Clinical Pediatric Dermatology Jayakar Thomas, Parimalam Kumar
Page numbers followed by b refer to box, f refer to figure, fc refer to flowchart, and t refer to table.
Aberrant mongolian spot 115f
Abrasions 4
Abscess 36f
Acantholytic cell 126, 128
Acanthosis nigricans 118, 118f, 119b
Acne 13t, 72, 72f
pustules of 73f
vulgaris 13, 72, 73b
Acneiform eruption 13t
Acquired immunodeficiency syndrome 39
Acrodermatitis enteropathica 121, 122, 122b
Acrofacial vitiligo 110f
Acute inflammatory pruritic eruption 74
Addison's disease 20, 112, 119
Adrenal insufficiency 111
Adrenocorticotropic hormone 3
Albendazole 29
Albinism 112
type of 113
Allergic reaction 30
Alopecia 71, 121
areata 70, 70f, 71b, 71f, 112
multiple patches of 70f
nonscarring hair loss classical of 70f
extension of 71
totalis 71, 71f
universalis 18, 71
Ancylostoma 29
braziliense 29
Anemia, pernicious 111
Anesthesia, local 6
Angioedema 77, 78b, 79
Angiotensin-converting enzyme 127
Anhidrotic ectodermal dysplasia 101f
Annular lesions 16fc, 95
Anogenitalia 119
Anomalous dentition 103
Antecubital fossae 119
Antibacterial ointments 37
Antibiotics, systemic 32
Antihistamines 95
Apocrine glands 2, 4
Arthritis 93
Asboe–Hansen sign 19
Aspirin 79
Atopic dermatitis 58f, 62, 62f, 63b, 63f
Dennie–Morgan fold of 63f
Atopic eczema 103
Atrophic cicatricial alopecia 95
Auspitz's phenomenon 92
Auspitz sign 19
Autoimmune blistering
diseases 125
disorder 127
Autoimmune progesterone dermatitis 8
Autosomal dominant ichthyosis 98
Azathioprine 89, 127
Bacillus Calmette–Guérin immunization 39
Bacteria 69
Bacterial infection, secondary 28, 75f
Benzoyl peroxide gels 74
Beta-carotene, systemic 114
Black dot ringworm 57, 58
chemistry 112
laboratory examination of 112, 114
urea nitrogen 88
Borrelia burgdorferi 52
Bullous disorders 104
Bullous erythema multiforme 126
Bullous fixed-drug eruption 83f
Bullous impetigo 32, 33, 107, 126
Bullous lesions 80f
Bullous pemphigoid 127, 127f, 128b
Bunostomum 29
phlebotomum 29
Burns 4
Buttonhole sign 19
Café-au-lait spot 9
Candida albicans 122
Candidiasis 18
Carbaryl 28
Carbuncles 36
Castellani's paint 68
Cellulitis 34, 34t
diffuse warm erythematous swelling of 34f
Central nervous system 45
Cephalosporin 36, 37
Ceramides 2
Cetirizine 79
Chediak–Higashi syndrome 113
Chemotaxis 37
Cholesterol 2
Christ–Siemens–Touraine syndrome 102
Clitoris 5
Clouston syndrome 103
Cloxacillin 28, 34, 37, 105
Collagen fibers 3
Comedones 73f
Conical teeth 101f
Conjunctival ingestion 86f
Conjunctivitis 53
Corona seborrheica 67
Corticosteroids 73
lotions 76
systemic 92
Cotrimoxazole 28, 83f
Coudability sign 19
Coup d'Ongle sign 19
Coxsackievirus 52, 53
Crotamiton 26, 31
Crusts, removal of 32
Cushing's disease 119
Cutaneous larva migrans 18, 28, 29b
migrating eruption of 28f
Cutaneous lesions 55
Cutaneous tuberculosis 38
clinical features of 39t
treatment of 42
Cyclophosphamide 89, 127
Cyclosporine 89, 127
Cysts 74
Cytomegalovirus 53
Dandruff 65
Dapsone 127, 128
Darier sign 19
