The ultrastructure of the skin of human embryos. 3. The formation of the nail in 16-18 weeks old embryos

Physiology of the nail apparatus: Surgical consequences

Knowledge of nail physiology is mandatory to understand nail pathologies, and to know what to repair and what to expect from your repair. Unfortunately, nail physiology in humans is not completely understood. However, there are some data that have been validated and must be known before treating patients. The nail plate is mostly made of keratins. It is produced solely by the nail matrix. The nail bed is mostly responsible for nail pate adhesion. At the hyponychium, the plate loses its adherence. The hyponychium is the first barrier of defense preventing bacteria and fungi from invading the subungual area. All these structures, along with the nail folds, are responsible for the orientation of nail-plate growth. However, many questions, such as whether to replace the nail plate at end of procedure, remain open.

Ectopic plantar nail: a report of two cases

Ectopic nail is an extremely rare condition related to acquired or congenital anomalies. Almost 40 cases are reported in the literature, mostly in Japanese patients. In the majority of these patients, ectopic nails developed in the dorsal aspect of the fingers; they are associated in some cases with acquired or congenital growth anomalies or to polydactyly. Recently, we observed two male adult patients with true ectopic nails of the foot (sole and heel). Both patients were not affected by ectodermic dysplasia or foot malformations. The lesion relapsed after surgical excision in one case. Histology showed features of a well-developed and normal nail plate and matrix. A transmission electron microscope study was done in one case, showing typical aspects of onychocytes. The other nail was reproduced by a silicone replica technique and its superficial texture, shape and relationship with surrounding tissue were analysed by scanning electron microscopy.

Merkel cells in ontogenesis of human nails

Digital skin of human fetuses is known to contain a particularly high concentration of Merkel cells. Using antibodies against the simple epithelial cytokeratins (CK) 18 and 20, which are sensitive and specific Merkel cell markers, we studied immunohistochemically the main adnexal structure of digital skin, the nail anlage, in human fetuses (9-22 weeks of gestation) for the presence of Merkel cells. As early as week 9 some clustered Merkel cells were detected in the early matrix primordium. In specimens of week 12-15, abundant Merkel cells were found in the nail anlagen, particularly in the epithelium of the proximal nail-fold and the dorsal and ventral side of the apex region. In contrast, Merkel cells were essentially absent from the epithelium of the ventral matrix (surface-near portion), lunula and nail bed. Correspondingly, in these region, the adjacent dermis contained hardly any nerve fibres, whereas such fibres, as detected by neurofilament antibodies, were quite numerous adjacent to the proximal nail-fold epithelium. At week 22, the Merkel cell number in the nail anlage had decreased, and in adult nail matrix such cells were very rare. No Merkel cells were found in the dermal tissue surrounding the nail anlage while finger-tip skin of week 15, and particularly of week 22, exhibited single Merkel cells in the upper dermis next to clusters of such cells in the glandular ridges. We also found that Merkel cells were negative for CK 17.(ABSTRACT TRUNCATED AT 250 WORDS)

Continuous formation of nail along the bed

To resolve the problem of whether nail is formed continuously along the length of the nail bed as well as by the germinal matrix, nail thickness was measured at six anatomical points along the length of 20 normal big toe-nails removed after injury. Nail water content was constant at 9-10% along the nail length, and the nails did not shrink with dehydration. Approximately 79% of nail thickness was contributed by the nail matrix, and 21% by the nail bed. The rate of nail production was constant at 0.13 mm/mm along the lunula and 0.027 mm/mm along the whole bed from the distal lunula to the point of separation at the onychodermal band; the fractional change in linear growth and thickness showed less variation than absolute change. The continuous production of nail by the bed provides a simple biological solution to the problem of attachment of a continuously moving plate. It provides a source of entry of drugs into the distal nail plate, and a rationale for the use of much shorter courses of antifungal drugs than previously believed possible.

Vertically growing ectopic nail

A 64-year-old Japanese woman with an ectopic nail at the palmar tip of the left middle finger is reported. Interestingly, the nail grew vertically to a line horizontal to the surface epidermis. Atypically, it appeared at 60 years of age with no prior injury or trauma to explain inoculation of a nail matrix into the regional skin. Roentgenographically, there were no abnormal findings such as Y-shaped bifurcation of the distal phalanx of the affected finger. There are conflicting opinions concerning whether or not a proximal nail fold is critical for the nail to grow outward instead of upward. Although the present case had a wide proximal nail fold, it did not seem to play its role of compressing and assisting the nail plate to grow outward. Hence, it may be that the absence of a proper nail bed, rather than the absence of a proximal nail fold, promotes upward growth of a nail plate instead of outward growth.

