ABSTRACT
Glucose an d othe r monosaccharide s absorbe d b y th e smal l intestina l cell s ar e
transported into th e live r via portal circulation. L ive r cell s are freely permeable t o
glucose arrivin g i n thi s fashion . I n the liver , glucos e ma y ente r th e glycogenesi s
or th e glycolysi s pathway s (se e Chapte r 17) , o r i t ma y b e exporte d int o th e
circulation. Glucos e leave s live r cell s vi a a simpl e concentratio n gradient , be -
cause th e live r cell glucose concentratio n i s highe r tha n tha t o f th e bloodstream ,
especially i n the post-absorptiv e state , w h e n glucago n level s ar e h igh a n d thos e
of insul i n ar e low . I n th e variou s organs , glucos e i s metabolize d eithe r aerobi -
cally (e.g. , th e hear t or brain) or anaerobically. The latter results in lactate produc-
tion, wher e th e mai n lactate producers are the re d blood cells , intestina l cells a n d
white muscl e cells . Lactat e i s extracte d from th e bloodstrea m largel y by th e live r
and re d muscl e cells , wh ic h eithe r conver t i t t o glucos e vi a gluconeogenesi s
(liver) o r channe l i t into th e Kreb s cycl e (re d muscle). Glucos e a nd lactat e traffi c
is s h o w n i n Figure 18.1 .
