Page 478 - Atlas of Histology with Functional Correlations

subcutaneous layer with adipose tissue (8). Located inferior to the

subcutaneous layer (8) are skeletal muscle fibers (9), sectioned in transverse
and longitudinal planes.

Hair follicles (13) in the skin of the scalp are numerous, closely packed, and
oriented at an angle to the surface. A complete hair follicle in longitudinal
section is illustrated with parts of other hair follicles (13) sectioned in different

planes. A hair follicle (13) that is cut in a transverse plane exhibits the following:
the cuticle, internal root sheath (13a), external root sheath (13b), connective
tissue sheath (13c), hair bulb (13d), and the connective tissue dermal papilla
(13e). The hair passes upward through the follicle (13) to the skin surface.

Numerous sebaceous glands (11) surround each hair follicle (13). The
sebaceous glands (11) are aggregates of clear cells that are connected to a duct
that opens into the hair follicle (13) (see Figs. 12.4 and 12.5).

The arrector pili muscles (5, 10) are smooth muscles aligned at an oblique
angle to the hair follicles (13) and attach to the papillary layer of the dermis and

to the connective tissue sheath (13c) of the hair follicle (13). The contraction of
arrector pili muscles (5, 10) moves the hair shaft into a more vertical position.

Deep in the dermis or subcutaneous layer (8) are the basal portions of the
coiled sweat glands (6). Sections of the sweat gland (6) that exhibit lightly

stained columnar epithelium are the secretory portions (6b) of the gland. These
are distinct from the excretory ducts (6a) of the sweat glands (6), which are
lined by the stratified cuboidal epithelium of smaller, darker-stained cells. Each
sweat gland duct (6a) is coiled deep in the dermis but straightens out in the upper

dermis and follows a spiral course through the epidermis to the surface of the
skin (see Fig. 12.3).

The skin contains many blood vessels (14) and sensory receptors. These are
the Pacinian corpuscles (7) for pressure and vibration located in the

subcutaneous tissue (8). The Pacinian corpuscles (7) are illustrated in greater
detail and higher magnification in Figure 12.13.

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