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Phys4 GI Lect9
Phys4 Digestion and Absorption of Lipids
Question | Answer |
---|---|
Types of Endogenous Lipids | 1.Cholesterol. 2.Phospholipids. 3.Desquamated intestinal villus epithelial cells. |
Types of Exogenous Lipids | 1.Triglycerides (90%). 2.Cholesterol. 3.Phospholipids. |
Emulsification | suspension of fat droplets held apart by lecithin, bile salts, and FA. **Inc the SA of the lipids which makes them easier for enzymes to attack. |
What is a big emulsifying agent in the stomach? | Protein |
5 processes of Lipid assimilation | 1.Secretion of Bile & lipases. 2.Emulsification. 3.Enzyme hydrolysis of ester linkages. 4.Solubilization of lipolytic products w/in bile salt micelles. 5.Transportation in/out of enterocyte. |
Key Lipases not secreted by the Pancreas | 1.Lingual Lipase (pH 3-6, does still fnc in stomach). 2.Food Lipases (pH 3.5-9, works all thru GI). 3.Gastric Lipase & Gastric emptying. **All 3 important in newborns b/c their pancreatic enzymes are NOT developed. |
Which non-pancreatic lipase would be useful in Zollinger-Ellison disease? | Gastric Lipase b/c it can tolerate the high acidity. |
What are the 2 most important compounds/enzymes for the assimilation of fat? | 1.Pancreatic Lipase. 2.Bile. |
Fat stimulates the release of ______? | CCK which helps in fat digestion. **also GIP or Vago-Vagal reflex. |
Acid stimulates the release of _______? | Secretin. **Also somatostatin. |
What key function does CCK (stimulated by fat release) have on fat assimilation? | 1.Contraction of GallBladder. 2.Relaxation of sphincter of Oddi. |
What hormone causes secretion of HCO3- and fluid from pancreatic ductal and centroacinar cells? | Secretin. **Secretin is potentiated by ACh and CCK |
How does ACh effect the Gall Bladder? | it causes CONTRACTION. |
What are the 2 main things stimulating pancreatic acinar cells to release digestive enzymes? | 1.CCK. 2.ACh. |
3 main lipases secreted by the pancreas | 1.Lipase. 2.Phospholipase A2. 3.Cholesterol Esterase. |
Pancreatic Lipase | 1.Secreted: Active form (Co-lipase w/ it is inactivated and must activated by bile salts and prevent bile salt interference w/ lipase). 2.Action: Cleaves FA at the 1 & 3 position of tiglycerides. |
Pancreatic Phospholipase | 1.Secreted: Inactive form (activated by bile salts). 2.Action: Cleaves FA at the 2 position of triglycerides. |
Pancreatic Cholesterol Esterase | Secreted: Inactive (Fnc enhanced WITH bile salts). 2.Action: Cleaves FA from Cholesterols, Non-specific esterase that can also cleave 2-monoglycerides. |
3 ways by which Lipids cross the Membrane to enter Enterocytes | 1.Simple diffusion. 2.Collision (similar to pinocytosis). 3.Carrier proteins. |
What is the main function of the Micelle in lipid absorption? | they FERRY (transport) lipids across the unstirred water layer of the Acid Microclimate Disequilibrium Zone. **It then dumps the lipid contents at the enterocyte. |
Do short and medium chain FA need Micelle transportation to reach the Enterocytes? | NO, they can difuse directly through and enter the enterocyte. **Only long chain FA need Micelle transport. |
Pathway of Long-chain FAs reforming lipid compounds and joining ApoproteinB within the Enterocyte. | 1.Reconverted into triglyc, phospholip, & esters w/in smooth ER. 2.Forms lipid droplets. 3.ApoproteinB synthesized in rough ER join droplets in SER. 4.Chylomicrons & VLDLs glycosylate apoproteinB in golgi. |
Pathways of ApoproteinB associated lipid compounds with chylomicrons or VLDLs being reabsorbed back across the basolateral membrane into he lymph. | 1.Vesicles bud off golgi carrying chylomicrons or VLDLs and fuse with basolateral membrane. 2.Exocytosis. 3.Chylomicrons & VLDLs cross large interendothelial channels to enter the lymph. |
Are short and medium chained FAs absorbed into the BL or Lymph? | They move through the enterocyte and directly enter the BL along with glycerol. |
What could cause a problem with emulsification? | Rapid gastric emptying. |
What could cause a problem with the quality or quantity of pancreatic lipases? | 1.Hyperacidity (Zollinger Ellison's). 2.Obstruction. 3.Cystic Fibrosis (Dec HCO3- secreted). 4.Chronic Pancreatitis. |
What could case a problem within the enterocyte leading to abnormal lipid assimilation | 1.abetalipoproteinemia: defective MTP which combines apoproteinB with lipids to form chylomicron. 2.Inadequate Absorption SA (celiac sprue, protazoan infection). 3.Lympthatic transport (Whipple's disease). |
What could cause a problem with bile salt micelles and thus abnormal lipid assimilation? | 1.Biliary Obstruction. 2.Bile salt synthesis. 3.Bacteria Overgrowth. 3. |