Digestion of fats Flashcards
What type of bile acids are formed in the liver?
Primary bile acids.
What type of bile acids are formed by bacterial action in the intestine?
Secondary bile acids.
Name two primary bile acids.
Cholic acid. Chenodeoxycholic acid.
Where in the enterocyte are the products of lipase digestion built back up into TAG to for chylomicrons?
The smooth endoplasmic reticulum.
Describe peristalsis.
The circular muscle fibres behind the bolus of food contract to constrict the gastrointestinal tract and force the bolus of food forwards; and the longitudinal fibres in front of the bolus of food contract to shorten the gastrointestinal tract so the walls bulge out so it can receive the bolus. This wave of contraction is repeated many times.
What are the two pathways of lipid metabolism?
Exogenous (happens after a meal), and endogenous (happens all the time).
What enzyme converts chylomicrons to chylomicron remnants?
Lipoprotein lipase on the luminal surface of the endothelium.
What proportion of bile salts are excreted in the faeces, what proportion are reabsorbed?
5% excreted in faeces, 95% reabsorbed in ileum to be recycled.
What protein transports free fatty acids in the blood?
Albumin.
Why is cholesterol transported in lipoproteins as cholesterol ester?
Cholesterol is amphipathic, cholesterol ester is non-polar, it needs to be non-polar to be inside the phospholipid monolayer.
Name one of the biggest apoproteins, which is found on the surface of VLDLs and is very important.
Apoprotein B-100.
What is the function of chylomicrons?
To deliver dietary lipids to adipose tissue for storage, and to the liver via chylomicron remnants.
What is the function of VLDLs?
To deliver triglycerides synthesised in hepatocytes to adipose tissue for storage, and therefore form IDLs and LDLs.
What is the function of LDLs?
To deliver cholesterol to any cells in the body that need it, including macrophages.
What is cholesterol used for?
Repairing plasma membranes, synthesising steroid hormones and bile salts.
What is the function of HDLs?
Reverse cholesterol transport, remove excess cholesterol and transport it to the liver.
What is the function of Apo C-2?
Apo C-2 activates the enzyme endothelial lipoprotein lipase, which breaks down TAG in chylomicrons and VLDLs to produce free fatty acids.
What is the function of Apo E?
Apo E is the docking protein for chylomicron remnants to be taken up into hepatocytes by receptor-mediated endocytosis.
What is the function of Apo B-100?
Apo B-100 is the apoprotein on LDLs, and is the docking protein that binds to LDL receptors so that LDL is taken up by cells by receptor-mediated endocytosis. The cholesterol ester is then broken down inside the cell to supply the cell with cholesterol.
What is a coated pit?
Region of plasma membrane specialised for receptor-mediated endocytosis.
What is the only way to remove cholesterol from the body?
HDL takes cholesterol from extrahepatic tissues to liver by reverse cholesterol transport, liver converts it into bile salts. small portion of bile salts excreted in the faeces each day.
What is newly formed HDL?
Discoidal HDL produced by liver and intestine - a disc of phospholipid bilayer enriched with the apoproteins LCAT and A-1.
Which transporter does discoidal HDL interact with so that cholesterol is pumped out of cells?
ABC-1.
What is the function of LCAT?
Converts cholesterol (amphipathic) to cholesterol ester (non polar) so that it can be stored between the two layers of the bilayer disc - swelling them out to form a spherical lipoprotein particle.
What happens after HDL3 is converted to HDL2 after taking up more cholesterol ester?
HDL2 is taken up into the hepatocytes by receptor-mediated endocytosis at SR-B1 receptor, then hepatic lipase converts cholesterol ester back to cholesterol, then cholesterol converted to bile salts.
What does LCAT stand for?
Lecithin Cholesterol Acyl Transferase.
Which enzyme do cells use to synthesise cholesterol directly from acetyl coA?
HMG CoA reductase (the enzyme statins inhibit).
What forms the plaques in coronary heart disease?
Macrophages have a “scavenger system” so their uptake of LDL can’t be regulated. They become saturated with cholesterol ester, the cells die and plaques form.
How do cells regulate their cholesterol level?
Inhibit HMG CoA reductase, or inhibit synthesis of LDL receptors.
Name the major function of white adipose tissue.
Releases fatty acids for use for energy during exercise and starvation.
Why does the blood glucose level not drop to zero during starvation?
Glucose is a universal fuel for all cells - it is needed by the central nervous system and used for aerobic glycolysis in cells that lack mitochondria like erythrocytes and retina cells. Fatty acids CAN’T cross the blood-brain barrier, so can’t be used by the CNS, and fatty acids can’t be used in respiration except in mitochondria, so can’t be used by erythrocytes. Ketone bodies are used to fuel the CNS also.
Name two main ketone bodies.
Acetoacetate, and 3-hydroxybutyrate.
What produces the sweet smelling breath of a patient with very high ketone body concentration (e.g severe diabetic)?
Acetoacetate spontaneously decarboxylating to acetate.
Name the hormone that controls glucose entry into cells.
Insulin.