receptors (answer b).They phagocytose epidermal antigens and present
them in association with class II MHC molecules to a helper T cell. Meiss-
ner’s corpuscles detect texture and shape during active touch and are found
in the thick skin of the digits (answer c).Transient vibratory stimuli are
detected by Pacinian corpuscles (answer d).
195.The answer is c.(Junqueira, pp 360–366. Kumar, pp 1256–1257.)The
cells labeled with the arrows contain numerous Keratohyalin granules and
are located in the stratum granulosum. Those cells also produce lamellar
granules, which form a bidirectional lipid bilayer barrier to penetration of
substances. The skin or integument is composed of an epithelial layer
(epidermis) and underlying connective tissue (dermis). The epidermis
consists of four to five strata (from the basement membrane to the skin sur-
face): stratum basale, stratum spinosum, stratum granulosum, stratum
lucidum, and stratum corneum. The basal layer contains most of the
mitotic cells (answers a and b)and is attached to the basement membrane
with hemidesmosomes. The stratum spinosum contains cells, with numer-
ous cytoplasmic tonofilaments and intercellular desmosomes (answer d).
The stratum basale +stratum spinosum =stratum Malpighii). Those layers
are hyperproliferative in psoriasis. Normally, gradual replacement occurs in
the epidermis; new cells are produced in the stratum basale, and migration
toward the surface occurs as they gradually differentiate. The stratum
lucidum is a translucent layer typical of thick skin. The stratum corneum
contains as many as 20 layers of flattened cells.
In deep wounds, new epithelial cells are obtained from the epithelium
of the hair follicles and sweat glands located in the dermis (answer e).
196.The answer is b.(Guyton, pp 540–542. Junqueira, pp 367–368. Ross
and Pawlina, pp 452–455, 472–473.)The Pacinian corpuscle is the primary
sensory receptor for vibratory sensation. The Ruffini endings are the simplest
encapsulated receptor and are associated with collagen fibers (answer a).
Mechanical stress results in displacement of the collagen fibers and stimu-
lation of the receptor. The Meissner and Merkel’s corpuscles respond to
texture and 2-point discrimination, respectively (answers c and d).Free
nerve endings detect light pressure and touch (answer e).In the vignette,
the Schwannoma (a nerve sheath tumor arising from Schwann cells)
results in impairment of proprioception (position sense) and vibratory
sense ipsilaterally while pain and temperature are impaired contralaterally.
308 Anatomy, Histology, and Cell Biology