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Layers of Skin

• Epidermis• Dermis• Subcutaneous layer

• hypodermis

Stratifiedsquamousepithelium

Dense irregularconnectivetissue

Adipose tissue

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(a)

Hair shaft

Epidermis

Hair follicle

(b)

Sebaceous gland

Dermis

Sweat

Epidermis

Dermis

Hair shaft

Sweat gland pore

Capillary

Stratum corneum

Stratum basale

Dermal papilla

Arrector pili muscle

Lamellated (Pacinian) corpuscle

Basement membrane

Sebaceous gland

Hair follicle

Sweat gland

Nerve cell process

Adipose tissue

Blood vessels

Muscle layer

Sweat gland duct

Subcutaneouslayer

TTactile (Meissner’s) corpuscle

Epidermis

• Lacks blood vessels

• Keratinized

• Thickest on palms and soles (0.8-1.4mm)

• Melanocytes provide melanin

• Rests on basement membrane

• Stratified squamous epithelium

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Epidermis

There are five (5) layers of the epidermis:• Stratum corneum• Stratum lucidum• Stratum granulosum• Stratum spinosum• Stratum basale

Stratum corneum

Stratum lucidum

Stratum granulosum

Stratum spinosum

Stratum basale

Basementmembrane

Dermis

Dermal papilla

(a) (b)

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b: © The McGraw-Hill Companies, Inc./Al Telser, photographer

Skin and Its TissuesSkin Functions

1. Protection- Physical barrier

a. from water lossb. from injuryc. from chemicals and microorganisms

- Chemical barriera. pH or 5-6b. prevents microorganism growth

- Biological barriera. Langerhan’s cells (epidermis)b. Macrophages and mast cells (dermis)

2. Excretion (minimal, most through kidneys!)- urea- uric acid

3. Regulation of body temperature -

Skin and Its TissuesSkin Functions

4. Cutaneous Sensation- Light touch detection = Meissner's Corpuscle's

a. egg-shaped;b. located in dermal papillae;c. populate areas in the fingertips, palms, soles, eyelids, tip of tongue, nipples, clitoris, tip of

penis.

- Pressure detection = Pacinian Corpuscle'sa. onion-shaped;

b. located in deep dermis and subcutaneous regions

- Free nerve endingsa. respond to temperature changes or to factors

that can damage tissuesb. extend into epidermis

Skin and Its TissuesSkin Functions

5. Vitamin D Synthesis- UV rays in sunlight activate its synthesis;- Vitamin D is required for bone homeostasis.

6. Blood Reservoir- The dermis houses about 10% of the body's blood vessels.- Skin only requires 1-2% of the body’s blood

7. Immunity- Langerhan’s cells (macrophages);- interact with T-helper cells in immune responses.

Skin and Its Tissues

Skin and Its Tissues

• Accessory structures of the skin originate from the epidermis and include:

• Hair follicles• Nails• Skin glands

Skin and Its TissuesHair Follicles 1. Epidermal cells that form a tube-

like structure that extends into the dermis

2. Three parts:1. Hair shaft2. Hair root3. Hair papilla

3. Cells that move upward and away from the nutrient supply (papilla) become keratinized and die

3. Pigments include:eumelanin – brownish-

blackpheomelanin – reddish-

yellow

4. Arrector Pili Muscle = a bundle of smooth muscle associated with

every hair follicle. a.

causes hair to stand on end ("goose bumps")

when frightened or cold.

Skin and Its Tissues

Nails

1. Epithelium undergoing keratinization

2. Three parts:

1. Nail plate

2. Nail bed

3. Lunula

3. Functions:

a. manipulation;

b. protection of digit

ends.

Skin and Its TissuesSebaceous Glands 1. holocrine gland (simple

cuboidal epithelium)

2. associated with every hair follicle

3. Secretion = sebum (oil)

a. fat b. cellular material

4. Sebum is secreted into hair follicle

5. Function: Sebum keeps skin &

hair soft, pliable and virtually waterproof.

.