Deep tendon reflexes 21
Dengue 52
Dennie–Morgan sign 64
Dental hygiene 103
Depigmented asymptomatic patches 110f
Depigmented hairs 110f, 111f
Dermal chronic inflammatory infiltrate 97
Dermal papillae 5
Dermatitis 62
herpetiformis 8
layers of 1
primary function of 3
Dermoepidermal junction 2
Dermoscopy 23, 72
Diabetes mellitus 34
Diarrhea 121
Dinitrochlorobenzene 72
Dipyridamole 89
Doxepin 79
Drug reaction 81f
Dry scaly patch over cheeks 62f
Dyshidrosis 102
Eccrine glands 4
Echovirus 52
Ecthyma 33f
Ecthymatous deep lesions 44f
Ectodermal dysplasia syndrome 101, 101f, 102b, 102f
Eczema 62
infantile 63
Eczematization 27f
Eczematized scabies over palm 25f
intercellular 55, 67
intracellular 55
Elastic fibers 1
Elbow, erythematous dry scaly patch over flexural aspect of 62f
Emollients 99
Endocrine disorders 118
Endothelial cell 93
Eosinophilia, high levels of 79
Eosinophils 64
Epidermal acrosyringium 76
Epidermal appendages 2, 4b
Epidermal lipids 2
Epidermis, layers of 1
Epidermolysis bullosa 104, 104f, 105, 105b
dystrophic type of 104f, 105f
Epidermophyton 56, 59
Epstein–Barr virus 52, 53
Erosive cheilitis 109
Eruptive syringoma 41
Erysipelas 34t, 35, 35f
episodes of 36
Erythema 13, 20, 31f, 68, 68f
induratum 41
infectiosum 52
multiforme 13, 17, 80, 80f, 81b, 81f, 82, 83f, 84f
target lesions of 80f
treatment of 82
nodosum 38f
Erythematosquamous eruption 67
Erythematous dry patches 62f
Erythematous macular rash 51f, 52f
Erythematous maculopapular rash 80f
Erythematous oval patches 96f
Erythematous papules 80f
sparing 68f
Erythroderma 9, 92
drug-induced 8
Erythromycin 28, 36, 128
Exanthem 97
Exocytosis 97
lashes 71f
manifestations 112
Eyebrow, alopecia areata of 71f
Eyelid, fixed-drug eruption of 83f
Fibroblasts cell 93
Fish-scale pattern 98f, 99f
Fixed-drug eruption 82, 82f84f, 85b
multiple lesions of 84f
Flaccid bulla, irregular erosions of 125f
Flavivirus 52
Follicular hyperkeratosis 124
Follicular lesions 17fc
Fountain sign 19
Free fatty acid 2
infections 56
lesions, diagnosis of 22
Furuncles 36, 36t
Gamma benzene hexachloride 26, 28
Genetic disorders 98
Giant lesions 48
Gingiva 21
Gingivitis, desquamative 109
Glans penis 5
Gluteal area 59f
Glycolic acid 101, 120
Gougerot–Carteaud syndrome 119
Gram's stain 3, 107
Granular cell layer 99
Granuloma pyogenicum 50f
Gray patch scaly ringworm 56, 58
Guttate psoriasis 16, 92, 93, 97
Haemophilus influenzae 34
and nails affection 95
bulb 5
diseases of 70
follicles 4, 5
loss, pattern of 20, 20fc
Hairy nevus, congenital 117
Hand, foot, and mouth disease 53, 55b
Hansen's disease 9, 10, 18, 21, 42, 43b
anesthetic patch of 42f
plaque of 42f
spectrum of 44t
Hematologic tests 79
Hemorrhagic bullae 104f, 105f
Henoch–Schönlein purpura 87, 88b, 88f
diagnosis of 88
Hepatitis 79
B virus 52
Herald patch 96
Hermansky–Pudlak syndrome 113
Herpes simplex 47, 48b, 80
erythematous base classical of 47f
virus 47
Herpes zoster 16, 46, 46b, 46f
treatment 47b
Herpetiform clusters 46
