Essentials of Human Anatomy

Skin

Dr Fadel Naim Ass. Prof. Faculty of Medicine IUG

1

Anatomy of Skin

• Skin (integument) is body’s largest organ • Approximately 1.6 to 1.9 m 2 adult in average-sized • Integumentary system describes the skin and its appendages —the hair, nails, and skin glands • Thin and thick skin – “Thin skin”—covers most of body surface (1 to 3 mm thick) – “Thick skin”—soles and palms (4 to 5 mm thick) Slide 2

Functions of Skin

Function of Integumentary System

A. Regulation of Body Temperature B. Protection from Dehydration and Infection C. Respond to Temperature, Pressure, Pain D. Excretion of Water, Salts, Urea (nitrogenous waste) E. Synthesis Vitamin D (essential for Ca + P absorption) F. First Defensive Barrier of Immune Response

Functions of the Skin

• Protection – Physical barrier to microorganisms – Barrier to chemical hazards – Reduces potential for mechanical trauma – Prevents dehydration – Protects (via melanin) excess UV exposure Slide 4

Functions of the Skin

• Sensation – Skin acts as a sophisticated sense organ – Somatic sensory receptors detect stimuli that permit us to detect pressure, touch, temperature, pain, and other general sensations Slide 5

Functions of the Skin

• Flexibility – Skin is supple and elastic, thus permitting change in body contours without injury • Excretion – Water – Urea/ammonia/uric acid Slide 6

Functions of the Skin

• Hormone (Vitamin D) production – Exposure of skin to UV light converts 7-dehydrocholesterol to cholecalciferol — a precursor to vitamin D – Blood transports precursor to liver and kidneys, where vitamin D is produced – Process and end result fulfill the necessary steps required for vitamin D to be classified as a hormone Slide 7

Functions of the Skin

• Immunity – Phagocytic cells destroy bacteria – Langerhans cells trigger helpful immune reaction working with “helper T cells” Slide 8

Functions of the Skin

– Heat loss • approximately 80% of heat loss occurs through the skin; remaining 20% occurs through the mucosa of the respiratory, digestive, and urinary tracts Slide 9

Layers of Skin

• • •

Epidermis Dermis Subcutaneous layer

•

beneath dermis

•

not part of skin

Epidermis

• • • • • •

Lacks blood vessels Keratinized Thickest on palms and soles (0.8-1.4mm) Melanocytes provide melanin Rests on basement membrane Stratified squamous

Structure of the Skin

• Epidermis – Cell types • • •

Keratinocytes —

constitute over 90% of cells present; principal structural element of the outer skin

Melanocytes —

pigment-producing cells (5% of the total); contribute to skin color; filter ultraviolet light

Langerhans cells —

dendritic (branched) antigen-presenting cells (APCs), they play a role in immune response Slide 12

Epidermis

Layers of Epidermis

•

stratum corneum

• • • •

stratum stratum stratum stratum lucidum granulosum spinosum basale

Structure of the Skin

• Epidermis – Cell layers •

Stratum germinativum (growth layer) —

describes the stratum spinosum and stratum basale together – –

Stratum basale (base layer)

are shed

—

single layer of columnar cells; only these cells undergo mitosis, then migrate through the other layers until they

Stratum spinosum (spiny layer)

shapes; cells rich in RNA

—

cells arranged in 8 to 10 layers with desmosomes that pull cells into spiny Slide 14

Structure of the Skin

– Cell layers • • •

Stratum granulosum (granular layer) —

cells arranged in 2-4 layers and filled with keratohyalin granules; contain high levels of lysosomal enzymes

Stratum lucidum (clear layer) —

cells filled with keratin precursor called

eleidin;

absent in thin skin

Stratum corneum (horny layer)

—most superficial layer; dead cells filled with keratin (barrier area) Slide 15

Structure of the Skin

–

Epidermal growth and repair

•

Turnover or regeneration time

refers to time required for epidermal cells to form in the stratum basale and migrate to the skin surface

—about 35 days

•

Shortened turnover time

will increase the thickness of the stratum corneum and result in

callus formation

• Normally

10% to 12%

of all cells in stratum basale enter mitosis daily • Each group of

8 to 10 basal cells in mitosis with their vertical columns of migrating keratinocytes

is called an

epidermal proliferating unit, or EPU

Slide 16

Structure of the Skin

• Dermal-epidermal junction – A definite

basement membrane,

specialized fibrous elements, and a polysaccharide gel serve to “glue” the epidermis to the dermis below – The junction serves as

a partial barrier

to the passage of some cells and large molecules Slide 17

Structure of the Skin

• Dermis – Sometimes called “true skin”—much thicker than the epidermis and lies beneath it – Gives strength to the skin – Serves as a reservoir area for storage of water and electrolytes Slide 18

