Mauro Romero Leal Passos - Atlas of Sexually Transmitted Diseases: Clinical Aspects and Differential Diagnosis

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Springer International Publishing AG 2018

Mauro Romero Leal Passos (ed.) Atlas of Sexually Transmitted Diseases

1. The Skin and Eruptives Lesions

Mauro Romero Leal Passos 1

(1)

Universidade Federal Fluminense, Niteri, Rio de Janeiro, Brazil

1.1 Introduction

The skin is the largest organ of the human body, and corresponds to 15% of the bodys weight. Although there are topographical variations, it is composed of three basic structures layered in the following order: hypodermis (subcutaneous layer), dermis and epidermis.

This covering tissue that bounds the individual of his environment has as vital functions the protection against external aggressions, the maintenance of fluids in the body, and the thermoregulation, besides playing an important sensorial role. Due to its great accessibility to inspection, unlike the viscera, the skin becomes one of the major components of the physical beauty providing self-esteem and social coexistence. Frequently, aesthetic changes cause inferiority feelings and unthinkable social discrimination to people for the rest of their lives.

This inspection easiness requires the knowledge of a number of skin changes related only to aesthetics, in order to differentiate them from those that actually bring harm to health.

The cutaneous integrity is fundamental so that the skin can properly put in practice its prevention function against the access of toxic agents, microorganisms and excess of ultraviolet radiation to the body, impede the loss of fluids, and protect against excess of temperature, mechanical forces and low-voltage electric current.

1.2 Skin Structure and Function (Fig. )

1.2.1 Epidermis

The epidermis is a stratified, keratinized, not vascularized pavement epithelium of ectodermal origin. The epidermis originates the following cutaneous attachments: pilosebaceous follicle, sudoriparous glands, hair, and nails. Its main functions are the relative impermeability, which prevents the free movement of fluids and molecules in both directions, the protection from the entry of microorganisms, as well as from excessive ultraviolet radiation and low-voltage electric power.

Fig. 1.1

Skin Structure and Function

As it is not vascularized, the epidermis depends on the supply of nutrients through the dermis, with which establishes a relationship of interdependence.

The dermis basic element is the keratinocyte, which during its migration towards the surface undergoes a differentiation process, whose goal is the production of keratin. When the keratinocyte reaches the surface, it is transmuted into an inviable and anucleated cell full of keratin, which will then perform the main epidermic functions.

The epidermis is divided into four cell extracts, characterized by degrees of its keratinocytes differentiation and morphology. The nearest layer to the dermis is the basal layer, following towards the surface the spinous extract, the granulous and finally the corneal (Fig. ).

Fig. 1.2

Epidermis

1.2.1.1 Basal or Germinative Layer

As the corneas cells are continuously removed, the maintenance of the epidermis depends on a permanent replacement of new cells. This replacement is promoted by the keratinocytes mitosis of the basal layer, which are little differentiated, and retain proliferative capacity. The basal layer is composed of a single layer of cylindrical cells, with the largest axis perpendicular to the dermoepidermal junction. In normal skin, around 10% of the basal cells are in mitosis. At any given time this percentage could increase depending on the physiological (repair) or pathological (e.g., psoriasis) needs.

1.2.1.2 Spinous Extract

It consists of several layers of polygonal keratinocytes under differentiation process. These are rich in cytoplasmic tonofilaments, grouped more compactly, as the cell progresses toward the surface. These tonofilaments are the precursors of keratin.

1.2.1.3 Granulous Extract

It consists of variables layers of flattened keratinocytes containing granules of keratohyalin associated with cytoplasmic tonofilaments. These granules seem to contribute to the formation of the cytoplasmic matrix of corneal cells.

1.2.1.4 Corneal Extract

It consists of 815 layers of flattened anucleated keratinocytes. The cytoplasm is completely filled with a very resistant and insoluble fibrous protein called keratin.

As it is the final product of the keracinocyte differentiation, the corneal extract is the main responsible for the protective functions of the epidermis. Although it is not completely impermeable, it is an excellent barrier to the movement of fluids, molecules and microorganisms, and any damage to its integrity harms this function extremely.

Its low water content is the unique and exclusive feature that raises difficulties to the establishment of microorganisms on the surface of the skin.

The epidermic extracellular space is extremely impermeable, allowing the nutrition of all epidermic layers, except the corneal extract. A water-soluble barrier is located in the boundary between the granulous and the corneal extract. This barrier is probably responsible for the abrupt transformation of the viable cornified cells in not viable ones, because it disables the nutritional supply to those cells located above it. The impermeable property of this region appears to be caused by two factors: a special substance secreted at this level and represented by Odland bodies or lamellar bodies, and a type of intercellular contact found only there, named zonula occludens , in which there is an intimate union between the adjacent cytoplasmic membranes.

There are still two other specialized types of epidermal intercellular contact: the gap junction and the desmosome. The gap junction sets a free traffic corridor between the adjacent cells and plays an important role in the differentiation of the epidermis as a whole; only missing in the corneal extract.

The demosomes are the main and most numerous types of epidermal intercellular contact. They occur in all layers, providing stability to the tissue. The hemidesmosomes occur between the basal cells and the basal lamina (Fig. ).

Fig. 1.3

Epidermal intercellular contacts

1.2.1.5 Dermoepidermic Junction

The dermoepidermic junction corresponds to the basal membrane in the optical microscopy. The electronic microscopy is a complex structure comprising the cytoplasmic membrane of the basal cells, the lucid blade (empty space), the basal lamina and the most superficial portion of the papillary dermis. Promoting adhesion between the basal cells and the basal lamina, are the hemidesmosomes, and between this and the dermis, the anchoring fibrils and microfibrills (Fig. ).

Fig. 1.4

Dermoepidermal junction

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