Hidrotic ectodermal dysplasia 102f
Hookworm 29
Horny keratotic papules 123f
Human immunodeficiency virus 23, 39, 92
Human papillomavirus 50b
Hurler's syndrome 116
Hutchinson's sign 46, 47
Hyaluronic acid 3
Hydrated petrolatum 64
Hydrocortisone lotion 68
Hydroxyzine 79
Hyper-immunoglobulin E syndrome 37
Hyperinsulinemia 120
Hypogonadal syndromes 119
Hypohidrosis 103
Hypopigmented macules 60f
Hypopigmented patch 10fc
Hypopigmented skin diseases 10t
Ibuprofen 84f
Ichthyosis 98f, 101f
vulgaris 98, 98f, 99b
Immunity, cell-mediated 49
E 78
M 109
Impetigo 24f, 32b
contagiosa 31, 31f, 32
Infections 24, 69
bacterial 31
Infectious exanthem 51, 52b
Intestinal mucosa 29
Intralesional steroids 72
Irritant contact dermatitis 69
Itchy erythematous plaques 80f
Itchy papules 24f
Itchy pigmented round patch 83f
Itraconazole 58
Ivermectol 28
Janus kinase inhibitor 64
Kaposi's varicelliform eruption 52f, 53
Keratin tonofilaments 99
Keratinocytes 2, 3, 93
Keratosis pilaris 99
Kerion 57, 58
Ketoconazole 60, 61
Koebner's phenomenon 19, 95, 112
Koplik's spots 53
Labia minora 5
Lamina densa 4
Langerhans cells 1
Larva currens 29
Larva migrans, multiple tracks of 29f
Leiner's disease 67
Leishman bodies 22
Leopard syndrome 9
Lepra reaction 42f
Lesions 9, 26
primary 9
resolution of 115f
secondary 9
urticarial 128
Levocetirizine 79
planopilaris 16
planus 93, 94, 94b, 94f
treatment of 82f
scrofulosorum 41
striatus 63f
Linear immunoglobulin A 107
dermatosis 107, 108b
Linear lesions 17
Lip, hemorrhagic crusting of 81f, 86f
Lupus vulgaris 39, 40, 42
atrophy of 38f
plaque of 40
Lyell's syndrome 86
Lymph node 5
tuberculosis of 41
Lymphadenopathy 27f, 66f
Lymphangitis 35
Lymphocytes 64
Lymphoproliferative disorders 46
Malassezia furfur 60
Malathion 28
Mastocytosis 78f
Mechanobullous disorders 104
Meissner corpuscles 5
Melanin accumulates 3
Melanocyte 3
stimulating hormone 3
Melanophages 116
Merkel cells 1, 3
Metastatic tuberculous abscess 40
Methotrexate 127
Meyerson's eczema 48f
Miconazole cream 61
Microsporum 56, 59
audouinii 57
canis 57
Miliaria 74
profunda manifests 76
rubra 74, 75b, 75f, 76
over interscapular region 75f
Milky-white papules 95
bodies 49
contagiosum 48, 48f, 49b
Mongolian spots 115, 116, 116b
patches of 115f
Mouth disease 53f, 54f
Mucocutaneous junction 5
Mucous membrane 53, 82, 107, 112, 122, 128
Multiforme 17
Multinucleated giant cell 22, 47
Multiple bullae 106f
Multiple furunculosis 36f
Mupirocin 37, 105
Musculocutaneous perforators 5
Mycetoma 22
Mycobacteria 41
bovis 39
leprae 42, 43
tuberculosis 39
Mycophenolate mofetil 127
Mycoplasma 81
apparatus, examination of 21
dystrophy 70f
Napkin dermatitis 68, 68f, 69b
Nasal furuncles 37
Necator americanus 29
Necrotizing vasculitis 79
Nephrotic syndrome 122
Neural crest
cells 3
origin 1
Neutrophil chemotaxis 108
Nevomelanocytic nevus, congenital 116, 117, 117b, 117f
Nikolsky sign 19, 87, 107, 126
positive 86f, 125f
Nodular scabies, persistent itchy nodule of 25f
Nodules 74
