Skin and the Integumentary System

Chapter 6

What exactly is skin?

• It is an organ composed of several kinds of tissues• Largest organ• Performs many functions

– Maintains Homeostasis– Prevents harmful substances such as chemicals and

microorganisms from entering body– Prevents water loss– Maintains temperature– Houses sensory receptors– Contains immune cells– Produces chemicals such as Vitamin D– Excretes wastes

Two main layers and one below*1. Epidermis

- Outer layer

- Composed of stratified squamous epithelium

2. Dermis- Inner layer- Thicker than epidermis- Made up of connective tissue, smooth muscle tissue,

nervous tissue, blood, and other types of epithelial tissue (glands for example)

*Beneath the dermis is the subcutaneous layer

The epidermis and dermis are separated by the basement membrane that the stratified squamous epithelium is attached to

EPIDERMIS• Lacks blood vessels• Made up of 4 or 5 layers

– Stratum Basale (closest to basement membrane)– Stratum Spinosum– Stratum Granulosum– Stratum Lucidum (Optional)– Stratum Corneum

As each layer gets pushed upward, the cells change their shape and become more squamous or flattened.

Stratum Basale

• The deepest layer – the contains cells that are actively dividing– Attached to the basement membrane– They are closest to the dermis, which contains

blood vessels, so they receive nutrients and O2– As they divide, they push the older cells toward the

top. Cell division prevents wear and tear – the more the use of the body part, the more the cell division (calluses, corns, etc.)

– Specialized cells in this layer called melanocytes, produce melanin, which provides skin color

Stratum Basale

Stratum Spinosum

• A thick layer of squamous epithelial cells right above the stratum basale

Stratum Spinosum

Stratum Granulosum

• A granular layer of squamous epithelium above the stratum spinosum

Stratum Granulosum

Stratum Lucidum• An optional layer of squamous epithelium – only found

in thick skin • Found in palms of hand or soles of feet

Stratum Lucidum

Stratum Corneum– Topmost layer of squamous epithelium. Flatten cells– These cells are called Keratinocytes, because their

cell membranes thicken with a protein called keratin.

– This hardens them, makes them waterproof.– The farther the keratinocytes travel from the stratum

basale, the less nutrients they have, so they eventually die.

– The older keratinocytes develop many desmosomes

– The tough sheet of dead cells is called the Stratum Corneum and is shed (exfoliation)

Stratum Corneum

Layers of the Epidermis

Melanocytes

Melanocytes and Melanin

• Although melanocytes are found in the stratum basale, their product – melanin can be found in other cells of the epidermis and sometimes even in the cells of the connective tissue underneath

• This is because the melanocytes transfer the melanin to the neighboring cells via cellular extensions called dendrites – this process is called cytocrine secretion

More about Melanin• Melanin absorbs UV radiation – prevents skin cancer• Skin color depends mainly on the amount of the brown pigment

melanin produced in the skin. • All people have about the same number of melanocytes.

However, the melanocytes of dark-skinned people produce more melanin than do those of light-skinned people. The amount of melanin produced in each person's skin is determined mainly by heredity.

• Exposure to sunlight increases the production of melanin, causing light skin to tan. In some cases, melanin builds up in small spots, forming freckles.

• As someone grows older, the melanocytes produce melanin at uneven rates, which causes some areas of the skin to remain light and others to darken. These dark spots are sometimes called age spots or liver spots.

Cytocrine Secretion

Sunburn (Solar Erythema)

•Too much UV radiation•Epidermal cells become “sick”•Skin becomes red, swollen and painful•Cell undergo Apoptosis or programmed cell death•Apoptosis kills damaged cells to prevent skin cancer•Stratum basale will replace lost cells

Skin Cancer

• Over exposure to UV light and other genetic and environmental conditions will cause skin cancer

• Thymine dimers (T-T) form in the DNA of DNA repair enzyme genes

• So DNA damage, misspellings cannot be proof-read or repaired

• Mutations develop, leading to cancer

• This occurs in a rare genetic disorder called Xeroderma pigmentosum

The Dermis

• Below epidermis• Boundary between epidermis

and dermis is uneven due to dermal papillae that extend into ridges in the epidermis

• This creates ridges and fingerprints on the palm of the hand and fingers

• Fingerprints are unique and genetically determined

Dermis, cont’d.

• Two types of nerve receptors in the dermis:

1. Pacinian corpuscles: stimulated by heavy touch or pressure2. Meissner’s corpuscles: stimulated by light touch

• Made up of irregular dense connective tissue containing collagen and elastic fibers

• Contains smooth muscle, blood vessels, nerve tissue, hair follicles, sweat glands, and sebaceous glands.

