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The Skin

Skin – our largest organ

—Accounts for 7% of body weight…it weighs twice as much as your brain!
—Divided into three distinct layers
—Epidermis (‘epi” means above something)
—Hypodermis (“hypo” means deep to something)
—A hypodermic needle means a long hollow needle that reaches all the way from the epidermis to the hypodermis.
Functions of skin
¨Cushions and insulates and is waterproof
¨Protects from chemicals, heat, cold, bacteria
¨Screens UV
nSynthesizes vitamin D with UV
nRegulates body heat
nPrevents unnecessary water loss
nSensory reception (nerve endings)


—Primarily made up of keratinized stratified squamous epithelium
—The EPIDERMIS is the layer that gives strength to the skin.
—Varies in thickness from a few cells (eyelids) to dozens of cells thick (palms and soles of feet)
—It does not have any vascularization (blood supply), so it relies on absorbing oxygen and nutrients from the blood vessels in the dermis deep to it.
—The nails are made in the epidermis.
 Layers of the Epidermis


—Stratum corneum (most superficial layer of epidermis)
—Stratum lucidum (only in thick skin)
—Stratum granulosum
—Stratum spinosum
<span style="font-family:" font-size:18px"="">—Stratum basale (the deepest layer of epidermis)

 How to remember the layers of the epidermis



—The epidermis has five layers. From deep to superficial, they are the stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum.
—To remember which one is the deepest layer, visualize your basement. That is the stratum basale.
—To get from your basement (deepest layer) to the roof (superficial layer), walk up your basement careful! They are covered with cactus spines (stratum spinosum).
—That leads you to the kitchen, where someone has spilled sugar all over the floor (stratum granulosum).
—Then you go upstairs and stop to put on suntan lotion before you go to the roof. The stratum lucidum is like a layer of suntan lotion; it protects from UV rays, but is only present on the palms and soles, so that's where you picture yourself applying the lotion.
—Now you are ready to go to the roof and enjoy a nice popcorn (stratum corneum).

STRATUM BASALE: has 4 types of cells

—The cell type that makes the epidermis is a KERATINOCYTE
—Keratin is a protein made by these cells.
—Keratin is waterproof and strong
—Merkel cells: used as sensory receptors for the sense of light touch.
—MACROPHAGES: ingest debris
—MELANOCYTES produce MELANIN (dark brown pigment; the only color pigment we can produce)
—Everyone has the same number of melanocytes
—But they don’t all make the same amount of pigment, so people have different skin colors.




—Greek "melan " ("black, dark") and "cholē" ("bile"). Medical practitioners once adhered to the system of humors—bodily fluids that included black bile, yellow bile, blood, and phlegm. An imbalance of these humors was thought to lead to disorders of the mind and body. One suffering from an excess of black bile (believed to be secreted by the kidneys or spleen) could become sullen and unsociable—liable to anger, irritability, brooding, and depression. Today, doctors no longer ascribe physical and mental disorders to disruptions of the four humors, but the word "melancholia" is still used in psychiatry as a "subtype" of clinical depression.
—Melanin is a dark brown pigment, found in the epidermis.
—This is the only layer of the epidermis where the cells are dividing.
—As new cells are made in the S. Basale, the older cells get pushed up and become the next layer (S. Spinosum)


—They are now attached to each other by desmosomes, which are pointy/spiny (“spinosum”)
—The cells are still alive, but they no longer divide in this layer. They are not dead, just in “menopause”!
—Also contains Langerhan’s cells, which are white blood cells that function in the immune response. They are made in the red bone marrow.
—The stratum spinosum provides the strength to the epidermis
—As more new cells are made in the S. basale, the S. spinosum layer is pushed up to become the S. granulosum layer.
—The cells in the S. granulosum begin to die because they are now too far from nutrient source (in dermis).
—The cells now have a grainy appearance, so this layer is called the stratum granulosum.
—Keratin is a waxy protein substance only found in the epidermis. It makes up the nails, hair, and is also in each superficial skin cell.
—It can absorb water like a chamois cloth that is used to dry your car, so keratin swells when soaking wet. It makes the skin look wrinkled on your fingers and toes when you are in the tub too long.
—The water evaporates when you dry off, and because of water’s cohesive abilities, it sticks to itself and pulls more water out of your body, so soaking in the tub will dry your skin out…unless you put lotion on right away to block evaporation and keep the water in the epidermal layers. Lotions will not penetrate to the epidermis or dermis, just water.



