11 



Absorption 



The specific gastrointestinal site where the majority of 

 Zn is absorbed has not been identified (Solomons and Cousins, 

 1984) . All of the sections of the small intestine may have a 

 functional importance in Zn absorption (Cousins and Hempe, 

 1990) . 



Several investigators (Steel and Cousins, 1985; Hoadley 

 et al . , 1987) have reported that two kinetic processes are 

 involved in absorption, passive diffusion and carrier-mediated 

 components that may represent paracellular and intracellular 

 absorption pathways. Carrier-mediated Zn absorption may 

 increases during periods of low Zn intake, suggesting the 

 stimulation of a carrier system to absorb greater amounts of 

 Zn during a deficient state (Hoadley et al . , 1987) . In 

 contrast, the diffusion component of Zn absorption is 

 unaffected by Zn deficiency, and absorption via this process 

 is proportional to luminal Zn concentration. Metallothionein 

 (MT) synthesis is influenced both by dietary Zn level and by 

 plasma Zn concentration and can regulate the quantity of Zn 

 entering the body, thus playing a central role in Zn 

 homeostasis (Cousins and Hempe, 1990) . 



Transport and Tissue Uptake 



Albumin appears to be the main Zn carrier in blood with 

 approximately 70% of the Zn bound to it (Vikbladh, 1950). 

 Other Zn-containing components of plasma are oc2-macroglobulin 



