Integumentary System Reviewer: Skin, Hair and Nail PDF

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It's an integumentary reviewer that you can use for reviewing for examination it's from a summary of Holes, Mariebs, Tortora, and Seeleys...

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INTEGUMENTARY SYSTEM INTRODUCTION -The skin, the largest organ in the body, and its accessory structures constitute the integumentary system -The skin, or integument, is composed of two discrete tissue layers, an outer epidermis and a deeper dermis, resting on subcutaneous tissue, the hypodermis.

SKIN AND ITS TISSUES -Skin is a protective covering, helps regulate body temperature, houses sensory receptors, synthesizes chemicals, and excretes wastes. -It is composed of an epidermis and a dermis separated by a basement membrane. -A subcutaneous layer, not part of the skin, lies beneath the dermis. The subcutaneous layer is composed of areolar tissue and adipose tissue that helps conserve body heat. This layer contains blood vessels that supply the skin; the subcutaneous tissue is loose connective tissue that contains collagen and elastic fibers. The subcutaneous tissue attaches the skin to underlying structures and is a site of lipid storage. - The subcutaneous tissue just deep to the skin is known as the hypodermis. Strictly speaking, the hypodermis is not part of the skin, but it shares some of the skin’s protective functions. The hypodermis, also called superficial fascia because it is superficial to the tough connective tissue wrapping (fascia) of the skeletal muscles, consists mostly of adipose tissue.

Epidermis - The epidermis is stratified squamous epithelium that lacks blood vessels and divided into five strata: 1. The stratum basale (stratum germinativum, or basal cell layer), consists of keratinocytes (The cell membranes of older skin cells), which produce the cells of the more superficial strata. The deepest layer; contains cells that divide and grow. - A single row of cuboidal or columnar cells that divide and grow; this layer also includes melanocytes 2. The stratum spinosum (prickly layer) consists of several layers of cells held together by many desmosomes; beneath the stratum granulosum - Many layers of cells with centrally located, large, oval nuclei and developing fibers of keratin; cells becoming flattened. 3. The stratum granulosum (granular layer) consists of cells filled with granules of

keratohyalin. Cell death occurs in this stratum; beneath the stratum corneum - Three to five layers of flattened granular cells that contain shrunken fibers of keratin and shriveled nuclei 4. The stratum lucidum (clear layer) (between the stratum granulosum and the stratum corneum) consists of a layer of dead, transparent cells; is in the thickened skin of the palms and soles; - Cells appear clear; nuclei, organelles, and cell membranes are no longer visible 5. The stratum corneum (horny layer) consists of many layers of dead squamous cells. The most superficial cells slough off. The outermost layer; is composed of dead epidermal cells. - Many layers of keratinized, dead epithelial cells that are flattened and nonnucleated

Cells of the Epidermis The cells populating the epidermis include keratinocytes, melanocytes, dendritic cells, and tactile cells. Keratinocytes - The chief role of keratinocytes (“keratin cells”) is to produce keratin, the fibrous protein that helps give the epidermis its protective properties (Greek Kera = horn). Most epidermal cells are keratinocytes. -Keratinization is the transformation of the living cells of the stratum basale into the dead squamous cells of the stratum corneum. ■ Keratinized cells are filled with keratin and have a protein envelope, both of which contribute to structural strength. The cells are also held together by many desmosomes. -Soft keratin is present in skin and the inside of hairs, whereas hard keratin occurs in nails and the outside of hairs. Hard keratin makes cells more durable, and these cells are not shed Melanocytes - the spider-shaped epithelial cells that synthesize the pigment melanin (melan = black), are found in the deepest layer of the epidermis. As melanin is made, it accumulates in membrane-bound granules called melanosomes that motor proteins move along actin filaments to the ends of the melanocyte’s processes (the “spider arms”). - Melanin, a (dark) pigment produced from the amino acid tyrosine, provides skin color and protects underlying cells from the effects of ultraviolet light. - Melanocytes transfer melanin to nearby epidermal cells. - All humans have about the same concentration of melanocytes. Skin color is largely due to the amount of melanin in the epidermis.