—The secret ingredient of all moisturizers is WATER.  They work superficially on the epidermis.  Although keratin is waterproof, it swells when wet. 
—So, if you put a moisturizer on skin, stratum corneum expands, and hides wrinkles. 
—You get the same effect by soaking in the tub and putting on any lotion, and that’s cheaper than expensive creams. 
—As more new cells are made in the S. basale, the cells are all pushed up again, and the S. granulosum layer becomes the S. Corneum.
—In this layer, the dead cells fill up with KERATIN.
—The cells lose their nucleus and fuse to squamous (flat) sheets, which are shed from the surface in about 2 weeks. This process is called desquamation.
—The main difference between thick skin and thin skin relates to the thickness of the Stratum corneum.
—It takes about 15-30 days for a cell to move from the stratum basale to the stratum corneum and another 2 weeks for it to shed
—We lose half a million cells per hour; 1.5 grams a day
—That can be a major source of dust in the house
—Dust allergies are actually from  the feces and saliva of dust mites which eat the dead skin. One house has 3 million poops per day from dust mites!
—Why do black-skinned people have lighter colored palms and soles?
—Only the Stratum Basale has pigment-containing cells, but the stratum lucidum contributes the color of protein, which is an orange- tan color.
—In the palms and soles, the stratum lucidum is present. The tan colored protein blocks the underlying melanocytes from view.
Conditions of the Epidermis
—If you frequently rub one area of the skin, it stimulates cell division = callous
—If you rub the skin too hard, the stratum basale tears away from the basement membrane, and causes a gap, which fills with fluid: BLISTER. 
—The epidermis then dies because it’s too far away from nutrients.  That’s why the top of a blister dries up.
                                                                                                                                               If the blisters are small (less than 5 mm in diameter), they are known as vesicles; if they are larger (greater than 5 mm in diameter), they are termed bullae. 
 Skin Healing
—Individual skin cells do not have a high metabolic rate, and construction of scar tissue is more difficult than making normal skin. You get a scar only if the dermis is excessively damaged.
—Remember that the epidermis does not have blood supply and the fibroblasts are only present in the dermis, and they make the collagen and repair wounds. 
—The skin is capable of repair, even after serious damage, because stem cells persist in both the epidermis and the dermis.
Conditions of the Epidermis

Skin Cancer:

—This is the most common cancer in the USA, and the major risk factor of all skin cancers is exposure to ultraviolet light.

Three major types:




1)BASAL CELL CARCINOMA: Cancer of the cells in the stratum basale (except not the melanocytes).
—The most common type of skin cancer, accounts for about 75% of the skin cancers.
—Almost never metastasizes or crosses the basement membrane, so is almost never fatal.
—It is the most easily cured: surgical removal, no chemotherapy or radiation usually needed.
—Symptoms are minor: shiny nodules, usually on nose, face, or other sun exposed areas.

NOTE: signs are what a doctor sees, symptoms are what a patient experiences.

1)BASAL CELL CARCINOMA: Cancer of the blood vessels.
•Almost never metastasizes or crosses the basement membrane
•Looks like shiny nodules
1)BASAL CELL CARCINOMA: Cancer of the blood vessels.
•Almost never metastasizes or crosses the basement membrane
•Looks like shiny nodules


—  25% of all skin cancers


—  25% of all skin cancers
—  Will metastasize if not treated.

  Will metastasize if not treated

3) MELANOMA: cancer of the melanocytes of the epidermis; least common (about 1% of skin cancer)

—Highly metastatic, causes 75% of skin cancer deaths.
—Asymmetrical, sharp but irregular borders and edges
—Not uniform in color.

3) MELANOMA: cancer of the melanocytes of the epidermis; least common (about 1% of skin cancer)

—Highly metastatic, causes 75% of skin cancer deaths.
—Asymmetrical, sharp but irregular borders and edges
—Not uniform in color.

