RT Book, Section
A1 Barrett, Kim E.
A1 Barman, Susan M.
A1 Boitano, Scott
A1 Reckelhoff, Jane F.
SR Print(0)
ID 1142557289
T1 Gastrointestinal Physiology: Introduction
T2 Ganong's Medical Physiology Examination & Board Review
YR 2017
FD 2017
PB McGraw-Hill Education
PP New York, NY
SN 9780071832328
LK accessmedicine.mhmedical.com/content.aspx?aid=1142557289
RD 2024/04/19
AB For  unicellular  organisms,  nutritional  requirements  can  be  satisfied  by  membrane  transport  proteins  that  permit  the  uptake  of  specific  molecules.  However,  for  multicellular  organisms,  the  challenges  of  delivering  nutrients  to  appropriate  sites  in  the  body  are  significantly  greater.  Further,  most  of  the  food  we  eat  is  in  the  form  of  macromolecules,  and  even  when  these  are  digested,  most  of  the  end  products  are  water-soluble  and  do  not  readily  cross  cell  membranes.  Thus,  the  gastrointestinal  system  has  evolved  to  permit  nutrient  acquisition  and  assimilation  into  the  body,  while  prohibiting  the  uptake  of  undesirable  substances.