Advanced Laser Education Content - Part 2 Skin Anatomy

This page contains treatments advanced education content about laser and treatments. 


Integumentary System

System contains:

  • Hair follicles and shafts
  • Nails
  • Eccrine glands – sweat
  • Apocrine glands – scent
  • Sebaceous glands – oil
  • Arrectore pilorum muscles (goose bumps)
  • Mammary glands

Function of Integumentary System

  • Temperature regulation
  • Protection
  • Sensory perception
  • Excretion of waste
  • Immunity
  • Storage
  • Vitamin D production

Skin’s 5 primary functions

  • Heat regulation
  • Absorption
  • Excretion
  • Elimination
  • Sensation

Characteristics of skin

  • Thinnest on lips and eyelashes
  • Thickets on palms and soles
  • Friction and pressure increases tissue thickness
  • Exposure toughens skin
  • Cold contracts
  • Heat relaxes
  • Thickness about 0.5mm-4.0mm

Stratification of skin

  • Epidermis - Thin, avascular layer composed of cells containing keratin in different stages of growth and degeneration
  • Dermis - Thick, highly vascular layer composed of connective tissue
  • Hypodermis or Subcutaneous - Tissue and fat that connects skin to muscles and bones

Skin - Epidermis

  • The epidermis is the outer layer of the skin
  • Consists of 90% stratified squamous epithelial cells
    • Primarily contains keratinocytes in progressive stages of differentiation from deeper to more superficial layers
  • Has no blood vessels; avascular
    • Receives nutrients by diffusion from the underlying dermis from the underlying dermis through the basement membrane, which separated of layer
  • Average thickness of 0.1 mm

The 4 types of epidermal cells

  • Keratinocytes: 90% of the cells, consist of a protein called keratin
  • Melanocytes: 8% they produce the pigment melanin
  • Langerhans cells: work with the immune system
  • Merkyl cells are responsible for the sense of touch

The 5 levels of the epidermis

  • Horny layer (Stratum Corneum)
  • Lucid layer (Statum Lucidum)
  • Granular layer (Statum Granulosum)
  • Pickle-cell or Spiny layer (Statum Spinosum)
  • Basal (Base) Layer (Stratum Basale or Germinativum)

Stratum Corneum (horny layer)

  • The stratum corneum is the upper outermost layer of epidermis
  • It consists of layers of dead, dehydrated, flattened, fused-together, non-nucleated cells (keratinocytes) whose cytoplasm is filled with keratin
  • This layer is usually 20-30 layers thick but can range in thickness from 15-100 or more cells depending on anatomic location
  • In the very outer layers of the stratum corneum, the moisture barrier has a slightly acidic pH (4.5 to 6.5)
  • The slightly acidic layers of the moisture barrier are called the acid mantle
  • The acidity is due to a combination of the secretions from the sebaceous and sweat glands
  • The acid mantle functions to inhibit the growth of harmful bacteria and fungi
  • The acidity helps maintain the hardness of keratin proteins, keeping them tightly bound together

The 2 important functions of the Stratum Corneum (horny layer)

  • Barrier - It is a barrier from the outside environment which prevents invasion by certain substances such has microorganisms, chemical substances, allergens, bacteria and many forms of pollution
  • Hydration - It minimizes trans-epidermal water loss and thus only protects the skin itself but also the body as a while from dehydration

Stratum Lucidum

  • A thin layer of extremely flattened, closely packed, dead cells marking the upper most border of the status granulosum
  • This layer gets its name from its appearance, which is due to the fact that the cells are translucent or clear with the cell boundaries
  • Found in hairless skin on soles and palms
  • Contain eleidin (intracellular protein)
  • Translucent
  • Filled with Keratin
  • Cell boundaries are no longer recognizable

Stratum Granulosum

  • This layer gets its name from its appearance of the presence of granules which are formed in the layer
  • These granules contain keratohyalin which mature into keratin
  • Where the cornification (keratinization) of the keratinocytes begins
  • Most mature layer where cells are synthetizing keratin
  • Membrane coating granules are discharged into this layer, in the intracellular spaces
  • This helps make the skin impermeable to water
  • Granules attach to the cell membrane and release a lipid-containing cement which contributes to cell adhesion and to the horny layer barrier
  • Is 3-5 layers of flattened polygonal cells
  • These are rod like structures containing lipids

Stratum Spinosum

  • Layer right above basal layer
  • Contains 8-10 rows of cells which change from columnar to polyhedral shape
  • Cells have a prickly surface with spiny appearance (Langerhaus cells located)
  • This is the main proliferative layer where the keratinocytes are differentiating
  • The differentiating keratinocytes synthesize cytokeratin, which clump together to form tonofilaments
  • The tonofibril converge to form desmosomes, which are layers of lipids
  • The desmosomes connect the keratinocytes together
  • The Merkyl’s discs are found in this layer, responsible for touch sensation

Stratum Basale

  • This is the lowest layer of the epidermis
  • It forms the border between the epidermis and the dermis
  • Consists of a single layer of low columnar cells, which rests on the basement membrane
  • Cells are bound together by desmosomes and attached to the basement membrane by hemidesmosomes
  • Basal cells provide continuous regeneration of the skin through cell division
  • Half the cells migrate upward, the other half stays to divide again
  • It takes about 14 days for the cells to move through this layer
  • This layer contains stem cells, it is also where melanocytes are located

Skin Thickness

  • Skin varies in thickness among anatomical location, sex and age of the individual
  • Varying thickness primarily represents a difference in dermal thickness, as epidermal thickness is rather constant throughout life and from one anatomic location to another
  • Skin is thicket on the palms and soles of the feet while the thinnest skin is found on the eyelids and the post-auricular region