Skin and Its TissuesSweat Glands 1. Two types (based on glandular secretion)

A. Eccrine glands

- Structure: 1. coil in deep dermis2. duct in dermis3. pore at surface

- Characteristics: 1. respond to elevated temperature /

exercise 2. no odor in secretion 3. function throughout life 4. not associated with hair follicles 5. Location: forehead neck back

- Secretion (merocrine) = water plus 1. salts and 2. wastes (urea and uric acid)

Skin and Its Tissues

Skin and Its TissuesSweat Glands or Sudoriferous Glands

B. Apocrine glands - Structure: ducts terminate into hair follicles

- Characteristics: 1. respond to stress / emotions 2. odor in secretion 3. begin to function at puberty &

continue through life 4. associated with hair follicles 5. Location: axillary regions and groin - Secretion (apocrine) = water above plus

1. oil and 2. cellular debris

3. Modified Sweet Glands 1. Ceruminous glands = external ear;

secretion = earwax;2. Mammary glands = breasts; milk.

Skin and Its TissuesSubcutaneous Layer (hypodermis)

1. beneath skin

2. Structure = adipose tissue & blood vessels

3. Function = insulation

Regulation of Body Temperature

Body temperature – balance between heat production and heat loss

At rest, the liver, heart, brain, and endocrine organs account for most heat production

During vigorous exercise, heat production from skeletal muscles can increase 30–40 times

Normal body temperature is 36.2C (98.2F); optimal enzyme activity occurs at this temperature

Temperature spikes above this range denature proteins and depress neurons

Regulation of Body Temperature

Core and Shell Temperature

Organs in the core (within the skull, thoracic, and abdominal cavities) have the highest temperature

The shell, essentially the skin, has the lowest temperature

Blood serves as the major agent of heat transfer between the core and shell

Core temperature remains relatively constant, while shell temperature fluctuates substantially (20C–40C)

Mechanisms of Heat Exchange

The body uses four mechanisms of heat exchange Radiation – loss of heat in the form of infrared rays Conduction – transfer of heat by direct contact Convection – transfer of heat to the surrounding air Evaporation – heat loss due to the evaporation of water

from the lungs, mouth mucosa, and skin (insensible heat loss)

Evaporative heat loss becomes sensible when body temperature rises and sweating produces increased water for vaporization

Role of the Hypothalamus

The main thermoregulation center is the preoptic region of the hypothalamus

The heat-loss and heat-promoting centers comprise the thermoregulatory centers

The hypothalamus: Receives input from thermoreceptors in the skin and

core Responds by initiating appropriate heat-loss and heat-

promoting activities

Heat-Promoting Mechanisms

Low external temperature or low temperature of circulating blood activates heat-promoting centers of the hypothalamus to cause: Vasoconstriction of cutaneous blood vessels Increased metabolic rate Shivering Enhanced thyroxine release

Heat-Loss Mechanisms

When the core temperature rises, the heat-loss center is activated to cause: Vasodilation of cutaneous blood vessels Enhanced sweating

Voluntary measures commonly taken to reduce body heat include: Reducing activity and seeking a cooler environment Wearing light-colored and loose-fitting clothing

Mechanisms of Body Temperature Regulation

Hyperthermia

Normal heat loss processes become ineffective and elevated body temperatures depress the hypothalamus

This sets up a positive-feedback mechanism, sharply increasing body temperature and metabolic rate

This condition, called heat stroke, can be fatal if not corrected

Heat Exhaustion

Heat-associated collapse after vigorous exercise, evidenced by elevated body temperature, mental confusion, and fainting

Due to dehydration and low blood pressure Heat-loss mechanisms are fully functional Can progress to heat stroke if the body is not cooled

and rehydrated

Fever Controlled hyperthermia, often a result of infection,

cancer, allergic reactions, or central nervous system injuries

White blood cells, injured tissue cells, and macrophages release pyrogens that act on the hypothalamus, causing the release of prostaglandins

Prostaglandins reset the hypothalamic thermostat The higher set point is maintained until the natural

body defenses reverse the disease process

Hypothermia – low body temperaturea. very dangerous if core body temperature drops below 94 Fb. limbs can withstand about 65 F because

they contain no vital organs