Nonsteroidal anti-inflammatory drugs 88
Numerous acantholytic cells 22
Nutritional disorders 121
Oculocutaneous albinism 113f
classification of 113
Onychodysplasia 102, 103
Opaque cosmetics 116
Ophthalmic zoster 47
Oral acitretin 100f
Oral antihistamines 31
Oral cavity 21
Oral griseofulvin 58
Oral ketoconazole 66, 68
Oral lesions 95
Oral mucosa 121f
Oral mucosal lesions 51
Oral penicillin 36
Oral photochemotherapy 95
Oral retinoids 95
Oral steroids 109
Oral tetracyclines 74
Oral zinc 122
Otitis externa 67
Pacini corpuscles 5
Pain, abdominal 88f
Palmoplantar keratoderma 20
Palms 5
examination of 20
Palpable purpura 88f
Papular urticaria 30, 30b, 30f
Papules 73f, 74
Papulonecrotic tuberculid 41
Papulosquamous disorders 90
Parakeratosis 93
Parasitic infections 80
Patch tests 22
Pediculosis capitis 26, 27b, 27f
Pediculus humanus 27
Pemphigus 8, 126
erythematosus 125
foliaceus 125
prevalence of 125
vegetans 125
vulgaris 19, 125, 125f, 126b
Perianal wart 50f
Perifollicular scaly macules 65f
Perioral dermatitis 68
Periporitis 75f
Periungual wart 50f
Permethrin 26, 28
Phenolphthalein 84
Phenylbutazone 84, 86
Photosensitive eczema 66f
Phrynoderma 123, 123b, 123f
horny follicular papules of 123f
Pigmentary disorders 110
Pigmentation 82f
Pigmented lesion 117
Pigmented macule 10fc
Pigmented papule 11fc
Piperonyl butoxide 28
Pityriasis 60
alba 114, 114b, 114f, 115
rosea 96, 96f, 97b
rubra pilaris 11
versicolor 60, 60b, 60f
Platelet disorder 113
Plucked hair bulb 113
Plummer sign 19
Poikiloderma 13
Polycyclic lesions 108f
Popliteal fossae 99
Postherpetic neuralgia 47
Potassium hydroxide 59
Prednisolone 95, 128
Prednisone 128
Pressure urticaria 78f, 78f
Pruritus 97
Pseudoacanthosis nigricans 119f
Pseudo-Darier sign 19
Psoriasis 90, 91f, 92b, 93
congenital erythrodermic 90f, 91f
papules of 91f
pustular 91f
Psoriatic erythroderma 7
Psoriatic plaque 8
Pterygium unguis 95
Purulent discharge 56f
Pustular eruption, primary 13fc
Pustules 73f, 75f
Pyogenic infection
acute 31
secondary 26
Pyrethroids 28
Radioallergosorbent test 79
Ramsay hunt syndrome 47
Regional lymph nodes 45, 47
Retroauricular erythema 65f
Salt-split skin 109
Sarcoptes scabiei 24, 25
Sarecycline 74
Satellite lesion 18
Scabies 13, 24, 24f, 25b
classical 24f
lesions of 26
pustules of 24f
examination of 20, 57
hair 103
seborrheic dermatitis of 66f
vitiligo of 110f
Scaly plaque 14fc
Scarlatiniform 18
syndrome 107
Scarring alopecia 56
Scrofuloderma 40
Sebaceous glands 4
Sebaceous lipids 2
Seborrhea 72f, 73f
Seborrheic dermatitis 65, 65f, 66, 66b, 66f
Seborrheic eruptions 66
Secondary bacterial infection 28, 75f
management of 45
Serologic tests 79, 112
Serology 23
Serum vitamin A 124
Sexual abuse 50f
Simple emollient cream 115
abnormal 99
appendages of 1
biopsy 23, 116
cancers, development of 114
care 114
consists 1
diseases 22
signs of 9
disorders 69
erosion of 104f
functions of 1, 2b
lesions 19fc, 53, 59, 61, 63, 74, 79, 82, 94, 96
auscultation of 20
palpation of 19
lines 55
