Page 785 - Textbook of Pathology, 6th Edition

Intraepidermal nerve endings are present in the form of and connective tissue components. The hair shaft is made 769
Merkel cells which are touch receptors. up of an outer sheath and pigmented cortex and inner
medulla.
DERMIS
4. ARRECTORES PILORI. These are small bundles of
The dermis consists of 2 parts—the superficial pars papillaris smooth muscle attached to each hair follicle. When the muscle
or papillary dermis, and the deeper pars reticularis or reticular contracts, the hair becomes more erect, the follicle is dragged
dermis. The dermis is composed of fibrocollagenic tissue upwards so as to become prominent on the surface of the
containing blood vessels, lymphatics and nerves. In the skin skin producing what is known as ‘goose skin’.
of fingers, arteriovenous shunts or glomera are normally 5. NAILS. The nails are thickenings of the deeper part of
present. The specialised nerve endings present at some sites the stratum corneum that develop at specially modified
perform specific functions. These are as under: portion of the skin called nail bed. The nail is composed of
Pacinian corpuscles concerned with pressure are present
in the deep layer of skin. clear horny cells, resembling stratum lucidum but are much
more keratinised.
Meissner corpuscles are touch receptors, located in the
papillae of skin of palms, soles, tips of fingers and toes. HISTOPATHOLOGIC TERMS
Ruffini corpuscles are cold receptors found in the external
genitalia. Before describing pathology of common skin diseases, the
End-bulbs of Krause are cold receptors found in the external following pathologic terms in common use need to be defined
genitalia. for understanding of dermatopathology:
Besides these structures, the dermis contains cutaneous Acanthosis: Thickening of the epidermis due to hyperplasia
appendages or adnexal structures. These are sweat glands, of stratum malpighii.
sebaceous glands, hair follicles, arrectores pilorum and nails:
Acantholysis: Loss of cohesion between epidermal cells with
1. SWEAT GLANDS. These are of 2 types—eccrine and formation of intraepidermal space containing oedema fluid
apocrine. and detached epithelial cells.
i) Eccrine glands. They are present all over the skin but are Dyskeratosis: Abnormal development of epidermal cells CHAPTER 26
most numerous on the palms, soles and axillae. They are resulting in rounded cells devoid of their prickles and having
coiled tubular glands lying deep in the dermis. Their ducts pyknotic nuclei. Dyskeratosis is a feature of premalignant
pass through the epidermis on the surface of the skin as pores and malignant lesions and is rarely seen in benign conditions.
via which they empty their secretion i.e. sweat. The glands Hyperkeratosis: Thickening of the horny layer.
are lined by two main types of secretory cells: basal, Parakeratosis: Abnormal keratinisation of the cells so that
acidophilic, clear or chief cells, and the superficial, basophilic, the horny layer contains nucleated keratinocytes rather than
dark granular cells. The secretory cells are surrounded by the normal non-nucleate keratin layer. The Skin
myoepithelial cells.
Spongiosis: Intercellular oedema of the epidermis which may
ii) Apocrine glands. Apocrine glands are encountered in progress to vesicle formation in the epidermis.
some areas only—in the axillae, in the anogenital region, in
the external ear as modified glands called ceruminous glands, Pigment incontinence: Loss of melanin pigment from dama-
in the eyelids as Moll’s glands, and in the breast as mammary ged basal cell layer so that the pigment accumulates in the
glands. Apocrine glands are also tubular glands but have melanophages in the dermis.
larger lumina. Apocrine glands have a single layer of
secretory cells which contain acidophilic, PAS-positive, DERMATOSES
prominent granular cytoplasm. The type of secretion in
apocrine glands is decapitation secretion as if the cytoplasm Dermatosis is a common term used for any skin disorder.
of the secretory cells is pinched off (apo = off). Dermatosis may be of various types such as genetic,
inflammatory, infectious, granulomatous, connective tissue,
2. SEBACEOUS (HOLOCRINE) GLANDS. Sebaceous bullous and scaling type. A few common examples of each
glands are found everywhere on the skin except on the palms of these groups are described below.
and soles. They are often found in association with hair but
can be seen in a few areas devoid of hair as modified I. GENETIC DERMATOSES
sebaceous glands such as in the external auditory meatus,
nipple and areola of male and female breast, labia minora, 1. ICHTHYOSIS. Two important forms of ichthyosis are—
prepuce, and meibomian glands of the eyelids. Sebaceous ichthyosis vulgaris and sex-linked ichthyosis.
glands are composed of lobules of sebaceous cells containing Ichthyosis vulgaris is an autosomal dominant disorder.
small round nuclei and abundant fatty, network-like It is more common and appears a few months after birth as
cytoplasm. scaly lesions on the extensor surfaces of the extremities.
3. HAIR. The hair grows from the bottom of the follicle. It
has, therefore, an intracutaneous portion present in the hair Histologically, the characteristic feature is association of
follicle and the shaft. The hair follicle consists of epithelial hyperkeratosis with thin or absent granular layer.