Full-thickness Skin

Subcutaneous Layer

• Below dermis• Composed of loose connective tissue• No clear boundary between dermis and

hypodermis• Contains adipose tissue layer for

insulation• Contains major blood vessels that form a

network called the Rete cutaneum – these send smaller extensions into the dermis

Subcutaneous Layer - Hypodermis

Accessory Organs of the Skin

• Hair follicles

• Nails

• Skin glands– Sebaceous glands– Sweat glands (a.k.a sudoriferous glands)

• Eccrine• Apocrine

Hair Follicles

• Follicles are present on all skin excepts palms, soles, lips, nipples

• In some areas that grow hair, the hair may be fine, while in others it may be thick

• A hair grows out of a deep tube that extends from the surface of the skin, all the way into the dermal layer – this is a follicle

• Each hair follicle is also connected to sebaceous glands that produce oils and other secretions

Hair Follicle, cont’d.

• The follicle contains the growing hair

• The base of the hair is composed of actively dividing epidermal cells

• These epidermal cells are nourished by dermal blood vessels that project into connective tissue that then project into the hair base – this vascularized connective tissue projection is called the hair papilla

Hair Growth• As the epidermal cells divide,

they push older cells upward through the follicle

• As the older cells move away from the nutrient supply, they become keratinized and die

• These dead keratinized epidermal cells are what make up a strand of hair

• Hair color is genetically determined and is pigmented by melanocytes - the more the melanin in the dead epidermal cells, the darker the hair

A strand of hair has three layers: cuticle, cortex, and medulla.  The outermost covering, cuticle consists of hard overlapping protein scales that point toward tips end.  The cortex contains pigment granules that give hair its color.  The medulla is a hollow tube within the hair, which may be present or absent.  Depending on the hair, this hollow tube is continuous, or fragmented. 

Hair Color• White – lacks melanin (albinism)• Gray hair – a mix of pigmented and

unpigmented hair• Black and brown – tons of melanin• Blonds – Less melanin• Red hair – contains an extra pigment

called trichosiderin (iron based)

Goosebumps!• Smooth muscle attached to each hair follicle can

contract and cause short hairs to stand on end• These muscle bundles are called arrector pili

muscles• They appear when scared, excited, cold, etc.

Nails

• Evolved to protect the tips of fingers and toes

• Consists of:– Nail plate (the actual nail)– Nail bed (skin surface on

which the nail plate sits)

• Nail plates are synthesized by special epithelial cells at the base of the nail – a region called a Lunula (half moon shaped)

• As epithelial cells divide, they become keratinized, hard and scaly, and get pushed over the nail bed

Good Nails, Bad Nails

Psoriasis of the nails

Nail Biting

Glands - Sebaceous

• Holocrine glands• Usually associated with hair follicles• Specialized epithelial cells in this gland produce

a fatty secretion that accumulates and bursts through cells

• The final product is a mix of cell debris and fatty fluid – this is called Sebum

• Sebum is secreted into hair follicles• Keeps skin and hair soft, flexible and waterproof• Too much sebum causes pores to clog and

results in acne

Acne

Glands - Sweat

1. Eccrine sweat glands– Most numerous on body– Eccrine ducts are independent of hair

follicles– Respond to heat – secrete sweat to cool

body– Fluid is mostly water, salt, urea and uric acid– Reaches surface of skin through a pore

Eccrine Sweat Glands

Glands - Sweat

2. Apocrine sweat glands– Only found in armpits, groin, nipples– Apocrine ducts open into hair follicles– Become active during puberty– Secrete when excited, upset, anxious, etc.– Apocrine sweat is also basically water and

salts, but also contains sebum and other fats that bacteria love and metabolize – this creates the bad odor in arm pits, etc.

Apocrine Sweat Glands

Temperature Regulation

• Humans (Mammals) are homeotherms ( warm-blooded). This means we maintain a fairly constant body temperature

• We do this mainly by adjusting our rate of cellular respiration and by using organs such as the skin to warm and cool us down

Heat loss is caused by:

• Radiation – heat from body radiates to cooler surroundings

• Conduction – heat from body transfers directly to a cooler surface (your rear end warms your seat, so it feels warm to the touch)

• Convection – heat from the body escapes to cooler air around the body

• Evaporation – when sweat evaporates, it takes body heat away with it, cooling the body

Heat Loss, cont’d.In cold weather, blood vessels

constrict, so that heat is retained in the body.

In hot weather, blood vessels dilate, so heat is lost by convection and radiation Evaporative cooling

As water molecules evaporate, they carry some of the heat with them, thus cooling the surface

they leave behind

Hyperthermia

• Normal body temp – 37C or 98.6F• Body temperature can get elevated during hot

days and physical exercise • Body also elevates temperature (fever) to fight

infection, because some bacterial and viral enzymes are denatured at above normal temperatures

• But extremely high fevers can cause:– Dehydration and loss of electrolytes– the body’s own enzymes and proteins to denature and

lead to death

Cool it!

• Body temperature is reduced by sweating, staying in a cool environment and slowing physical activity

• Drinking plenty of fluids• Fevers can be reduced

by taking ibuprofen and acetaminophen

Hypothermia

• Caused by over exposure to cold temperatures

• Starts with shivering, followed by mental confusion, numbness, lethargy, loss of consciousness and eventually death

Accidents

• Cuts

• Burns

Clots

When an injury such as a cut occurs, platelets become activated platelets. They change their shape, become sticky and build up on a blood vessel wall to form a plug. Platelets are also involved in the secretion of chemical platelet factors into the blood plasma. In a complex series of reactions fibrinogen is converted into fibrin, an insoluble protein that forms an intricate network of tiny threads called fibrils. Blood cells and plasma are tangled in the network of fibrils to form the clot.

