Chapter 6

Skin and the Integumentary system

Skin contains many different types of tissue

General Structure

• Two distinct regions or layers compose the skin:• Epidermis = outermost layer

– keratinized stratified squamous ET

• Dermis = inner layer– keratinized epithelium (hair follicles)– glandular epithelium (sweat, sebaceous glands)– dense irregular CT (collagen)– smooth muscle tissue (arrector pili muscles)– nervous tissue (Meissner's & Pacinian Corpuscles)– blood vessels

• Subcutaneous layer (hypodermis)= adipose tissue– distinct layer beneath skin

SKIN AND ITS TISSUES

(Cutaneous Membrane)

Skin Functions

Protection:• Physical barrier

– from water loss– from injury– from chemicals and microorganisms

• Chemical barrier– pH or 5-6– prevents microorganism growth

• Biological barrier– Langerhan’s cells (epidermis)– Macrophages and mast cells (dermis)

• Excretion (minimal, most through kidneys!):– urea– uric acid

Functions cont.

• Regulation of body temperature

• Cutaneous Sensation:– Light touch detection = Meissner's Corpuscle's– egg-shaped– located in dermal papillae– populate areas in the fingertips, palms, soles,

eyelids, tip of tongue, nipples, clitoris, tip of penis– Pressure detection = Pacinian Corpuscle's– onion-shaped– located in deep dermis and subcutaneous regions

Functions cont.

• Vitamin D Synthesis:– UV rays in sunlight activate its synthesis– Vitamin D is required for bone homeostasis

• Blood Reservoir:– The dermis houses about 10% of the body's blood

vessels– Skin only requires 1-2% of the body’s blood

• Immunity:– Langerhan’s cells (macrophages)– interact with T-helper cells in immune responses

Epidermis • Four distinct layers determined by the

extent of keratinization in the epithelial cells– thickest on palms and soles (0.8-1.4mm)

1. Stratum corneum = outermost layer– composed of dead epithelial cells filled with the

protein keratin

• Stratum lucidum = translucent layer cells separating s. corneum from s. granulosum– extra layer only in thick skin of soles & palms

2. Stratum granulosum is composed of 3-5 layers of flattened granular cells (filled with keratin granules)

Epidermis cont.

3. Stratum spinosum is composed of many layers of spiky cells with large nuclei

4. Stratum basale (germinativum)= innermost layer– directly above basement membrane – composed of a single row mitosing cuboidal

epithelial cells and – composed of melanocytes– specialized cells that produce the pigment

melanin

Epidermis Function

• Main Function = Protection (keratin):– prevents moisture loss (waterproof)– prevents injury by penetration– prevents microorganisms/chemicals entry

• Pigment = Melanin: – determines skin color– is produced by melanocytes in stratum basale

(germinativum)

Dermis

• inner layer of skin

• binds epidermis to underlying tissues

• on average 1.0-2.0mm thick

• Contains several tissue types and structures

Dermis

• Structure: two distinct layers

• papillary layer (20%) is below epidermis– composed of loose areolar CT– surface forms dermal papillae (finger-like

projections into the epidermis) that form fingerprints in thick skin

– Meissner's Corpuscles (sensory receptor for light touch)

Dermis cont.

• reticular layer (80%) = dense irregular CT– which give skin its strength and resiliency bundles

of collagen fibers– elastic fibers– reticular fibers – Pacinian corpuscles –sensory receptors for deep

pressure

• The dermis houses epidermal derivatives or accessory organs (see below)

• Main Function = nourishment of epidermis

Subcutaneous Layer

• Subcutaneous Layer (hypodermis) = beneath skin

• Structure = adipose tissue, blood vessels, loose connective tissue

• Function = insulation

ACCESSORY ORGANS OF THE SKIN

(Epidermal Derivatives)

Hair Follicles

• Structure: – root or base in deep dermis– follicle throughout dermis– hair shaft in epidermis

• Keratinization– made of epithelial cells – cells in root = active mitosis– cells in follicle = maturing & accumulating keratin– cells in epidermis = dead epithelial cells

• full of keratin = exposed hair or hair shaft

Hair Follicles cont.

• Pigment = Melanin

• Arrector Pili Muscle = a bundle of smooth muscle associated with every hair follicle – causes hair to stand on end ("goose bumps")

when frightened or cold

Nails

• Epithelium undergoing keratinization (active mitosis in lunula)

• Functions: – manipulation– protection of digit ends

Sebaceous Glands

• holocrine gland (simple cuboidal epithelium)• Usually associated with hair follicles• Secretion (holocrine) = sebum (i.e. oil)

– fat – cellular material

• Sebum is secreted into hair follicle• Function: Sebum keeps skin & hair soft, pliable and

virtually waterproof• Disorders:

– acne (hypersecretion of sebum; ducts clog & inflame)– seborrhea (hyperproduction of sebum; oily scales)

ACCESSORY ORGANS OF THE SKIN

(Epidermal Derivatives)

Skin Glands

• Skin Glands (Sweat Glands or Sudoriferous Glands)

• Two types (based on glandular secretion):

Merocrine (Eccrine) Glands

• Structure: – coil in deep dermis– duct in dermis– pore at surface

Skin Glands cont.