Dendritic Cells - The star-shaped dendritic cells arise from bone marrow and migrate to the epidermis. Also called Langerhans cells after a German anatomist, they ingest foreign substances and are key activators of our immune system, as described later in this chapter. Their slender processes extend among the surrounding keratinocytes, forming a more or less continuous network. Tactile Cells - Occasional tactile (Merkel) cells are present at the epidermal-dermal junction. Shaped like a spiky hemisphere, each tactile cell is intimately associated with a disc-like sensory nerve ending. The combination, called a tactile or Merkel disc, functions as a sensory receptor for touch.

Dermis -The dermis (derm = skin), the second major skin region, is strong, flexible connective tissue - Its cells are typical of those found in any connective tissue proper: fibroblasts, macrophages, and occasional mast cells and white blood cells. The dermis is connective tissue divided into two layers: 1. The papillary layer is areolar connective tissue in which fine interlacing collagen and elastic fibers form a loosely woven mat that is heavily invested with small blood vessels. -It has projections from called dermal papillae and is composed of loose connective tissue that is well supplied with capillaries. -The more superficial papillary layer exhibits dermal papillae that protrude into the epidermis above, as well as dermal ridges. Dermal ridges and epidermal ridges together form the friction ridges that produce fingerprints. - Friction ridges, are assumed to enhance the gripping ability of the fingers and feet like tire treads help grip the road. 2. The reticular layer is the main layer. It is dense irregular connective tissue consisting mostly of collagen, dense irregular connective tissue binds the epidermis to underlying tissues - The dermis, composed mainly of dense, irregular connective tissue, is well supplied with blood vessels, lymphatic vessels, and nerves. Cutaneous receptors, glands, and hair follicles reside within the dermis. It also contains muscle cells, blood vessels, and nerve cell processes. -Dermal blood vessels supply nutrients to all skin cells and help regulate body temperature. -Nervous tissue is scattered throughout the dermis.

Skin Color - Skin color reflects the amount of pigments (melanin and carotene) in the skin and the oxygenation level of hemoglobin in blood. - Melanin (reddish yellow to brownish black) production is stimulated by exposure to ultraviolet radiation in sunlight. Melanin, produced by melanocytes and transferred to keratinocytes, protects the keratinocyte nuclei from the damaging effects of UV radiation. -Skin color is affected by emotional state. Alterations in normal skin color (jaundice, bronzing, erythema, and others) may indicate certain disease states. - Carotene (yellow to orange pigment) an ingested plant (like carrots) pigment, can cause the skin to appear yellowish. - Increased blood flow produces a red skin color, whereas decreased blood flow causes pale skin. Decreased oxygen content in the blood results in a bluish color, a condition called cyanosis. - The pinkish hue of fair skin reflects the crimson color of the oxygenated pigment hemoglobin in the red blood cells circulating through the dermal capillaries

Appendages of the Skin 1. Skin appendages, which derive from the epidermis, include hairs and hair follicles, nails, and glands (sweat and sebaceous).

ACCESSORY STRUCTURES OF THE SKIN 1. Nails - A nail is a scalelike modification of the epidermis that forms a clear protective covering on the dorsal surface of the distal part of a finger or toe - Nails are protective covers on the ends of fingers and toes. -The nail root is covered by skin, and the nail body is the visible part of the nail. - Nearly all of the nail is formed by the nail matrix, but the nail bed contributes. -The actively growing region is the nail matrix -The lunula is the part of the nail matrix visible through the nail body. - The nail is stratum corneum containing hard keratin. - They consist of keratinized epidermal cells. - The thickened proximal portion of the nail bed, called the nail matrix, is responsible for nail growth.

