Dermatology Course
Aim: to train the candidate so that he can diagnose
and treat common skin affections
STRUCURE AND FUNCTION OF THE SKIN
PROF. HAYDER AL-HAMAMY
• Three Major Layers—Epidermis, Dermis, Hypodermis:
– Epidermis: major permeability barrier, innate immune
function, adhesion, ultraviolet protection.
– Dermis: major structural element, three types of
components—cellular, fibrous matrix, diffuse and
filamentous matrix. Also site of vascular, lymphatic, and
nerve networks.
– Hypodermis (subcutis): insulation, mechanical integrity,
containing the larger source vessels and nerves.
• Permeability
barrier
Epidermis Atopic dermatitis
Ectodermal dysplasias
Ichthyoses
Keratodermas
Exfoliative dermatitis
Bullous diseases
Protection from
pathogens
Thermoregulation
Sensation
Epidermis Verruca vulgaris
Dermis
Ecthyma
Cellulitis
Leishmaniasis
Human immunodeficiency virus
Tinea pedis/corporis
Epidermis Ectodermal dysplasias
Dermis
Raynaud
HypodermisHyperthermia
Epidermis Diabetic neuropathy
Ultraviolet protection
Wound
repair/regeneration
Physical appearance
Dermis
Leprosy
HypodermisPruritus
Postherpetic neuralgia
Epidermis Xeroderma pigmentosum
Oculocutaneous albinism
Epidermis Keloid
Dermis
Venous stasis ulcer
Pyoderma gangrenosum
Epidermis Melasma
Dermis
Vitiligo
HypodermisScleroderma
Lipodystrophy
Epidermis
major cells: Keratinocytes
other cells: melanocytes, Langerhans’ cells, Merkel’s cells
Basal layer:
columnar cells
dividing cells for renewal of epidermis pushes cells into the upper 3
layers to end in stratum corneum “ the major barrier of the skin”
Keratin: A protein cytoskeleton of keratinocytes
Spinous layer: mid-epidermis
spines between the cells on light microscopy polyhedral cells
progressively flatten as they move upwards
contain “lamellar granules” which are secretory organelles containing
lipids
with large bundles of keratin fillaments
Spines are desmosomes which are adhesion structures between
keratinocytes bind keratinocytes, resist mechanical stress, calcium
dependent
Granular layer
cytoplasm contains basophilic kerato-hyaline granules
cornified envelope of the cell is developed
Stratum corneum
complete differentiation of keratinocytes, loss of the nucleus, flattened
cornified cells
function: mechanical protection+ barrier to water loss & permeation of
soluble substances from the environment.
Barrier function = protein covered cells+ extracellular lipid matrix
Melanocytes
derived from the neural crest
dendritic cells
reside in the basal layer
synthesize pigment “melanin” stored in “melanosomes” organelles then
transferred to neighboring keratinocytes
Merkel’s cells
slow adapting mechanoreceptors located at sites of high-tactile sensitivity
in between keratinocytes
contain neuro-secretory granules
Langerhans’ cells
dendritic cells
antigen processing & presenting cells
mostly suprabasal in position
convoluted nucleus
pale staining cytoplasm containing charecterstic rod or racket-shaped
structures called “ Birbeck granule”
Dermo-epidermal junction
3 major parts
1- lamina lucida – hemidesmosomes ‘half desmosomes’+plasma
membrane of the keratinocytes
2- lamina densa – basal lamina – type IV collagen
3- sublamina densa – anchoring fibrils type VII collagen
Dermis
connective tissue element of the skin
2 major regions
1- papillary dermis; upper, rete ridges,
mechanical support & nutrition to the epidermis
2- reticular dermis deeper
Fibrous matrix
1- collagen fibers
major bulk of the dermis ‘75% of dry weight of dermis’
tensile strength & elasticity
banded periodically
2- elastic fibers complex mesh assembelled into a contineuos network
Cellular component
fibroblasts: mesenchymally derived cells responsible for the synthesis &
degredation of fibrous & diffuse matrix
monocytes & macrophages defense system
mast cells
dermal dendritic cells
Diffuse matrix
glycosaminoglycans & proteoglycans form the ground substance in which
fibers are embedded & holds water
Nerves
one million nerve fibers
myelinated & non-myelinated freenreve endings- heat & pain
mechanoreceptors pacinian& Meissners corpuscles
itch receptors
Sweat glands
1- eccrine sweat glands at the dermoepidermal junction with their ducts
empty to the skin surface
2- apocrine sweat glands connected to the hair follicle
Pilosebaceous follicle