GI 5 Flashcards
what does the pancreas contain?
-contains endocrine secretory epithelium (islets): insulin and glucagon
-exocrine secretory epithelium: digestive enzymes and NaHCO3 (3 categories)
-stimuli for exocrine include distension of small intestine (long reflex), neural signals (para input), CCK
what is the activation in the pancreas?
-many pancreatic digestive enzymes released as zymogens
-trypsinogen converted to trypsin by endopeptidase (brush border enzyme)
-trypsin then activates zymogens
what is the table of the zymogens vs active enzymes?
-some secreted in active form
what is bicarbonate secretion of the pancreas?
-bicarbonate produced in duct cells neutralizes acid entering from stomach
-high levels of carbonic anhydrase
-apical HCO3-/Cl- exchanger and CFTR channel
-basolateral NKCC2, Na/K ATPase, K+,Na/H exchanger
-cystic fibrosis alters pancreas secretions
what are the graphs liver?
what does the liver secrete?
bile
-a non-enzymatic solution secreted from hepatocytes
-xenobiotics and drugs excreted in bile
what are the three main components of bile?
-bile salts (bile acid/amino acid)
-bile pigments (bilirubin)
-cholesterol
what is fat digestion?
fats and related molecules include: triglycerides (90%), cholesterol, phospholipids, long fatty acids and fat soluble vitamins
-complicated by the fact that fats are not very water soluble
-a coarse emulsion of large fat droplets in chyme broken to smaller, stable particles by bile salts
what are the graphs of fat digestion?
what is fat absorption?
-micelles come in to contact with brush border: fatty acids and monoglycerides diffuse through enterocyte membrane
-cholesterol is transported
-triglycerides reformed in ER and packed with cholesterol in chylomicrons
what is the graph of the enterohepatic circulation?
what are gallstones?
-hardened deposits likely due to excess cholesterol or bilirubin
-upper right abdominal pains, jaundice
-gallbladder removal
what carbohydrates are ingested?
starch and sucrose
-glucose polymers (glycogen, cellulose), disaccharides (lactose, maltose), monosaccharides (glucose and fructose)
how are carbohydrates broken down?
-amylase (salivary and pancreatic) break down glucose polymers to disaccharides (maltose)
-disaccharides are then broken down by intestinal brush border enzymes known as disaccharidases (into monosaccharides to be absorbed into blood stream)
what is carbohydrate absorption?
-normally glucose is phosphorylated when entering a cell, but enterocytes primarily use glutamine so glucose-6-phosphate is not formed and free glucose stays high facilitating basolateral transport
what is protein digestion?
-not all proteins equally digestible: plant protein vs egg protein
-30-60% of digested proteins are not from ingested foods: dead cells, enzymes and mucus
what is endopeptidase?
-attack peptide bonds in the amino acid chain forming fragments
-released as zymogens
-pepsin, trypsin and chemotrypsin
what is exopeptidase?
release single amino acids from peptides one at a time
-aminopeptidases: amino-terminal end (brush border enzyme)
-carboxypeptidases: carboxy-terminal end (more significant)(pancreatic carboxypeptidase A1 A2 and B)
what is protein absorption?
protein digestion primarily results in free amino acids dipeptides and tripeptides
-most single AA’s on Na cotransporters (apical) and Na exchangers (basolateral)
-di and tri peptides on oligopeptide transporter (H+ cotransporter)
-most olios digested to single AA’s in cell (peptidases) and exit via Na-AA exchanger
what is protein absorption of larger peptides?
some peptides larger than 3 AA’s transported via transcytosis after binding to a receptor on the luminal surface
-small peptides could potentially act as antigens stimulating antibody production causing an allergic reaction
-peptide absorption high when infant (villi are small)
-may play a role in food intolerances or allergies
what is vitamin and mineral absorption?
-fat soluble vitamins (A, D, E and K) absorbed with fats
-water soluble (C and most B) are reabsorbed by mediated transport
-B12 is absorbed in the ileum after forming a complex with intrinsic factor released from parietal cells
-mineral absorption is usually by active transport (certain are regulated: iron) (usually motility and secretion are only regulated)
what is ion and water absorption?
most water absorbed in the small intestine
-this same mechanism exists in the colon