2. Hair follicles/Hair -Hairs, or pili, are flexible strands produced by hair follicles and consist largely of dead, keratinized cell - Hair covers nearly all regions of the skin. A hair has three concentric layers of keratinized cells: the medulla, cortex, and cuticle. ■ The medulla (“middle”), its central core, consists of large cells and air spaces. The medulla, which is the only part of the hair that contains soft keratin, is absent in fine hairs. ■ The cortex, a bulky layer surrounding the medulla, consists of several layers of flattened cells. ■ The outermost cuticle is formed from a single layer of cells overlapping one another like shingles on a roof. This arrangement helps separate neighboring hairs so the hair does not mat. - Each hair develops from epidermal cells at the base of a tube-like hair follicle. - As newly formed cells develop and grow, older cells are pushed toward the surface and undergo keratinization. -Hair pigment is made by melanocytes at the base of the hair follicle and transferred to the cortical cells. Various proportions of melanin of different colors (yellow, rust, brown, and black) combine to produce hair color from blond to pitch black. -Lanugo (fetal hair) is replaced near the time of birth by terminal hairs (scalp, eyelids, and eyebrows) and vellus hairs. At puberty, vellus hairs can be replaced with terminal hairs (appear in the axillae and the genital region. - A hair follicle has three parts: shaft, root, and hair bulb. The root and shaft of a hair are composed of dead keratinized epithelial cells. In the center, a cortex of cells containing hard keratin surrounds a medulla composed of cells containing soft keratin. The cortex is covered by the cuticle, a single layer of cells filled with hard keratin. -The hair bulb produces the hair in cycles, with a growth stage and a resting stage. - A hair follicle is richly vascularized and well supplied with nerve fibers. Arrector pili muscles pull the follicles into an upright position, producing goose bumps, and propel sebum to the skin surface when they contract.

3. Skin glands - Sweat glands are located in nearly all regions of the skin. - Each sweat gland consists of a coiled tube. - Sweat is primarily water but also contains salts and waste products. Sweat (Sudoriferous) Glands -Eccrine (merocrine) sweat glands, with a few exceptions, are distributed over the entire body surface. Their primary function is thermoregulation. They are simple coiled tubular glands that secrete a salt solution containing small amounts of other solutes. Their ducts usually empty to the skin surface via pores. -Eccrine sweat glands, located on the forehead, neck, back, palms, and soles, respond to elevated body temperature or emotional stress. -Apocrine sweat glands, which may function as scent glands, are found primarily in the axillary and anogenital areas. Their secretion is similar to eccrine secretion, but it also contains proteins and fatty substances on which bacteria thrive. -Apocrine sweat glands, located in the axillary regions, groin, and around the nipples, moisten the skin when a person is emotionally upset, scared, in pain, or sexually aroused - Ceruminous glands (cera = wax) are modified apocrine glands found in the lining of the external ear canal. - Mammary glands, another variety of specialized sweat glands, secrete milk. Sebaceous (Oil) Glands -Sebaceous glands secrete sebum (secrete an oily substance), which softens and waterproofs both the skin and hair. - Sebaceous glands are usually associated with hair follicles. -Sebaceous glands occur all over the body surface except for the palms and soles. They are simple alveolar glands; their oily holocrine secretion is called sebum. Sebaceous gland ducts usually empty into hair follicles. -Sebum lubricates the skin and hair, prevents water loss from the skin, and acts as a bactericidal agent. Sebaceous glands are activated (at puberty) and controlled by androgens.

Physiology of the Integumentary System

Homeostatic Imbalances of Skin

1. Protection - The skin protects by chemical barriers (the antibacterial nature of sebum, defensins, cathelicidins, the acid mantle, and the UV shield of melanin), physical barriers (the hardened keratinized and lipid-rich surface), and biological barriers (dendritic cells, macrophages, and DNA) -The skin protects against abrasion and ultraviolet light, prevents the entry of microorganisms, helps regulate body temperature, and prevents water loss. -Hair protects against abrasion and ultraviolet light and is a heat insulator. - Nails protect the ends of the digits

1. The most common skin disorders result from infections.

2. Body temperature regulation - The skin vasculature and sweat glands, regulated by the nervous system, play an important role in maintaining body temperature homeostasis. - Through dilation and constriction of blood vessels, the skin controls heat loss from the body. - Sweat glands produce sweat, which evaporates and lowers body temperature. 3. Cutaneous sensation - Cutaneous sensory receptors respond to temperature, touch, pressure, and pain stimuli which allow for proper responses to the environment. 4. Metabolic functions - A vitamin D precursor is synthesized from cholesterol by epidermal cells. Skin cells also play a role in some chemical conversions. - Skin exposed to ultraviolet light produces cholecalciferol, which is modified in the liver and then in the kidneys to form active vitamin D. - Vitamin D increases blood calcium levels by promoting calcium uptake from the small intestine 5. Blood reservoir - The extensive vascular supply of the dermis allows the skin to act as a blood reservoir. 6. Excretion - Sweat contains small amounts of nitrogenous wastes and plays a minor role in excretion. kin glands remove small amounts of waste products (e.g., urea, uric acid, and ammonia) but are not important in excretion.

