ethnicity is different...
it is based on shared cultural heritage, ancestry, language, and traditions.

review  question:

which layer of the epidermis produces keratinocytes and melanocytes?

1. basal cell carcinoma affects the stem cells in the stratum basale often on the head, neck, arms, and back which are exposed to the sun. Basal cell carcinomas spread along the stratum basale and then start to grow toward the surface and become an uneven patch, bump, growth, or scar on the skin surface. 
​​2. squamous cell carcinoma affects the keratinocytes of the stratum spinosum. This cancer, seen as lesions often on the scalp, ears, and hands, is the second most common skin cancer with 2 of 10 skin cancers are squamous cell carcinomas. Because it is more aggressive than basal cell carcinoma, it must be surgically removed in order to prevent the cancer from metastasizing.
3. melanoma is characterized by an uncontrolled growth of melanocytes. Aa melanoma often develops from a mole. It can be hard to detect before it has metastasized. Melanomas usually appear as asymmetrical brown and black patches with uneven borders and a raised surface. Treatment usually requires surgical removal and chemo. 

 Rosacea is a chronic inflammatory skin condition.
Often mistaken for acne or eczema, rosacea usually affects the face. Symptoms include flushing, irritated skin, broken blood vessels, lesions and eye problems.

people have roughly the same number of melanocytes. differences in skin color are due to variations in the amount of melanin produced by these melanocytes, not the number of melanocytes.

sunshine and skin color

review  question:
why are the cells of the stratum corneum dead?

thick skin

review  question:
describe the four types of exocrine glands.

Vitamin D facilitates calcium absorption and bone formation

 skin pigmentation protects against the intensity of UV radiation which damages cellular DNA

what is pigmentation?

                    Integumentary System

acne occurs on parts of the skin that exhibit
a lot of sebaceous glands (face/back). Hormones stimulate the release of sebum. Then hair follicles become blocked due to an overproduction and accumulation of sebum and keratin.
This plug is initially white = whitehead.
The sebum is then oxidized turning black = blackhead. Acne results from infection by acne-causing bacteria.

BUT folate degrades

when exposed to high UVR

fyi:
lamellar granules release lipids to form
the skin's permeability barrier, protecting against water loss and other environmental stressors. 

Eczema is an allergic reaction that manifests as dry, itchy patches of skin that resemble rashes often with 
swelling of the skin, flaking, and sometimes bleeding. 

Wound Healing

so the evolutionary pressure produced gradations in pigmentation

review  question:
where are the blood vessels and nerve endings located?

blood supply

review  question:
​explain the  relationship between UV radiation, vitamin D synthesis, folate and pigmentation.

here's the science...
genetic diversity exists within populations, but there are no clear genetic boundaries between groups that align with racial categories. 

Accessory Structures

nails are made of keratin protein just like hair, skin, and the hooves, horns, feathers, and claws of other animals. 
nails are just dead cells filled with keratin. as new cells are produced, they push out the old ones which causes the nail to grow.

Innervation

the supposition that race is a social construct comes from anthropologist Franz Boas who sought to prove that race was not a biological categorization during a time when race-based science and the eugenics movement were becoming mainstream.

this info below is FYI

folate is
vitamin B9 and is necessary
for DNA synthesis, cell growth,
metabolism and to protect against fetal neural tube defects.

 dermis:
​inner layer of connective tissue with collagen, elastic and reticular fibers. loads of blood vessels, glands and nerve endings. Papillae extend into epidermis.

the enzymes that produce vitamin D need sunlight to function

Scars occur when collagen-rich skin is made during wound healing by fibroblasts.
The scar tissue is fibrous and does not regenerate hair follicles, sweat or sebaceous glands.

 functions

glands

AND vitamin D synthesis
requires UV radiation

 weighing 10 lbs and covering 2 square meters and exhibiting the largest sensory system in the body

race is a concept created and defined by society rather than a biological reality. the way societies categorize and give meaning to these differences is a human invention and has  been used to create hierarchies and justify inequalities.
the concept of race as we know it today emerged in the context of colonialism and slavery, where it was used to justify power structures and the exploitation of certain groups. the concept of race emerged in the context of colonialism and slavery in order to justify
 exploitation. 

Psoriasis is thought to be an auto-immune condition (T-cells attack the body's own skin cells)
which causes the body to make new skin cells more often. These extra skin cells pile up on the surface of the skin forming scales and itchy, dry patches. Psoriasis may be triggered by infections, stress, and cold. Although it usually affects the skin, sometimes it can affect nails or joints.

keratinocyte turn over

review  question:

describe the
 functions of the
integumentary
system.

jaundice is characterized by yellowing of the skin and eyes. it occurs due to a buildup of bilirubin in the blood. when there’s too much bilirubin in your blood, it starts to leak into tissues around your blood vessels which makes your skin and the whites of your eyes yellow.
bilirubin is a yellow pigment produced when red blood cells are broken down. Normally, the liver processes and removes bilirubin from the bloodstream, but if the liver is unable to do so effectively, or if too much bilirubin is produced, jaundice can occur. 

hair

epidermis

review  question:
​skin color is due to the concentration of a pigment
called __. this pigment is produced by cells called ____.
Is skin color determined by the number of these cells an individual has or by the amount of pigment they produce?

  burns
are classified by extent of the injury and the surface area affected  

Melanin absorbs UVR

Marcia
​and Millie Biggs

 epidermis:
​outer layer of 
stratified squamous cells
no blood vessels so obtains O2 and nutrients via diffusion from lower layers

 hypodermis (subQ):
​subcutaneous areolar & adipose tissue that binds skin to muscle. Sub Q fat serves to insulate and offers energy reserve. 

thick vs thin skin:

Vitiligo is a chronic skin condition characterized by the loss of pigmentation which results in pale patches on the skin. It's an autoimmune disorder.
the immune system attacks melanocytes.
as with many autoimmune conditions, the exact cause is unknown.

dermis

Pathology

nails 

skin cancer

thin skin

1. papillary layer: 
    loose, areolar connective tissue

 2. reticular layer = fiber mesh
      elastin fibers for elasticity
      collagen fibers for structure and                strength

review  question:

describe the
structures of the three layers of skin.

evolutionary balancing act...
not too much,
not too little
UV radiation

cell types:

review  question:

how do the dermal papillae interface with the epidermal ridges?

review  question:
what's the purpose of:

a sebaceous gland
arrector pili muscle

dermal papilla​?

melanocytes are specialized cells that produce melanin.

melanin is a pigment responsible for skin, hair and eye color. melanin is trasnsferred from the melanocytes to the keratinocytes to protect them from UV radiation. V

variation in skin pigmentation (melanin concentration)
​is an evolutionary adaption to the intensity of UV radiation...

at northern latitudes with less UV radiation,
​ pigmentation is less critical. 

1. first-degree burns are superficial, affect only the epidermis and heal quickly
2. second-degree burns affects both the epidermis and a portion of the dermis and cause                       blistering of the skin
3. third-degree burns extend deep into the epidermis and dermis and destroy nerve endings
​4. fourth-degree burns are most damaging, affecting the both the dermis, epidermis as well as                 underlying muscle and bone.