Integu

men

tary System

Facts about your Skin

• Inegument = means covering

• Integumentary System- skin, nails, hair, membranes, sweat, & oil glands

• Surface Area = 1.2 to 2.2 square meters• Weight = 4 to 5 kg• Thickness 1.5 - 4.0 mm • 7% of average body weight for an adult

Functions of Skin Protection

Cushions and insulates and is waterproof Protects from chemicals, heat, cold

Not helpful against organic solvents, heavy metals or plant

oils from poison oak Screens UV Acid Mantel keeps down bacteria ~pH 5 Macrophages gobble up invaders

Synthesizes vitamin D with UV

Functions of the Skin

Regulates body heat Sweat 500ml a day if about 31-32 C vessel dilate & constrict

Prevents unnecessary water loss But Lipid soluble – Vitamins and steroids in

Sensory reception (nerve endings)ThermoreceptorsPacinian receptors

• Bumps and deep pressure

Meissner’s corpuscles & Merkel disks• Aware of caress of clothing

Layers of the Skin

1) Epidermis

2) Dermis

3) Hypodermis

1) Epidermis

• Epi = Upon• Keratinized stratified squamous epithelium

• nutrients reach by diffusion/ avascular

• Outer layer of dead skin cells called cuticle with living level underneath

. “Ashiness” is caused by this layer of dead skin cells being very

rough and raggedy

• DUST you see around is made up of dead skin cells!

Epithelium: layers (on left) and cell types (on right)

Remember…

• Four basic types of tissue

– Epithelium – epidermis just discussed

– Connective tissue - dermis

– Muscle tissue

– Nervous tissue

2) DERMIS

Thick, tough, leathery, flexible layer Made of connective tissueVascularized – contains blood vesselsAnchors the epidermisCritical in Temperature regulation – contract and expand

In the dermis:• Oil glands• Sweat glands• Hair follicles• Fat tissue• Nerves• Connective tissue• Blood vessels

Tw

o layers P

apillary – areolar connective tissue; includes dermal

papillae R

eticular – “rticulum” (netw

ork) of collagen and reticular fibers

Fingerprints, palmprints, footprints

Dermal papillae lie atop dermal ridges Elevate the overlying epidermis into epidermal ridges Are “sweat films” because of sweat pores Genetically determined

Flexion creases• Deep dermis from continual folding

Finger Print

3) HYPODERMIS

• Subcutaneous Tissue /Hypodermis / superficial fascia– not really part of skin, but helps with protective

functions– superficial to connective tissue around bones– loose enough for free movement– Adipose tissue – different patters of accumulation for

men and women (grows when we gain weight)– shock absorber & insulator– Deep pressure receptors

Cells of the Epidermis

• Keratinized stratified squamous epithelium

• Four distinct cell types – Keratinocytes

– Melanocytes

– Merkel Cells

– Langerhans’/ Epidermal Dendrite Cells

Keratinocytes

o Most epidermal / superficial cellso Produce keratin – “kera”= horn . Fibrous protein

that gives stretcho Constantly in mitosis & pushed upwardso By the time they are on the surface they are deado New epidermis every 25-45 dayso Friction= keratin formation is accelerated

therefore callus- a thickening of the epidermis

Melanocytes o Spider shaped epithelial

cells that make Melanino Deepest layers of the

epidermiso Melanin made & collects

in granules called melanosomes

o Actin filaments move them along till they are taken up by Keratinocytes

o Granules accumulate on the superficial “sunny side” of the Keratinocytes nuclei & protect nucleus from harmful UV rays

Merkel Cells

o Shaped like a spiky hemisphere

o Help with sensory of touch

Langerhans’ Cells / Epidermal Dendrite Cells

Macrophages (pac mans) that help activate our immune system

Layers of the Epidermis

• Thick skin= covers palms, fingertips, and soles of the feet– FIVE layers/ strata

• Thin Skin= rest of the body– FOUR layers (no

stratum lucidum)

Deep to Superficial:

stratum basalstratum spinosumstrata granulosumstrata lucidum strata corneum

Epidermis and dermis of (a) thick skin and (b) thin skin(which one makes the difference?)

   Stratum basale/ stratum germinativum/ Basal Layer

– Deepest epidermal layer– Single row of cells– Attached to dermis w/ a wavy boarder line– 10-25% of cells are melanocytes & their

branches– undergoing mitosis

stratum spinosum/Prickly Layer

• several cell layers thick

• keratinocyte in this layer are spiny

strata granulosum/ Granular Layer

• 3-5 cell layer

• keratinocyets flatten & start to die– not enough oxygen and nutrients b/c pushed

away from blood source

strata lucidum/ Clear Layer

o       thin translucent band

o       only in thick skin

o       start making distinct layer

strata corneum/ Horny Layer

• 20-30 cells thick• ¾ of epidermal thickness• thickened plasma membrane of cells protects

from abrasion & penetration• glycolipid acts as a “water proof”• protects body from heat and water loss• “dandruff” 18kg= 40 lbs in a lifetime

Skin Color

1. Melanin• same # of melanocytes

• kind + amount of melanin made & retained– Darker = more darker melanosomes & retain longer

• Freckles & pigment moles are accumulation of melanin

• Sunlight causes melanin buildup– to protect from UV

Skin Color

2. Carotene– Yellow-orange pigment

– Accumulate in the stratum corneum

– Palms of hands, soles of feet

– Eat lots of rich carotene foods- becomes more obvious

3. Hemoglobin– Pinkish hue of light skin b/c can be seen through light

skin

Skin Appendages

• Derived from epidermis but extend into dermis

• Include– Hair and hair follicles– Sebaceous (oil) glands– Sweat (sudoiferous)

glands– Nails

HAIR

• Hair growth: averages 2 mm/week– Active & Resting phase then Shed– At the base of the follicle, hair papilla

• Contains blood vessels and nerves

Bulb• Contains matrix – epithelial cells responsible for

growth

– Contains melanocytes

• Functions of hair– Warmth – Sense light touch of the skin– Protection – scalp

• Hair color– Amount of melanin for black or brown; distinct form of

melanin for red– White: decreased melanin and air bubbles in the medulla– Genetically determined though influenced by hormones

and environment

Hair and hair follicles: complexDerived from epidermis and dermis

Everywhere but palms, soles, nipples, parts of genitalia

*“arrector pili” is smooth muscle*

Hair papilla is connective tissue________________

Hair bulb: epithelial cells surrounding papilla

Nails

• hard keratin

• Corresponds to hooves and claws

• Grows from nail matrix

Sebaceous (oil) glands

• Entire body except palms and soles• Oils and lubricates

Sweat Glands

• Entire skin surface– except nipples and

part of external genitalia

• Prevent overheating• 500 ml to 12 L /day! • Humans most

efficient (only mammals have)

• Produced in response to stress as well as heat