SUBCUTANEOUS TISSUE, SKIN GLANDS, SKIN NERVE FIBERS BASICS OF DERMATOLOGY (3) DERMATOLOGY FOR THE USMLE

DERMATOLOGY FOR THE USMLE

BASICS OF DERMATOLOGY (3)

SUBCUTANEOUS TISSUE, SKIN GLANDS, SKIN NERVE FIBERS

4	SUBCUTANEOUS TISSUE: Also known as subcutis or hypodermis; embryonic origin is the mesoderm. Located below the dermis and provides insulation, shock absorption, energy storage and structure to the skin. The subcutis is composed of mature white adipocytes and contains large blood vessels, lymphatics and nerves. USMLE Pearls: Adipose inflammation in this layer is known as panniculitis The classic example of panniculitis is erythema nodosum, which most commonly presents as painful, red nodules over the pretibial area.
5	SKIN GLANDS √ Apocrine sweat glands: Present at birth but become functional during puberty secondary to hormonal stimulation. Continuously secrete minute quantities of oily fluid of unclear function; oil degradation by skin commensals produce a malodorous smell Mainly located in the axillae, areola, external ear canal, eyelids and anogenital region √ Eccrine sweat glands: Also called merocrine sweat glands, main function is thermoregulation. Located throughout the body, with the highest density in the palms, soles and axillae. Eccrine sweat glands are not present in the lips, external ear, penis glans or vaginal labia. USMLE Pearls: Patients with cystic fibrosis secrete hypertonic sweat due to defective chloride channels in sweat glands. When exposed to hot climate or strenuous exercise, they can rapidly become dehydrated and hypotensive. √ Sebaceous glands: Produce sebum via holocrine secretion; these glands are under androgenic hormonal regulation and enlarge during puberty. Found throughout the body except on palms and soles. Highest density on the face, scalp, ears and upper trunk, hence pathologies affecting sebaceous glands will mainly affect these areas (seborrheic distribution) Sebaceous glands play a major role in the pathogenesis of acne vulgaris
6	SKIN NERVE FIBERS √ Free nerve endings: Most common type of sensory receptor in the skin, located throughout the epidermis and superficial dermis. Provide touch, pain and temperature sensation. Common types of free nerve ending fibers are: C-type fiber: Small, slow and unmyelinated. Aδ-type fiber: Small, fast and myelinated. √ Meissner corpuscles: Mainly located in the superficial dermis of glabrous (hairless) skin such as fingertips, palms, soles, genitalia, lips and tongue. Rapidly adapting mechanoreceptors that provide light touch, vibration and position sensation. √ Pacinian corpuscles: Mainly located in deep dermis and subcutaneous tissue. Lamellar or onion-shaped, rapidly adapting mechanoreceptors that provide vibration and pressure sensation. √ Ruffini corpuscles: Mainly located in deep dermis and subcutaneous tissue. Slowly adapting mechanoreceptors that provide stretching, continuous pressure and proprioception sensation. √ Merkel disks: Mainly located in the basal layer of epidermis and hair follicles. Slowly adapting mechanoreceptor that provides sustained pressure and deep static touch sensation.