Objectives

• Describe the structure of the skin

• Describe the functions of the skin

• Describe the melanin & its formation and explain related abnormalities

• Outline the common skin disorders

• Define dermatome and explain its clinical applications

• List the dermatomes & cutaneous nerves of the limbs

3 Layers

Epidermis

Dermis

Subcutaneous tissue or

Hypodermis

Epidermis: Stratified squamous

has 5 sub layers: Stratum corneum

Stratum lucidum

Stratum granulosum

Stratum spinosum

Stratum basale

Dermis: Composed of collagen

type I, elastic tissue, and reticular

fibers

Two LayersPapillary layer: contains collagen

fibers(elasticity), extends into the dermis,

Papillary ridges make up the lines on the

hand (fortune teller lines); cold & pain

receptors

Reticular layer: thicker, more dense and contains the sweat glands, sebaceous

glands (Pacinian Corpuscles:

Pressure/Vibration))

Epidermis

Appendages of the skin:Sweat Glands, Sebaceous Glands, Hair, Nail

Functional Characteristics

• Protection: The most important function of the skin , its effectiveness as a

barrier between the internal and external environments (guards against

injury, bacterial invasion, UV damage and desiccation)

• Regulation of body temperature: mediated by the hair coat, cutaneous

blood supply and sweat glands

• Secretion: from sweat, sebaceous and mammary glands

• Sensory Organ: innervation of the skin provides pain, touch, pressure and

temperature sensation.

• Reflects the physiological condition of the animal: skin and coat

condition are good indicators of overall health and alterations may

reflect a variety of external and internal disease processes (endocrine

disorders, nutritional problems i.e., Vitamin A deficiency is

characterized by very dry, hardened skin, dry lack-luster hair and hair loss.)

• Nutrition (Vitamin D Synthesis)

• Excretion: of dissolved salts by perspiration

Stratum

Corneum

Stratum

Granulosum

Epidermis has 4 clearly defined

layers

Stratum Corneum-loss of nuclei,

flattened, keratin; Keratinization

is “the process of epidermal

differentiation” (basal cells

membranous horny keratin)

Stratum Granulosum-contains

Keratohyalin granules

Stratum Spinosum-Polyhedral

prickle layer, desmosomes

(intercellular bridges form prickle

appearance)

Stratum Basale-Columnar

Germinative layer, transit time

to top layer-30days

A 5th layer Stratum Lucidum is

interposed between corneum &

granulosum in thick skin of palm &

sole

Epidermal Cell Types: 4 types

1) Keratinocytes (90%): represent the

majority of cells

2) Melanocytes (2-3%) : derived from

Neural Crest, “octopus-like” cells:

that produce melanin (absorbs UV light)

3) Langerhans Cells (<1%): dendritic

cells,located in the stratum spinosum;

dendritic (immune) cells that play a

pivotal role in induction of cutaneous

immune responses

(allergic reactions). Migrate to draining

lymph nodeT-cells

4) Merkel Cells: ubiquitous cells in the

skin that couple with axon terminals to

form mechanoreceptors (touch), abundant in

finger tips

• Melanocytes: octopus like cells that produce the pigment, melanin

• They don’t retain melanin but pass it on to neighboringKeratinocytes

• Melanocytes in epidermis; Each pigment cell transfers it’s melanosomes to about 40 basal

keratinocytes(skin reflection)

• Both light and dark skin individuals have melanin

• Two forms of melanin:

• Pheomelanin: yellow to red in color (Light Skinned)

• Eumelanin: dark brown to black (Dark Skinned)

• Light skinned people usually produce more pheomelanin

• Dark skinned people usually produce more eumelanin

• Melanin acts as a protective shell against ultraviolet radiation, sun burns

• Sun damage can change DNA and cause skin cancer—melanoma

• Tanning increases the number and size of melanin granules—stimulates growth of cells due to

the ultraviolet radiation

• Albinos people with very low to no melanin in their skin layer

• White mutation

90% of vitamin D comes from the sun

10% comes from fatty fish and egg yokes (vitamin D3)

Too much ultraviolet rays can cause break down of folic acid and

cause anemia

There is a strong correlation between the amount of sunlight a child

receives and if they develop multiple sclerosis as an adult/tropical

regions

Section from the fingetipProminent Papillary Ridges

Section from Abdomen: young femaleThick Dermis

Edipdermal Ridges

Thick Keratin layer

Granular

layer

Section from NoseProminent sebaceous glands

Section from scalpMultiple sections of hair follicles

ECZEMAIs pruritic,

excoriation results

from intense itching;

predisposes to

infection

Post inflammatory

hypo-or-hyper

pigmentation

Atopic dermatitis (Eczema)

