Human Skin

It's the largest organ of the integumentary system. Similar to pig skin.

All covered with hair follicles but appear hairless.

Protecting the body against pathogens and excessive water loss.

the protection of vitamin B folates.?

The skin type can range from dry to oil.

Such skin variety provides a rich and diverse habit for bacteria that numer roughly 1000 species

DNA repair enzymes

Small intestine is 15 to 20 times larger than skin. 1.5-2.0 m^2

1 cm2 100 sweat glands,3 blood vessels,10000 melanocytes and more than 300 nerve endings.

The skin cell is about 30um in diameter, ranging from 25-40um

Skin is composed of three primary layers: Epidermis, dermis and hypodermis.

Structure of the skin

Epidermis

a. is made up of stratified squamous epithelium with an underlying basal lamina.

b.cells in the deepest layers are nourished almost exclusively by diffused oxygen from the surrounding air, hahaha!

c.corneum, lucidum, granulosum, spinosum, basale.

1st most of the barrier function of epidermis localize to this layer.Hold water primarily.

2nd only on the palms and soles.

3rd Keratinocytes lose nuclei and their cytoplasm appears granular.containing Lipid

4th keratinocytes connected through desmosomes and produce lamellar bodies, from within the Golgi,enriched in polar lipids, glycosphingolipids, free sterols, phospholipids and catabolic enzymes.Langerhans cell in the middle of this layer.

5th melanocytes, Merkel cells more in fingertips and lips touch-sensitive sites, two layers: basal lamina(lamina lucinda and laina densa: collagen VII) and reticular connective tissue.  a barrier preventing malignant cells from invading the deeper tissue.

Time, 5-3rd 2 weeks, 3-1st 4 weeks,

the entire epidermis is replaced by new cell growth over a period of about 48 days.

d.this process is called keratinization.

e.no blood vessels, and nourished by diffusion from the dermis.

f.25-30 layers of dead cells

g.acidic pH 5.0

Dermis

consist of connective tissue and cushions the body from stress and strain.

tightly connected to the epidermis by the basement membrane.

harbours many nerve endings that provide the sense of touch and heat.

contains hair follicles, sweat glands, sebaceous glands, apocrine glands, lymphatic vessels and blood vessels.

divided into two areas: superficial called papillary region and the deep thicker area known as the reticular region.

papillary region

a bumpy surface.

strengthening the connection between the two layers of skins.

at the same time, influence the epidermis forms contours in the skin’s surface.  e.g. fingerprint or footprint to identification.

reticular region

much thicker

composed of dense irregular connective tissue including the dense concentration of collageous, elastic, and reticular fibers that weave throughout it.

strength, extensibility and elasticity.

Contained the root of the hairs, sebaceous glands, sweat glands, receptors, nails and blood vessels.

Tattoo ink is held in the dermis.

Stretch marks often from pregnancy and obesity, are also located in the dermis.

Subcutaneous tissue

(also called hypodermis or subcutis)

is not part of the skin.

consist of loses connective tissue, adipose tissue and elastin.

contains 50% of body fat.

Fat serves as padding and insulation for the body.

insulin and human growth hormones inject into subcutaneous tissue, highly vascular and absorbing quickly.storage.

Skin appendage

Skin color

skin  pigmentation in humans evolved to primarily regulate the amount of ultraviolet radiation (UVR) penetrating skin.

the color of the light skin people is determined mainly by the bluish-white connective tissue under the dermis and by the hemoglobin circulating in the vein of the dermis.

at least 5 different pigment :

a.Melanin     brown      BSM

b.melanoid       brown      throughout the epidermis

c.Carotene    yellow to orange      stratum corneum and fat cells in dermis and superficial fascia.

d.Hemoglobin    purple     in blood but not a pigment

e.Oxyhemoglobin     red     in blood but not a pigment

geographic distribution dark in equator and light closer to poles.

Female lighter than male. For light can help absorb more calcium for pregnant use.

Fitzpatrick scale classification of skin colour in 1975

skin aged, thinner and easier damaged. Less blood flow and lower glandular activity

Function

the synthesis of vitamin D by the action of UV on certain parts of the skin but not all.

0.25-0.40 mm of the skin,

medicine can be administered through the skin.

water resistance, the skin acts as a water-resistant barrier so essential nutrients are not washed out of the body.

Skin flora

1000 species of bacteria from 19 bacterial phyla have been found.

Actinobacteria 0.518

Firmicutes 0.244

Proteobacteria 0.165

Bacteroidetes 0.063

Propionibacteria and Staphylococci were the main species in sebaceous areas.

Nanoparticles 40 nm in diameter and smaller have been successful in penetrating the skin.

Spherical better than oblong.

TiO2, ZnO, Ag can't penetrate the skin.

The PEG and PEG-amine surface groups allowed for the greatest penetration of particles.

However, the carboxylic acid coated particles didn't penetrate past the stratum corneum.

UVR damage transdermal water loss (TEWL), take 3-5days to reach the peak, most penetration.

Other skin damaging methods, increasing permeability, include Tape stripping, Skin abrasion, and Chemical enhancement.

a. remove the top layer of skin

b.shave the top 5-10 micrometers off

c.PVP, DMSO(dimethyl sulfoxide), and oleic acid.

Electroporation, after it, 100micrometers can easily permeate.

transdermal patch

Sunblock and sunscreen

a. Titanium dioxide（TiO2） and zinc oxide（ZnO） are two of the important ingredients in sunblock.

b. a faster rate breaking down once exposed to sunlight, and radiation could penetrate to the skin.

Diet

vitamin A, normalizing keratinization and downregulating sebum (contributing to acne)

vitamin D, downregulating immune system of skin and epithelial proliferation while promoting differentiation.

vitamin C, anti-oxidant that regulates collagen synthesis, forms barrierlipids, regenerates vitamin E and provides photo protection.

vitamin E, a membrane antioxidant and protection against harmful UV rays.

Helpful food for skin:

fruits, vegetables, whole-grains, dark leafy greens, nut, and seeds.

Earwax

The wet type is dominant. (A), African and European 

The dry type is recessive. (a), East Asian and native Americans help them reduct in sweat or body odor to live in cold climates.

However, 30-50% of South Asian, Central Asians and Pacific Islanders have the dry cerumen,even though they are in hot weather.