scrapings, examination of 22
structure of 1, 1b
surface lipids 2b
testing 42
urticarial 109
Slit-skin smear 22
Small peptide fragments 3
Sodium thiosulfate 61
Soft tumorous nodules 40
Soles, examination of 20
Spongiosis 64, 97
Staphylococcal scalded skin syndrome 33f, 106, 106b, 106f
Staphylococcus aureus 107, 122
Stenosis, pulmonary 9
Steroid, systemic 30f
Stevens-Johnson syndrome 9, 81, 126
Streptococcal pharyngitis 93
Streptococcus pyogenes 34
Strongyloides 29
stercoralis 29
Subcorneal pustule 32
Sublamina densa 108
Sulfapyridine 127, 128
Sulfonamides 84, 86
Sulfones 86
Superficial dermis 6
Superficial erythematous vesicles 75f
Superficial papillary dermis 3
Superficial pustules 91f
Sweat glands 4, 70
Sweating, loss of 102f
Synthetic pyrethroid 28
Systemic lupus erythematosus 8, 80
Teeth, loss of 102f
Telangiectasia 68
Tetracyclines 84
Tetramethrin 28
Thiabendazole 29
Thyroiditis 111
Tidemark dermatitis 69
Tinea capitis 56, 57b
noninflammatory type of 56f
Tinea corporis 58, 59b, 59f
Tinea faciei 58f
fixed-drug eruption of 84f
wart over dorsum of 50f
Topical immunotherapy 72
Topical steroids 72
Toxic epidermal necrolysis 9, 83f, 85, 86b, 86f, 86f
development of 84f
Toxic shock syndrome 52
Toxocariasis 29
Tranquilizers 95
Treponema pallidum 53
Tretinoin 120
Triamcinolone 95
Trichodysplasia 102
Trichophyton 56, 59
rubrum 59
schoenleinii 57
tonsurans 57
violaceum 57
Triglycerides 2
Tuberculids 41
acute miliary 3941
eruptive 38
genitourinary 41
hematogenous 38
inoculation 38
intestinal 41
primary inoculation 41
pulmonary 38f, 41
secondary 38
verrucosa cutis 38, 40, 42
Tuberculous gumma 40
Tumor necrosis factor-alpha 42
Tyrosine hair bulb test 114
Tzanck smear 44f
Tzanck test 22
Ulcerative oral lesions 95
Ultrapotent topical steroids 128
Uncinaria 29
stenocephala 29
Urticaria 8, 13, 77, 77f, 78f
acute 77f, 78
drug-induced 77f
idiopathic 78f
Varicella 16, 44, 45b
pneumonia 45
symptoms of 45
virus infection 44f
zoster immune globulin 45
Vascular reactions 77
Vaseline gauze 37
Verruca vulgaris 50f, 51
Verrucosa cutis 38f
Verrucous plaque 12fc
Vesicles 68f
elbows 53f
gluteal region 54f
Viral exanthem 51f, 52f
Viral infections 40, 44
Viral warts 49, 50b
Visceral larva migrans 29
Vitamin A 123, 124
deficiency 123
supplements 124
Vitiligo 110, 110f, 111b, 111f
areata, isolated 110f
macules 111
mimics leprosy 110
periorificial 111f
treatment of 112
vulgaris, asymptomatic patches of 111f
Warty tuberculosis 38
Wickham's striae 94, 95
Wood's lamp 57, 111
examination 61, 112
Wooly hair 118f
absorption, disorder of 121
deficiency 121, 122b
Zosteriform 16, 46
Chapter Notes

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Structure and Functions of Skin1

Dermatological problems are seen by pediatricians every day and comprise around one-quarter of a busy outpatient clinic. Most children and adolescents present with skin disorders can be easily diagnosed and treated. This chapter will present a brief account of some such skin conditions.
