Page 109 - Veterinary Histology of Domestic Mammals and Birds, 5th Edition

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Muscle tissue

(textus muscularis)

All cells have the capacity for movement. Processes such of glands and forms part of the wall of blood and lym-
as mitosis, phagocytosis and the amoeboid migration of phatic vessels. Smooth muscle cells also perform important
white blood cells into extravascular tissue all involve some functions in the lung, genital apparatus and the skin.
degree of mobility or contraction. In higher organisms, a
specialised form of contractility is expressed by cells that Fine structure of smooth muscle cells
constitute muscle tissue. (myocytus nonstriatus)
The primary distinguishing feature of muscle tissue is Smooth muscle tissue is composed primarily of spin-
the transformation by muscle cells of chemical energy dle-shaped smooth muscle cells measuring 20–500 μm
(adenosine triphosphate, ATP) into mechanical energy in length (Figures 4.1 to 4.5 and Table 4.1). The term
and heat. This functional specialisation necessitates the ‘smooth’ is used for this muscle type because its myofila-
differentiation of specific structural features. Based on its ments lack the ordered arrangement observed in striated
physiological function, muscle tissue is divided into two muscle. The ovoid to oblong, usually slightly notched
types: nucleus is typically located centrally, becoming shortened
during muscle contraction. The cytoplasm (sarcoplasm)
· smooth muscle and contains numerous mitochondria and a variably devel-
· striated muscle. oped endoplasmic reticulum (sarcoplasmic reticulum).
The functions of the endoplasmic reticulum include stor-
age of Ca . Micropinocytic vesicles (caveolae) are found
2+
Smooth muscle along the cell membrane, predominantly at the ends of the
(textus muscularis nonstriatus) cell (Figures 4.5 and 4.6). These are believed to be involved
2+
As well as forming the muscular component of most inter- in transport of Ca . An increase in sarcoplasmic Ca
2+
nal organs, smooth muscle surrounds the secretory ducts and associated muscle contraction is triggered by various

4.1 Smooth muscle of small intestine in longitudinal and transverse section (cat). Haematoxylin and eosin stain
(x200).

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