Counter-current blood flow in tissues: protection against adverse effects.

Histological studies indicate parallel arrangements of small arteries and veins as well as arterioles and venules in a number of tissues, such as kidney (cf. Solez and Heptin-stall, 1980), skin (Sparks, 1978), placenta (Barcroft and Barron, 1946), heart (Hutchins et al., 1986), and intestine (cf. Jodal and Lundgren, 1986). There exists also functional evidence for inert gas back-diffusion in counter-current blood flow in several tissues, such as muscle (Piiper et al., 1984; cf. Wagner, 1987), brain (Stosseck, 1970), and heart (Roth and Feigl, 1981). Effros et al. (1984) also observed counter-current diffusion of labeled n-butanol in the rabbit renal cortex.