CHAPTER 5

The Integumentary System

INTRODUCTION

The organs of the integumentary system include the skin and its accessory structures including hair, nails, and glands, as well as blood vessels, muscles and nerves. Note that all 4 of the basic tissue types

are well-represented in this organ system.

INTRODUCTION

The Integument is an organ system comprised of many organs such as hair and multiple types of glands.

INTRODUCTION

The integument can also be thought of as a cutaneous membrane that covers the outer surface of the body. It is the largest organ by surface area and

weight. Its area is about 2 square meters (22 square

feet) and weighs 4.5–5kg (10–11 lb), about 16% of body weight.

It is 0.5–4 mm thick, thinnest on the eyelids, thickest on the heels.

We lose almost a kg of skin epithelium a year that becomes a major part of household “dust”.

INTRODUCTION

Besides protection, the skin contributes to: Regulation of body temperature Sensory perceptions Synthesis of vitamin D Emotional expression

It also serves as an important reservoir of blood.

STRUCTURES OF THE SKIN

The skin has 3 major layers: The outer, thinner layer is called the

epidermis and consists of epithelial tissue.

The inner, thicker layer is called the dermis and consists of C.T.

The subcutaneous (subQ) layer (also called the hypodermis) is located underneath the dermis.

Epidermis

Hair shaft

Dermis Reticularlayer

Papillarylayer

Hypodermis(superficial fascia)

Dermal papillae

Pore

Subpapillaryvascular plexus

Appendagesof skin • Eccrine sweat gland• Arrector pili muscle• Sebaceous (oil) gland• Hair follicle• Hair rootNervous structures

• Sensory nerve fiber• Pacinian corpuscle• Hair follicle receptor (root hair plexus)

Cutaneous vascularplexus

Adipose tissue

STRUCTURES OF THE SKIN

STRUCTURES OF THE SKIN

Dermatologist are doctors who treat

disorders of all layers of the

integumentary system.

THE EPIDERMIS

The epidermis is composed of keratinized stratified squamous epitheliumwhich contains four major types of cells: Keratinocytes Melanocytes Langerhans cells Merkel cells

THE EPIDERMIS

Dermis

1. Stratum corneum

2. Stratum granulosum

3. Stratum spinosum

4. Stratum basale

THE EPIDERMIS

THE EPIDERMIS

Types of skin: Thin (hairy) skin covers all body regions

except the palms, palmar surfaces of digits,

and soles.

Thick (hairless)

skin covers the

palms, palmar

surfaces of

digits, and

soles.

THE EPIDERMIS

Skin Pigments Melanin is produced by melanocytes in the

stratum basale• Eumelanin (brown to black)• Pheomelanin (yellow to red)

Freckles are clusters of concentrated melanin triggered by exposure to sunlight.

Having more freckles is a genetic trait.

THE EPIDERMIS

Skin Pigments Nevi (“birthmarks” or moles) are chronic

lesions of the skin – they are, by definition, benign.

Malignant melanoma is a cancer of melanocytes.

THE EPIDERMIS

Skin Pigments

Vitiligo is a chronic disorder that causes depigmentation patches in the skin.

Albinism is a congenital disorder

THE DERMIS

The dermis is composed of

connective tissue containing

collagen and elastic fibers.

It contains two regions: The papillary region The reticular region

THE DERMIS

Dermal papillaeSubpapillaryvascular plexus

• Eccrine sweat gland

Epidermis

Hair shaft

Dermis Reticularlayer

Papillarylayer

Hypodermis(superficial fascia)

PoreAppendagesof skin

• Arrector pili muscle• Sebaceous (oil) gland• Hair follicle• Hair rootNervous structures

• Sensory nerve fiber• Pacinian corpuscle• Hair follicle receptor (root hair plexus)

Cutaneous vascularplexus

Adipose tissue

The Dermis

Lines of cleavage are “tension lines” in the skin that indicate the predominant direction of underlying collagen fibers. Plastic surgeons make their incisions parallel to the

normal cleavage lines in order to minimize scarring.

Epidermal ridges reflect contours of the underlying dermal papillae and form the basis for fingerprints (and footprints) Function to increase firmness of grip by increasing

friction

THE SUBCUTANEOUS LAYER

The subcutaneous layer is also called the hypodermis, and it attaches the skin to underlying tissues and organs.

subQ

BENEFITS OF MULTIPLE LAYERS

Multiple layers in the skin allow for specialization. Adapted to fast turn-over, the

epidermis resists damage and offers protection to underlying tissues.

The dermis provides temperature stability and prevents dehydration, and yet is capable of limited healing.