Nail is produced by the normal nail bed: a controversy resolved

Nail thickness and mass (dry weight/unit surface area) of 21 toenails, removed from 19 patients after accidental injury, were measured over the mid point of the lunula, at the nail plate immediately distal to the lunula and at the distal end of the nail bed. Nail thickness increased from 43% of the final thickness over the mid-point of the lunula to 81% at its distal margin, the remaining increase in thickness being formed by the nail bed. The changes in nail mass were comparable. We conclude that ventral nail produced by the nail bed comprises about one-fifth of the terminal nail thickness and mass.

Physicochemical characterization of the human nail: permeation pattern for water and the homologous alcohols and differences with respect to the stratum corneum

In order to develop a basic concept of the permeability of the human nail plate and thus create a better understanding of the toxic potentials and therapeutic possibilities of substances applied to the nail, avulsed cadaver nails have been placed in specially constructed diffusion chambers and their permeation by water and the n-alkanols through dodecanol, all in high aqueous dilution, has been investigated. The permeability coefficient of water is 16.5 X 10(-3) cm h-1 and that for methanol is 5.6 X 10(-3) cm h-1. Ethanol's permeability coefficient measured 5.8 X 10(-3) cm h-1. Permeability coefficients decreased systematically thereafter to a low value of 0.27 X 10(-3) cm h-1 at n-octanol. The middle chain length alkanols, n-pentanol through n-octanol, have similar permeability coefficients but n-decanol and n-dodecanol show higher rates of permeation. The data suggest that, as a membrane, the hydrated human nail plate behaves like a hydrogel of high ionic strength to the polar and semipolar alcohols. Declining permeability rates appear linked to decreased partitioning into the complex matrix of the plate as the compounds become hydrophobic. The results for n-decanol and n-dodecanol introduce the possibility that a parallel lipid pathway exists which favours the permeation of these exceedingly hydrophobic species.

The sequence of events in the differentiation of the epidermis in fetal rats with particular reference to membrane-coating granules

The sequence of events in the establishment of a keratinised epidermis has been related to age and crown rump length in fetal rats. Differentiation of the epidermis occurs under cover of the periderm throughout gestation. Ten stages are defined between 12d intra-uterine life and birth. Membrane-coating granules (MCGs) appeared at 18d (Stage 4) after the appearance of tonofilaments but before the appearance of the first "fetal" keratohyaline granules (KHGs) at 19d (Stage 5). Measurement of the position of MCGs within the cells showed a less marked concentration near the superficial border of the cells than that found at later stages. As KHGs formed, exocytosis of MCGs occurred into the intercellular space immediately deep to the periderm. It is suggested that after 19d (Stage 5) the periderm serves to retain the contents of the MCGs in this space so providing the permeability barrier and that prior to that stage the periderm itself probably provides the permeability barrier of fetal skin.

Localization of specific carbohydrate configurations in human skin using fluorescein-labelled lectins

The binding of three fluorescein-labelled lectins by normal human skin has been studied. The patterns of bound fluorescence seen were characteristic for each lectin, indicating that saccharide residues were available for lectin localization in the skin. Concanavalin A (glucose and mannose specific) and ricin 120 (galactose specific) presented similar patterns of localization of fluorescence in the epidermis and dermis. Both lectins presented a continuous band at the dermo--epidermal junction, but with concanavalin A the band was broader, while with ricin 120 the junctional band was thinner and more closely associated with the epidermal interface. With the peanut lectin (galactose specific) fluorescence outlined the periphery of the keratinocytes in the upper Malpighian and granular cell layers only; no junctional band was seen and the dermal appendages and collagen did not fluoresce. The stratum corneum did not fluoresce with any of the lectins studied.

Mucosubstances in the normal human oesophageal epithelium. A comparison of periodic acid-silver and phophotungstic acid techniques

Normal human oesophageal epithelium was investigated with the periodic-acid-silver methenamine technique and its variations to demonstrate neutral mucosubstances at the ultrastruct level. The results were compared with the acid phosphotungstic acid method. Neutral mucosubstances were shown in the cell coat and membrane coating granules by both techniques. The silver methods also demonstrated glycogen, the Golgi apparatus and dense bodies. The periodic acid-silver methenamine technique outlined positive material in the intercellular space of the prickle cell layer, but the other silver methods did not.

On the structure of the normal nail. A scanning electron microscope study

A scanning electron microscopic (SEM) study of cut surfaces in normal human nails have confirmed the previous description of nail structure, i. e. the hard dorsal nail plate supported by the plastic intermediate nail plate.