The 4 different types of skin

  • Mucocutaneous - A region of the body in which mucosa transitions to the skin, found at the lips tongue nostrils
  • Mucous membrane - Lining inside the body’s orifices
  • Glabrous - Skin without hair, the thick skin found on palms and soles. Epidermal ridges are more prominent in thick skin. 
  • Hairy - The skin covers most of the body and contains hair follicles

Keratinization

  • The conversion of squamous epithelial cells into keratinized horny material; such as hair, nails or scaly skin

Epidermis cycle of regeneration

  • Renews itself every 28 days through:
    • Reproduction
    • Differentiation
    • Desquamation  
      • The mechanical sloughing-off of the uppermost horny cell layer

The 5 processes of keratinocyte turnover

  • The keratinocytes participate in the continuous turnover (renewal) of the skin’s surface by passing through 5 overlapping processes:
    • Cell renewal or mitosis
    • Differentiation
    • Keratinization
    • Cell death
    • Exfoliation (the sloughing-off of dead cells from the skins surface)

The 4 function-specific specialized populations of cells

  • Major population:
    • Keratinocytes
    • Melanocytes
  • Minor population:
    • Langerhans Cells
    • Merkels Cells

Skin - Dermis

The 2 sublayers of the dermis

  • Papillary Layer
  • Reticular Layer

Primary function of the dermis

  • To sustain and support the epidermis
  • The dermis is 20-40 times thicker than the epidermis
  • The dermis is a complex network of:
    • Collagen fibers
    • Sweat glands
    • Hair roots
    • Nervous cells
    • Nervous fibers
    • Blood
    • Lymph vessels

The dermis consists of

  • Fibrous collagen mixed with elastin fibers that support the epidermis
  • Fibers give skin its permeability to return to normal state after deformation
  • A gel like ground substance that accounts for the skin’s ability to accommodate changes in the body weight or size

Cellular components of the dermis

  • Fibroblasts - Manufacture various fibers like fibroblasts that hold collagen
  • Microphages - Clean up with specialized white blood cells
  • Plasma cells - Specialized white blood cells produce antibodies
  • Mast cells - Specialized which blood cells

Papillary Dermis

Contains vascular networks that have 2 important functions:

  • Support the avascular epidermis with vital nutrients.
  • Provide a network of thermo-regulation

Reticular Dermis

  • Makes up 80% of the dermis
  • Provides extensibility and elasticity to the skin
  • Contains a rich supply of nerves, with both free and encapsulated endings.

Skin - Subcutis (subcutaneous layer)

  • This is the fat layer below the dermis
  • It is what attaches the dermis to the underlying musculature
  • It is made of spongy connective tissue and fat cells
  • Contains blood vessels and nerves
  • Fat cells are held in place by collagen fibers called connective tissue septa
  • Also deep-seated hair bulbs are found in this layer

Functions of the Subcutis

  • Insulation - Insulates the body from cold and heat
  • Nourishment - Stores nutrients in the form of liquid fat
  • Padding - Cushioning the skin in the general, palms of hands, soles of feet and buttocks
  • Appearance - Stabilizes the position of the skin

The glands of the skin

  • Sudoriferous Glands
  • Sebaceous Glands

Sudoriferous Glands (sweat)

Structure

  • Tubular organs consisting of coiled glomerulus
  • Contain secretory ducts that open at the skin surface to form a pore
  • Abundant over entire body, predominant in axilla, forehead, palms and soles of feet

Function:

  • Eliminate waste materials by perspiration
  • Control body temperature
  • evaporation

Sebaceous glands

Structure:

  • Lanugo hair begins growth in lobe
  • Located on dermis
  • On every body part, except palms and soles
  • Numerous on face

Function:

  • Produces and excretes sebum (a fatty substance)
  • Protects skin and hair be reducing evaporation and bacteria growth
  • Lubricates and conditions skin, hair and scalp

Mechanism for Pigment

  • Melanocytes make little packets of pigments called melanosomes
  • After a melanocyte makes the melanosome, it passes it to the keratinocyte (cells that make up the bulk of skin)
  • The keratinocytes store the melanosomes over its nucleus
  • Melanin in the melanosome absorbs ultraviolet radiation before it reaches the nucleus and therefore DNA of keratinocytes
  • Keratinocytes are originally colorless skin calls
  • Melanin pigment is located throughout the body and gives skin and hair color
  • As the keratinocytes are filled with more melanin pigments, coloring of the skin occurs

The 4 types of Epidermal cells

Keratinocytes 90%

  • Filled with keratin (protein)
  • Waterproof barrier

Melanocytes 8%

  • Produces melanin (pigment)
  • Pass melanin to keratinocytes

Langerhans cells

  • Working in skin with immune system
  • Easily damaged by UV light

Merkel Cells

  • In deepest layer of hairless skin
  • Sensory transduction - touch

Langerhans cells

  • Very sensitive to damage from ultraviolet light
  • Originate from the bone marrow and are found in all layers of the epidermis. Most prominent in the status spinosum, lymph nodes, lungs and the gastrointestinal tract.
  • Serve as antigen-presenting cells
  • Involved in the signaling the immune system

Collagen

  • It is the most abundant dermal constituent
  • Produced by fibroblasts
  • Is a protein and constitutes about 70% of dry weight of the dermis

The 5 most common forms of Collagen

  • Type I Collagen - forms the familiar eosinophilic collagen fibers of ordinary fibrous connective tissue. Example: dermis, tendon, organ sheath, fascia.
  • Type II Collagen – reinforces cartilage
  • Type III Collagen – forms reticular fibers and also occurs in basement membranes and bone
  • Type IV Collagen – occurs in the basal lamina around smooth and skeletal muscle fibers
  • Type V Collagen – is an interlinking collagen important for formation of basement membranes