1. Protection: Prevents water evaporation from the body as well as water and vapor penetration into the body. It also protects the body from physical, chemical and biological insults and ultraviolet radiation.
2. Vitamin D: manufacture in the skin that is exposed to UV radiation. Vit. D is an irradiated Ergosterol, which is a derivative of cholestrol.
3. Absorption: many substances, toxins and medication can be absorbed by the skin.
4. Secretion: sweat and sebum(greasy substances)
5. Organ of Sensation
6. Thermo-Regulation

• Thin: Tend to be on the ventrical side of the body. (eyelid, medial side of the arm.. etc)
• Thick: Tend to be on dorsal side of the body. (Palm and sole of feet are examples)

• Epidermis
• Dermis (corium)

• Papillary region: The top part which is connected to the Epidermis. Seperated from dermis by layer of nasal lamina and basement membrane. Type III collagen.
• Reticular region: The bottom part which is connected to the Hypodermis. Thicker region.Type I collagen

Also called Superficial Fascia 

• Layers of fat connected to the bottom (reticular region) of the Dermis.
• Also connected to Deep Fascia/Epimysium.

• Keratinocytes (85%)
• Melanocytes
• Langerhanse cells
• Merker cells

• Karatohyhlin granules pack the cell and causes apoptosis.
• Its is then called a Cornocyte of stratum corneum.

• Oxyhemoglobin: in the cpillary bed of upper dermis and the amount of these capillaried impart red tint.
• Caroten:yellow tint
• Melanin: a brown or black pigment which is produced in the melanocytes of the epidermis.

• Round cell bodies with ittegular extensions that branch between keratinocytes.
• Not attached to keratinocytes.
• Have hemidesmosomes with basal lamina.

• Melanocytes are equal.
• Dark skinned people have more Melanin.

• Tyrosine→ DOPA→ Dopaquinine→ melanin (enzyme Tyrosinase)

Pheomelanin

Rich in cysteine and have round melanosomes

• Rapid production of melanin in the melanocytes.
• Darkening of skin after exposure to UV light of sun (UVA and UVB)
• Chronic exposure to sun light is proved to cause serious damage and tumors of the skin.

• Hereditary disease
• Absense of Tyrosinase
• Pale skin and lack of melanin in other parts of the body such as the iris of the eye.

• Absense or hypofunction of melanocytes
• Localized or sometimes generalized depigmented skin.
• (What MJ says he has)

• Pregnancy mask.
• Hyperpigmentation of the skin, especially the face, during pregnancy due to hormonal changes.

• Hyperpigmentation of the skin.
• Hypofunction of adrenal gland and increase ACTH.
• Might be due to stimulation of melanocyte stimulating factor.

• Dendritic cells
• Stain them with gold chloride
• contain granules called Birbeck/Vermiform in it's cytoplasm.
• They are antigen presenting cells (APC) found in lymph nodes and spleen.

• Found in basil lamina of epidermis in thick skin such as the tip of the finger.
• Free nerve endings transverse basal lamina and enter epidermis will make a Merkel-Nurite Corpuscle or Merkle Disc.
• Acts as mechnoreceptor

• Not a straight line especially in thick skin
• Projection of dermis in epidermis is called Dermal ridges.
• Projection of epidermis into dermis is called Epidermal Papilla.

• Patches of silver scales of epidermis due to increase in proliferation of cells of stratum basale.
• Decrease of cycle time
• Epidermal thickness and rapid renewal. (7-10 days instead of 20-30)
• cells at top layer are partially nucleated

Icthyosis

• Increased keratinization and causes the epidermis to be rough and in severe cases like tressterial animals.

• development of group of vesicles and bullae(blister).
• Acantholysis: seperation of keratinocytes from each other.
• Autoimmune: IgG are directed against antigen in the desmosomes in the epidermis. This causes seperation of epidermal cells.
• Bullous Pemphigoid: IgG produced against antigen in basal lamina and the whole epidermis seperates from dermis.
• Scaled skin: due to burn or other physical insults, various damages and destruction of epidermis and dermis may happen.

two sets of vascular plexuses at the level of papillary dermis and a deeped one between dermis and hypodermis.

The direction of the fibroblasts and fibrous elements.

• Infection in the dermis of the skin.
• like likely to happen where the skin has been broken.

• Two types of mucopolysacharidosis that ground substance will be affected.

• Defect of various types of collagen, causes laxity and hyperextensibility of skin ligament.

• Connective tissue disorder in which skin becomes inelastic and hangs loosely in folds.
• Loosening of skin
• Also due to aging

• Increase in elastic collagen fiber of dermis mostly due to UV light.

• Palm and sole of feet
• Lateral part of feet
• Glans penis and clitoris
• Inner surface of prepuce
• Labia minora

• Bulb: terminal expansion of an active hair.
• Papilla: deep recess in the under side of the bulb. The cells here have inductive influence on the activity of the follicle. The epithelial cells covering it are comparable to those of the stratum basale.

• Lanugo: the hair that covers the fetus.
• Terminal: The coarser hair that replaces the lanugo right before birth.
• Neither have Medulla

• Medulla
• Cortex
• Cuticle

• smooth muscle fibers extended between papillary dermis and connective tissue sheath of hair follicle.
• cause goose bumps.

1. Anagen: continuous growth. 900 days
2. Catagen: regression phase 100 days
3. Telogen: resting phase 50-100 days

• Alopecia Areata: discoid(having the form of a disc) patches of hair loss.
• Alopecia Totalis: total loss of hair of the scalp.
• Trachtilomania: loss of hair due to traction or trauma.

• nail Matrix

• Nail plate: what we refer to as the nail
• Lunula: light area towards the cuticle. Where you can see pulsation of the capillaries.
• Nail Matrix: what the nail grows from
• Nail bed: what the nail matrix rests on.
• Eponychium: area under cuticle.
• Hyponychium: area under free edge of nail.
• Cuticle: skin fold at base of nail.

• bacteril entering and puss collection in the nail folds.

• A collection of blood(hematoma) underneath the nail.

also called Pilosebacious glands

• Connected to hair follicle above the arrector pilli. Can copen directly into skin in places without hair.
• produces Sebum. Mixture of lipids, cholesterol, triglyceride, and squalene.
• Holocrine release. Protoplasmic destruction and cell death. Flow of sebum is continuous.
• Inactive until puberty. Can make hair and skin greasy. Why you smell if you don't shower for days.

• Disturbance in flow of sebum
• Local inflamation of Sebaceous(Pilosebaceous) glands.
• More in boys than in girls, especially during puberty.

• Eccrine sweat glands
• Apocrine sweat glands

• Scattered on the surface of the whole body.
• Are in the skin at birth.
• Develop from epithelium of epidermis.
• Secretion is watery and does not smell.
• Mode of secretion is Merocrine: contents fuse with PM and are released directly out of gland.
• Innevervated by Cholinergic nerves.

• Develop at puberty.
• Open into hair follicles in axilla, around nipple, anus, and pubic area.
• Mode of secretion is apocrine and some holicrine.
• Mole glands of eyelid and Ceromenous glands of external auditory canals are modified apocrine glands.
• Innervated by Adrenergic nerves.

• Coiled secretary portion is lined by Light and Dark cells.
• Clear cells are located towards the lumen on a basement membrane
• Star shaped Myoepithelial cells contract to expel sweat out of coiled portion.

• Glands: Stratified Columnar Epithlium
• Ducts: Stratified Cuboidal

• skin disease that affects apocrine sweat glands.
• Abcesses or boils form

• excessive sweating