Skin

Integumentary system

Skin + Appendages: Hair, Nails, Sweat

Skin

Living, Waterproof, Stretchy, Regenerative

The Largest “Organ” of the body

Do blood supply travel through the epidermis

No. capillary beds do not extend to the epidermis but they are rigth underneath

What is in the dermis

Sensory glands and nerve endings

At what point is the skin no longer skin?

At the hypodermis (superficial surface)

Skin function

Protect

Sensory receptor

Synthesizes Vitamin D3

Excretes substances

Protect

- Prevent dehydration & electrolyte imbalance

- Thermal regulation

- Barrier to mechanical & chemical trauma

- Barrier to micro-organisms

- Barrier to UV & other types of radiation

Sensory receptors

Many- 230

embedded in the skin

Synthesizes Vit. D

UV rays + precursors in epidermis (7-dehydrocholesterol- produced by the body)

- required for Ca++ absorption in the gut

Excretes substances

Urea, salts, H2O (what mosts happens in the kidney)

Skin: Layers

Epidermis

Dermis

Hypodermis

Epidermis

Epithelial tissue (outermost layer)

Dermis

Connective tissue

Blood supply, glands, supports epidermis through nutrient transport

What counts a sthe skin?

Epidermis and Dermis

Not the skin

Hypodermis

Hypodermis

Deep to the dermis

a.k.a. Subcutaneous connective tissue

a.k.a. Superficial fascia

Not a true skin layer

Skin: Epidermis

• Stratified squamous keratinized epithelium

• Generally: multiple distinct layers of cells

Thick/Thin skin determination based on thickness of epidermis only

What are the layers of cells

- Thick skin (5 layers) – sole of feet - ≤5mm

- Thin skin (4 Layers) – dorsum of hand - <1mm

Keratinocyte

primary cell type (generic skin cells)

- Produces fibrous, protective protein – Keratin

- Held together by desmosomes (form of cellular adhesion)

- Originate in the deepest layer (basale) of the epidermis

- Typically, turn over every 35-45 days

Most skin cells are

keratinized

Keratinized cells don’t have what?

They dont have enzymatic activity. Its just for structure

Epidermis Layers

Stratum:

Basale

Spinosum

Granulosum

Lucidum

Corneum

Stratum Basale

- Deepest layer of epidermis

- Typically 1 Cell Thick

• Maintain mitotic ability

 Primary source for renewing epidermal layers
Majority of the cells here are keratinized

Stratum Basale

Special Cells

Merkel’s cells

- associated with nerve

- function as touch receptor

***The nerve is not in the epidermal layer, but in the dermis that is connected to the merkel cell

Stratum Basale

Special Cells

Melanocytes

- 10-25% of basal cells

- “Spider” shaped

- produce dark skin pigment – Melanin made from tyrosine (AA)

- transferred to keratinocytes (It is not physically made here,, but transferred)

- pigment protects from UV radiation

- Melanin v/s Neuromelanin

Creation of melanin

L-Tyrosine - L- Dopa - Dopaquinone - Melanin

Stratum

Spinosum

- Spiny layer

- Several layers thick

- Deepest of its layers

maintains mitotic ability

-They contain intracellular fluid when pulled apart

Stratum Spinosum

Special Cells

Langerhans cells

- star shape

- macrophage-like cell

- involved in immune response (They are mediated in the skin)

Stratum

Granulosum

- Alive (granular appearing)

- 3-5 layers thick

- Cells making:

• Keratin

• Lamellated granules produce lipid based waterproofing glue (add carbs and proteins to produce a waterproof barrier)

What cells are alive vs dead

Alive - Basale, spinosum, granulosum

Dead - Corneum, lucidum

Stratum

Lucidum

A couple of cell layers

thick

- Dead cells, organelles

disintegrating

Stratum

Corneum

Multiple layers thick

- Dead cells –

• organelles gone keratin present H2O-proof

- Cells “flake off

Friction Blister

Liquid blister with cytoplasm is released when the cells are pulled apart. It is bloody if it occurs in the bottom layers

The roof of the blister is formed by the layers above it (the stratum granulosum and stratum corneum), while the floor of the blister is formed by the bottom of the stratum spinosum, the stratum basale, and the underlying dermis.

What is in the Dermis

Papillary dermis

Reticular dermis

Hypodermis

Subcutaneous Tissue

• Not a true layer of the skin

• Loose connective tissue & adipose (fat)

• Acts as interface between skin & underlying structures

• Very rich in blood supply

Vasodilation vs vasoconstriction

Dilation : heat loss

Constriction : heat retention

Regeneration

Injured/damaged/destroyed tissue is replaced

with new, functional tissue of the original type

Replace cells with active cells

Fibrosis

injured/damaged/destroyed tissue is replaced by

fibrous dense connective tissue (scar tissue),

non-functional tissue

Replace damaged cells with connective tissue

Life Cycle

&

Migration of an

Epidermal Cell

Migrate up by going through mitosis all the way to the coreum where they are then slawed off

High rates of mitosis mean

Higher risks of disease because of cell division

Ex. Cancer