Today's Medical Assistant 2th edition Chapter 06 Integumentary System

The Integumentary System Lesson 6.1 The Integumentary System Describe the structures of the two layers of the skin. State three names for the layer of tissue that anchors the skin to underlying organs, and describe the structure of this layer. List three factors that influence skin color. Describe the structure of hair and nails and their relationship to the skin.

The Integumentary System (cont’d) Lesson 6.1 The Integumentary System (cont’d) Discuss the characteristics and functions of the various glands associated with the skin. List and describe four functions of the integumentary system. Describe ways in which the aging of an individual affects the integumentary system. Identify pathology related to the integumentary system.

Structure of the Skin Includes glands, hair, nails, and other structures that are derived from it Sometimes called the cutaneous membrane Consists of two layers: Epidermis: outer layer Dermis: inner layer Anchored to underlying structures by subcutaneous tissue The major organ of the integumentary system is the skin, an organ with which we are very familiar. Two word roots are associated with skin: derm- and cutane- (as in cutaneous membrane). Epidermis means upon (above) the dermis. (Epi- means above or upon.) Subcutaneous means below the skin. (Sub- means below or under.)

Structure of the Skin How thick is the epidermis compared to the dermis? Is the skin really as thick as this picture implies, or is the picture greatly magnified? What arises within the skin and/or at the top of the subcutaneous tissue?

Epidermis Consists of stratified squamous epithelium No blood vessels present Cells receive nutrients by diffusion from vessels in the underlying tissue Cells on the bottom actively grow and divide The epidermis is the outer layer of skin. Because it is constantly exposed to trauma, its cells grow and divide rapidly. How long does it take for skin to heal?

Epidermis Cells are pushed upward Receive fewer nutrients Undergo keratinization Keratin is deposited in the cell Cell changes shape By the time the cells reach the surface, they are: Flat (squamous) Dead Cells are sloughed off and replaced by other cells What is keratin? (A substance deposited in the cell that hardens the cell.) What happens to skin cells as they are pushed toward the outer surface?

Epidermis As cells are pushed upward, they take on different appearances and characteristics Form distinct regions Five regions (strata) of cells: thick skin (soles of feet and palms of hand) Four strata: skin that covers the rest of body What is a stratum of the skin? (Region of cells.) Where is skin the thickest? (The soles of feet and hands have five strata, whereas the rest of the skin has only four.)

Epidermis Strata of the epidermis Stratum basale Stratum spinosum Consists of actively dividing columnar cells and melanocytes (produce melanin) Stratum spinosum Consists of several layers of cells with spiny processes This layer combined with the stratum basale is called the stratum germinativum The stratum basale is the bottom layer of epidermis (closest to the dermis). It produces cells that remain in this layer and cells that are pushed upward. The melanocytes are specialized cells found in the stratum basale. (Melan- means black, -cyte means cell) What do melanocytes produce? (Melanin, a dark pigment.) The stratum spinosum is thicker than the stratum basale and contains spiny processes. It can produce some extra cells but not as many as the stratum basale. The combination of the stratum basale and stratum spinosum is termed the stratum germiativum, because the cells that are pushed up to the epidermis originate in these two layers.

Epidermis Strata of the epidermis Stratum granulosum Stratum lucidum Thin region consisting of two or three layers of flattened cells Keratinization begins in this layer Stratum lucidum Translucent band consisting of a few layers of flattened, anucleate cells Present only in thick skin Cells in the stratum granulosum begin to harden and flatten as they are pushed up. The stratum lucidum is the layer that is present only in thick skin such as the soles of the hands and feet.

Epidermis Strata of the epidermis Stratum corneum Outermost region Makes up ¾ of the epidermal thickness Consists of 20-30 layers of flattened, dead, keratinized cells Cells are continually shed and replaced Keratin present is a tough, water-repellent protein: provides protection against water loss The stratum corneum is the thickest layer of skin. It takes about 5 weeks for a cell to move from the stratum basale to the outside of the stratum corneum. Are the cells of the stratum corneum dead or alive? Thick or flat?

Dermis Dense connective tissue Contains hair, nails, and certain glands Contains both collagenous and elastic fibers: provide strength and elasticity If skin is overstretched: dermis may be damaged Leaves white scars called striae (“stretch marks”) The dermis is also called the stratum corium. What type of fiber allows the skin to stretch? (Elastic fibers.) Stretch marks are a sign of damage to the dermis caused by overstretching. When a damaged tissue cannot completely repair itself, a type of connective tissue called scar tissue is formed in the area. Although the body tries to mimic the original tissue, scar tissue does not have all the specialized fibers and cells of the original tissue.

