Chapter 5 Integumentary System Shaft of a hair protruding through the skin Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Integumentary System skin, hair, glands, nails Functions Protection Against abrasion and UV light Prevents entry of microorganisms Prevents dehydration Sensation Sensory receptors detect heat, cold, touch, pressure, pain Temperature regulation by controlling Blood flow through skin Sweat gland activity Vitamin D production Excretion of small amounts of waste products

Skin SA – 1.2-2.2 m2 and weighs 4-5 kg (9-11 lbs)!! 3 major regions Epidermis: outermost region (superficial) Resists abrasion Reduces water loss Dermis: middle region (bulk of skin) Responsible for most structural strength of skin Leather produced from dermis of animals…ewww. Subcutaneous tissue (hypodermis): deepest region Not really part of skin Connects skin to underlying muscle or bone

Fig. 5.1

Tab. 5.1

Epidermis keratinized stratified squamous epithelium 4 distinct cell types 4-5 layers Outer portion exposed to external environment protection

4 Cell Types of Epidermis Keratinocytes Most abundant Produce fibrous protein keratin Gives skin its protective properties Melanocytes Produce brown pigment melanin Found in deepest layers of epidermis Langerhans’ cells Epidermal macrophages Help activate immune system Merkel cells Touch receptors in association with sensory nerve endings

Layers of Epidermis Stratum Basale (Basal Layer) Deepest, firmly attached to dermis Structural strength provided by desmosomes and hemidesmosomes single row of youngest keratinocytes Cells undergo mitotic divisions ~every 19 days 10-25% are melanocytes

Layers of the Epidermis Stratum Spinosum Melanin granules and Langerhans’ cells abundant Melanin taken up by keratinocytes, accumulates on “sunny side” to protect nucleus from UV damage Stratum Granulosum Drastic changes in keratinocyte appearance Keratohyaline and lamellated bodies (waterproofing) accumulate in cells Above this layer epithelial cells die because too far from dermis

Layers of the Epidermis Stratum Lucidum Thin, transparent band superficial to S. Granulosum few rows of flat, dead keratinocytes only in thick skin (soles, palms) Stratum Corneum Outermost layer of keratinized cells ¾ of epidermal thickness 20-30 cell layers thick, all dead Millions rub off everyday. Totally new every 25-45 days. Functions: Waterproofing Protection from abrasion and penetration Rendering body relatively insensitive to biological, chemical, and physical assaults

Fig. 5.2b

Fig. 5.3

Thick and Thin Skin Only 4 strata all 5 epithelial strata fewer cell layers per stratum lucidum usually absent Hair found only in thin skin all 5 epithelial strata Stratum lucidum No hair

Skin Color Melanocytes produce melanin inside melanosomes (vesicles, from golgi), then transfer melanin to keratinocytes size and distribution of melanosomes determine skin color genetic but influenced by UV (tanning) and hormones Increased blood flow produces red skin color (Erythema) decreased flow causes pale skin Decreased oxygen content in blood  bluish color (cyanosis) Carotene, ingested plant pigment, can cause skin to appear yellowish

Fig. 5.4

Dermis 2nd major skin region strong, flexible conn tissue Cell types: fibroblasts, a few adipose cells, macrophages 2 layers: papillary reticular

Papillary layer of Dermis Areolar conn tissue w/collagen & elastic fibers superior surface- peg-like projections “dermal papillae” Genetic fingerprints & footprints Contains blood vessels that supply overlying epidermis With nutrients Remove waste products Aid in regulating body temperature

Reticular layer of Dermis Dense irregular conn tissue ~80% of thickness of skin Collagen fibers add strength and resiliency to skin Elastin fibers provide stretch-recoil properties Striae (stretch marks) caused when skin overstretched, dermis ruptures and leaves visible lines

Reticular layer Elastin and collagen fibers oriented more in one direction than in others produce cleavage, or tension, lines Fig. 5.5

Subcutaneous Tissue Deep to the skin Adipose (primarily) and areolar connective tissue Not really part of skin Stores fat, connects skin to underlying structures (mainly muscles) Shock absorber, insulator Increases as you gain weight