Dermis

•

On average 1.0-2.0mm thick

•

Contains dermal papillae

•

Binds epidermis to underlying tissues

•

Irregular dense connective tissue

•

Muscle cells

• •

Nerve cell processes Specialized sensory receptors

•

Blood vessels

•

Hair follicles

•

Glands

Structure of the Skin

• Dermis – Contains various structures: • Arrector pili muscles and hair follicles • Sensory receptors • Sweat and sebaceous glands • Blood vessels – Rich vascular supply plays a critical role in temperature regulation Slide 20

Structure of the Skin

• Dermis – Layers of dermis: • •

Papillary layer —

composed of dermal papillae that

project into the epidermis

; contains fine collagenous and elastic fibers; contains the

dermal-epidermal junction

; forms a unique pattern that gives

individual fingerprints Reticular layer —

contains

dense, interlacing white collagenous fibers and elastic fibers

to make the skin

tough yet stretchable

; when processed from animal skin, produces

leather

Slide 21

Lines of Cleavage

• Tension lines in the skin identify the predominant orientation of collagen fiber bundles. • Clinically and surgically significant because cuts can result in slow healing and increased scarring.

Structure of the Skin

• Dermis remains a scar • Dermal growth and repair • The dermis does not continually shed and regenerate itself as does the epidermis Slide 24

Subcutaneous Layer

•

hypodermis

•

loose connective tissue

•

adipose tissue

•

insulates

•

major blood vessels

Structure of the Skin

• Hypodermis – Also called subcutaneous layer or superficial fascia – Deep to the dermis, forming connection between the skin and other structures – Not part of the skin Slide 26

Slide 27

Skin Color

Genetic Factors

•

varying amounts of

•

melanin varying size of melanin

•

granules albinos lack melanin Physiological Factors

•

dilation of dermal blood

•

vessels constriction of dermal blood

• •

vessels accumulation of carotene jaundice Environmental Factors

•

sunlight

• • •

UV light from sunlamps X rays darkens melanin

Skin Color

–

Melanin

• Basic determinant of skin color is quantity, type, and distribution of melanin –

Beta carotene

• (group of yellowish pigments from food) can also contribute to skin color –

Hemoglobin

• color changes also occur as a result of changes in blood flow – Redder skin color when blood flow to skin increases – Cyanosis—bluish color caused by darkening of hemoglobin when it loses oxygen and gains carbon dioxide (Figure 6-9) – Bruising can cause a rainbow of different colors to appear in the skin –

Other pigments

• from cosmetics, tattoos, and bile pigments in jaundice Slide 29

Basis of Skin Color

• The color of skin and mucous membranes can provide clues for diagnosing certain problems, such as – Jaundice • yellowish color to skin and whites of eyes • buildup of yellow bilirubin in blood from liver disease – Cyanosis • bluish color to nail beds and skin • hemoglobin depleted of oxygen looks purple-blue – Erythema • redness of skin due to enlargement of capillaries in dermis • during inflammation, infection, allergy or burns Slide 30

Skin glands

Sebaceous glands

• Secrete sebum—oily substance that keeps hair and skin soft and pliant; prevents excessive water loss from the skin • usually associated with hair follicles • Lipid components have antifungal activity • Simple, branched glands • Found in dermis except in palms and soles • Secretion increases in adolescence; may lead to formation of pimples and blackheads Slide 31

Sweat Glands

•

Widespread in skin

•

Originates in deeper dermis Or hypodermis

•

Eccrine glands

•

Apocrine glands

•

Ceruminous glands

•

Mammary glands

Sweat glands

• Eccrine glands

–Most numerous sweat glands; quite small –Distributed over total body surface with exception of a few small areas –Simple, coiled, tubular glands –Function throughout life –Secrete perspiration or sweat; eliminate wastes; and help maintain a constant core temperature Slide 33

Sweat glands

• Apocrine glands

–Located deep in subcutaneous layer –Limited distribution—axilla, areola of breast, and around anus –Large (often more than 5 mm in diameter) –Simple, branched, tubular glands –Begin to function at puberty –Secretion shows cyclic changes in female with menstrual cycle Slide 34

Sweat glands

Ceruminous glands • Modified apocrine sweat glands • Simple, coiled, tubular glands • Empty contents into external ear canal alone or with sebaceous glands • Mixed secretions of sebaceous and ceruminous glands called cerumen (wax) • Function of cerumen to protect area from dehydration; excess secretion can cause blockage of ear canal and loss of hearing Slide 35

Hair

• Distribution—over entire body except palms of hands and soles of feet and a few other small areas • Fine and soft hair coat present before birth called

lanugo

• Coarse pubic and axillary hair that develops at puberty called

terminal hair

Slide 36

Functions of Hair

• Protection • Heat retention • Prevents the loss of conducted heat from the scalp to the surrounding air • Facial expression • Sensory reception • Visual identification • Chemical signal dispersal

Hair Follicles

• • • •

Epidermal cells Tube-like depression Extends into dermis Hair root

• • • • •

Hair shaft Hair papilla Dead epidermal cells Melanin Arrector pili muscle

A.

B.

