Microtriches (singular
microtrix) are the highly specialized
microvilli covering the entire surface of the tegument of
cestodes. They are fine hair-like filaments distributed throughout the surface of the body, both unique to and ubiquitous among cestodes, giving the body surface a smooth and silky appearance. They are different from typical microvilli in that they contain conspicuous electron dense materials at the tip. Due to their morphological variation they make up unique defining structures in cestodes. Since cestodes are devoid of any
digestive system and
, the tegument with its microtriches is the principal site of absorption and secretion. In fact the tegument highly resembles the gut of
animals turned inside out.
[Smyth JD, McManus DP (1989). The Physiology and Biochemistry of Cestodes. Academic Press, pp. 5-8. ]
Structure
The microtriches are fine cylindrical tubular filaments, with smooth rounded ends, and arranged in rows corresponding to the regular ridges of the tegument. Microtriches are documented to exhibit wide range of morphology in different
species of
tapeworms, and serve as an identifying character among the members of
Eucestoda.
[Lumsden RD, Hildreth MB (1983). The fine structure of adult tapeworms. In: Biology of the Eucestoda Vol.1 (C Arme & PW Pappas, eds). Academic Press, New York, USA, pp. 177-233. ] They are also of special interest in pharmacology as they are the basic interface of the tapeworm with its surrounding, thus serve as the primary site of absorption of nutrients and the target site of anthelmintics.
[Mansour TE, mansour JM (2002). Chemotherapeutic Targets in Parasites. Cambridge University Press, UK, pp. 192-297. ]
Though microtriches have been described for several decades, the consensus terminology for the structure was made only at the turn of the 21st century. Standardised terms were resolved based on discussions that occurred at the International Workshops on Cestode Systematics in Storrs, Connecticut, United States in 2002, in České Budějovice, Czech Republic in 2005 and in Smolenice, Slovakia in 2008.
Functions
All cestodes lack
digestive system and
, therefore, the tegument with its microtriches constitute the principal site of absorption of nutrients and elimination of waste materials. Moreover, the microtriches are the primary structures for host-
parasite interface, and are
metabolism performing all the vital activities such as sensory, absorptive and secretory functions. Thus, their structure constitutes an effective amplification of the total surface area of the tegument. The surface
carbohydrate complex called
glycocalyx is responsible for inhibition of the host digestive enzymes, absorption of
cations and
bile salts, and enhancement of the host
amylase activity.
[Cheng TC (1986). General Parasitology, 2nd edn. Academic Press, Division of Hardcourt Brace & Company, USA, pp. 253-2546. ] The acidic glycosaminoglycans of the
glycocalyx are specific for inhibiting a number of digestive enzymes of the host.
[Bogitsh BJ, Carter CE, Oeltman TN (2005). Human Parasitology, 3rd Edition. Academic Press, pp. 177-179. ] The microtriches in cestodes, and pits and spines in
trematodes increase the surface area of the teguments for enhanced absorption of
. In addition, they act as
sensory organs for detecting the surrounding environmental cues and primary target site of
anthelmintic.
The capacity of the tegument to absorb exogenous materials is proportional to the number and extent of pits or microtriches and the number of
mitochondria in the distal cytoplasm.
[Smyth JD, Halton DW (1983). The Physiology of Trematodes. Cambridge University Press, UK, pp. ]
See also
External links