Clotting and Healing

Scars

• If a cut is deep into the dermis, new connective tissue develops in the normal epidermis

• This new “skin” lacks hair follicles, sweat glands, and other components of normal skin

BurnsBurn injuries can be classified as thermal (heat), chemical, or

electrical.• Thermal (heat) burns. Not all thermal burns are caused by

flames. Contact with hot objects, flammable vapor that ignites and causes a flash or an explosion, and steam or hot liquid are other common causes of burns.

• Chemical burns. A wide range of chemical agents can cause tissue damage and death if they come in contact with the skin. As with thermal burns, the amount of tissue damage depends on the duration of contact, the skin thickness in the area of exposure, and the strength of the chemical agent. Chemicals will continue to cause tissue destruction until the chemical agent is removed. Three types of chemicals-acids, alkalis, and organic compounds-are responsible for most chemical burns.

• Electrical burns. The severity of an injury from contact with electrical current depends on the type of current (direct or alternating), the voltage, the area of the body exposed, and the duration of contact.

Burn Assessment

For assessment purposes, the body is divided into regions representing 9% (or a multiple of 9)

Three degrees of burns

• First-degree burns are usually limited to redness (erythema), a white plaque and minor pain at the site of injury. These burns usually extend only into the epidermis.

• Second-degree burns additionally fill with clear fluid, have superficial blistering of the skin, and can involve more or less pain depending on the level of nerve involvement. Second-degree burns involve the superficial (papillary) dermis and may also involve the deep (reticular) dermis layer.

• Third-degree burns additionally have charring of the skin, and produce hard, leather-like eschars. An eschar is a scab that has separated from the unaffected part of the body. Frequently, there is also purple fluid. These types of burns are often painless (insensate) because nerve endings have been destroyed in the involved areas.

Aging• Dermis slows down synthesis of collagen and elastin• Fat is lost from subcutaneous layer, so wrinkles appear• Hair follicles reduce in number, hair growth slows or stops• Blood supply to skin, hair and nails is reduced, so nails

change texture, become brittle• Loss of nerve tissue in skin makes less sensitive to

environmental stimuli• Reduced blood supply makes an older person more

susceptible to hypothermia

Young skin vs. Old

Skin Diseases/Rashes

• Chickenpox

• Shingles

• Herpes

• Smallpox

• Fifth Disease

• Impetigo

• Lyme Disease

• Scarlet Fever

• Psoriasis

Chickenpox

• Caused by the varicella-zoster virus. It is characterized by fever and an itchy and blistered rash. It is a highly contagious disease. Although chickenpox-related complications are relatively rare among healthy children, the disease could be more dangerous among infants and the older age groups.

Shingles

• The varicella-zoster virus remains latent or dormant in the body and can later be reactivated and cause shingles (herpes zoster). This new version is NOT contagious.

Herpes

• The herpes simplex virus can cause oral or genital herpes

• There are two types of Herpes Simplex Virus. Both types can cause genital herpes and oral herpes. HSV type 1 usually infects the lips.

• Herpes Simplex Virus type 2 is the usual cause of genital herpes. However, it also can infect the mouth during oral sex.

Smallpox• Smallpox (also known by the

Latin names Variola or Variola vera) was a highly contagious viral disease unique to humans. It is caused by two virus variants called Variola major and Variola minor. V. major is the more deadly form, with a typical mortality of 20–40 percent of those infected. The other type, V. minor, only kills 1% of its victims. Many survivors are left blind in one or both eyes from corneal ulcerations, and persistent skin scarring—pockmarks—is nearly universal.

Fifth Disease (human parvovirus B19)

• Fifth disease is a mild rash illness that occurs most commonly in children. The ill child typically has a "slapped-cheek" rash on the face and a lacy red rash on the trunk and limbs. Occasionally, the rash may itch. An ill child may have a low-grade fever, malaise, or a "cold" a few days before the rash breaks out. The child is usually not very ill, and the rash resolves in 7 to 10 days.

Impetigo• Impetigo, a contagious skin infection that usually

produces blisters or sores on the face and hands, is one of the most common skin infections among kids.

• It is generally caused by one of two bacteria: group A streptococcus or staphylococcus aureus. Impetigo usually affects preschool and school-age children, especially in the summer months.

Scarlet fever

• Caused by an infection with group A streptococcus bacteria. The bacteria make a toxin (poison) that can cause the scarlet-colored rash from which this illness gets its name.

Lyme Disease

• Lyme disease is caused by the bacterium Borellia burgdorferii and is transmitted to humans by the bite of infected blacklegged ticks. Typical symptms include fever, headache, fatigue, and a characteristic skin rash called erythema migrans. Most cases of Lyme disease can be treated successfully with a few weeks of antibiotics. If left untreated, infection can spread to joints, the heart, and the nervous system.

Typical “bull’s eye” rash

THE END