The integument or skin covers the entire external surface of the human body and is the principal site of interaction with the surrounding world. It serves as a protective barrier preventing internal tissues from exposure to trauma, ultraviolet radiation, extreme temperature, toxins, and bacteria. Other important functions include sensory perception, immunologic surveillance, thermoregulation, and control of insensible fluid loss.
The skin consists of two mutually dependent layers: (1) the epidermis and (2) dermis that rest on a fatty subcutaneous layer, the subcutis. The epidermis is derived primarily from surface ectoderm but is colonized by pigment-containing melanocytes of neural crest origin, antigen-processing Langerhans cells of bone marrow origin, and pressure-sensing Merkel cells also of neural crest origin. The dermis is derived primarily from mesoderm and contains collagen, elastic fibers, blood vessels, sensory structures, and fibroblasts. During the 4th week of embryologic development, the single cell thick ectoderm and underlying mesoderm begin to proliferate and differentiate.2
The specialized structures formed by the skin, including teeth, hair, hair follicles, fingernails, toenails, sebaceous glands, sweat glands, and apocrine glands also begin to appear at approximately this period in development. Teeth, hair, and hair follicles are formed by the epidermis and dermis, while the epidermis alone forms fingernails and toenails. Hair follicles, sebaceous glands, sweat glands, apocrine glands, and mammary glands are considered epidermal glands or epidermal appendages, because they develop as downgrowths or diverticula of the epidermis into the dermis. The definitive multilayered skin is present at birth, but skin is a dynamic organ that undergoes continuous change throughout life as outer layers are shed and replaced by inner layers. Skin also varies in thickness among anatomic location, sex and age of the individual. This 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 thickest on the palms and soles of the feet (1.5 mm), while it is thinnest on the eyelids and in the postauricular region (0.05 mm). Children have relatively thin skin, which progressively thickens until the 4th or 5th decade of life after which it begins to thin. This thinning is also primarily a dermal change, with loss of elastic fibers, epithelial appendages, and ground substance. The epidermis contains no blood vessels and is entirely dependent on the underlying dermis for nutrient delivery and waste disposal via diffusion through the dermoepidermal junction. The epidermis is a stratified squamous epithelium consisting primarily of keratinocytes in progressive stages of differentiation from deeper to more superficial layers. The named layers of the epidermis include the stratum germinativum, stratum spinosum, stratum granulosum, and stratum corneum. The stratum germinativum or basal layer is immediately superficial to the dermoepidermal junction. This single cell layer of keratinocytes is attached to the basement membrane via hemidesmosomes.
As keratinocytes divide and differentiate, they move from this deeper layer to the more superficial layers. Once they reach the stratum corneum, they are fully differentiated keratinocytes devoid of nuclei and are subsequently shed in the process of epidermal turnover. Cells of the stratum corneum are the largest and most abundant of the epidermis. This layer ranges in thickness from 15 to 100 or more cells depending on anatomic location and is the primary protective barrier from the external environment.
The cells of the stratum corneum are referred to as corneocytes which are embedded in a lipid-rich matrix composed of free fatty acid, cholesterol, and ceramides. The sebaceous lipids include triglycerides, wax esters, and squalene. The surface lipids of the skin made up of sebum-derived lipids and cell surface lipids play an important role both in health and disease (Box 3).3
Melanocytes, derived from neural crest cells, primarily function to produce a pigment, melanin, that absorbs radiant energy from the sun and protects the skin from the harmful effects of ultraviolet radiation. Melanin accumulates in organelles termed melanosomes that are incorporated into dendrites anchoring the melanosome to the surrounding keratinocytes. Ultimately, the melanosomes are transferred to the adjacent keratinocytes where they remain as granules. Melanocytes are found in the basal layer of the epidermis as well as in hair follicles, the retina, uveal tract, and leptomeninges. These cells are the sites of origin of melanoma. In areas exposed to the sun, the ratio of melanocytes to keratinocytes is approximately 1:4. In areas not exposed to solar radiation, the ratio may be as small as 1:30. Absolute numbers of melanosomes are the same among the both sexes and various races. Differing pigmentation among individuals is related to the size of melanosomes and their interspacing rather than cell number. Sun exposure, melanocyte-stimulating hormone (MSH), adrenocorticotropic hormone (ACTH), estrogens, and progesterones stimulate melanin production. With aging, a decline is observed in the number of melanocytes populating the skin of an individual. Since these cells are of neural crest origin, they have no capability to reproduce. Langerhans cells originate from the bone marrow and are found in the basal, spinous, and granular layers of the epidermis. They serve as antigen-presenting cells. They are capable of ingesting foreign antigens, processing them into small peptide fragments, binding them with major histocompatibility complexes, and subsequently presenting them to lymphocytes for activation of the immune system. An example of activation of this component of the immune system is contact hypersensitivity. Merkel cells, also derived from neural crest cells, are found on the volar aspect of digits, in nail beds, on the genitalia, and in other areas of the skin. These cells are specialized in the perception of light touch.
