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Intro/Anatomy of Skin, Hair and Nails

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Intro/Anatomy of Skin, Hair and Nails - Stratum spinosum 1 – Intro/Anatomy of o Superficial to stratum basale, named for spiny- appearing desmosomes between cells o Keratins 1 and 10 are expressed in this layer and are skin, hair and nails mutated in epidermolytic hyperkeratosis (aka bullous congenital ichthyosiform erythroderma) Vital Functions - Stratum basale o Located just above the basement membrane, is - Sensation, barrier, immune surveillance, UV protection, composed of 10% stem cells thermoregulation o Keratins 5 and 14 are expressed in the basal layer Fun facts and are mutated in patients with epidermolysis bullosa simplex (EBS) - The skin is the largest human organ, 15% of a person’s body weight Major CELL TYPES of the epidermis - Skin cancer = most common cancer worldwide; affects 1 in 5 1. Keratinocytes people (KC) (“squamous cells”, “epidermal cells”) o Make up most of epidermis, produce keratin - Our skin is constantly being renewed, with the epidermis 2. Melanocytes (MC) turning over q40-56 days, results in average person shedding o Neural-crest derived 9 lbs of skin yearly o Normally present in ratio of 1 MC : 10 KC’s Skin thickness varies based on…. o Synthesize and secrete pigment granules called melanosomes - Location: epidermis is thickest on palms/soles at ~ 1.5mm o *** Different races and skin types actually have the (thickness of a penny), thinnest on eyelid/postauricular at ~ same amount of melanoCYTES but differ in the 0.05mm (paper) number, size, type, and distribution of - Age: Skin is relatively thin in children, thickens up until our melanoSOMES, with fairer skin types having more 30’s or 40’s, and then thins out thereafter. lighter-colored pheomelanin and darker skin types - Sex: Male skin is generally thicker than female skin in all having more of the dark eumelanin. locations 3. Langerhans Cells Overall Anatomy o Consist of 3-5% of the cells in the stratum spinosum, are derived from bone marrow, function as antigen- - Epidermis presenting cells - Dermoepidermal junction (DEJ) o Stain with S-100, CD1a, vimentin, Langerin, peanut - Subcutaneous tissue agglutinin o Contain Birbeck granules, which appear on electron The Epidermis microscopy as tennis racket-shaped organelles Layers o Ultraviolet radiation decreases the number of Langerhans cells, which may explain the mechanism - Stratum corneum (most superficial) of PUVA/narrow-band UVB in decreasing o Serves as a barrier, helping to keep the good stuff in inflammation in psoriasis (such as water) and the bad stuff out such as 4. Merkel Cells bacteria and allergens. o Located just above the basal cell layer of the o Structure is analogous to bricks and mortar epidermis and in the bulge region of hair follicles (corneocytes=bricks which are embedded in the o Believed to function as slow-adapting touch mortar of lipids such as ceramides) receptors o Not present on mucosal sites o Give rise to Merkel cell carcinomas, which are rare, - Stratum lucidum aggressive skin cancers on the head and neck of o Only present on the palms/soles, appears clear on elderly Caucasian patients H&E - Stratum granulosum The DERMOEPIDERMAL JUNCTION (DEJ) – to be discussed in the o Produces the cornified cell envelope (composed of vesiculobullous podcasts lipids and proteins; helps skin function as a mechanical and water barrier) o Not present on mucosal sites The Dermis where aromatase converts androstenedione to estrone (possible link between obesity and breast cancer) Papillary dermis (superficial) THE ADNEXA (skin appendages) - Appears wavy in 2D on biopsy specimens, as papillary dermis interdigitates with downward projections of epidermis (“rete Eccrine Glands ridges”) - Release sweat to help regulate body temperature by cooling - Contains the sub-papillary plexus, which contains arterioles, the skin when the sweat evaporates. capillaries, venules, lymphatics, and nerves - Located nearly everywhere on the skin except for the lips, - Contains Meissner corpuscles which sense touch and the external auditory canal, the glans penis, and the labia pressure. minora and clitoris. Reticular dermis (deeper) - The total mass of eccrine glands in our body is about the same as one kidney and can make up to 1.8 liters of sweat in - Has its own plexus but contains larger blood vessels. an hour! - Clinical correlation: Clark’s levels for melanoma staging - NOT associated with the hair follicle o Level 1 = in situ in the epidermis - Have muscarinic acetylcholine receptors which bind o Level 2 = tumor reaches papillary dermis acetylcholine released from sympathetic nerves, which o Level 3 = tumor fills papillary dermis explains why we sweat when we’re nervous o Level 4 = tumor reaches reticular dermis o Nervous situation → sympathetic nerves are