Shaft

- projects above surface of epidermis 1. medulla - polyhedral cells with eleidin 2. cortex - elongated cells with/out pigment 3. cuticle - outermost layer, like shingles on roof

Root

- below epidermis, penetrates into the dermis C.

1.

2.

3.

4.

5.

D.

Hair Follicle

hair - at the base a a single external root sheath - basale and spinosum extension internal root sheath - internal hair cell layers bulb - base of hair cell papilla - in the bulb, provides nourishment for hair matrix - origin of new hair cells

arrector pili

hair to rise - smooth muscle, cause E.

nerve bundle responds to touch

hair root plexuses

Slide 40

Slide 41

Slide 42

Appearance of hair

• Color – result of different amounts, distribution, types of melanin in cortex of hair • Growth – hair growth and rest periods alternate; hair on head averages 5 inches of growth per year • Sebaceous glands – attach to and secrete sebum (skin oil) into follicle • Male pattern baldness results from combination of genetic tendency and male sex hormones Slide 43

Hair Thinning and Baldness

•

Alopecia

– hair thinning in both sexes • True, or frank, baldness – Genetically determined and sex-influenced condition

Nails

– Consist of epidermal cells converted to hard keratin – Nail body—visible part of each nail – Root—part of nail in groove hidden by fold of skin, the cuticle – Lunula—moon-shaped white area nearest root Slide 45

• Nail bed—layer of epithelium under nail body – contains abundant blood vessels • Appears pink under translucent nails • Growth—nails grow by mitosis of cells in stratum germinativum beneath the lunula; average growth about 0.5 mm per week, or slightly over 1 inch per year Slide 46

Burns

• Tissue damage from excessive heat, electricity, radioactivity, or corrosive chemicals that destroys (denatures) proteins in the exposed cells is called a

burn.

• Generally, the systemic effects of a burn are a greater threat to life than are the local effects.

• The seriousness of a burn is determined by – Its depth – Extent – Area involved – The person’s age and general health. • When the burn area exceeds 70%, over half of the victims die Slide 47

Burns

• Destruction of proteins of the skin – chemicals, electricity, heat • Problems that result – shock due to water, plasma and plasma protein loss – circulatory & kidney problems from loss of plasma – bacterial infection Slide 48

Types of Burns

• First-degree – only epidermis (sunburn) Slide 49

Types of Burns

• Second-degree burn – destroys entire epidermis & part of dermis – fluid-filled blisters separate epidermis & dermis – epidermal derivatives are not damaged – heals without grafting in 3 to 4 weeks & may scar Slide 50

Types of Burns

• Third-degree or full-thickness – destroy epidermis, dermis & epidermal derivatives – damaged area is numb due to loss of sensory nerves Slide 51

Rule of Nines

Cycle of Life: Skin

• Children – Skin is smooth, unwrinkled, and characterized by elasticity and flexibility – Few sweat glands – Rapid healing Slide 53

Cycle of Life: Skin

• Adults – Development and activation of sebaceous and sweat glands – Increased sweat production • Body odor – Increased sebum production • Acne Slide 54

Cycle of Life: Skin

Aging

• Skin repair processes take longer due to reduced number and activity of stem cells. • Skin forms wrinkles and becomes less resilient. • Skin’s immune responsiveness is diminished.

• Skin becomes drier due to decreased sebaceous gland activity.

• Altered skin and hair pigmentation.

Cycle of Life: Skin

Aging

• Sweat production diminishes. • Blood supply to the dermis is reduced leading to impaired thermoregulation. • Hair thinning and loss. • Integumentary production of vitamin D 3 diminishes. • Development of skin cancers.

Skin and Aging Process

Skin Cancer

• The most common type of cancer. • The greatest risk factor is exposure to UV rays of the sun. • The highest incidence is in people who have had severe sunburns, especially as children.

Skin Cancer

• Most skin tumors are benign and do not metastasize • The three major types of skin cancer are: – Basal cell carcinoma – Squamous cell carcinoma – Melanoma

Basal Cell Carcinoma

• Least malignant and most common skin cancer • Stratum basale cells proliferate and invade the dermis and hypodermis • Slow growing and do not often metastasize • Can be cured by surgical excision in 99% of the cases

Squamous Cell Carcinoma

• Arises from

keratinocytes

spinosum of stratum • Arise most often on scalp, ears, and lower lip • Grows rapidly and metastasizes if not removed • Prognosis is good if treated by radiation therapy or removed surgically

Melanoma

Cancer of melanocytes is the most dangerous type of skin cancer because it is: – Highly metastatic – Resistant to chemotherapy

Melanoma

Melanomas have these characteristics (ABCD rule) –

A

: Asymmetry; the two sides of the pigmented area do not match –

B

: Border is irregular and exhibits indentations –

C

: Color (pigmented area) is black, brown, tan, and sometimes red or blue –

D

: Diameter is larger than 6 mm (size of a pencil eraser)

Melanoma

• Treated by wide surgical excision accompanied by immunotherapy • Chance of survival is poor if the lesion is over 4 mm thick

THE END