Digestion and Absorption of Proteins and Fats Flashcards
Describe the general overview of protein digestion.
Describe what happens to the stomach when food arrives from the esophagus and particularly what happens to proteins in the food.
Food arrival in stomach stretches the stomach which activates stretch receptors. Some of the H+ in the stomach is also neutralized because the H+ starts breaking up nutrients, which raises the pH and activates chemoreceptors. These actions stimulate cells in the submucosal and myenteric plexi of the gut to cause the following:
- Triggers nerves to generate pattern of depolarization that causes mixing waves of stomach (myenteric plexus)
- Stimulate mucous cells to secrete mucus, chief cells to secrete pepsinogen, parietal cells to secrete HCl and IF, G cells to secrete gastrin (submucosal plexus)
- Presence of partially digested peptides in stomach also stimulates G cells to secrete Gastrin.
Gastrin enters blood stream and stimulates chief cells and parietal cells to increase their secretions and it also further stimulates mixing waves, thus increasing stomach motility.
HCl in stomach cleaves proteins and also pepsinogen –> pepsin which begins to cleave proteins in stomach further.
Once contents of stomach reach duodenum, how are proteins further broken down?
I think the acid from stomach and vagal stimulation are happening in tandem in this image.
What is the difference bewteen an enteropeptidase and an exopeptidase?
Enteropeptidase - hydrolyze interior peptide bond
Exopeptidase - hydrolyze terminal peptide bond
What are the ultimate products of protein digestion?
Amino acids, dipeptides, tripeptides, short oligopeptides
Once proteins have been acted upon by pancreatic enzymes, what is the fate of:
- Free amino acids
- Short oligopeptides
- Di and tripeptides?
How are free amino acids absorbed across the gut wall?
How are di and tripeptides absorbed across the gut wall?
What are the different forms in which we can absorb lipids?
Short and medium chain fatty acids are […] to […] carbons long.
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Short and Medium Chain Fatty Acids
- Are [more or less] soluble than long chain fatty acids
- [Do or do not] require bile acids for digestion and absorption
- By what routes are they absorbed?
- Where are they absorbed?
- Clinical use
- In clinical use, additionally, protective against colon cancer
What is the role of lingual lipase vs. gastric lipase?
The majority of lipid digestion occurs in the […]
Small intestine
How is bile release triggered?
- CCK from duodenum cells enters blood –> contract gallbladder. Happens in tandem with vagal input which also triggers gallbladder contraction –> bile salts from gallbladder enters common bile duct.
- Secretin from duodenum cells enter blood –> stimulate liver to secrete bile into bile ducts –> combines with bile from gallbladder in common bile duct
- Bile enters small intestine via sphincter of Oddi
What are the 3 major pancreatic lipases we need to know?
Pancreatic lipase (+ colipase co-factor)
Secretory phospholipase A2
Cholesterol esterase
Describe the steps in lipid digestion beginning with the arrival of fat in the duodenum from the stomach.
Micelles –> absorbed into intestinal mucosal cells –> packaged into Chylomicrons –> absorbed into lacteals –> lympathic system –> circulatory system –> tissues –> liver –> tissues
In addition to fat, what other important substances are found in micelles?
Fat soluble vitamins (ADEK)
Micelles are absorbed where in the GI tract?
Jejunum
Describe the general ways in which micelles are absorbed?
- Micelle can use transporter NPC1L1 and enter epithelial cell as whole micelle
- Micelle can release fatty acids which then are transported into epithelial cells via MVM-FABP
- Once inside epithelial cells the fats are made into chylomicrons
Where are vitamins A,D,E, and K absorbed?
Jejunum (within micelles)
Why are fat soluble vitamins more dangerous than water soluble?
Can accumulate inside cells at toxic levels
Where are bile salts absorbed?
What else is absorbed at the same location?
Ileum
Vit B-12, Vit C
What is a concern following ileal resection?
Bile acids not absorbed, bile acid pool is depleted
What is a concern in patients with celiac disease and short bowel syndrome?
Decreased intestinal cells leading to reduced area for lipid absorption
What is a concern for patients with Zollinger-Ellison syndrome?
They have hypersecretion of gastrin (Gastrinoma) that causes increased gastric acid secretion, low duodenal pH, and inactivation of pancreatic enzymes including pancreatic lipase
When a person has a condition that results in the malabsorption of lipids, what might be a symptom they report?
Oily and foul smelling stools –> steatorrhea
