Chapter 2

The Integumentary System

Integumentary System The body’s covering Includes: skin, nails, and hairs Skin: cutaneous membrane The skin (integument), is the largest organ of

the body covering over 7600 cm2 (3000 in2)

Structure Two main parts

Epidermis - surface epithelial layer Dermis - deeper connective tissue layer

Subcutaneous (subQ) layer or hypodermis lies deep to dermis; is not part of the skin

Integumentary System

Epidermis Keratinized stratified squamous epithelium Cell types (4):

Keratinocytes Melanocytes Langerhans cells Merkel cells

Epidermal Cells Keratinocytes

90% of epidermal cells 4-5 layers Produce keratin Protects skin Waterproofs skin

Epidermal Cells Melanocytes

Produce melanin that gives color to skin, hairs Transfer pigment to keratinocytes Make up 8% of epidermal cells

Epidermal Cells Langerhans cells

Immune response

Merkel cells Sense of touch Consist of tactile disc and neuron for touch sensation

Epidermal Layers Four Layers (strata)

Stratum basale Includes stem cells; new cells arise here

Stratum spinosum: 8-10 cell layer Cells beginning to look flattened

Stratum granulosum makes keratin Losing cell organelles and nuclei Have waterproofing lipid

Stratum corneum: flattened dead cells Cells here consist mostly of keratin. Cells here are shed and replaced from below.

Layers of the Epidermis

Dermis The dermis has several important

characteristics: is composed of connective tissue containing

collagen and elastic fibers contains two layers the outer papillary region consists of areolar

connective tissue containing thin collagen and elastic fibers, dermal papillae (including capillary loops), corpuscles of touch and free nerve endings

Dermis

The deeper reticular region consists of dense irregular connective tissue containing collagen and elastic fibers adipose cells, hair follicles, nerves, sebaceous (oil) glands, and sudoriferous (sweat) glands

Striae or stretch marks can appear if the skin is stretched too much

Dermis

Lines of cleavage - “tension lines” in the skin indicate the predominant direction of underlying collagen fibers

Epidermal ridges reflect contours of the underlying dermal papillae and form the basis for fingerprints (and footprints); their function is to increase firmness of grip by increasing friction.

Dermatoglyphics - the study of the pattern of epidermal ridges

Skin ColorNormal skin color is caused by the expression of a combination of i)

melanin, ii) carotene & iii) hemoglobin.Melanin – brown-black pigment produced in the melanocytes of the

stratum basaleAll races have virtually same # of melanocytes, but the amount of

melanin produced + degree of granular aggregation of the melanin determine whether an individual’s skin color is black, brown, tan or white

Melanin – protective device against UV damageGradual exposure to sunlight promotes the increased production of

melanin within the melanocytes – tanningAlbino – normal melanocytes but lacks the enzyme tyrosinase

(tyrosine melanin)Vitiligo – lacks of melanocytes in localized area – white spot

Albino vitiligo

Coloration of the Skin

Carotene – yellowish pigment found in epidermal cells and fatty parts of the dermis

Carotene is abundant is the skin of Asians + melanin – yellow-tan skin

Hemoglobin – not a pigment, oxygen-binding pigment found in RBC

Oxygenated blood flowing through the dermis gives the skin its pinkish tones

Accessory Structures Hair Skin glands Nails

Hair Found on most skin surfaces

Not on palmar surfaces of hand and fingers or plantar surfaces of feet

Made of fused keratinized cells

Consists of shaft and root Surrounded by hair follicle

Base is bulb which includes growing matrix producing cells

Nerves in hair root plexuses Muscle that pulls on hair: arrector pili

Causes hair to stand on end

Hair

Humans have three distinct kinds of hairLanugo is a fine, silky fetal hair that appears during

the last trimester of development. Not evident on a baby at birth unless it has been born prematurely.

Angora hair grows continuously in length, as on the scalp of males and females and on the face of males.

Definitive hair grows to a certain length and then ceases to grow. It is the most common type of hair. Eg. eyelashes, eyebrows, pubic & axillary hair.

Glands Sebaceous gland: secrete oily sebum

Connected to hair follicles; keeps hair from drying out

Sudoriferous (sweat) gland Eccrine sweat gland Wide distribution – thermoregulation Apocrine sweat gland Axilla, groin, areolae, beard Contain other cell material

Ceruminous (wax) gland Wax combines with sebum to produce earwax

Nails Plates of packed hard

dead keratinized cells Nail body: major visible

portion Free edge: part

extending past finger or toe

Root: cells deep to here (in nail matrix) form new nail cells

Nails

Functions of Skin Temperature regulation Protection Sensory reception Excretion and absorption: small amounts Vitamin D synthesis

Thermoregulation

Body temperature tends to increase as a result of exercise, fever, or an increase in environmental temperature.

Homeostasis is maintained by the loss of excess heat. The blood vessels (arterioles) in the dermis dilate and allow

more blood to flow through the skin, thus transferring heat from deeper tissues to the skin.

To counteract environmental heat gain or to get rid of excess heat produced by the body, sweat is produced.

The sweat spreads over the surface of the skin, and as it evaporates, heat is lost from the body.

Thermoregulation

If body temperature drops below normal, heat can be conserved by a decrease in the diameter of dermal blood vessels, thus reducing blood flow to the skin.

With less warm blood flowing through the skin, however, the skin temperature decreases.

If the skin temperature drops below approximately 15 degrees Celsius, blood vessels constrict, which helps to prevent tissue damage from the cold.

Contraction of the arrector pili muscles causes hair to stand on end, but with the sparse amount of hair covering the body, this does not significantly reduce heat loss in humans.

Hair on the head, however, is an effective insulator.

Aging Adolescence: can develop acne Most effects in dermis, with visible signs

of aging by about age 40. These include: Loss of collagen fibers Loss of elasticity Loss of immune responses Decreased melanocyte functions:

gray hair, skin blotches Thinning of skin and hairs

Anti-aging treatments

Conditions of the skin & associated structures indicating nutritional deficiencies or body dysfunctions

Condition Deficiency CommentsGeneral dermatitis Zinc Redness & itching

Scrotal or vulva dermatitis

Riboflavin Inflammation in genital region

Hyperpigmentation B12, folic acid, or starvation

Dark pigmentation on backs of hands & feet

Dry, stiff, brittle hair Protein, kcal, & other nutrients

Usually occurs in young children or infants

Follicular hyperkeratosis

Vit A, unsaturated fatty acids

Rough skin due to keratotic plugs from hair follicles

Pellagrous dermatitis Niacin & tryptophan Lesions on areas exposed to sun

Thickened skin at pressure point

Niacin Noted at belt area at the hips

Spoon nails Iron Thin nails that are concave of spoon-shaped

Dry skin H20 or thyroid hormone Dehydration, hypothyroidism, rough skin

Oily skin (acne) Hyperactivity of sebaceous glands

Spoon nail

Additional Info: Sun Safety Tips Watch the clock

Avoid exposure from 10AM – 4PM Sunblock SPF 15 or 30 if at high risk

UVA/UVB Apply 30min before exposure Reapply every 2hrs

Wear sunglasses & protective clothing Do not prolong sun exposure just because

you are wearing sunscreen!

Copyright 2010, John Wiley & Sons, Inc.