DERMAL-EPIDERMAL JUNCTION (DEJ), DERMIS BASICS OF DERMATOLOGY (2) DERMATOLOGY FOR THE USMLE

DERMATOLOGY FOR THE USMLE

BASICS OF DERMATOLOGY (2)

DERMAL-EPIDERMAL JUNCTION (DEJ), DERMIS

2	DERMAL-EPIDERMAL JUNCTION (DEJ): Also known as dermoepidermal junction or basement membrane zone (BMZ), functions to provide attachment and communication between the epidermis and dermis. The DEJ is connected to the overlying epidermis by hemidesmosomes and to the dermis by anchoring fibrils (composed of type VII collagen). Other important BMZ structures include the lamina lucida and lamina densa USMLE Pearls: Destruction of DEJ structures may result in subepidermal blistering disorders. Common examples include bullous pemphigoid (BP) and epidermolysis bullosa acquisita (EBA), which produce autoantibodies against hemidesmosomes and type VII collagen, respectively.
3	DERMIS: Embryonic origin is the mesoderm The dermis provides structural and nutritional support for the epidermis. Composed mostly of mucopolysaccharide gel, collagen and elastic fibers. Main cell type is the fibroblast, responsible for synthesis of collagen and elastin. The dermis may be predominantly infiltrated by different cell types during pathological processes. Common examples are: √ Allergic reactions: Lymphocytes and eosinophils. √ Acute inflammatory reactions: Neutrophils (< 24 hours) and lymphocytes (> 24 hours). √ Chronic diseases and infections: Lymphocytes and plasma cells. Functions of the dermis √ Communication: Specialized nerve fibers provide touch, pressure, pain and temperature sensation to communicate and interact with the external environment. Patients with syringomyelia, diabetes and leprosy lose cutaneous sensation and often suffer from recurrent skin trauma or burns. √ Nutrients and waste exchange: Blood vessels and capillaries provide nutrients to the epidermis and exchange toxins, medications and waste products. Blood circulation disorders may result in skin ulcers and necrosis; common examples include vasculitis and embolic occlusion √ Support: Dense collagen and elastic fibers provide structural support to overlying epidermis. Collagen production disorders such as EhlersDanlos syndrome may result in loose, lax skin. √ Thermoregulation: Adaptation to different temperatures by regulating vasodilation and vasoconstriction of dermal vessels. Faulty thermoregulation may result in hyperthermia or hypothermia. √ USMLE PEARLS: In nutritional deficiencies, the skin is often the first to show signs. Common clinical manifestations are: Angular stomatitis: Riboflavin (vitamin B2), cobalamin, zinc and niacin (vitamin B3) deficiency. Glossitis: Folate, cobalamin (vitamin B12) and iron deficiency. Non-healing wounds: Zinc and ascorbic acid (vitamin C) deficiency. Hair loss, dry skin and pruritus: Protein and calorie deficiency. Pale skin: Iron-deficiency anemia. Layers of the Dermis √ Papillary dermis: Superficial dermal layer located below the epidermis. Mainly composed of loose and thin collagen, elastic fibers and capillaries. √ reticular dermis: Deep dermal layer beneath the papillary dermis made up 90% of dense collagen and elastic fibers. Contains pilosebaceous units, glands, sensory nerve fibers, blood vessels and lymphatics.	THICK SKIN (HAIRLESS)   THIN SKIN (HAIRY) SKIN ANATOMY