characteristic Birbeck granules, shaped like a tennis racquet in their cytoplasm. Each cell possesses five to nine dendritic processes, which extend out in the same horizontal plane.
Langerhans cells are antigen‐presenting cells, taking up the antigen and transporting it to the lymph node. They play an important immunological role in the skin and are involved in the sensitisation and activation of contact allergic dermatitis as well as participating in the immune surveillance of the skin. These immunological functions are particularly important in the lower female genital tract as these sites are exposed to a wide range of antigens. They may be involved in oncogenic HPV infection, and it has been shown that Langerhans cell counts are lower in HIV patients with vulval intraepithelial neoplasia [37].
Merkel cells
These cells are found throughout the skin, situated singly or in clusters in the basal layer of the epidermis. The dendritic cytoplasmic processes surround adjacent keratinocytes, and they interact with free nerve endings in the skin. They act as mechanoreceptors for light touch, but may have endocrine and inflammatory functions [38].
The basement membrane zone
The basement membrane zone is a complex area with two layers, the upper lamina lucida and the lower lamina densa. The major components are type IV collagen and laminins with hemidesmosomes, anchoring filaments, and fibrils forming attachment structures. The vulval and vaginal basement membrane zone components are the same as those in non‐genital skin [39].
The dermis
The dermis lies below the epidermis and above the subcutaneous fat. It has two layers: the papillary dermis and the reticular dermis. The upper papillary dermis projects upwards into the rete ridges and is composed of fine collagen fibres, running at right angles to the surface, together with reticular and elastic fibres. This arrangement supports vascular and lymphatic channels as well as nerve endings. The lower reticular is composed of coarse collagen fibres lying parallel with the surface. Thicker elastic fibres accompany the collagen fibres to prevent it being overstretched. In the perineal area, smooth muscle fibres similar to those seen in the nipple, penis, and scrotum are also present. The vascular and lymphatic plexuses that drain the papillary dermis lie within the reticular dermis, which also contains the nerve fibres associated with the papillary nerve terminals.
References
1 5 Kreklau, A., Vâz, I., Oehme, F. et al. Measurements of a 'normal vulva' in women aged 15‐84: A cross‐sectional prospective single‐centre study. BJOG. 2018 Dec; 125(13): 1656–1661.
2 6 Lloyd, J., Crouch, N.S., Minto, C.L. et al. Female genital appearance: ‘normality’ unfolds. BJOG. 2005 May; 112(5): 643–646.
3 10 Brodie, K., Alaniz, V., Buyers, E. et al. A Study of adolescent female genitalia: What is normal? J Pediatr Adolesc Gynecol. 2019 Feb; 32(1): 27–31.
4 22 Moyal‐Barracco, M., Leibowitch, M. and Orth, G. Vestibular papillae of the vulva. Lack of evidence for human papillomavirus aetiology. Arch Dermatol. 1990; 126: 1594–1598.
5 30 Day, T., Holland, S.M. and Scurry, J. Normal vulvar histology: Variation by site. J Low Genit Tract Dis. 2016 Jan; 20(1): 64–69.
6 31 van der Putte, S.C.J. Anogenital ‘sweat’ glands. Histology and pathology of a gland that may mimic mammary glands. Am J Dermatopathol. 1991; 13: 557–567.
7 32 Kazakov, D.V., Spagnolo, D.V., Kacerovska, D. and Michal, M. Lesions of anogenital mammary‐like glands: An update. Adv Anat Pathol. 2011 Jan; 18(1): 1–28.
8 33 Konstantinova, A.M., Stewart, C.J.R., Kyrpychova, L. et al. An immunohistochemical study of anogenital mammary‐like glands. Am J Dermatopathol. 2017 Aug; 39(8): 599–605.
9 34 Konstantinova, A.M., Kyrpychova, L., Belousova, I.E. et al. Anogenital mammary‐like glands: A study of their normal histology with emphasis on glandular depth, presence of columnar epithelial cells, and distribution of elastic fibers. Am J Dermatopathol. 2017 Sep; 39(9): 663–667.
3 Vulval Physiology and Changes Through Life
Fiona M. Lewis
CHAPTER MENU
Changes through life Neonate Childhood Puberty Reproductive years Sexual response Pregnancy Menopause
The main roles of the vulval epithelium are to provide a barrier function and to regulate an immune response. There are variations at different sites and at different times during life, with hormonal alterations being the predominant influence [1]. These normal changes can also be modified by oral contraceptives and hormone replacement therapy.
The principal hormones involved in these changes are oestrogens, progestogens, and small amounts of androgens. Oestrogen has many effects on skin and mucosa [2]. It increases support by thickening the collagen, hydrates by increasing mucopolysaccharides and hyaluronic acid, and also stimulates melanogenesis. The effects of progesterone are not so well understood, but this hormone is known to increase vascularity and sebum secretion.
Immunohistochemical studies have identified receptors for these hormones at different sites within human skin [3]. Further studies in the female genital skin have mapped out their distribution in the vulva and vagina, showing variation with different stages of the menstrual cycle [4], with oral contraceptive use [5], and at menopause [6]. Oestrogen receptors are mainly found in the labia minora and vagina. Androgen receptors are most commonly seen in the keratinocytes of the labia majora as well as the adnexal structures and fibroblasts. Progesterone receptors were found only on vaginal epithelium and inner labia minora. There is little difference in this distribution before and after menopause.
Barrier function
The barrier function of skin is dependent on the degree of hydration, the presence of a stratum corneum, and occlusive factors. Vulval keratinised skin differs from that elsewhere in hydration, permeability, and friction, but there is no significant difference between pre‐and post‐menopausal age groups. There is little information on variations in these functions on the mucosal surface of the inner vulva, but it has been assumed that this will be similar to that of the oral mucosa, where there is a considerable increase in permeability.
Transepidermal water loss (TEWL) is the rate at which water diffuses across