3) MELANOMA: cancer of the melanocytes of the epidermis; least common (about 1% of skin cancer)

—Highly metastatic, causes 75% of skin cancer deaths.
—Asymmetrical, sharp but irregular borders and edges
—Not uniform in color.

3) MELANOMA: cancer of the melanocytes of the epidermis; least common (about 1% of skin cancer)

—Highly metastatic, causes 75% of skin cancer deaths.
—Asymmetrical, sharp but irregular borders and edges
—Not uniform in color.

Autoimmune conditions of the skin -

—Atopic dermatitis (autoimmune allergy to own skin)
—Contact dermatitis (allergy to something touched)
—Seborrheic dermatitis



—Itchy red skin that comes and goes.
—The most frequently occuring form of eczema is ATOPIC DERMATITIS.

Caused by an autoimmune reaction

—Triggered by allergens like soaps, cosmetics, clothing, detergents, jewelry, or sweat.
—Can be triggered by hot weather or stress.
—Tends to run in families.

Treatment is lubricant creams daily and steroid creams during outbreaks

Contact Dermatitis-

—Localized reaction from an allergy to something you touch.
—Common allergens are plastic shoes, latex gloves, detergents, perfume, makeup, jewelry, etc.
—People with a history of pollen allergies are more likely to get contact dermatitis from other  objects.
Seborrheic dermatitis -
—In Children, it is called “Cradle Cap”
—In Adults, it is called severe dandruff
—Caused by an allergy to the fungus that we all have around our hair roots.
—The skin cells proliferate in an attempt to shed the fungus. The result is severe dandruff that does not respond to regular dandruff shampoo.
—Treatment is shampoo with ketoconazole (steroid) or coal tar. Usually works for one year, then you have to switch to another product for a year, then switch back.


—An autoimmune disease of the skin (the body’s immune system thinks the skin is foreign so it attacks it).
—Causes silvery flaking of skin, especially knees, elbows, scalp.
—It is not itchy
—There are treatments, but no cure.
—Treatments include shampoo with coal tar or steroids.

1)  PAPILLARY LAYER (Papillary = “Pimple”.  Has bumps)

—The papillary layer of the dermis; LOOSE connective tissue.
—Has ridges to increase surface area for contact with the epidermis because the blood vessels and nutrients from them are only in the dermis.
—The papillary layer in the DERMIS is what forms our fingerprints.
—Surgeons make incisions on the body based on the lines of cleavage of the skin formed by the papillary layer of the DERMIS


—DENSE IRREGULAR Connective Tissue
—Gives the dermis its strength.
—Remember, the epidermis is the strongest layer of the SKIN, and the stratum spinosum is the strongest layer of the epidermis. But the reticular layer of the dermis is the strongest layer of the DERMIS.
—The dermis has lots of COLLAGEN and ELASTIN (elastic fibers)
—The DERMIS is where most of the body’s collagen is found.
—Stretch marks are caused from tiny tears in the collagen of the DERMIS.
Leather is made of the dermis
—The dermis is also the area where all the skin glands of the body are located.
—A transdermal patch (nicotine patch, etc) must diffuse all the way from the epidermis into the dermis to reach the blood vessels there.
—The blood vessels in the dermis are what gives a pink color to Caucasian people.
Dermis Conditions-

What happens when you get cut?

—Bleed, then clot
—Macrophages eat foreign bodies and dead cells
—Fibroblasts lay down collagen to repair the wound. If they produce more than normal, you get a SCAR.
—If skin is cut with the grain (line of cleavage), scar is not bad; it does not have tension on it.  Against the grain, the scar is worse.
—Some people are more prone to scar tissue than others.
Keloid Scars-
—Thick, red, sometimes painful scars
—More common in African American, Native American, and Asian races
—Treatment with cortisone injections
—Keloid scar formers can get internal adhesions also

BURNS: Three types:

—FIRST DEGREE:  Minor burn to the epidermis; sunburn
—SECOND DEGREE: Dermis separates from epidermis; blister
—THIRD DEGREE: Hypodermis is burned. (most severe type of burn)


—2˚ and 3˚ burns over a large part of the body gives a survival chance proportional to the amount of skin left. 60% burn = 60% chance of dying.


