CHAPTER 6: INTEGUMENTARY SYSTEM

CHAPTER 6: INTEGUMENTARY SYSTEM

I. INTRODUCTION

The integumentary system is the first body system we will study.  Before we begin any study of a body system, we will first think about the organs/tissues that work together to perform the function(s) of that system. 

The integumentary system consists of a major organ, skin, and many epidermal derivatives (accessory organs), which include hair follicles, sebaceous glands, sweat glands, and nails.

In addition, the organs of the integumentary system are composed of many different tissues that perform common functions.  These tissues include stratified squamous epithelium, glandular epithelium, dense irregular CT, smooth muscle tissue, blood vessels, adipose tissue, and nervous tissue.  The functions that these tissues collectively perform are many.  Functions of the skin include protection, excretion, regulation of body temperature, sensory reception, immunity, synthesis of Vitamin D, and blood reservoir.

II. SKIN (Cutaneous Membrane)

A.   General Structure:

                        1. Two distinct regions or layers compose the skin:

                                    a. Epidermis = outermost layer. ( superficial layer )

keratinized stratified squamous ET.

b. 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), and

blood vessels.

b. Subcutaneous layer = adipose tissue; distinct layer beneath skin).

B.        General Functions:

                        Each skin layer has its own unique function:

1. Epi(UPON)dermis = protection.

most superficial layer

2. Dermis = nourishment of epidermis.

3. Subcutaneous layer = insulation.

Layers (strata) from deep to superficial: (Come, Let’s Get Sun Burned)
1. Stratum corneum
2. Stratum lucidum
3. Stratum granulosum
4. Stratum spinosum
5. Stratum basale

C. Epidermis:

1. Structure = keratinized stratified squamous epithelium.

a.      Five distinct layers determined by the extent of keratinization in the epithelial cells:

a.     Stratum corneum = outermost layer composed of dead epithelial cells filled with the protein keratin.( most superficial layer )

b.     Stratum lucidum = translucent layer cells separating stratum corneum from stratum granulosum - only in thick skin of soles & palms( extra layer)

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

d.     Stratum spinosum is composed of many layers of rounded cells with large nuclei

e.     Stratum basale = innermost ( Deepest ) 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.

STEM CELLS ARE DIVIDING CELLS

- divide to regenerate new cells

- cytes= cells is to

            2.  Function = Protection (keratin): 

                                    a.         moisture loss (waterproof).

                                    b.         injury.

                                    c.         microorganisms/chemicals

3. Pigment = Melanin:

                                    a. determines skin color:

                                    b. is produced by melanocytes in stratum basale;

                                    c. People of different races have essentially the same # of melanocytes, but the amount of melanin produced varies (determined by DNA)

                                    d. other factors also affect melanin production: UV rays, chemicals, drugs (antihistamines & antibiotics);

·      Main function is to protect DNA,Nuclei

Note that other factors may affect skin color (but not melanin production):

·      Carotene may accumulate in s. corneum = yellow

·      Hemoglobin (Hb) in dermal blood vessels = pink

·      Lack of Hb in dermal blood vessels = blue (cyanosis.)

D.  Dermis: inner layer of skin; binds epidermis to underlying tissues.

1.     Structure - two distinct layers:

a.     papillary layer (20%) is a below epidermis:

                                                                          i.     composed of loose areolar CT;

                                                                        ii.     surface forms dermal papillae (finger-like projections into the epidermis) which house many

                                                                      iii.     Meissner's Corpuscles (sensory receptor for light touch).

b.     reticular layer (80%) = dense irregular CT; bundles of collagen fibers, elastic fibers, and reticular fibers which give skin its strength and resiliency.

The dermis houses epidermal derivatives or accessory organs

·      Function = nourishment of epidermis.

E. Subcutaneous Layer = beneath skin

·      Structure = adipose tissue & blood vessels.

·      Made up of areolar and adipose

o   Function = insulation.

III. ACCESSORY ORGANS (Epidermal Derivatives)

Consider these structures as extensions of the epidermis (i.e. They are epithelium), although they are located in the dermis.

A.   Hair Follicles:

a.     Structure:

                                               i.     root or base in deep dermis.

                                             ii.     follicle throughout dermis.

                                           iii.      hair shaft in epidermis.

b.     Keratinization

                                               i.     cells are epithelium

                                             ii.     cells in root = active mitosis

                                           iii.      cells in follicle = maturing & accumulating keratin

                                            iv.     cells in epidermis = dead epithelial cells; full of keratin = exposed hair or hair shaft.

c.     Pigment = Melanin

d.     Arrector Pili Muscle = a bundle of smooth muscles associated with every hair follicle. 

                                               i.     causes hair to stand on end ("goose bumps") when frightened or cold.

B.    Merocrine (Eccrine) Glands

a.     Structure:

                                               i.     coil in deep dermis

                                             ii.     duct in dermis

                                           iii.     pore at surface

b.     Characteristics:

                                               i.     respond to elevated temperature / exercise

                                             ii.     no odor in secretion

                                           iii.     function throughout life

                                            iv.     not associated with hair follicles

c.     Location:

                                               i.     Forehead

                                             ii.     Neck

                                           iii.     Back

d.     Secretion (merocrine) = water plus

                                               i.     salts and wastes (urea and uric acid)

C.   Apocrine glands:

a.     Structure: ducts terminate into hair follicles

b.     Characteristics:

                                               i.     respond to stress / emotions

                                             ii.     odor in secretion

                                           iii.     begin to function at puberty & continue through life

                                            iv.     associated with hair follicles

c.     Location:

                                               i.     Armpits

                                             ii.     Groin

d.     Secretion (apocrine) = sweat above plus oil and cellular debris.

e.     Modified Apocrine Glands

                                               i.     Ceruminous glands = external ear; secretion = earwax

                                             ii.     Mammary glands = breasts; milk.

D.   Sebaceous Glands:

a.     holocrine gland (simple cuboidal epithelium)

b.     associated with every hair follicle

E.    Secretion (holocrine) = sebum (i.e. oil), fat, cellular material

a.     Sebum is secreted into hair follicle

b.     Function: Sebum keeps skin & hair soft, pliable and virtually waterproof!

F.    Disorders: 

a.     acne (hypersecretion of sebum; ducts clog & inflamed

b.     seborrhea (hyperproduction of sebum; oily scales).

IV. Skin Functions

A.   Protection:

a.     from water loss

b.     from injury

c.     from chemicals and microorganisms.

B.    Excretion (minimal, most through kidneys!)

a.     Urea

b.     uric acid

C.    Regulation of body temperature

D.   Cutaneous Sensation:

a.     Light touch detection = Meissner's Corpuscle's

                                               i.     egg-shaped

                                             ii.     located in dermal papillae

                                           iii.     populate areas in the fingertips, palms, soles, eyelids, tip of tongue, nipples, clitoris, tip of penis

b.     Pressure detection = Pacinian Corpuscle's

                                               i.     onion-shaped 

                                             ii.     located in deep dermis and subcutaneous regions

                                           iii.     populate areas in the joints, tendons, muscles,  mammary glands, and external genitalia.

E.    Vitamin D Synthesis

a.     UV rays in sunlight activate its synthesis

b.     Vitamin D is required for bone homeostasis.

F.    Blood Reservoir:

                        The dermis houses about 10% of the body's blood vessels.

G.   Immunity:

a.     Langerhans cells (macrophages)

b.     interact with T-helper cells in immune responses.

V.        Life Span Changes

·      Aging skin exhibits:

o   Wrinkling

o   Sagging

o   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.