Hair Lanugo (fetal hair) replaced near time of birth by terminal hairs (scalp, eyelids, eyebrows) and vellus hairs At puberty, vellus hairs replaced with terminal hairs Hairs are columns of dead, keratinized epithelial cells Each hair consists of shaft above skin root below skin hair bulb - site of hair formation growth stage and resting stage Contraction of arrector pili, smooth muscles, causes hair to “stand on end”  “goose bumps”

Fig. 5.6

Sebaceous Glands Simple or compound alveolar glands found all over body except palms & soles Soften skin when stimulated by hormones Secrete oily secretion called sebum Acne: active inflammation of sebaceous glands

Sweat Glands Different types prevent overheating of body Secrete cerumen and milk Up to 3 million/person Merocrine sweat glands produce sweat, cools body: most numerous in palms and soles Apocrine sweat glands: axillary and genital areas. Ducts empty into hair follicles. Produce organic secretion, broken down by bacteria to cause body odor Ceruminous glands: modified merocrine glands in external ear canal, secrete cerumen (ear wax) Mammary glands: specialized sweat glands, secrete milk

Fig. 5.7

Nails nail is Stratum Corneum containing hard keratin nail root covered by skin nail body = visible part of nail Nearly all nail formed by nail matrix, but nail bed contributes lunula = part of nail matrix visible through nail body (white “crescent”)

Fig. 5.8

5 Integumentary System Functions 1. Protection Skin Protects against abrasion, UV Prevents entry of microorganisms Helps regulate body temperature Prevents water loss Hair heat insulator Nails protect ends of digits 2. Sensation sensory receptors for heat cold touch pressure pain

Integumentary System Functions 3.Temp Regulation Skin Controls heat loss from body (dilation and constriction of blood vessels) Sweat glands Produce sweat, evaporates, lowers body temperature 4. Vitamin D Production UV stimulates production of a precursor molecule in skin that’s modified by liver and kidneys into vit D Vit D increases calcium uptake in intestines 5. Excretion Skin glands remove small amounts of waste products but not important in excretion

Blood Vessel Dilation, Fig. 5.9

Cancer: Basal Cell Carcinoma Least malignant and most common skin cancer Stratum Basale cells proliferate and invade dermis and hypodermis Slow growing, do not often metastasize 99% Can be cured by surgical excision

Squamous Cell Carcinoma Arises from keratinocytes of Stratum Spinosum Arise most often on scalp, ears, lower lip Grows rapidly, metastasizes if not removed Prognosis is good if treated by radiation therapy or removed surgically

Melanoma Cancer of most dangerous type of skin cancer because it is: Likely to metastasize Resistant to chemotherapy

Melanomas ABCD rule A: Asymmetry; the 2 sides of pigmented area do not match B: Border irregular w/indentations C: Color (pigmented area) is black, brown, tan, sometimes red or blue D: Diameter larger than 6 mm (size of a pencil eraser) Treated by wide surgical excision accompanied by immunotherapy Chance of survival is poor if lesion is over 4 mm thick

Burns First-degree: only epidermis is damaged localized redness, swelling, pain Second-degree: epidermis and upper regions of dermis damaged Symptoms mimic first degree burns blisters also appear Third-degree: entire thickness of skin is damaged Burned area appears gray-white, cherry red, or black; no initial edema or pain nerve endings are destroyed

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Rule of Nines Estimates severity of burns Divides body into areas ~ 9%, or multiples of 9%, of total body area Younger patients are different Burns considered critical if: Over 25% of body has 2nd degree burns Over 10% of body has 3rd degree burns 3rd degree burns on face, hands, or feet

Effects of Aging on the Integumentary System Epidermal replacement of cells slows and skin becomes thinner Decreased elasticity and loss of subcutaneous tissue leads to wrinkles Subcutaneous fat layer diminishes, leading to intolerance of cold Skin becomes dry and itchy Sweat and sebaceous glands are less active number of melanocytes decreases

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