Skin Cancer 2. The most common cause of skin cancer is exposure to ultraviolet radiation. 3. Basal cell carcinoma and squamous cell carcinoma are cured if they are removed before metastasis. Melanoma, a cancer of melanocytes, is less common but more dangerous.

Burns - Partial-thickness burns damage only the epidermis (first-degree burn) or the epidermis and the dermis (second-degree burn). -Full-thickness burns (third-degree burns) destroy the epidermis, the dermis, and usually underlying tissues - In severe burns, the initial threat is loss of protein- and electrolyte-rich body fluids, which may lead to circulatory collapse. The second threat is overwhelming bacterial infection. -The extent of a burn may be evaluated by using the rule of nines. The severity of burns is indicated by the terms first degree, second degree, and third degree. Third-degree burns are full-thickness burns that require grafting for successful recovery.

Developmental Aspects of the Integumentary System - The epidermis develops from embryonic ectoderm; the dermis (and hypodermis) develops from mesoderm. - The fetus exhibits a downy lanugo coat. Fetal sebaceous glands produce vernix caseosa, which helps protect the fetus’s skin from its watery environment. From Infancy to Adulthood - A newborn’s skin is thin. During childhood the skin thickens and more subcutaneous fat is deposited. At puberty, sebaceous glands are activated and terminal hairs appear in greater numbers. Aging Skin - In old age, the rate of epidermal cell replacement declines and the skin and hair thin. Skin glands become less active. Loss of collagen and elastic fibers and subcutaneous fat leads to wrinkling; delayed-action genes cause graying and balding. Photodamage is a major cause of skin aging

Homeostatic Interrelationship Between the Integumentary System and other Body Systems (Marieb’s)

■ Respiratory system furnishes oxygen to skin cells and removes carbon dioxide via gas exchange with blood

Skeletal System Chapters 6–8

Digestive System Chapter 23 ■ Skin protects digestive organs; provides vitamin D needed for calcium absorption; performs some of the same chemical conversions as liver cells ■ Digestive system provides needed nutrients to the skin

■ Skin protects bones; skin synthesizes a vitamin D precursor needed for normal calcium absorption and deposit of bone (calcium) salts, which make bones hard ■ Skeletal system provides support for skin

Muscular System Chapters 9–10 ■ Skin protects muscles ■ Active muscles generate large amounts of heat, which increases blood flow to the skin and may activate sweat glands in skin Nervous System Chapters 11–15 ■ Skin protects nervous system organs; cutaneous sensory receptors for touch, pressure, pain, and temperature located in skin (see Figure 5.1 ■ Nervous system regulates diameter of blood vessels in skin; activates sweat glands, contributing to thermoregulation; interprets cutaneous sensation; activates arrector pili muscles Endocrine System Chapter 16 ■ Skin protects endocrine organs; converts some hormones to their active forms; synthesizes a vitamin D precursor ■ Androgens produced by the endocrine system activate sebaceous glands and are involved in regulating hair growth Cardiovascular System Chapters 17–19 ■ Skin protects cardiovascular organs; prevents fluid loss from body; serves as blood reservoir ■ Cardiovascular system transports oxygen and nutrients to skin and removes wastes from skin; provides substances needed by skin glands to make their secretions Lymphatic System/Immunity Chapters 20–21 ■ Skin protects lymphatic organs; prevents pathogen invasion; dendritic cells and macrophages help activate the immune system ■ Lymphatic system prevents edema by picking up excessive leaked fluid; immune system protects skin cells Respiratory System Chapter 22 ■ Skin protects respiratory organs; hairs in nose help filter out dust from inhaled air

Urinary System Chapters 25–26 ■ Skin protects urinary organs; excretes salts and some nitrogenous wastes in sweat ■ Urinary system activates vitamin D precursor made by keratinocytes; disposes of nitrogenous wastes of skin metabolism Reproductive System Chapter 27 ■ Skin protects reproductive organs; cutaneous receptors respond to erotic stimuli; highly modified sweat glands (mammary glands) produce milk ■ During pregnancy, skin stretches to accommodate growing fetus; changes in skin pigmentation may occur...