TY  - CHAP
M1  - Book, Section
TI  - The Gastrointestinal System
A1  - kibble, Jonathan D.
PY  - 2020
T2  - The Big Picture Physiology: Medical Course & Step 1 Review, 2e
AB  - The  gastrointestinal  (GI)  system  consists  of  the  GI  tract  and  the  accessory  exocrine  glands.The  GI  tract  includes  the  mouth,  the  esophagus,  the  stomach,  the  small  intestine,  and  the  large  intestine.The  major  accessory  glands  are  the  salivary  glands,  the  liver,  the  gallbladder,  and  the  pancreas.The  GI  system  is  traditionally  two  functions:Assimilation  of  nutrients.Excretion  of  waste  products  via  the  biliary  system.Mucosal  immunology  is  a  third  major  function  of  the  GI  system.The  GI  system  is  the  largest  immunological  compartment  in  the  body  reflecting  the  need  to  protect  against  microbial  pathogens  but  also  allow  immunological  tolerance  to  antigenic  substances  in  the  diet.The  mucosa-associated  lymphoid  tissue  (MALT)  are  lymphoid  aggregates  in  the  intestine  known  as  Peyer's  patches:Specialized  cells  in  the  overlying  epithelium  called  microfold  or  M-cells  take  up  antigens  from  the  lumen.Peyer's  patches  contain  T  and  B  lymphocytes.CD4  T-cells  recognize  extracellular  antigens  (e.g.,  pathogenic  microorganisms).CD8  T-cells  recognize  intracellular  antigens  (e.g.,  tumors  and  viruses).B-cells  in  MALT  mostly  secrete  immunoglobulin  A.Assimilation  of  nutrients  from  food  occurs  in  the  following  sequence  (Figure  7-1):Chewing  (mastication)  breaks  food  down  to  create  a  bolus  for  swallowing.  Saliva  lubricates  food  and  provides  enzymes  for  digestion.  It  takes  about  10  seconds  for  swallowed  food  to  travel  down  the  esophagus  to  the  stomach.Food  remains  in  the  stomach  for  1–4  hours.  Stomach  motility  mixes  and  grinds  food  into  small  particles  suitable  for  delivery  to  the  small  intestine  via  the  pyloric  sphincter.  Exocrine  secretions  from  the  stomach  mucosa  help  to  dilute  and  dissolve  food;  gastric  acid  assists  in  dissolving  and  denaturing  the  components  of  food.Entry  of  food  into  the  small  intestine  is  coordinated  with  the  delivery  of  major  exocrine  secretions  from  the  biliary  system  and  the  pancreas.Pancreatic  enzymes  are  essential  for  digestion.  The  pancreas  also  secretes  HCO3−,  which  neutralizes  acid  from  the  stomach.Contractions  of  the  gallbladder  deliver  stored  bile  to  the  intestine.  Bile  acids  are  the  major  organic  component  of  bile  and  are  important  for  lipid  assimilation.Food  moves  through  the  small  intestine  within  7–10  hours.  Motility  patterns  in  the  fed  state  mix  food  with  digestive  enzymes  and  distribute  nutrients  over  the  absorptive  surface.  All  significant  absorption  of  nutrients  occurs  in  the  small  intestine.Transit  through  the  large  intestine,  from  the  cecum  to  the  sigmoid  colon,  usually  occurs  over  a  period  of  12–24  hours.Functions  include  fluid  and  electrolyte  transport  and  fermentation  of  undigested  carbohydrates  (e.g.,  cellulose).Storage  of  fecal  waste  occurs  in  the  distal  large  intestine;  elimination  of  fecal  waste  typically  occurs  within  1–3  days  after  ingestion  of  a  meal.  
SN  - 
PB  - McGraw Hill
CY  - New York, NY
Y2  - 2024/04/16
UR  - accessmedicine.mhmedical.com/content.aspx?aid=1172667182
ER  -