Dermis Sensory receptors are present in the dermis Detect changes in the environment, such as heat, cold, pain, pressure, and touch Sensory receptors on the nerves initiate the transmission of nerve impulses to the spinal cord and brain. What different sensations can be perceived with the fingers? Are the sensory receptors in the dermis or the epidermis?

Dermis Layers of the dermis Papillary layer: upper layer Contains numerous papillae (projections) that extend into the epidermis Papillae form distinct patterns on the palms, fingertips, and soles of feet Reticular layer: deeper and thicker than papillary layer Projections of the papillary layer of the dermis form fingerprints and patterns on the soles of the feet. In both areas, these ridges prevent slipping of fingers and feet. These are genetically determined and unique for each individual. They are the basis of fingerprints and footprints. The reticular layer gains strength and elasticity because fibers run in many directions.

Subcutaneous Layer Not actually a part of the skin Loosely anchors skin to underlying organs Also known as: Hypodermis Superficial fascia Consists of loose connective tissue and adipose tissue Function: Cushions underlying organs Heat insulator in temperature regulation Provides energy when necessary Subcutaneous layer is not actually part of the skin but is sometimes called the hypodermis because it is below the dermis. (Hypo- means below or under.) Subcutaneous layer is thicker in some areas than others because of larger deposits of adipose tissue (fat). This is genetically determined, and the pattern varies in men and women. Adipose tissue helps humans float in water, because water is denser than fat.

Skin Color Melanin: responsible for skin color Produced by melanocytes (located in stratum basale) Everyone has same number of melanocytes Activity of the melanocytes is genetically controlled Large number of melanin granules: results in dark skin Fewer granules: result in lighter skin Both genetic and physiologic factors determine the activity of the melanocytes. Although most individuals have the same number of melanocytes, the number of active granules with them varies according to genetic inheritance.

Skin Color Melanin: responsible for skin color Inability to produce melanin: results in albinism Very light skin, white hair, and unpigmented irises in the eyes Ultraviolet light increases melanocyte activity: more melanin is produced Skin becomes darker or tanned Albinism (Alba means white) is usually a genetic mutation that results in the inability to produce melanin. How do you know that white mice and rats are albino? (Pink eyes.) How does sitting in the sun result in a tan?

Skin Color Carotene: yellowish pigment Some people have carotene (in addition to melanin) Causes yellow tint to the skin Pinkish tint: due to blood vessels in the dermis What causes the skin to have a yellow tint? What causes a pink tint to the skin?

Epidermal Derivatives Derived from the stratum basale of epidermis Embedded in the reticular layer of dermis The accessory structures of the skin are the hair, nails, sweat glands, and sebaceous (oil) glands.

Hair and Hair Follicles Location of hair Found on nearly all body surfaces Absent: Palms of the hands, soles of the feet, lips Hair is composed of dead, keratinized epithelial cells Where do human beings have the most hair? Where is hair absent? What determines the amount of hair an individual has? Does this vary by sex?

Hair and Hair Follicles Hair is made up of: Shaft: portion that extends beyond the surface of the epidermis Root: portion that is below the surface of the skin Enclosed in a hair follicle: extends through epidermis and embedded in dermis The hair consists of a shaft and a root and is enclosed in a follicle. A follicle is a small group of cells arranged around a circular cavity.

Hair and Hair Follicles Hair is made up of: Medulla: central core of the hair Cortex: several layers of cells surrounding medulla Cuticle: outermost covering of the hair Consists of a single layer of overlapping, keratinized cells The hair itself is dead and contains no nerves. It consists of several layers. Split ends form when the cuticle is abraded and keratin fibers project from the tip of the hair shaft.

Hair and Hair Follicles Hair follicle: produces hair Hair bulb: encloses root of hair Papilla of dermis: contains blood supply Single layer of stratum basale cells: provide mitotic cells that produce the hair Hair color: determined by type of melanin produced by melanocytes (in stratum basale) Yellow, brown, and black pigments: present in varying proportions to produce different hair colors With age: melanocytes become less active Hair in which melanin is replaced with air bubbles is white Why is a blood supply needed by the hair bulb? Why does hair turn gray and then white?

Hair and Hair Follicles Hair follicle: produces hair Arrector pili muscle Attached to hair follicles Contraction: causes the hair to “stand on end” and “goose bumps” Action is controlled by nervous system in response to cold and fright When does the arrector pili muscle contract? In furry mammals, the ability for the hair to contract causes an animal to look larger when it is frightened. This may scare a predator. If the hair contracts when an animal is cold, more heat can be trapped in the fur. These mechanisms don’t work well for humans, because they do not have enough hair over their bodies.