The primary function of the dermis is to sustain and support the epidermis. The dermis is a more complex structure and is composed of two layers: (1) the more superficial papillary dermis and (2) the deeper reticular dermis. The papillary dermis is thinner, consisting of loose connective tissue containing capillaries, elastic fibers, reticular fibers, and some collagens. The reticular dermis consists of a thicker layer of dense connective tissue containing larger blood vessels, closely interlaced elastic fibers, and coarse bundles of collagen fibers arranged in layers parallel to the surface. The reticular layer also contains fibroblasts, mast cells, nerve endings, lymphatics, and epidermal appendages. Surrounding the components of the dermis is the gel-like ground substance, composed of mucopolysaccharides (primarily hyaluronic acid), chondroitin sulfates, and glycoproteins. The deep surface of the dermis is highly irregular and borders the subcutaneous layer, the panniculus adiposus, which additionally cushions the skin. The fibroblast is the major cell type of the dermis. These cells produce and secrete procollagen and elastic fibers. Procollagen is terminally cleaved by proteolytic enzymes into collagen that aggregates and becomes cross-linked. These tightly cross-linked collagen fibers provide tensile strength and resistance to shear and other mechanical forces. Elastic fibers constitute <1% of the weight of the dermis, but they play an enormous functional role by resisting deformational forces and returning the skin to its resting shape. The dermoepidermal junction is an undulating basement membrane that adheres the epidermis to the dermis. It is 4composed of two layers: (1) the lamina lucida and (2) lamina densa. The lamina lucida is thinner and lies directly beneath the basal layer of epidermal keratinocytes. The thicker lamina densa is in direct contact with the underlying dermis. These structures are the target of immunologic injury in diseases such as bullous pemphigoid and epidermolysis bullosa. Epidermal appendages are intradermal epithelial structures lined with epithelial cells with the potential for division and differentiation. These are important as a source of epithelial cells, which accomplish re-epithelialization should the overlying epidermis be removed or destroyed in situations such as partial thickness burns, abrasions, or split-thickness skin graft harvesting. Epidermal appendages include sebaceous glands, sweat glands, apocrine glands, and hair follicles (Box 4). They often are found deep within the dermis, and in the face may even lie in the subcutaneous fat beneath the dermis. This accounts for the remarkable ability of the face to re-epithelialize even the deepest cutaneous wounds. Sebaceous glands, or holocrine glands, are found over the entire surface of the body except the palms, soles, and dorsum of the feet. They are largest and most concentrated in the face and scalp where they are the sites of origin of acne. The normal function of sebaceous glands is to produce and secrete sebum, a group of complex oils including triglycerides and fatty acid breakdown products, wax esters, squalene, cholesterol esters, and cholesterol. Sebum lubricates the skin to protect against friction and makes it more impervious to moisture. It also has antimicrobial properties. Sweat glands, or eccrine glands, are found over the entire surface of the body except the lips, external ear canal, and labia minora. They are most concentrated in the palms and soles of the feet. Each gland consists of a coiled secretory intradermal portion that connects to the epidermis via a relatively straight distal duct. The normal function of the sweat gland is to produce sweat, which cools the body by evaporation. The thermoregulatory center in the hypothalamus controls sweat gland activity through sympathetic nerve fibers that innervate the sweat glands. Sweat excretion is triggered when core body temperature reaches or exceeds a set point. Apocrine glands are similar in structure but not identical to eccrine glands.
