ABSTRACT
A h u m a n bein g normall y ingest s 90-15 0 g fa t pe r d a y Abou t 90 % o f thi s i s
triglyceride. I n addition, bil e brings into th e intestina l tract 1-2 g cholestero l a n d
4 - 5 g phosphoglycerid e daily . Dietar y fa t i s largel y wate r insoluble , an d i t i s
therefore necessar y t o break it up int o th e smalles t possibl e particle s for digestiv e
enzyme action . Th e smalle r and th e mor e numerou s th e particles , th e greate r i s
their tota l surfac e are a an d faste r an d mor e effectiv e i s thei r digestion . Surfac e
area A ca n be represente d b y Equatio n (19.1), wher e R i s th e particl e radius, n i s
the numbe r o f particles , an d K x an d K 2 ar e constants :
The emulsifyin g agent s (biologi c detergents ) tha t allo w fo r l ipi d digestio n
are th e phosphoglyceride s (bot h endogenou s an d exogenous ) and , mor e impor -
tantly, th e bile salts. Th e latte r ar e amphipathi c derivative s o f cholestero l (se e
later) synthesize d i n th e liver . There is a tota l poo l o f abou t 3 - 5 g bil e salt s i n th e
organism, w h i c h ente r th e smal l intestine vi a the bil e duct . Bile , w h i c h include s
bile salts , ma y b e store d i n th e gallbladde r an d release d u p o n th e actio n o f
cholecystokinin. Th e bile salt s and lipid digestion product s for m micelles tha t are
3-10 n m i n diameter , an d thes e micelle s presen t l ipi d digestio n product s t o th e
intestinal mucosa l cell s fo r absorption . Thi s occur s largely in the d u o d e n u m an d
je junum, leavin g bil e salt s behind . Bil e salt s ar e the n resorbe d i n th e i leu m an d
make thei r w ay bac k t o th e liver , althoug h abou t 50 0 m g pe r da y m a y appea r i n
the feces . Dur in g a singl e day , a tota l o f 40-5 0 g bil e salt s ma y circulat e throug h
the smal l intestine: enterohepatic circulation.