Nails Thin plates of dead stratum corneum Contain a very hard type of keratin Nail body: visible portion of the nail Nail root: covered with skin Eponychium or cuticle: fold of stratum corneum Grows onto proximal portion of nail body Nails protect the ends of the fingers and toes. They also can be used for self-defense or aggression. Where is the nail root?

Nails Nail bed: formed by stratum basale growing under nail body Nail matrix: responsible for nail growth Lunula: the portion of the body over the matrix Whitish, crescent-shaped area Nails appear pink due to rich supply of blood vessels in underlying dermis Where does nail growth occur? What do we call the white crescent-shaped area at the base of the nail? Why do nails appear pink? Circulation to the fingers can be assessed by pressing on the end of the nail.

Glands Sebaceous glands Generally associated with hair follicles Found in all areas of the body that have hair Those not associated with hair follicles: open directly onto surface of skin Sebum: oily secretion from a sebaceous gland Keeps hair and skin soft and pliable Inhibits growth of bacteria on skin Helps prevent water loss What is a gland? The glands of the skin are exocrine glands because they secrete substances through ducts. The sebaceous glands are stimulated by sex hormones, so they become more active during adolescence and less active after menopause. What is the function of sebum?

Sweat (Sudoriferous) Glands Widely distributed over the body Except for lips, nipples, and parts of the external genitalia Most numerous: palms and soles There are more than 2.5 million sweat glands. What parts of the body do not have sweat glands?

Sweat (Sudoriferous) Glands Types of sweat glands: Merocrine sweat glands: most numerous and widely distributed Coiled tube embedded in the dermis Duct opens onto surface of the skin through a sweat pore Secretion: primarily water with a few salts When the body’s temperature increases, glands produce sweat (perspiration): cooling effect on body Most common type of sweat gland is the merocrine sweat gland. Secretions from the merocrine glands do not contain cells or parts of cells (unlike sebaceous glands, whose secretions contain disintegrated cells from the gland itself).

Sweat (Sudoriferous) Glands Types of sweat glands Apocrine sweat glands: larger than merocrine glands Located in axillae and external genitalia Ducts open into hair follicles in these regions Secretion: consists of water, salts, and organic compounds (fatty acids and proteins) Become active at puberty Stimulated by the nervous system in response to pain, emotional stress, sexual arousal Secretion is broken down by bacteria: causes body odor The apocrine sweat glands become active at puberty. The ducts of those located in the groin and axillae open into hair follicles. What stimulates sweating?

Ceruminous Glands Modified sweat glands found in the external auditory (ear) canal Secrete an oily, sticky substance: cerumen (earwax) Repels insects and traps foreign material Cerumen, which is called ear wax, is a secretion found in the ears. What color is cerumen when it is secreted? After it ages? (Orange when secreted, brown after it ages.)

Functions of the Skin Protection Forms a protective covering Keratin in the cells: waterproofs the cells and helps prevent fluid loss from the body Oily secretions of sebaceous glands are acidic: inhibit bacterial growth on skin Unbroken skin: first line of defense against invading organisms Melanin: absorbs light and helps protect underlying tissues from the damaging effects of ultraviolet light. Protects underlying tissues from mechanical, chemical, and thermal injury The first function of intact skin is protection. What can penetrate skin? Can microorganisms penetrate intact skin? What is the function of melanin?

Functions of the Skin Sensory reception Dermis contains sensory receptors for heat, cold, pain, touch, and pressure Relays information about the environment to the brain Changes can be made to prevent or minimize injury Also a means of communication between individuals The second function of skin is to obtain information about the environment. How can an individual learn what is in the environment through the skin?

Regulation of Body Temperature When there is excess heat in the body Small arteries in the dermis dilate Brings the heat to the surface: can escape into surrounding air Sweat glands become active Sweat evaporates to provide cooling of the body Is the third function of skin to regulate body temperature? What structures in the skin help to cool the body? How?

Regulation of Body Temperature If body temperature falls below normal: Sweat glands are inactive Blood vessels in skin constrict Reduces amount of heat transferred from deeper tissues to surface If it is cold, what happens to the capillaries in the skin and subcutaneous tissue? What happens to the hair follicle?

Synthesis of Vitamin D Vitamin D Required for absorption of calcium and phosphorus Essential for normal bone metabolism and muscle function Skin cells contain a precursor molecule Converted to vitamin D when exposed to ultraviolet rays of sun Vitamin D is a fat-soluble vitamin. It is formed after exposure to UVB radiation from a steroid chemical in the skin that contains cholesterol. The term steroid refers to the chemical shape of the molecule. Fat-soluble vitamins can be stored by the body in adipose tissue. For what purpose does the body use vitamin D? What does precursor mean? In what part of the world are individuals most susceptible to vitamin D deficiency? What food product is enriched with vitamin D to counteract this potential deficiency?

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