—Epidermis and dermis are destroyed from pressure, underlying tissue is exposed.
—How decubitus ulcers form:
—If you’re sitting down, weight of the body presses against blood vessels, no blood flow to skin of buttocks.  In you, it’s ok, because you’ll be walking around again soon.  But if it goes on longer than a couple of hours because one can’t move, tissues can’t get oxygen.  Ulcer forms, can get gangrene (tissue death).
—It can also become systemic (bacteria enter the wound, travel in the blood), which can cause death.  Whose fault is it?  The nurse’s, for not moving the patient every couple of hours
—Cellulitis is inflammation in subcutaneous layers of the skin, due to infection.
—Cellulitis can be caused by normal skin flora (bacteria) or by exogenous bacteria, and often occurs where the skin has previously been broken: cracks in the skin, cuts, blisters, burns, insect bites, surgical wounds, intravenous drug injection or sites of intravenous catheter insertion.
—Treatment with appropriate antibiotics is needed, and recovery periods last from 48 hours to six months.

SKIN COLOR; Caused by four things:

1)  MELANIN: (dark brown pigment). More melanin, darker the skin.

2) CAROTENE: (a yellowish/orange pigment found only in plants). Accumulates more in the skins of Asians and Native Americans.

3) SKIN THICKNESS: thinner skin see blood vessels, looks pinker

4) HEMOGLOBIN: The DERMIS contains the blood vessels that give Caucasians the pink color to the skin.  Even veins are red because blood is red.  But when you look at veins through the adipose layer (the hypodermis), they look blue.


Dietary sources of carotene (These are also high in Vitamin A)

—sweet potatoes
—cantaloupe melon


—Why does a bruise look black and blue?  The vessels in the hypodermis are ruptured, and the blood leaks out; looks blue.  As it ages, the hemoglobin breaks down to a green color, then a yellow color.

The color of the bruise depends on the age of the bruise

CYANOSIS: Bluish color to skin.

—Caused by superficial blood vessel constriction in the dermis or lack of blood flow to skin
—Occurs for two reasons:

1) Cold

2) Not enough oxygen in body to go around.  The oxygen is conserved for the vital organs, so oxygen to skin and nails is shut down.


—Pigment is injected into the dermis. If the needle is sterile, there’s no health risk.
—However, the pigment diffuses with time.  What looks good in your 20’s will look like a blob when you’re 50.


—Some of the largest sebaceous glands are associated with the smallest hairs (face). 
—Pimples begin when oil gland ducts (sebaceous glands) become blocked by viscous (thick) sebum and the gland swells. It opens up the pore and the skin bacteria can get in and start an infection.
—The sebum in the gland is exposed to oxygen and turns black, called a blackhead.
—The black part of a blackhead is oxidized sebum.
—In puberty, there is an increase in hormones, and an increase in gland secretion, leading to pimples.
—Acne and skin aging:
—After years and years these cells become more and more damaged. Eventually, the collective cells that make up organs become so damaged the organ fails to function, such as the loss of vision or hearing as people age. This process of damage and dysfunction of the vital organs eventually leads to death.
—Most of this damage is caused by free radicals. Free radicals are minute chemical particles (atoms or groups of atoms) which are frequently the by-products of chemical processes. For example, when two chemicals join together to form another chemical, some particles are eliminated and these can be free radicals. Free radicals have at least one unpaired electron, causing the chemical particle to be unstable. To become stabilized the particle must obtain an electron from some another chemical. By taking an electron from another chemical, the free radical becomes a stable chemical, but the other chemical now becomes a free radical and its chemical structure is changed. It must then steal an electron. Thus the chain reaction (of atoms stealing electrons) continues and can be thousands of events long.
—The skin produces hydrogen peroxide to fight each acne infection and this may continue for weeks, until the infection is resolved. Hydrogen peroxide is a free radical which causes skin damage and skin aging. Over a period of time the volume of hydrogen peroxide acts just like continual sun exposure, damaging skin components such as collagen and causing the skin to sag and wrinkle.
Acne Vulgaris-
—Acne develops as a result of blockages in hair follicles.
—Hyperkeratinization and formation of a plug of keratin and sebum (a microcomedo) is the earliest change.
—Enlargement of sebaceous glands and an increase in sebum production occur with increased androgen (DHEA-S) production at adrenarche.
—The microcomedo may enlarge to form an open comedone (blackhead) or closed comedone (milia)
Clinical Manifestations-


