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Anatomía Y Fisiología De La Piel

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Anatomía Y Fisiología De La Piel ANATOMÍA 1 Y FISIOLOGÍA DE LA PIEL Agustín Buendía Eisman1, José Mazuecos Blanca2 y Francisco M. Camacho Martínez3 1 Profesor Titular de Dermatología. Facultad de Medicina. Universidad de Granada. 2 Catedrático de Escuela Universitaria. Área de Dermatología. Facultad de Medicina. Universidad de Sevilla. 3 Presidente de Honor de la Academia Española de Dermatología. Catedrático de Dermatología. Universidad de Sevilla. Manual de Dermatología, 2.ª edición. Editores: J. Conejo-Mir, J. C. Moreno, F. M. Camacho, pp. 2-27. ISBN Volumen I: 978-84-7885-628-2. ISBN Obra completa: 978-84-7885-627-5. ISBN Volumen II: 978-84-7885-629-9. Contenido • Estructura general de la piel • Manto cutáneo ácido lipídico • Funciones de la piel • Hipodermis • Embriología de la piel • Vasos y nervios cutáneos • Estructura de la epidermis • Tendencias en la investigación del desarrollo • Sustancia fundamental y estructura de la piel • Anejos cutáneos • Bibliografía Características generales ◗ La piel consta de tres capas bien diferenciadas: epidermis, dermis Está formada por fibras, como las de colágeno y las elásticas, y e hipodermis. por células, como los fibrocitos, mastocitos e histiocitos. Tiene ◗ La epidermis está constituida por queratinocitos, melanocitos, dos áreas bien distinguibles: superior, o dermis papilar, e inferior o células de Largenhans y células de Merkel. dermis reticular. ◗ La capa más externa de la epidermis o capa córnea se forma por ◗ La hipodermis es la tercera capa, encargada de almacenar lípidos la apoptosis de los queratinocitos. para aportar energía al organismo y aislante térmico. ◗ Las uniones entre queratinocitos son mediante desmosomas; y ◗ Las funciones de la piel son: protección, termorregulación, entre la capa basal y la dermis, mediante hemidesmosomas. sensorial, secretora y excretora, inmunológica y producción de vitamina D. ◗ La dermis es una capa conjuntiva que alberga los plexos vasculonerviosos y sirve de sostén a la epidermis y a sus anejos. 2 © 2018. Grupo Aula Médica MANUAL DE DERMATOLOGÍA, 2.ª EDICIÓN - VOLUMEN I 01_anatomia.qxp:_Dermatologia_01.qxd 3/12/09 11:31 Página 4 01_anatomia.qxp:_Dermatologia_01.qxd 3/12/09 11:31 Página 10 4 Imágenes clave Estrato córneo 10 Epidermis Los desmosomas forman una unión simétrica, tienen Dermis un diámetro de 0,1-0,5 nm y están formados por unos Unión ajustada papilar Transmembrana: ocludina, claudina componentes transmembrana y otros de la propia placa Placa: ZO, cingulina, simplequina, 7H6 Temas generales Temas electrón-densa, con un espacio intercelular central (Figs. Conectada al citoesqueleto de actina 7, 8 y 11). Los componentes transmembrana son unas Unión adherente Transmembrana: cadherinas E y P glicoproteínas, familias de las cadherinas, formando aso- Placa: cateninas a y b, placoglobina ciaciones heterófilas de desmogleínas y de desmocoli- Conectada al citoesqueleto de actina Desmosoma Temas generales Temas nas; hay tres desmogleínas (desmogleínas 1-3) y otras Transmembrana: desmocolinas, desmogleinas Dermis tres desmocolinas (desmocolinas 1-3), y los de la placa Placa: desmoplaquinas, placoglobina reticular son otras tres proteínas (desmoplaquina, placoglobina Conectados al citoesqueleto intermedio y placofilina), que son las que fijan las cadherinas a los Unión de tipo hendidura tonofilamentos de queratina, que se disponen perpen- Transmembrana: conexón (6 conexinas) dicularmente a ella (Fig. 12). Hipodermis Figura 2. Foto histológica de piel y su división en capas. Figura 2. Foto histológica de piel y su división en Membrana basal Figura 1. Dibujo esquemático de la piel. capas. Las uniones adherentes son estructuras transmembrana elec- trón-densas compuestas por cadherina E, la cual forma interac- Hemidesmosoma ¿Adhesión focal? ciones calcio-dependientes con la cadherina E de la célula adya- vasos y nervios, y se ve perforado por los anejos, unos glan- cente. Estas interacciones se conexionan con la membrana Figura 11. Diferentes proteínas que constituyen las uniones celula- dulares (glándulas sebáceas y sudoríparas ecrinas y apocri- plasmática por medio de una red de proteínas adhesivas que resFigura en la epidermis. 