Page 110 - Veterinary Histology of Domestic Mammals and Birds, 5th Edition

92 Veterinary Histology of Domestic Mammals and Birds

factors, including depolarisation (via the neurotransmitters as insertion sites for intermediate filaments, in which
VetBooks.ir acetylcholine and noradrenaline), mechanical stretching the contractile actin filaments are enmeshed (Figures 4.5
and 4.6).
and chemical stimuli.
Dense bodies are considered to be equivalent to the
In histological sections of smooth muscle, the myofila-
ments within the smooth muscle cells (actin-, myosin- and Z line of striated muscle. Myosin filaments are inter-
intermediate filaments) appear to be oriented in various spersed among the network of actin filaments. These are
directions, forming a network (Figure 4.5). soluble, highly labile proteins that increase in number dur-
The actin filaments (1 μm in length) are anchored to ing contraction. They are not attached to dense bodies.
each other and to the inner surface of the plasmalemma Intermediate filaments (desmin) form the cytoskeleton
by dense bodies (areae densae). Dense bodies also serve of smooth muscle cells. They are not contractile.

4.2 Longitudinal section of a bundle of smooth muscle fibres in the stomach (cat). The nucleus of smooth muscle
cells is situated centrally. The surrounding sarcoplasm is drawn out, conforming to the fusiform shape of the
cell. The surface of the smooth muscle cell is invested by connective tissue (endomysium). Goldner’s Masson
trichrome stain (x200).

4.3 Transverse section of a bundle of smooth muscle fibres in the stomach (cat). The nucleus is located centrally.
In some cases, the section has passed through a region of the sarcoplasm in which the nucleus is not present.
Connective tissue surrounds individual cells (endomysium) and fibre bundles (perimysium). Haematoxylin and
eosin stain (x480).

Vet Histology.indb 92 16/07/2019 14:56