o Level 5 = Tumor invades subcutaneous tissue activated → release acetylcholine → binds Breslow’s depth: measures tumor depth in mm’s from the receptors on our eccrine sweat glands → sweat is granular layer or base of an ulcerated melanoma to the bottom of released → you’re a hot mess the tumor o Explains why botulinum toxin injections, which block acetylcholine release, are effective for hyperhidrosis Dermal Cell Types patients. - Fibroblasts - produce collagen, elastin, and ground Apocrine Glands substance. o Collagen - 70% of the dry weight of skin, important - Locations (“4 A’s”) - the axilla, areola of the nipple, the in wound healing (Type III fetal collagen → stronger anogenital region, and the auditory canal where they type I collagen) contribute to cerumen (earwax) formation ▪ COLLAGEN 1 AND 3 SYNTHESIS IS o Also make up the Moll’s glands of the eyelids (not to DOWNREGULATED BY CORTICOSTEROIDS be confused with Meibomian glands, which are of (→ ATROPHY) AND UV LIGHT sebaceous origin) (→PHOTOAGING). UPREGULATED BY - Secrete odorless variety of proteins, carbohydrates, RETINOIC ACID. ammonia, lipids, and iron → digested by bacteria that create o Elastic fibers – help skin elasticity odorous byproducts → body odor ▪ Decrease in number with aging and are also - Apocrine glands begin to function at puberty and are mainly defective in Marfan’s syndrome due to stimulated by sympathetic adrenergic stimuli. fibrillin-1 mutations. Sebaceous Glands o Ground substance – glycosaminoglycans (GAGs) and mucopolysaccharides - Associated with hair follicles (unlike eccrine glands) ▪ E.g. hyaluronic acid → maintains water - Located everywhere except the palms and soles (which are within the dermis and is often used in hairless) many cosmetic fillers - Secrete sebum (composed mostly of triglycerides, wax - Adnexa – hair follicles, sebaceous and apocrine glands, esters, squalene, and free fatty acids) eccrine glands - Under hormonal influence rather than neurologic influence - Other cells/tissues: blood vessels, lymphatics, and nerves as is seen with eccrine and apocrine glands THE SUBCUTANEOUS TISSUE (“Sub-Q”) Hair follicles - is composed of lipocytes and fibrous septa containing - Fun facts collagen and larger blood vessels and nerves. o Humans contain 5 million hairs on average - Functions as an energy store, an insulator that protects o On average, people have 100,000 hairs on the scalp underlying muscles and bones, and as an endocrine organ and lose 100 scalp hairs daily. ▪ Blondes have thicker hair (~120k), red o Telogen effluvium = early cessation of anagen phase heads have ~80k so that >20% of hairs are in telogen phase. ▪ Hair on the scalp grows roughly 1 - Occurs approximately 3-5 months after a cm/month trigger such as an emotionally stressful o Hair color depends on melanocytes in the hair bulb event, severe illness, or pregnancy transferring melanosomes, which are pigment (prolonged anagen phase until delivery). granules, to the keratinocytes in the bulb matrix. Nails o Darker hair has mostly eumelanin, whereas blonde or red hair has more pheomelanin. - *Add diagram of hair anatomy? Hair anatomy - 3 zones: infundibulum, isthmus, and inferior segment - Infundibulum: from surface down to sebaceous gland insertion o Apocrine gland insertion is Above sebaceous gland insertion o Location of inflammation in lichen planopilaris - Isthmus: from sebaceous insertion down to the Hair bulge (location of arrector pili insertion) o Location of inflammation in discoid lupus (Discoid = Deeper) - Inferior segment – everything inferior to hair bulge - Hair bulb o Located in deep dermis or superficial sub-Q for anagen hairs ▪ Want to undermine beneath this plane in surgery, otherwise risk permanent hair loss - Helpful in dermatology because specific nail changes are (e.g. beard, scalp) caused by a variety of conditions including psoriasis, alopecia - Layers of hair from outside to in… areata, renal disease, and liver disease, amongst others o Glassy membrane (outermost) o Outer root sheath - Fingernails grow 2-3 mm per month on average and take 4-6 o Inner root sheath – itself has 3 layers… months to regrow its entire length. 1. Henle’s layer (outermost) - Toenails grow approximately 1 mm per month and take 12 to 2. Huxley’s layer (“Henle hugs Huxley”) 18 months to regrow. 3. Cuticle (innermost) - Nail plate – hard part of the nail o Hair shaft – also with 3 layers - Lateral nail fold – the skin abutting the lateral sides of the - Cuticle (outermost) – gives hair its shine nail plate after using conditioner - Proxima nail fold – skin proximal to cuticle - Cortex - Cuticle (eponychium) - cornified epithelium overlying the - Medulla lunula Hair growth - Lunula - white crescent-shaped region under the proximal nail plate - Anagen phase (active growth) - that represents the distal nail matrix. o
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