11. Diferentes proteínas que constituyen las nas) y otros queratinizados (pelos y uñas). Capa córnea incluyen α-catenina, β-catenina y p120ctn. uniones celulares en la epidermis. Las uniones tipo hendidura (gap) son un grupo de canales intercelularesEstrato conocidos lúcido como conexones, que forman cone- Inmediatamente por debajo, y separada por la unión xiones entreCapa los granulosa citoplasmas de los queratinocitos adyacen- dermo-epidérmica, se encuentra la dermis, estrato tes. Los conexones se originan en el aparato de Golgi conjuntivo 20 a 30 veces mayor que la capa anterior, 01_anatomia.qxp:_Dermatologia_01.qxdmediante el ensamblaje 3/12/09 de seis subunidades 11:31 Página de conexinas 19 , que alberga en su interior los plexos vasculonervio- sintetizadas en el retículo endoplásmica, siendo después sos y sirve de sostén a la epidermis y a sus anejos. transportados a la membrana plasmática, donde se agregan Está formada por un componente fibroso, que con otros conexonesCapa espinosa y, en combinación con los agregados del incluye fibras de colágeno (principal estructura de la queratinocito adyacente, forman la unión gap. La función de estas uniones tipo hendidura es la transferencia de moléculas dermis) y fibras elásticas. Sus células constitutivas de bajo peso molecular (< 1000 Da) y de intercambio de iones son los fibroblastos, como las células más importantes, entre células vecinas. los mastocitos y los histiocitos. Estos dos componen- Las uniones ajustadas están compuestas de moléculas Desmocolina tes se encuentran dentro de una sustancia funda- transmembranaCapa basal e intracelulares, como la ocludina y las clau- 19 mental, en la que predominan los mucopolisacári- dinas. Tienen como función la de controlar la permeabilidad Desmogleína dos hidratados, con gran capacidad para retener y paralelasepidérmica a la superficiey la de mantener cutánea la polaridad en la dermis celular. profunda, Placoglobina Tallo agua. PlacofilinaMúsculo piloso siendo más gruesas.Dermis La síntesis de las fibras elásticas por erector del pelo Por debajo de la dermis se encuentra la hipodermis, los fibrocitos consta de dos etapas. En la primera se secre- Desmoplaquina panículo adiposo o tejido celular subcutáneo, que, Figura 15.Epidermopoyesis Inmunohistoquímica de los melanocitos Figura 3. Esquema de las capastan de laal epidermis. espacio extracelular las microfibrillas agrupadas de Figura 12. Componentes de los desmosomas. aparte de contener algunos elementos vasculonervio- en la capa basal con tinciones de plata. forma Enlineal la cinética produciéndose celular de la una epidermis, polimerización el concepto posterior- más impor- sos, es un perfecto aislante térmico y sirve de pro tec- mente.tante En la es segunda el tiempo se de produce regeneración la secreción celular (turnoverde la tropoe- time), ción frente a los traumatismos a los órganos internos. lastinaque dentro define de el los tiempo cilindros medio preformados de una población de microfibri-celular para La capa basal tiene una serie de controles estimuladores Ya debajo existe una fascia fibrosa profunda, que se reproducirse a sí misma; es decir, el intervalo entre dos mito- y/o inhibidores que permiten, en determinadas circunstan- llas; la elastina se une a ellas por medio de uniones Epidermis considera el límite cutáneo. sis sucesivas de las células germinativas epidérmicas. cias, producir más o menos células. covalentesAunque conocidas turnover como time desmosinastambién se emplea e isodesmosinas. para definir el Estas fibras son muy numerosas al nacer, observándose Dermis paso de una célula desde el estrato germinativo a la capa cór- Factores estimuladores como neabandas epitelial, de materialnos parece amorfo más lógico rodeadas emplear de elun término gran númerotiempo de microfibrillas de tránsito para de elastina.denominar Pocos este periodo. meses despuésYa hemos I Familia del Factor de crecimiento epidérmico (EGF, Glándula del nacimiento,indicado que aumenta es de 52 ala 75 cantidad días; sin embargo,de elastina un epitelio amorfa pso- y «Epidermal Growth Factor»). El EGF humano es un polipép- riásico sólo necesita de 8 a 10 días. El hecho de que el tamaño ecrinatido que estimula la proliferación y diferenciación celular ya se comprueba la organización típica de las fibras elásti- Vaina epitelial de la epidermis permanezca constante, hace pensar que la en un amplio rango de tejidos. Se encuentra en las glándu- externa cas maduras.tasa de producción Durante celularla vida en adulta,el estrato las germinativo fibras elásticas está equi- las salivales, plaquetas y algunas glándulas del duodeno. muestranlibrada pocas con lavariaciones pérdida celular a excepciónen el estrato decórneo. una discreta El EGF incrementa la epidermopoyesis uniéndose a unos Glándula reducción de las microfibrillas y la presencia de algunas apocrina Glándula sebácea inclusiones electrón-densas y de márgenes irregulares, lo de la piel Anatomía y fisiología que se hace más evidente sobre los cincuenta años. Vaina epitelial interna cutícula 1. Pelo corteza Morfométricamente, las fibras elásticas representan el médula 3-4% del total de la dermis en el recién nacido, no cambiando significativamente hasta la quinta década Matriz de la vida, a partir de la cual aumentan al 5% y en los Vaso sanguíneo Papila del tejido conectivo ancianos llegan al 7-8%. Este aumento se debe al mayor diámetro de las fibras y
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