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

Functions of the Integumentary System Consists of the skin, hair, glands, and nails Functions Protection Against abrasion and UV light Prevents entry of microorganisms Prevents dehydration Sensation Sensory receptors that can detect heat, cold, touch, pressure, and pain Temperature regulation by controlling Blood flow through the 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)!! Consists of three major regions Epidermis: outermost region (superficial) Resists abrasion Reduces water loss Dermis: middle region (bulk of skin) Responsible for most of the structural strength of the skin Leather is produced from the dermis of animals…ewww. Subcutaneous tissue (hypodermis): deepest region Not really part of the skin Connects the skin to underlying muscle or bone

Fig. 5.1

Tab. 5.1

Epidermis Composed of keratinized stratified squamous epithelium, consisting of four distinct cell types and four or five layers Cell types include keratinocytes, melanocytes, Merkel cells, and Langerhans’ cells Outer portion of the skin is exposed to the external environment and functions in protection

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

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

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

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

Fig. 5.2b

Fig. 5.3

Thick and Thin Skin Only four epithelial strata contains fewer cell layers per stratum Stratum lucidum is usually absent Hair is found only in thin skin has all five epithelial strata Stratum lucidum No hair

Skin Color Melanocytes produce melanin inside melanosomes (vesicles, from golgi), then transfer the melanin to keratinocytes The size and distribution of melanosomes determine skin color Melanin production is determined genetically but can be influenced by UV light (tanning) and hormones Increased blood flow produces a red skin color (Erythema), whereas a decreased flow causes pale skin Decreased oxygen content in the blood results in a bluish color called cyanosis Carotene, an ingested plant pigment, can cause the skin to appear yellowish

Fig. 5.4

Dermis Second major skin region containing strong, flexible connective tissue Cell types include fibroblasts, a few adipose cells and macrophages Composed of two layers: papillary and reticular

Layers of the Dermis Papillary layer Areolar connective tissue with collagen and elastic fibers Its superior surface contains peg-like projections called dermal papillae Genetically determined Responsible for fingerprints and footprints (films of sweat) Contains blood vessels that supply the overlying epidermis With nutrients Remove waste products Aid in regulating body temperature

Layers of the Dermis Reticular layer Dense irregular connective tissue Accounts for approximately 80% of the thickness of the skin Collagen fibers in this layer add strength and resiliency to the skin Elastin fibers provide stretch-recoil properties Striae (stretch marks) are caused when skin is overstretched, the dermis ruptures and leaves visible lines

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

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

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

Fig. 5.6

Sebaceous Glands Simple or compound alveolar glands found all over the body except on the palms and soles Soften skin when stimulated by hormones Secrete an oily secretion called sebum Acne is an active inflammation of the sebaceous glands.

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

Fig. 5.7

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

Fig. 5.8

Integumentary System Functions Protection Skin Protects against abrasion and UV light Prevents the entry of microorganisms Helps regulate body temperature Prevents water loss Hair Acts as a heat insulator Nails protect the ends of the digits Sensation Skin contains sensory receptors for heat cold touch pressure pain

Integumentary System Functions Temperature Regulation Skin Controls heat loss from the body by dilation and constriction of blood vessels Sweat glands Produce sweat, which evaporates and lowers body temperature Vitamin D Production UV light stimulates the production of a precursor molecule in the skin that is modified by the liver and kidneys into vitamin D Vitamin D increases calcium uptake in the intestines Excretion Skin glands remove small amounts of waste products but are not important in excretion

Blood Vessel Dilation, Fig. 5.9

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 of Stratum Spinosum 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: Likely to metastasize Resistant to chemotherapy

Melanoma Melanomas have the following 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) Treated by wide surgical excision accompanied by immunotherapy Chance of survival is poor if the lesion is over 4 mm thick

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

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Rule of Nines Estimates the severity of burns Divides body into areas that are ~ 9%, or multiples of 9%, of the total body area Younger patients are different Burns considered critical if: Over 25% of the body has second-degree burns Over 10% of the body has third-degree burns There are third-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, and the number of melanocytes decreases

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