Chapter 6 Integumentary System

Pretest The nails are part of the integumentary system. True or False The nails are part of the integumentary system. The thickest layer of the epidermis is the stratum corneum. Cerumen provides waterproofing for the skin. Sensory receptors allow the body to detect changes in the environment. The subcutaneous layer cushions underlying organs.

Pretest, cont. True or False The ultraviolet rays of the sun increase melanocyte activity. The face does not contain hair. Hair is produced by hair follicles. The neck and chest have the most sweat glands. Vitamin A is necessary for the absorption of calcium in the body.

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

Structure of the Skin, cont. From Jarvis C: Physical examination and health assessment, ed 5, St. Louis, 2008, Saunders

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

Epidermis, cont. 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

Epidermis, cont. As cells are pushed upward: 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

Epidermis, cont. Strata of the epidermis Stratum basale 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

Epidermis, cont. 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

Epidermis, cont. Stratum corneum Outermost region Makes up 3/4 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

Epidermis, cont.

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”)

Dermis, cont. Sensory receptors are present in the dermis Detect changes in the environment, such as heat, cold, pain, pressure, and touch

Dermis, cont. Layers of the dermis Papillary layer: upper layer Contains numerous papillae (projections) that extend into the epidermis On the palms, fingertips, and soles of feet: papillae form distinct patterns Genetically determined and unique for each individual Basis of fingerprints and footprints Reticular layer: deeper and thicker than papillary layer

Subcutaneous Layer Not actually a part of the skin Loosely anchors skin to underlying organs Also known as: a. Hypodermis b. Superficial fascia 4. Consists of loose connective tissue and adipose tissue 5. Functions: Cushions underlying organs Heat insulator in temperature regulation Provides energy when necessary

Skin Color Melanin: responsible for skin color Produced by melanocytes (located in stratum basale) Everyone has same number of melanocytes Activity of the melanocytes: genetically controlled Large number of melanin granules: results in dark skin Fewer granules: result in lighter skin

Skin Color, cont. 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

Skin Color, cont. 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

Epidermal Derivatives Derived from the stratum basale of epidermis Embedded in the reticular layer of dermis

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

Hair and Hair Follicles, cont. 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

Hair and Hair Follicles, cont. c. Medulla: central core of the hair d. Cortex: several layers of cells surrounding medulla e. Cuticle: outermost covering of the hair Consists of a single layer of overlapping, keratinized cells

Hair and Hair Follicles, cont. 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

Hair and Hair Follicles, cont. c. 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

Hair and Hair Follicles, cont.

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, cont. 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

Nails, cont. From Jarvis C: Physical examination and health assessment, ed 5, St. Louis, 2008, Saunders

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

Glands, cont. From Jarvis C: Physical examination and health assessment, ed 5, St. Louis, 2008, Saunders

Glands, cont. 2. Sweat (sudoriferous) glands a. Widely distributed over the body • Except for lips, nipples, and parts of the external genitalia • Most numerous: palms and soles

Glands, cont. 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

Glands, cont. 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

Glands, cont. 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

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

Functions of the Skin, cont. 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

Functions of the Skin, cont. 3. 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

Functions of the Skin, cont. 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

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

Posttest The epidermis consists of simple squamous epithelial tissue. True or False The epidermis consists of simple squamous epithelial tissue. Skin cells grow and multiply in the stratum basale layer of the epidermis. Melanocytes produce a yellow pigment. Sebaceous glands are embedded in the dermis. An individual with a large number of melanin granules in their skin will have dry skin.

Posttest, cont. True or False The part of the hair that is visible is known as the shaft. The central core of the hair is known as the cuticle. Shivering is caused by contraction of the arrector pili muscles. Sebum keeps hair and skin soft and pliable. Merocrine glands are responsible for body odor.