—Closed comedone (Whitehead): when a pore clogs up beneath the skin and closes.
—Open comedone (Blackhead): when a pore clogs up and reaches the surface of the skin, but stays open.
—Papules: inflamed, tender lesions that pop up as small, pink bumps on the skin.
Pustules: pimples topped by white or yellow pus-filled lesions.
Cysts and nodules - large, inflamed, pus filled lesions deep under the skin that can cause pain and scarring.


2.Inflammatory: Inflammatory lesions vary from small papules with an inflammatory areola to pustules to large, tender, fluctuant nodules (nodular).
3.Scars: These appear as depressed or hypertrophic papules of varying sizes and shapes.
Acne Vulgaris: Cause-
—The tendency to develop acne runs in families.
—. Other associations such as chocolate and salt aPSYCHOLOGICAL
—It is associated with increased stress levels
—A high glycemic load diet is associated with worsening acne. There is also a positive association between the consumption of milk and a greater rate and severity of acnere not supported by the evidence. However, products with these ingredients often contain a high glycemic load.
—Hormonal activity, such as menstrual cycles and puberty, may contribute to the formation of acne.
—During puberty, an increase in male sex hormones called androgens cause the follicular glands to grow larger and make more sebum.

Use of anabolic steroids may have a similar effect

—Development of acne vulgaris in later years is uncommon, although this is the age group for rosacea, which may have similar appearances.

True acne vulgaris in adult women may be a feature of an underlying condition such as pregnancy and disorders such as polycystic ovary syndrome or the rare Cushing's syndrome

Furuncles (BOILS)

—Unlike pimples, boils are caused by bacteria that enter a gland and invade into the hypodermis.
—They are local infections that swell to a size that is larger than pimples.

They are not blackheads. 

—Most boils run their course within four to ten days. For most people, self-care by applying a warm compress or soaking the boil in warm water can help alleviate the pain and hasten draining of the pus ("bringing the boil to a head").
—Once the boil drains, the area should be washed with antibacterial soap and bandaged well.
—In serious cases, prescription oral or topical antibiotics are used.
—A carbuncle is a mass of boils which drains pus onto the skin. It is usually caused by bacterial infection, most commonly Staphylococcus aureus, or Streptococcus pyogenes, which can turn lethal.
—The infection is contagious and may spread to other areas of the body, or other people; those living in the same residence may develop carbuncles at the same time (mass of boils)
WARTS-Warts are caused from a virus that can only get in if there is a break in the skin. It starts multiplying itself, forming a benign local tumor. Therefore they are found on the hands of people who get a lot of scratches and the feet of those who go outside without shoes.

Cancer starts out as a mutation in one gene in one cell.  Then the mutated cell starts dividing rapidly and taking over the whole area.

—LEUKEMIA is a cancer in blood-forming cells.
—LYMPHOMA is a tumor developing in lymphatic tissues.
—CARCINOMA is a tumor developing in any part of the epithelium.
—MELANOMA is a tumor developing in the pigment-producing cells of the skin. It is a particular type of carcinoma.
—SARCOMA is a tumor developing in muscles, bones, organs, and connective tissues.


—Normal cells have specialized functions, but cancer cells do not differentiate and do not contribute to the function of the body.
—They have large or multiple nuclei with mutated chromosomes.
—Cancer cells grow and divide rapidly until they accumulate and form a lump of cancer cells called a tumor.  A BENIGN tumor is an accumulation of non-cancerous cells because they stay in their own capsule (encapsulated) and do not invade.


—Since these tumors need nutrients, they create new blood vessels just for them to feed on.


