin (Cont.) Structure Skin pigment: Deepest epidermal layer is responsible for production of pigment, which gives color to the skin The brown pigment melanin is produced by specialized cells in this layer Blisters are caused by breakdown of union between cells or primary layers of skin The amount and type of melanin in your skin depends first on the skin color genes you have inherited; however, other factors such as sunlight exposure can modify this hereditary effect.

Microscopic View of the Skin Figure 6-3: The epidermis is raised at one corner to reveal the ridges in the dermis.

Photomicrograph of the Skin Figure 6-4: New cells of the epidermis are produced in stratum germinativum. The deep region of the skin is the dermis. Courtesy Edward Reschke.

The Skin (Cont.) Structure Dermal-epidermal junction Dermis 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 The deeper cells of the epidermis are packed tightly together.

The Skin (Cont.) Structure 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 Dermis also contains nerve endings, muscle fibers, hair follicles, sweat and sebaceous glands, and many blood vessels The subcutaneous tissue is sometimes called the superficial fascia or hypodermis.

Accessory Organs of The Skin Hair, nails, and skin receptors Hair (Figure 6-5) 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 The human body is covered with millions of hairs. A few areas of the skin are hairless – the lips, palms of hands, and soles of feet.

Hair Follicle Figure 6-5 shows a hair follicle and its related structures.

Accessory Organs of The Skin Hair, nails, and skin receptors Nails (Figure 6-7) 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 Nails are classified as sensory organs. Under the nail lies a layer of epithelium called the nail bed.

Structure of Nails Figure 6-7, A: Fingernail viewed from above. Figure 6-7, B: Sagittal section of fingernail and associated structures.

Accessory Organs of The Skin Hair, nails, and skin receptors Skin receptors (Figure 6-3) Specialized nerve endings: Make it possible for skin to act as a sense organ Lamellar corpuscle (Pacini corpuscle): Capable of detecting pressure Tactile corpuscle (Meissner corpuscle): Capable of detecting light touch Skin receptors relay messages to the brain concerning sensations like touch, pain, and pressure. Burn injuries destroy skin receptors.

Skin Receptors Two skin receptors are visible in Figure 6-3: the tactile (Meissner) corpuscle and the lamellar (Pacini) corpuscle.

Accessory Organs of the Skin Skin glands Types Sweat or sudoriferous Sebaceous Sweat or sudoriferous glands 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 Two types of skin glands: sweat (sudoriferous) and sebaceous. Eccrine sweat glands are the most numerous, important, and widespread of the sweat glands. Sweat assists in the elimination of waste products. Pinpoint-size openings on the skin are called pores.

Accessory Organs of the Skin (Cont.) Skin glands Sweat or sudoriferous glands Types Apocrine sweat glands Found primarily in the skin in the axilla (armpit) Larger than eccrine glands Thicker secretion Sebaceous glands Secrete oil for the hair and skin Grow where hairs grow Tiny ducts open into hair follicles Sebum secretion increases during adolescence Instead of watery sweat, apocrine glands secrete a thicker secretion. Odor from apocrine gland secretion is caused by the contamination/decomposition of the secretion by skin bacteria. When sebum secretion increases during adolescence, it is stimulated by the increased blood levels of the sex hormones. Sebum secretion often darkens and forms into a blackhead (comedo).

The Skin (Cont.) Functions of the skin Protection; first line of defense against: Infection by microbes Ultraviolet rays from sun Harmful chemicals Cuts and tears 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 The most important functions of the skin are protection, temperature regulation, sense organ activity, excretion, and synthesis of vitamin D. The skin is also called the cutaneous membrane. When blood supply increases, skin reddens.

The Skin (Cont.) Functions of the skin Sense organ activity Excretion Skin functions as an enormous sense organ Receptors serve as receivers for the body, keeping it informed of changes in its environment Excretion Body rids itself of wastes Excess vitamins, drugs, and hormones can be excreted onto the skin by sweat 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 Cancer Most common types (Figure 6-8) Causes Kaposi sarcoma (KS) 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 The three most common types of skin cancer are squamous cell carcinoma, basal cell carcinoma, and malignant melanoma. Exposure to sunlight is the most important factor in causing skin cancer. Kaposi sarcoma is also known as human herpes virus 8 (HHV8).

Skin Cancer Lesions Figure 6-8: Examples of skin cancer lesions. A, Kaposi sarcoma. B, Squamous cell carcinoma. C, Basal cell carcinoma. D, Malignant melanoma. A: From Rakel R: Textbook of family medicine, ed 7, Philadelphia, 2007, Saunders. B: From Goldman L, Ausiello D: Cecil textbook of medicine, ed 23, Philadelphia, 2008, Saunders. C: From Noble J: Textbook of primary care medicine, ed 3, Philadelphia, 2001, Mosby. D: From Townsend C, Beauchamp RD, Evers BM, Mattox K: Sabiston textbook of surgery, ed 18, Philadelphia, 2008, Saunders.

Skin Cancer (Cont.) Squamous cell carcinoma Basal 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 If not treated, squamous cell carcinomas will eventually spread and infect other organs or areas of the body.

Skin Cancer (Cont.) Malignant melanoma Most serious form of skin cancer May develop from benign, pigmented moles or excess UV radiation Incidence in the United States is increasing ABCDE rule of self-examination (Table 6-1) Benign moles should be checked regularly for warning signs of melanoma. Adults who had more than two blistering sunburns before the age of 20 have much greater risk of developing melanoma.

Malignant Melanoma Use the ABCDE rule when checking for signs of malignant melanoma.

Burns Treatment and recovery or survival depend on total area involved and severity or depth of the burn Body surface area is estimated using the “rule of nines” (Figure 6-9) in adults Body is divided into 11 areas of 9% each Additional 1% located around genitals Burns aren’t just caused by fires or contacting a hot surface. Overexposure to UV light or contact with a harmful chemical can cause burns.

Courtesy Barbara Cousins. The “Rule of Nines” Figure 6-9: Dividing the body into 11 areas of 9% each helps to estimate the amount of skin surface burned in an adult. Courtesy Barbara Cousins.

Burns (Cont.) Classification of burns (Figure 6-10) First-degree (partial-thickness) burns Only the surface layers of epidermis involved Second-degree (partial-thickness) burns Involve the deep epidermal layers and always cause injury to the upper layers of the dermis An example of a first-degree burn is a typical sunburn. With second-degree burns, complete destruction of the dermis does not occur; scarring is common.

Burns (Cont.) Classification of burns Third-degree (full-thickness) burns Characterized by complete destruction of the epidermis and dermis May involve underlying muscle and bone Risk of infection is increased Fourth-degree (full-thickness) burns Extends below subcutaneous tissue and reaches muscle or bone May occur as result of high-voltage electrical burns Third-degree burns are initially insensitive to pain but intense pain is soon experienced. Fourth-degree burns may require skin grafting or amputation of limbs.

Classification of Burns Figure 6-10: Thickness of the damaged skin is one way to classify burns. A, First-degree burn. B, Second-degree burn. C, Third-degree burn. A: From Kliegman RM: Nelson textbook of pediatrics, ed 20, Philadelphia, 2016, Elsevier. B and C: Courtesy Dr. Richard L Judd, Dwight D Ponsell, from Mosby’s first responder, ed 2, St Louis, 1988, Mosby.

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