Pruritic inflammatory disorder in childhood,

progressing to adulthood

Genetically determined

Strong personal or family history of atopy

50% have asthma

Also associated allergic rhinitis, Hay fever &

urticaria

IgE antibody raised, Prick test +ve to

environmental allergens

Seborrhoeic Dermatitis

Scalp, face, flexures, upper arm

Overgrowth of yeast Pityrosporum Ovale

Term Seborrhoeic is misnomer, in fact these are exfoliated

cells of stratum corneum, not from sebum

Contact Dermatitis

• Contact dermatitis

• Interaction of

external substances

with the skin

• Type IV

hypersensitivity

reaction

Psoriasis

• Psoriasis is a chronic inflammatory disease

• A noncontagious skin condition that produces red, dry plaques of thickened skin

• The dry flakes and skin scales are thought to result from the rapid proliferation of skin cells that is triggered by abnormal lymphocytes from the blood

• Risk factors: genetic predisposition and environmental factors.

Melanoma

• Clinical Note: A Melanoma is a type of very aggressive and metastatic neoplasm that arises from the uncontrolled mitosis and migration of melanocytes. Melanomas can occur in areas of haired skin

• Ultraviolet-light-induced mutations in melanocytes is the single most important environmental factor in the induction of cutaneous melanomas

• Identification of potentially malignant pigmented lesions is best remembered by using the first five letters of the alphabet as follows:

• A for asymmetry

• B for border irregularity

• C for color multiplicity

• D for diameter greater than ¼ inch

• E for evolution

Malignant Melanoma

Dermatome• A dermatome is a specific both-sided region of

skin supplied by a single pair of spinal nerve from a spinal segment

• Each pair of spinal nerves serve its own dermatome although the boundaries of adjacent dermatomes overlap to some degree.

• Dermatomes are clinically important as damage or infection of a spinal nerve or dorsal root ganglion will produce characteristic LOSS OF SENSATION in CORRESPONDING REGIONS OF THE SKIN.

• There can be slight variations in the dermatome due to anatomical anomalies. Peripheral nerve compression or peripheral neuropathy (due to diabetes or vitamin deficiency) can cause regional loss of sensory and motor function. The location of affected dermatome provides clues to the location of injuries i.e., which spinal segment is affected

• More exact conclusions can be drawn if there is a loss of motor function or muscle function supplied by nerves from that segment.

Dermatomes of lower limb

• Lateral part of dorsum with little finger = S1

• Lateral part of sole with little finger = S1

• Anterior & lateral part of leg = L5

• Medial part of dorsum of foot with Great Toe= L5

• Front of thigh = L2, L3

• Buttock=S3, Back of thigh, Back of knee & leg =S2,

Sciatica pain felt across this path, in foot radiates

across lateral or medial part

• External genitals skin= L1

Cutaneous nerves of lower limb

Front of thigh

• Medial femoral & intermediate femoral cutaneous nerve of the thigh = From Femoral nerve

• Lateral cutaneous nerve of thigh = from lumbar plexus

Medial side knee=Obturator nerve, femoral nerve

Front of leg

• Medial part = Saphenous nerve, branch of femoral

• Lateral & lower 1/3rd of leg + most of dorsum foot =Superficial peroneal (fibular) nerve

Back of thigh

•Posterior femoral cutaneous

(from Sacral plexus)

Back of knee & leg

•Medial sural cutaneus arise

from TIBIAL

•Lateral sural cutaneous

arise from Common

Peroneal

•These two join to form

SURAL NERVE which

supplies skin of posterior

part of leg & lateral border of

the dorsum of foot, sole of

foot

Dermatome of upper limb

• Thumb & lateral border of forearm = C6

• Little finger & medial border of forearm = C8

• Index, middle & ring fingers = C7

• Front& back of arm = C5

• Medial side of upper forearm & elbow = T1

• Front of chest (clavicle to 2nd rib) = C4, then

from 2nd rib downwards, T2, T3, T4….

Epigastric region T6, Umbilicus T10

• Back of trunk corresponds to front of chest

above

Referred Pain

• Referred pain from the heart (Anginalpain) can be felt across medial border of arm (T1)

• Stomach pain can be felt over epigastricregion of anterior abdomen (T6)

• Pain originated from small intestine & appendix can be felt initially over umbilicus (T10)

• Gall bladder pain can be felt over tip of right shoulder (C4)

Shoulder skin by SUPRACLAVICULAR (C3, C4 Dermatome), Skin over Deltoid (AXILLARY N)

Skin over back of arm & forearm by RADIAL nerve, Lateral border of forearm by

MUSCULOCUTANEOUS, Medial border of forearm by MEDIAL CUTANEOUS N of FOREARM

Similar distribution over the palmar aspect; Lateral 3 & ½ fingers & corresponding

palm, thenar eminence by MEDIAN NERVE, Medial 1 & ½ fingers &

corresponding palm, hypothenar eminence by ULNAR NERVE