Chapter 06

Integumentary System

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Introduction A. Organs are body structures composed of

two or more different tissues.

B. The skin and its accessory organs make up the integumentary system.

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Skin and Its Tissues A.The skin is a large organ responsible for:

1. maintaining homeostasis through temperature regulation

2. protection of underlying tissues

3. preventing water loss,

4. housing sensory receptors

5. synthesizing certain chemicals

6. excreting wastes.

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B. The skin consists of an outer epidermis and a dermis, connected to underlying tissue by the subcutaneous layer

(hypodermis).

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Skin of Finger

Epidermis Dermis

EpidermisEpidermis

DermisDermis

Subcutaneous LayerSubcutaneous Layer

Fig06.01a

Epidermis

Dermis

Hair shaft

Sweat gland pore

Sweat

Capillary

Stratum corneum

Stratum basale

Dermal papilla

Arrector pili muscle

Basement membrane

Sebaceous gland

Hair follicle

Sweat gland

Nerve cell process

Adipose tissue

Blood vessels

Muscle

Sweat gland duct

Subcutaneous layer

(a)

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Fig06.01b

Hair follicle

Epidermis

Arrector pili muscle

Sebaceousgland

Dermis

©Image Source/Getty Images

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(b)

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C. Epidermis

1. The epidermis is made up of stratified squamous epithelium and lacks blood vessels.

2. This type of tissue is made up of layers of flattened cells that are

designed to protect underlying layers.3. It makes up the outer layer of skin, and lines the mouth, throat, vagina, and anal canal.

.

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The layer of reproducing cells (the stratum basale), which lies at the base of the epidermis, is well-nourished by dermal blood vessels

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Fig06.02

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Stratum corneum

Stratum lucidum

Stratum granulosum

Stratum spinosum

Stratum basale

Basement membrane

Dermis

Dermal papilla

(a) (b)©The McGraw-Hill Companies, Inc./Al Telser, photographer

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3. Cells are pushed outward as new cells are formed, and

become keratinized as they die. Four or five layers may be seen: stratum basale, stratum spinosum, stratum granulosum, and stratum corneum are always present and the stratum lucidum is found in the thicker palms and soles.

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4. The epidermis is important because it protects against water loss,

mechanical injury, chemicals, and microorganisms.5. Melanocytes, which lie deep in the

epidermis and underlying dermis, produce a pigment called melanin that protects deeper cells from the sun's ultraviolet rays.6. Melanocytes pass melanin to

nearby cells through cytocrine secretion.

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Fig06.03b

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Epidermis

Dermis

(b)

Cellularextensionof melanocyte

Pigmentgranules

Golgiapparatus

Melanocytenucleus

Basementmembrane

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D. Skin Color

1. Skin color results from a combination of genetic,

environmental, and physiological factors.

2. Genetic differences in skin color result from differing

amounts of melanin and in the size of melanin granules.

3. Exposure to sunlight causes darkening of skin as

melanin production increases.

4. Circulation within dermal blood vessels affects skin color.

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E. Dermis

1. The dermis binds the epidermis to underlying tissues. Epidermal ridges and dermal papillae cause the border to be uneven.

2. The dermis consists of connective tissue with collagen and elastic fibers within a gel-like ground substance.

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3. Dermal blood vessels carry nutrients to upper layers

of skin and help to regulate temperature.

4. The dermis also contains nerve fibers, sensory fibers, hair

follicles, sebaceous glands, and sweat glands.

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Accessory Structures of the Skin

A. Nails

1. Nails are protective coverings over the ends of fingers and

toes.

2. Nails consist of a nail plate and stratified squamous epithelial

cells overlying the nail bed, with the lunula as the most actively growing region of the nail root.

3. As new cells are produced, older ones are pushed outward and

become keratinized.

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Fig06.04

Nail bed Nail plateLunulaCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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B. Hair Follicles 1. Hair can be found in nearly all

regions of the skin except palms, soles, lips, nipples, and portions of external genitalia.

2. Each hair develops from cells at the base of a tubelike

depression called the hair follicle. The dermis

contain the hair root.3. As new cells are formed, old cells are

pushed outward and become keratinized, and die

forming the hair shaft.

Fig06.05a

(a)

Hair shaft

Pore

Hair root(keratinizedcells)

Arrector pilimuscle

Sebaceousgland

Basementmembrane

Hair follicle

Region ofcell division

Eccrinesweat gland

Dermalbloodvessels

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Fig06.05b

(b)

Hair follicle

Hair root

Region of celldivision

Adipose tissue

©The McGraw-Hill Companies, Inc./Al Telser, photographer

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4. A bundle of smooth muscle cells, called the arrector pili muscle,

attaches to each hair follicle. These muscles cause goose bumps when cold or frightened.

5. Hair color is determined by genetics; melanin from melanocytes is responsible for most hair colors. Dark hair has eumelanin while blonde and red hair have pheomelanin.

6. The arrector pili muscle attaches to each hair follicle.

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C. Sebaceous glands

1. Sebaceous glands (holocrine glands) are associated

with hair follicles and secrete sebum that waterproofs and moisturizes the hair shafts.

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Fig06.07

Hair follicle

Sebaceous gland

©The McGraw-Hill Companies, Inc./Al Telser, photographer

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D. Sweat Glands 1. Sweat glands (sudoriferous

glands) are either eccrine, which respond to body temperature, or apocrine, which respond to body temperature, stress, and sexual arousal. The secretions exit via a surface pore.2. Modified sweat glands, called ceruminous glands, secrete wax in the ear canal.3. Mammary glands, another

modified type of sweat glands, secrete milk.

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Regulation of Body Temperature

A. Proper temperature regulation is vital to maintaining metabolic reactions.

B. The skin plays a major role in temperature regulation with the hypothalamus controlling it.

C. Active cells, such as those of the heart and skeletal muscle, produce heat.

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D. Heat may be lost to the surroundings from the skin through radiation.

E. The body responds to excessive heat by dilation of dermal blood vessels and

sweating.

F. The body responds to excessive cooling by constricting dermal blood vessels,

inactivating sweat glands, and shivering.

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Healing of WoundsA. Inflammation, in which blood vessels

dilate and become more permeable, causing tissues to become red and swollen, is the body's normal response

to injury.

B. Superficial cuts are filled in by reproducing epithelial cells.

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C. The blood clot and dried tissue fluids form a scab.

D. If the wound is deep, extensive production of collagenous fibers

may form an elevation above the normal epidermal surface forming a scar.

E. Large wounds leave scars and healing may be accompanied by the formation of granulations.

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