Chapter 6:
Skin and the
Integumentary
System
Introduction

Skin:




Largest organ
Otherwise known as cutaneous membrane
Forms barrier between our internal environment
and the external world
Vital in maintaining homeostasis
Regulates body temperature
 Prevents water loss
 Houses sensory receptors
 Synthesize biochemicals
 Excretes wastes (very small amount)


Makes up integumentary system
 Includes
skin and accessory organs
LAYERS OF SKIN
Layers

Two layers:
 1)
Epidermis:
 Outer
layer
 Composed of stratified squamous epithelial
tissue
 2)
Dermis
 Inner
layer
 Contains:




Connective tissues (collagenous fibers, elastic fibers, blood)
Epithelial tissue
Smooth muscle tissue
Nervous tissue
Layers

Other layers:
 1) Basement:

 2)
Anchors dermis to epidermis
Hypodermis or Subcutaneous:
Beneath skin
 Contains masses of loose connective and adipose tissue
 Binds skin to underlying organs

Epidermis

Characteristics:
Lacks blood vessels
 Composed of stratified squamous epithelium
tissue
 Divides and grow

Pushes older cells away from dermis and towards
surface
 Become less and less nourished and eventually die
 Keratinization: older cells harden and die (cytoplasm
fills with keratin protein)
 Healthy skin: balances cell division with cell death
 Areas of continual wear: causes fast cell division and
thickened layers called calluses (hands, soles of feet)
and corns (toes)

Epidermis

Layers of epidermis:

Stratum corneum:


Hardened outer layer
(mostly dead, keratinized cells)
Stratum lucidum:
Only present in palms and soles
of feet
 Hardened, thickened layer


Stratum granulosum:


Stratum spinosum:


Very thin layer
More spacious, numerous
Stratum basale:

Nourished by blood vessels in dermis, newest cells, most
nourished, next to basement membrane
Epidermis

Characteristics, cont.:
 Important
 Shields
protective functions
moist underlying tissues against:
Excessive water loss
 Mechanical injury
 Effects of chemicals, mutagens, pollutants
 Pathogens

 Contains
melanocytes (cells which produces
melanin – dark pigment that provides skin
color to protect against UV)
 Albinism:
inability to produce melanin
Epidermis: Skin Color


Largely due to amount of melanin
All people have the same average number of
melanocytes




Differences in color: come from the AMOUNT of
melanin the melanocytes produce
Most genetically determined
Environmental effects: UV (sun and artificial), X-rays
Physiological effects: blood in dermal layer
Red: well-oxygenated;
 Blue (very dark red)-deoxygenated



Called cyanosis
Yellow (diet) – yellow vegetables containing B-carotene
Dermis

Characteristics:

Contain dermal papillae (projections of the dermis
which extend into epidermal spaces)

Fingerprints are as a result of these projections
(determined by genes)
Binds epidermis to underlying tissues
 Composed of dense connective tissue (includes
collagenous and elastic fibers)
 Contains blood vessels (supply nutrients to all
skin cells, regulate body temperature)
 Nerve cells scattered throughout
 Contain hair follicles, sebaceous glands, sweat
glands

Subcutaneous Layer

Characteristics:
Otherwise known as hypodermis
 Contains loose connective and adipose tissues
 Composed of collagenous and elastic fibers
(continuous with those of dermis)
 No sharp boundary between this layer and dermis
 Adipose:

Insulates
 Regulates body temp (conserving body heat, not
allowing heat to enter)


Contains blood vessels
ACCESSORY GLANDS OF SKIN
Nails

Characteristics:
Protective coverings
 Consists of nail plate (overlies surface of the skin
called the nail bed)
 White, base of nail (lunula) – covers the most
actively growing portion of epidermis
 As cells divide here, they keratinize
 Then these keratinized cells become scales that
become part of nail plate

Thumb: slowest
 Middle: fastest

Hair Follicles
 Characteristics:
 Present
everywhere BUT palms, soles,
nipples
 Hair develops from group of epidermal cells
at the base of hair follicle
 Follicle extends from surface into dermis
 Cells nourished via dermal blood vessels
 As cells grow and divide, pushed upward
 As push upward, keratinize and die
Hair Follicles

Characteristics:
Remains become structure of hair (shaft extends
outward)
 Color: determined by genes (direct color and
amount of pigment)
 Arrector pili muscle – smooth muscle, attach to
each hair follicle


These muscles can be stimulated to contract (when heat
is needed) – produces gooseflesh (goosebumps)
Sebaceous glands
 Characteristics:
 Otherwise
known as oil glands
 Closely associated with hair follicles
 Holocrine glands (secrete oily mixture of
fatty and sebum – cellular wastes)
 Secrete
mixture through small ducts
 Sebum – helps keep hair and skin soft, pliable
and waterproof
Sweat glands

Characteristics:
Otherwise known as sudoriferous glands
 Exocrine gland
 Widespread
 Consists of:


Tiny coiled tube laying in subcutaneous layer or deep
dermal layer
Most numerous type: eccrine (respond to body
temperature changes)
 Common forehead, neck and back (produce
profuse sweat)

Sweat glands

Characteristics:

Sweat (fluid) carried away via duct which leads to
pore (on surface)
Sweat is mostly water
 Contains small amount of salt, wastes (urea, uric acid)


Apocrine glands:
Become active at puberty
 Secrete via same mechanism as eccrine glands
 Secrete when person is emotionally upset, frightened or
in pain
 Most numerous in groin and axillary region


Mammary glands:

Modified sweat glands, secrete milk
OTHER FUNCTIONS OF SKIN
Regulate body temperature




Humans: Internal temp = 98.6oF (37oC)
Mammals must balance heat gained with heat
lost
Skin plays vital role in maintaining this
homeostatic mechanism
As body temp drops, nerve impulses stimulate
structures in skin to conserve heat
Blood vessels contract, decreasing flow (reduces
heat loss)
 Sweat glands are inactive
 Muscle contract – producing heat

Regulate body temperature

As body temp rises, nerve impulses stimulate
structures in skin to release heat
Blood dilation (more blood enter, heat
carries/escapes)
 Warm blood reaches hypothalamus (which controls
body temperature set point)
 Eccrine sweat glands release sweat (as sweat
evaporates, heat is carried away from surface)


Hot vs. Cold
Healing Wounds

Inflammatory response:
 Normal
response to injury or stress
 Red, painful, warm, swollen
 Becomes
red when blood vessels dilate and
become more permeable (forces fluids to leave
vessels and enter tissue)
 Advantage: Provides tissue with more nutrients
and oxygen (aid in healing process)
Healing Wounds

Shallow cut
 Epithelium

will divide rapidly, filling in gap
Deep cut
 Blood
vessels break, clot forms
 Clot and tissues form scab (protect
underlying tissues)
 Fibroblasts migrate to injury and begin
forming new collagenous fibers (bind edges
of wound together)
 Scar: forms when connective tissue appears
on surface
Skin Disorders
Disorder Name
Description
Acne
Disease of sebaceous/oil glands
Alopecia
Hair loss
Birthmark
Congenital blemish, visible at birth
Boil
Bacterial infection hair follicle
Dermatitis
Inflammation of skin
Eczema
Noncontagious skin rash, itching, blistering, scaling
Herpes
Caused by herpes simplex virus, recurring formations of
small sores
Keloid
Elevated, enlarged scar tissue
Mole
Fleshy skin tumor, usually pigmented
Psoriasis
Chronic skin condition, red patches
Wart
Flesh-color, raised area, viral infection
Herpes
Dermatitis
Keloid
Alopecia
Boil
Psoriasis
Mole
Eczema
Wart