GI tract Flashcards
Somatostatin
secreted by D cells found in the duodenum and the pancreas (stimulated by bile acid secretion and decreased by the vagal nerve)
A major producer of somatostatin
Pancreas
Action of somatostatin
Controls acid/pepsinogen secretion through a negative feed back loop and inhibits the release of glucagon/insulin by the pancreas (also decreases gallbladder contraction)
Pancreatic amylase
Breaks down carbohydrates into simple sugars
Brush border enzymes
Assist in digestion and nutrient absorption
Pancreas secretes
Bicarbonate (to neutralize stomach acid)
Brush border activates
Pancreatic trypsin via enterokinase which activates the rest of the digestive enzymes
Digestion primarily occurs in the….
duodenum
Pancreatic lipase
Breaks down lipids
Gallbladder releases…
Bile that has been synthesized in the liver. Bile is useful in emulsifying fats.
Trypsin
activates chymotrypsin and other pancreatic enzymes
Trypsin and chymotrypsin digest
proteins into amino acids
Secretin
Released from S cells in the duodenum and is stimulated by fatty acid presence in the duodenum
Secretin stimulates
bicarbonate secretions from ductal cells in the pancreas (buffers chyme) and bile acid secretions from the liver (helps emulsify fats for digestion). Also decreases gastric acid secretion from the stomach to prevent an excess of acid.
Salivating amylase
breaks down carbs
Lingual lipase
breaks down fats (triglycerides)
Major site of alcohol absorption
Stomach
Folate absorption occurs in
both duodenum and proximal jujenum (primary site)
Bile reabsorption occurs in
terminal ileum
B12 (cobalamin) is absorbed in the
terminal ileum
Iron is primarily absorbed in the
duodenum
Chief cells secrete
pepsinogen (inactive)
Pepsinogen is activated by
H+ ions in the stomach
Pepsin
breaks down proteins into small polypeptide chains
Gastrin
is secreted by G cells and stimulates stomach into mixing its contents and also stimulates parietal cells to secrete HCl release (H+ ions)
Parietal cells
secrete HCl and intrinsic factor which helps in Vitamin B12 absorption
Mucous cells in the stomach
Release both mucous and bicarbonate to protect stomach lining
Large lipids are transported to the liver through
the hepatic portal as chylomicrons
Lacteals
transport chylomicrons through the lymphatic system
Carbohydrates and .. are absorbed through
active transport in the duodenum
The hepatic portal transports
nutrients to the liver for processing
Most fats
bypass first-pass metabolism in the liver and go straight to circulation through the lymphatic system
The colon is responsible for
electrolyte/water/bile reabsorption
Na+/K+ are absorbed in
transverse colon
I cells
release CCK in duodenum/jejunum which stimulates contraction of the gallbladder (release of bile)
CCK
released by I cells in the presence of amino acids and fatty acids in the duodenum and stimulates the contraction of the gallbladder, induces relaxation of the sphincter of oddi, & decreases gastric acid emptying.
chemical digestion that begins in the mouth involves
amylase (starch —> maltose) and lysozyme (antibacterial)
salivary glands
parietal, submandibular, sublingual
made up of: serous/mucous cells
intercalated ducts: may secrete lysozyme
striated ducts: modify primary saliva with electrolytes
saliva consist of
99.5% water, 0.5% electrolytes/proteins
serous cells
contain zymogen granules that contain amylase and lysozyme (enzymes that are present at all times) which is secreted through exocytosis
Initial salivary secretion are
isotonic with plasma
Final salivary secretion is
hypotonic with plasma (NaCl is only 1/7th of plasma)
Chief cells
are stimulated to secrete ACh and gastrin to produce pepsinogen for protein digestion
Parietal cells
are stimulated to secrete ACh and gastrin to produce HCl and intrinsic factor
Enterochromaffin cells (ECF)
stimulated by ACh and gastrin to release histamine which in turn stimulate parietal cells
Cephalic phase
seeing, smelling, tasting, chewing, swallowing stimuli
Pancreatic juice is
isotonic with extracellular fluid: NaCl @ low rates NaCl & HCO3- @ high rates K+ present at all rates Na & K concentrations are approx to plasma
Bile salts are synthesized from
cholesterol in the liver by Cyp7A1
cholangiocytes secrete
bicarb rich fluid under the regulation of secretin
Secretin targets the CFTR
regulates the Cl-/HCO3 exchanger to work
