skin structure function dermatome
Post on 22-Feb-2015
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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
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