—Pieces of the tumor break off and travel in the bloodstream to any new location, invade nearby tissues and continue their massive cell division and growth there. If there is a tumor in the lung, it is biopsied (the doctor surgically takes out a piece). If the cells are lung cells, it is lung cancer. But if the cells are pancreas cells, it is pancreatic cancer that has metastasized.


—There are many factors that play a role in the development of cancer, including heredity factors, carcinogens, and mutagens.
—CARCINOGEN is an environmental agent that contributes to cancer. Not everyone exposed to it gets cancer. Examples of a carcinogen are ultaviolet radiation, toxic chemicals, and viruses.

MUTAGEN is an agent that increases chances of DNA change or mutation. Everyone exposed for long enough will get DNA mutations, and possibly cancer. Examples are x-rays and some medicines (thalidimide; caused birth defects


—a) RADIATION is from overexposure to sunlight.
—b) ORGANIC CHEMICALS include tobacco, foods (salted pork), and pollutants



—PAP SMEARS detect cervical cancers. They just swab the cervix and look at the cells under a microscope.
—MAMMOGRAMS are diagnostic procedures to detect breast cancer. The breast is just placed on a special type of machine like an x-ray.
—20% of breast cancers are not detected by mammogram and can only be detected by ultrasound.
—Those at high risk for breast cancer should get an MRI instead of a mammogram, since the x-ray might induce cancer.
—COLONOSCOPY is a diagnostic procedure to detect colon cancer. A scope is inserted into the rectum so the doctor can look for polyps.

Particular types of cancers run in families, such as breast, lung, and colon cancer

The American Cancer Society says the following are signs of cancer: C-A-U-T-I-O-N

—Change in bowel or bladder habits (colon cancer)
—A sore that does not heal (skin cancer)
—Unusual bleeding or discharge
—Thickening or lump in breast or elsewhere (breast cancer)
—Indigestion or difficulty swallowing (GI system cancer)
—Obvious change in wart or mole (skin cancer)
—Nagging cough or hoarseness (lung cancer)



—DON’T smoke, sunbathe, drink alcohol, or get too many x-rays. Smoking cigarettes is associated with many types of cancers, including cancer of the lung, larynx, throat, and urinary bladder.


—DO be tested (self-breast exams and testicular self-exams every month, and Dr. check-ups), be aware of chemical hazards at work, and be aware that using estrogen for menopause symptoms must be combined with progesterone, otherwise there is an increased risk of cancer.


—Avoid fats, salty, smoke-cured, pork, and pickled foods.
—Eat plenty of fiber, green leafy vegetables and fruits, and eat cabbage, broccoli, Brussels sprouts, and cauliflower, vitamins A and C.
—For more information on smoke-cured meat, read the articles posted at the bottom of our Lecture Unit 1 webpage.



—A.   use broad-spectrum sunscreen
—B.   stay out of the sun altogether from 10-3
—C.   wear protective clothing
—D.   wear sunglasses
—E.   do not use tanning machines




—When someone has surgery to remove a tumor, it is often followed by radiation because the cancer cells may have spread throughout the body.  Cells that are in the process of dividing are the most likely cells to be killed by exposure to radiation. Since cancer cells are always in the process of dividing, exposing them to x-rays may kill them. The x-ray beam is coned down so just the tumor is exposed. However, scatter radiation kills off other cells that rapidly divide (stomach lining and hair follicles), so the side effects include baldness and nausea.


—This is for cancer that has metastasized. It is also good for cancer of the blood (leukemia). The drugs are designed to specifically kill just the cancer cells, but it tends to also kill off the normal blood cells that are just being formed in the bone marrow. Thus, bone marrow transplants are also needed sometimes.


—Someone needs to volunteer to donate a small piece of bone from the crest of their hip. This bone marrow will contain healthy new blood cells that can repopulate the depleted bone marrow of the sick person. These cells are injected into the sick person’s vein.


—Blood cells are taken from the sick person and are fused with an antibody that is specifically designed to seek out and destroy the cancer cell.


—This is new research, attempting to find a gene that will shrink tumors.


—This involves natural healing therapies such as biofeedback, acupuncture, and exotic foods. It’s worth a try if you’re going to die!