5They are concentrated in the axillae and anogenital regions. They probably serve a vestigial sexual function, because they produce odor and do not function prior to puberty. Hair follicles are complex structures formed by the epidermis and dermis. They are found over the entire surface of the body except the soles, palms, glans penis, clitoris, labia minora, mucocutaneous junction, and portions of the fingers and toes. Sebaceous glands often open into the hair follicle rather than directly onto the skin surface, and the entire complex is termed the pilosebaceous unit. The base of the hair follicle, or hair bulb, lies deep within the dermis and in the face may actually lie in the subcutaneous fat. A band of smooth muscle, the arrector pili, connects the deep portion of the follicle to the superficial dermis. Contraction of this muscle, under control of the sympathetic nervous system, causes the follicle to assume a more vertical orientation. Hair growth exhibits a cyclical pattern. The anagen phase is the growth phase, whereas the telogen phase is the resting state. The transition between anagen and telogen is termed the catagen phase. Phases vary in length according to anatomic location, and the length of the anagen phase is proportional to the length of the hair produced. At any one time at an anatomic location, follicles are found in all three phases of hair growth.
Cutaneous vessels ultimately arise from underlying named source vessels. Each source vessel supplies a three-dimensional vascular territory from bone to skin termed an angiosome. Adjacent angiosomes have vascular connections via reduced caliber (choke) vessels or similar caliber (true) anastomotic vessels. The cutaneous vessels originate either directly from the source arteries (septocutaneous or fasciocutaneous perforators) or as terminal branches of muscular vessels (musculocutaneous perforators). They emerge from the deep fascia in the vicinity of the intermuscular or intramuscular septa or near tendons and travel toward the skin, where they form extensive subdermal and dermal plexuses. The dermis contains horizontally arranged superficial and deep plexuses, which are interconnected via communicating vessels oriented perpendicular to the skin surface. Cutaneous vessels ultimately anastomose with other cutaneous vessels to form a continuous vascular network within the skin. Clinically, this extensive horizontal network of vessels allows for random skin flap survival. In addition to the skin's natural heat conductivity and loss of heat from the evaporation of sweat, convection from cutaneous vessels is a vital component of thermoregulation. Cutaneous blood flow is 10–20 times that required for essential oxygenation and metabolism, and large amounts of heat can be exchanged through the regulation of cutaneous blood flow. The thermoregulatory center in the hypothalamus controls vasoconstriction and vasodilatation of cutaneous vessels through the sympathetic nervous system. Skin lymphatics parallel the blood supply and function to conserve plasma proteins and scavenge foreign material, antigenic substances, and bacteria. Blind-ended lymphatic capillaries arise within the interstitial spaces of the dermal papillae. They course through the deep dermal and subdermal plexuses and numerous filtering lymph nodes on their way to join the venous circulation near the subclavian vein-internal jugular vein junction bilaterally. Sensory perception is critically important in the avoidance of pressure, mechanical or traumatic forces, and extremes of temperature. Numerous specialized structures are present in the skin to detect various stimuli. Merkel cells of the epidermis detect light touch. Meissner corpuscles also detect light touch. These are found in the dermal papillae and are most concentrated in the fingertips. Pacini corpuscles 6are found deep within the dermis or even in the subcutaneous tissue. These structures are specialized to detect pressure. Pain is transmitted through naked nerve endings located in the basal layer of the epidermis. Krause bulbs detect cold, whereas Ruffini corpuscles detect heat. Heat, cold, and proprioception also are located in the superficial dermis. Cutaneous nerves follow the route of blood vessels to the skin. The area supplied by a single spinal nerve, or single segment of the spinal cord, is termed a dermatome. Adjacent dermatomes may overlap considerably, and of importance to note when performing field blocks with local anesthesia.