by mtoom

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  • What enzymes are in the mouth? (1)
  • What enzymes are in the stomach? (2) 
  • Mouth:
  • Stomach:
  • What can move through tight junctions between intestinal epithelial cells?
  • What is this called? 
  • Ions
  • Paracellular transport
Carbohydrates are mostly absorbed in what part of the intestine?
  • Duodenum
    (although throughout small intestine) 
Bile acids are mostly absorbed in what part of the intestine?
  • Ileum = Distal small intestine
    (although throughout intestine)
Cobalamin is mostly absorbed in what part of the intestine?
  • Ileum = Distal small intestine
Iron and Folate are primarily absorbed in what part of the intestine?
  • Duodenum
Calcium is absorbed in what part of the small intestine?
Throughout the small intestine
Fat digestion is initiated where?
Hydrolysis and emulsification of fat begins where?
  • Gastric lipase hydrolyzes TAGs at 3' position 
Micelle formation takes place where?
Small intestine
How do micelles form?
Bile salts interact with lipid breakdown products: fatty acids and monoglycerides
  • Within the shell of the micelle, are poorly soluble lipid breakdown products such as cholesterol and fat soluble vitamins and long chain fatty acids
How do short and medium chain fatty acids get absorbed?
Pass directly into enterocyte:
  • By membrane flipping
  • By facilitated diffusion 
How do long chain fatty acids, cholesterol and monoglycerides get absorbed?
Dissociation of micelle is required, then binding proteins absorb into enterocyte
Once inside the enterocyte, what happens to short and medium chain fatty acids?
They are released basolaterally into the hepatic portal vein
Once inside the enterocyte, what happens to long chain fatty acids and monoglycerides?
Long chain fatty acids and monoglycerides are re-esterified into TAGs and leave the enterocyte in chylomicrons (along with cholesterol and fat soluble vitamins) which are packaged using apolipoproteins
Chylomicrons are secreted by exocytosis to where?
Basolaterally exocytosed into the central lacteals and lymph system, then draining into blood (and bypassing the liver)
What proportion of calories comes from:
  • Carbohydrates
  • Fats
  • Proteins 
  • Carbohydrates: 40%
  • Fats: 40%
  • Proteins: 20%
What are the 4 major types of dietary carbohydrates?
  • Starch
  • Dietary fibre
  • Dietary disaccharides
  • Dietary monosaccharides
    --glucose & fructose
Salivary amylase breaks down what type of carbohydrates?
Long chain carbohydrates
Activity of salivary amylase is reduced where?
In stomach, acid breaks it down
Digestion of partially-digested starches down to -ose sugars occurs by what mechanism?
Pancreatic amylase
Digestion of carbohydrates down to monosaccharides occurs where?
Brush border enzymes on apical microvilli of intestinal enterocytes
How do monosaccharides get into enterocytes?
GLUT transporters (facilitated diffusion), or SGLT1 which couples Na+ to bringing glucose into cells
In the stomach, HCl and pepsin catalyze the conversion of pepsinogen to pepsin (the active enzyme that digests proteins). Which catalyzes the conversion of trypsinogen to trypsin?
EEK (brush border enterokinase)
What does trypsin do? (2)
  • Digests proteins
  • Activates many other digestive enzymes in the small intestine
  • How are polypeptides, di- and tri- peptides, and free amino acids taken up into the enterocyte?
  • Can Di- and Tri- peptides be directly absorbed?
Numerous transporters, both energy dependent and independent
  • Polypeptides must be digested to di- and tri- peptides before uptake into enterocytes
  • Di- and tri- peptides can be absorbed directly by H+-dependent Pept-1 (coupled with Na+/H+ exchanger)
How are fat soluble vitamins absorbed?
After release from micelles, absorbed passively into enterocyte, then leave cell in chylomicrons
How are water soluble vitamins absorbed?
Transported across intestinal epithelium in various ways:
  • Facilitate diffusion
  • Active transport
  • Endocytosis
Chyme passes through the pyloric sphincter to get into the small intestine. What can inhibit this process? (2)
  • Enterogastrones
  • Duodenal mechnoreceptors
Major duodenal papilla connects what to the small intestines?
Hepatopancreatic ampulla (which is formed by the merger of the principal duct of the pancreas and the common bile duct).
The acid from the stomach is neutralized in the small intestine by different mechanisms depending on where it is:
  • Luminal
  • Juxtamucosal 
  • Luminal: Acid in lumen is neutralized by pancreatic HCO3-.
  • Juxtamucosal: Acid near mucosal lining is neutralized by duodenal mucosal HCO3- secretion.

