Page 74 - Veterinary Histology of Domestic Mammals and Birds, 5th Edition

56 Veterinary Histology of Domestic Mammals and Birds

cytoplasm before migrating towards the apical cell surface. and the shrinking and subsequent disintegration of the
VetBooks.ir During the subsequent secretory process the cell changes nucleus (pyknosis and karyorrhexis) in the apical portion
in shape, its apical surface bulging into the lumen, but of the cell (Figures 2.39 to 2.42).
retains its functional integrity. Most sweat glands are of
the apocrine type (Figure 2.35). Apocrine glands also occur CHEMICAL COMPOSITION OF THE SECRETION
in the eyelids and form the lining of the alveolae of the Based on the chemical composition of the secretion and
mammary gland and prostate gland. the structure of the cells in the secretory unit, exocrine
In the holocrine mode of secretion, the secretory prod- glands may be classified as (Tables 2.2 and 2.3):
uct is produced via fatty degeneration of the cell with the
cell remnants forming part of the secretion (e.g. sebaceous • serous,
gland). Characteristic features of this cellular transforma- • mucous or
tion include the continuous accumulation of fat droplets • seromucous (mixed) glands.

2.39 Exocrine, extra-epithelial, alveolar holocrine gland with multiple layers of epithelial cells (sebaceous gland;
schematic).

2.40 Skin (dog). In sebaceous glands,
lipid produced by the Golgi apparatus is
secreted together with the components
of the disintegrating cell, as sebum.
The secretion passes via a short duct
to be deposited onto the surface of an
associated hair. Sebaceous glands are
classified as extra-epithelial exocrine,
alveolar, holocrine glands. Haematoxylin
and eosin stain (x200).

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