• Characteristics:– respond to elevated temperature / exercise– no odor in secretion– function throughout life– not associated with hair follicles

• Location: forehead, neck, back

• Secretion (merocrine) = water plus – salts– wastes (urea and uric acid)

Skin Glands cont.

Apocrine glands

• Structure: ducts terminate into hair follicles

• Characteristics:– respond to stress / emotions– odor in secretion– begin to function at puberty & continue through

life– associated with hair follicles

• Location: armpits, groin

Skin Glands cont.

• Secretion (apocrine) = sweat similar to Merocrine plus:– oil and – cellular debris

• Modified Apocrine Glands– Ceruminous glands = external ear

• secretion = earwax

– Mammary glands = breasts• Secretion=milk

• the above structures are epithelial in nature and are actually specialized parts of the epidermis, even though their location is within the dermis

REGULATION OF BODY TEMPERATURE

Heat production and loss

• Heat production is mostly a by-product of cellular metabolism

• Heat loss is controlled by regulating dermal blood flow

• Vasodilation – increases dermal blood flow, which also increases heat loss

• Vasoconstriction – decreases dermal blood flow which decreases heat loss

Heat Loss

• Heat loss is by four methods1. Radiation

– most heat loss by this mode– infrared heat rays move from area of high heat

(i.e. the blood) to areas of low heat (i.e. the environment)

2. Conduction– less heat loss– heat moves by physical contact– the reason the seat you sit in is warm when you

stand up

Heat Loss cont.

3. Convection– heat loss to surrounding air– increases as air movement increases, that is why

turning on a fan cools your body

4. Evaporation– heat loss varies– if heat increases our sweating increases, so we

lose more heat by evaporating the sweat on the surface of our skin

Heat Production

• Low body temperatures require heat loss to be minimized

• The Hypothalamus signals for sweating to decrease (decreasing heat loss by evaporation) and dermal vasoconstriction (decreasing heat loss by radiation)– Usually this brings the body temperature back to normal

• If the body temperature remains low after the above action

• Heat must be produced• Shivering occurs and the tiny muscle contractions

involved produce heat

Figure 06.11

Problems in Temperature Regulation

• Hyperthermia – elevated body temperature– Two common causes– humid air decreases evaporation– air temperature exceeds body temperature, thus

heat is gained not lost

• Hypothermia – low body temperature– very dangerous if core body temperature drops

below 94 F– limbs can withstand about 65 F because they

contain no vital organs– cause is intentional during some surgical

procedures

Skin Color

• Genetic Factors– People of different races have essentially the

same number of melanocytes– the amount of melanin produced varies

(determined by DNA)

• Environmental Factors affect melanin production: by affecting gene expression– UV rays – chemicals– drugs (antihistamines & antibiotics)

Skin Color

• Physiologic Factors may affect skin color (but not melanin production):– Carotene may accumulate in s. corneum = orange– Hemoglobin (Hb) in dermal blood vessels = pink – Lack of Hb in dermal blood vessels = blue

(cyanosis.)– Inability to breakdown Hb (liver problems) =

yellow (jaundice)

HEALING OF WOUNDS AND BURNS

Cuts

• Epidermal cuts are closed by increased cell division in the stratum basale

• Deep cuts involve blood vessel damage resulting in bleeding.– This activates blood clotting mechanisms

Burns

• Superficial partial-thickness burns (1st degree)– Epidermis only– Reddening due to increased blood flow– Mild pain– Common in sunburn – Heals in a few days-2 weeks

• Deep partial-thickness burns (2nd degree)– Epidermis and some dermal damage– Reddening and blistering caused by blood vessel damage– Moderate pain– Common to physical contact with hot objects– Heals in 2-6 weeks without scars unless infected

Burns cont.

• Full-thickness burns (3rd degree)– Epidermis, entire dermis, and potentially

subcutaneal damage– Dry, leathery tissue with red or black color– Severe pain– Caused by prolonged heat or chemical contact– Healing rarely occurs due to lack of surviving skin

cells, skin replacements (grafts) are usually needed, usually extensive scarring

• Autograft – transplant from undamaged area of yourself• Homograft – temporary transplant from cadaver

Burns cont.

• Body Surface affected

• Estimated by “rule of nines”– All of the percentages in the next figures are

multiples/fractions of 9– Add up to 100%

• Important for determining treatment and prognosis

Life Span Changes

• Aging skin exhibits:– wrinkling– sagging– age spots or liver spots

• Efficient regulation of body temperature declines with age

– The number of sweat glands changes– Capillary beds in the skin shrink

• Synthesis of vitamin D declines as skin ages, which affects skeletal health