Pretty simple: Acid near mucosal lining is neutralized by bicarbonate from the lining, otherwise it's just neutralized by the pancreatic bicarbonate.
What are the 2 major types of products of the pancreas, and how does the tissue vary by product?
  • Endocrine: Islets
  • Exocrine: Acini and ducts
The pancreas is divided into what? Which are filled with what?
Lobules filled with acini
What is a pancreon?
Individual secretory/acinar units of the exocrine pancreas
  • Acinar cells: secrete digestive enzymes 
  • Centroacinar and duct cells: secrete bicarbonate
What is the role of PaSC (pancreatic stellate cells)?
Deposit ECM to facilitate tissue repair
What the role of acinar cells?
Synthesize, store and secrete digestive enzymes.
  • Synthesized and folded in rER, modified in Golgi
  • Transported from Golgi in condensing granules (to make pack digestive enzymes in tightly)
  • Mature zymogen granules accumulate to store enzymes
What happens when trypsinogen is activated?
Activation of a zymogen cascade
Some enzymes are secreted in active form. Which types? (3)
  • Amylase
  • Nucleases
  • Some lipase
What activates trypsinogen and where is it located?
EEK located in brush border in duodenum
What happens in hereditary pancreatitis?
Normally, autoactivated trypsin is neutralized by the action of CRTC (chymotrypsin C).
  • In hereditary pancreatitis, chymotrypsin C is non-functional. 
I mentioned before the acinar cells secrete digestive enzymes. Other elements of the pancreaton include centroacinar and duct cells. What do they secrete?
Alkaline fluid
  • Na+
  • HCO3-
  • Cl-
  • K+ 
In basal alkaline secretion of ductal cells, which transporter moves HCO3- out of cell apically?
AE transporter
  • Moves HCO3- out in exchange for Cl-
For basal alkaline secretion of ductal cells, why is the CFTR transporter so important?
  • What happens if it has a problem
The Cl- taken into the cell by AE is normally allowed to go back out via CFTR transporter. (Keeps charges balanced).
  • If it doesn't work,  then Cl- is trapped in the cell and HCO3- secretions stop because HCO3- secretion is dependent on AE which exchanges HCO3- and Cl- (and a charge gradient now exists).
What role do secretin and VIP have in regards to CFTR?
They initiate a signal transduction pathway (cAMP, PKA) that phosphorylates CFTR, increasing its activity.
In high alkaline fluid production, which transporter transports large amounts of additional bicarbonate into the ductal cell?
NBC transporter
  • NBC brings extra HCO3- into the cell (so that more alkaline solution can be made by the pancreas)
  • A putative bicarbonate cotransporter may appear in high alkaline state as well (known as BC)
What may happen in the pancreas in Cystic Fibrosis patients?
Non-functioning CFTR transporter will create a charge gradient in cells and stop efflux of bicarbonate.
  • Very thick pancreatic secretions are the result
  • Ducts get obstructed, and zymogens in the ducts autoactivate leading to chronic wounding and inflammation
What happens to pancreatic acini in Cystic Fibrosis?
They are lost/destroyed
Describe the cephalic stage of pancreatic secretion
  • Thoughts, tastes and smells of food induce some pancreatic stimulation as vagal nerves stimulate intrinsic nerves to produce ACh and VIP which activate:
  • -Enzyme secretion (acinar cells) [ACh only]
    -HCO3- secretion (ductal cells)
Describe the gastric phase of pancreatic secretion
  • Stretch-induced reflex from food induces some pancreatic stimulation as vagal nerves stimulate intrinsic nerves to produce ACh and VIP which activate:
  • -Enzyme secretion (acinar cells) [ACh only]
    -HCO3- secretion (ductal cells)
Describe the duodenal phase of pancreatic secretion

Chyme in the small intestine stimulates:
  • Secretin
  • CCK

These activate both acinar cells (enzymes) and duct cells (alkaline fluid)
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