Nutrient absorption external surfaces

The external surfaces of parasitic helminths, termed the tegument in cestodes and trematodes, and the cuticle in nematodes, are adapted to serve a wide range of biological functions. Though most research has focused on structural aspects or their roles in immune evasion (Chapter 16) and nutrient absorption, the external surfaces of helminths also serve important roles in locomotion, excretion and regulation of electrochemical and osmotic gradients. 

The mucosa of the GIT represents an interface between the external and internal environments. The expansive surface area is necessary for the efficient hydrolysis of foodstuffs and the absorption of energy and nutrients. The mucosa also influences the systemic availability of non-nutrient compounds in the diet, both beneficial and detrimental. Digestion and absorption of glucosinolates are critical determinants of health benefits (see Chapter 4) Similarly, the bioavailability and health benefits of phytoestrogens, such as genistein (see Chapters 5 and 10) are at least partly dependent on the carrier-mediated processes of absorption associated with the GIT (Oitate et al, 2001). Moreover, the metabolic activities of the mucosa can influence the systemic concentrations and forms of dietary phytochemicals, as exemplified by research with soy isoflavones (Andlauer et al., 2000). 

Iron uptake by iron-inefficient soybeans was not increased when they were placed in nutrient solutions that contained reductant (14). This may mean that reductants in the external solution indicate a leaky root resulting from the release of hydrogen into the nutrient solution. More important may be the adaptive production of reductants inside the root or at the root surface that keeps iron in the more available Fe2+ form (13). We have concluded that iron absorption and transport is controlled inside the root, and iron uptake is greatest while the iron-stress—response mechanism is functioning. 

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