The subcutaneous tissues insulate, store fat, and anchor the skin.

Sensory Receptors

The skin contains different types of sensory

receptors to differentiate between the

different tactile (“touch”) sensations. Light touch, pressure, vibration, itch and tickle

These sensory receptors are found in different layers:

Superficially

Merkel discs, free nerve endings (detect many stimuli),

Meissner corpuscles, and hair root plexuses

Deep

Pacinian corpuscles

ACCESSORY STRUCTURES OF THE

SKIN

HAIR

Hair is associated with the word “pili”. It is present on most surfaces except the

palms, anterior surfaces of fingers, and the soles of the feet.

It is composed of dead, keratinized epidermal cells.

Genetics determines thickness and distribution.

HAIR

The parts of a hair include: The shaft (above the skin surface) The follicle (below the level of the skin) A root that penetrates into

the dermis includes:• An epithelial root sheath• A dermal root sheath

HAIR

HAIR Types of hairs

Lanugo – fine, nonpigmented, downy hairs that cover the body of the fetus

Vellus hairs – short, fine, pale hairs barely visible to the naked eye

Terminal hairs – long, coarse, heavily pigmented hairs

Hair color is determined by the amount and type of melanin.

SKIN GLANDS

Sebaceous (oil) glands are connected to hair follicles. They secrete an oily substance called

sebum which does 2 important things: Prevents dehydration of hair

and skin Inhibits growth of certain bacteria

SKIN GLANDS

Skin sweat glands Eccrine sweat glands

Apocrine sweat glands

Photomicrograph of a sectioned eccrine gland (220x)

Secretory cells

Duct

Sweat pore

EccrineSweat gland

Skin Glands Eccrine sweat glands release sweat in

response to an emotional stress such as fear

or embarrassment. This type of sweating is

referred to as emotional sweating or a “cold

sweat”.

The secretory portion of apocrine sweat

glands is located mostly in the subcutaneous

layer, and the excretory duct opens into hair

follicles, with sweat secreted during

emotional stress and sexual excitement.

Much of body odor is due to apocrine

sweat.

SKIN GLANDS

Ceruminous glands are modified sweat glands located in the ear canal. Along with nearby sebaceous glands,

they are involved in producing a waxy secretion called cerumen (earwax) which provides a sticky barrier that prevents entry of foreign bodies into the ear canal.

NAILS

Nails are composed of hard, keratinized epidermal cells located over the dorsal surfaces of the ends of fingers and toes.

Nail structures include: Free edge Transparent nail body (plate)

with a whitish lunula at its base Nail root embedded in a fold of skin.

NAILS

Maintaining Homeostasis

Skin damage sets in

motion a sequence of

events that repairs the

skin to its normal (or

near-normal) structure

and function.

WOUND HEALING

Two kinds of wound-healing Epidermal wound healing Deep wound healing

WOUND HEALING

BurnsA burn is tissue damage caused by

excessive heat, electricity, radioactivity, or corrosive chemicals that denature (break down) the proteins in the skin cells. Burns destroy some of the skin's

important contributions to homeostasis—protection against microbial invasion and desiccation, and thermoregulation.

Burns are graded according to their severity.

BurnsA first-degree burn involves only the

epidermis It is characterized by mild pain and

erythema (redness) but no blisters and skin functions remain intact.

BurnsA second-degree burn destroys the

epidermis and part of the dermis - some skin functions are lost. Redness, blister formation, edema, and

pain result.

BurnsA third-degree burn is a full-thickness burn (destroys the epidermis, dermis, and subcutaneous layer). Most skin functions are lost, and the

region is numb because sensory nerve endings have been destroyed.

Burns

According to the American Burn Association's classification of burn injury, a major burn includes: 3o burns over 10% of body surface area;

or 2o burns over 25% of body surface area;

or Any 3o burns on the face, hands, feet, or perineum (which includes the anal and urogenital regions)

When the burn area exceeds 70%, more than half the victims die.

Development of the Integumentary SystemThe epidermis develops from the

ectoderm.

Nails, hair, and skin glands are epidermal

derivatives.

The dermis develops from the

mesoderm.

AGING

The integumentary system changes with age: Wrinkles develop. Dehydration and cracking occurs. Sweat production increases. An increase in the numbers of functional

melanocytes results in gray hair and atypical skin pigmentation.

Subcutaneous fat is lost, and there is a general decrease in skin thickness.

Nails may also become more brittle.

AGING

With age, there is also an increased susceptibility to pathological conditions (as demonstrated by this decubitus ulcer). These type of pressure

ulcers (“bed sores”) are an all-to-common occurrence in nursing homes.