HUMAN SYSTEMS QUESTION 1979:               L. PETERSON/AP BIOLOGY
             Describe the structure and function of the stomach, pancreas, 
        and small intestine as digestive and endocrine organs in the human.
        (For each organ, include the relevant cell type and their functions.
  
  STANDARDS:
     [1 point for each statement unless otherwise indicated]
  
  Stomach (max. 7 points)
  STRUCTURE:
  Regions = cardiac, fundic, pyloric / pyloric sphincter (1 pt. for 2 of 3)
  Layers of muscle; thick walls
  Presence of RUGAE (cellular composition = histology)
  DIGESTIVE FUNCTION:
  Mention chief cells and parietal cells
  OR
  Name and function of chief cells - secrete renin, lipase, pepsinogen
  Name and function of parietal cells - secrete HCl
  Presence of mucous coat protects the stomach
  Function of HCl = aids protein digestion OR converts pepsinogen to pepsin
  Pepsin - produced in inactive form to protect OR its function in protein digestion
  Churning aids mechanical digestion
  Absorption of alcohol, etc. in stomach
  ENDOCRINE FUNCTION:
  Name and function of gastrin = stimulates production of digestive juice
  Presence of Food = stimulus for gastrin release
  Factors such as stress effects gastrin/stomach function
  
  Small Intestine (max. 7 points)
  STRUCTURE:
  Increased surface area by folds or villi or microvilli
  Structure of villi = blood vessels, lymph
  Regions = duodenum, jejeunum, ileum
  DIGESTIVE FUNCTION:
  Name 3 enzymes from intestinal glands 
     (peptidases, sucrases, enterokinase, lipase, amylase, nuclease)
  Function of each enzyme (max. 2)
  Bile released in small amounts plus:
     a) produced in the liver or b) stored in gall bladder or c) emulsifier
  Site of most absorption
  Mechanical absorption of long fatty acids
  Peristalsis
  Change in pH
  ENDOCRINE FUNCTION:
  Secretin /function = stimulates release of alkaline secretions by pancreas
  Enterogasterone /function = inhibits stomach
  Cholecystokinin /function = stimulates gall bladder to release bile
  Pancreozymin /function = stimulates pancrease to secrete digestive enzymes
  Enterokinin /function = stimulates intestinal glands to secrete enzymes
  
  Pancreas (max. 7 points)
  STRUCTURE:
  Connects to small intestine by pancreatic duct
  Comprised of exocrine and endocrine cells
  DIGESTIVE FUNCTION:
  Secretion of pancreatic juice and digestive function of enzyme mixture
  OR
  Name 3 enzymes in pancreatic juice:
           amylase, trypsinogen, chymotrypsin, carboxypeptidase, lipase
  Function of each pancreatic enzyme (max. 2)
  Secretion of bicarbonate ions to neutralize
  ENDOCRINE FUNCTION:
  Mention of Islets of Langerhans - function in glucose metabolism
  Alpha cells secrete glucagon
  Glucagon stimulates liver to convert glycogen to glucose
  Beta cells secrete insulin
  Insulin stimulates uptake of glucose by cells