Flashcards in Physiology Lipid Digestion Deck (35):
What is phosphatidylcholine use for?
This is a phospholipid that is secreted as pulmonary surfactant
What are the ingested lipids?
What are the different phase of digestion?
Lingual Phase - Mouth
Gastric Phase - stomach
Intestinal phase - intestines
What is the function of bile?
emulsification of fats
What is the function of pancreatic lipase?
Hydrolysis of Triglycerides into monoglyceride and free fatty acids
How does Gastric Lipase function and what does it do?
It breaks down a triglyceride into a diglyceride and a free fatty acid.
This is done by gastric lipase hydrolysing one of the fatty acid tails.
Describe how gastric lipase sets up a positive feedback system?
Gastric lipase increase the amount of free fatty acid. Free fatty acids stimulates release of Cholecystokinin from the duodenum and release of Pancreatic lipase. It also increase gastric motility. This cause an increase in free fatty acids - therefore is a positive feedback loop.
What added secretions are added in the duodenum?
What secretes Bile salts and what is the function of a bile salt?
Bile salts are secreted by the gall bladder in response to CCK.
Bile salts are use give lipid molecules polarity and prevent build up of large fat droplets by emulsifying large lipid droplets into small droplets. (Increase surface area of lipids for pancreatic lipase)
They also allow lipids to become water soluble
Describe the nature of the charge on a bile salt?
They are amphipathic (both hydrophilic and hydrophobic regions )
Describe what happens in the failure of secretion of bile salts?
Secondary vitamin deficiency
What cofactor do bile salts require?
Colipase - this increases the efficiency and the access of the lipase.
Describe the hydrolysis of a triglyceride by Pancreatic lipase?
Cleaves the fatty acid chain off from the first and third position on the glyceride backbone.
The products produced is a 2-monoglyceride and two fatty acid chains .
What is typically contained in an emulsified lipid droplet?
Non-polar vitamin type lipids
How are free fatty acids and monoglycerides absorbed?
Enter the membrane of the enterocytes by passive diffusion
What factor affect is a fatty acid can be absorbed?
The length of the chain.
Short chain (i.e. < 6 carbon) and medium (i.e. 8-12 carbon ) fatty acids diffuse through the enterocyte, exit through the basolateral membrane and enter the villus capillaries
Long chain fatty (i.e. >12 carbon) fatty acids and monoglycerides are resynthesized to triglycerides in the endoplasmic reticulum and are subsequently incorporated into chylomicrons
What is the major difference in absorption of a chylomicron and a bile lipid droplets?
Chylomicrons are secreted inside of the cell and use a amphipathic basalt to increase emulsification
How are chylomicrons synthesised?
Long chained fatty acids are resynthesises into triglycerides in the cell
They are formed into cholesterol esters by the endoplasmic reticulum.
Phospholipids are incorporated into them - they form a Nascent Chylomicron. The Nascent chylomicron joins with ApoB-48 to form the chylomicron.
The chylomicron undergoes exocytosis
What is the course of the chylomicrons and how do they enter the systemic circulation?
Chylomicrons enter the lymphatic system and enter the systemic circulation via the Thoracic duct into the subclavian vein
Where are chylomicron triglycerides metabolised?
They are metabolised in the capillaries of the muscles and adipose tissue by Lipoprotein lipase - present on endothelial cells
What is the function of albumen?
To transport fatty acids round the body
What produces chylomicron remnants and what are their functions?
They can be sorted
Secreted unaltered in bile
Oxidised to bile salts
Remnants are secreted by hepatocytes
How is cholesterol absorbed?
Cholesterol is picked up by the carrier protein Riemann-Pick C1 like protein (NPC1L1)
NPC1L1 stimulates formation of a scaffold necessary for endocytosis of cholesterol
NPC1L1 stabilise the formation of a pit which contains cholesterol
NPC1L1 deposities chosterol in a pit were it accumulates
NPC1L1 allows the movement of cholesterol around on small protein motors which move on the microtubules and filaments
NPC1L1 moves back to the start to get more cholesterol
Describe how a statin works?
Statins prevent the accumulation of cholesterol and prevents the recycling of NPC1L1
Describe how Ezetimibe works?
Ezetimibe binds to NPC1L1, prevents internalization, and thus cholesterol absorption. Used in conjunction with statins in hypercholesterolaemia
How is calcium absorbed?
Calcium absorption occurs passively. It is paracellular transport were the calcium moves between the cells at the cellular junctions.
This occurs in the duodenum and upper jejunum
Calcium can be absorbed actively boa the Ca2+ TRPV6 channel
How is active Ca2+ absorption regulated?
1,25-dihydroxyvitamin D3 (calcitriol) and parathyroid hormone (increases 1,25-dihydroxyvitamin D3 synthesis)
Describe how Iron is absorbed?
Fe3+ (reduced/ferric iron) is absorbed by cells by the DMT1 and SLC11A2 receptor
Or, Haem can be absorbed by the cell through the Haem carrier Protein 1
What happens to Haem if it is absorbed?
The Haem needs to be broken down. This is done by Haem oxidase which converts Haem to Fe2+ (ferrous iron)
What is the storage form of Iron called?
What is not bound iron called?
What is the other name of vitamin B12?
Describe how vitamin B 12 is absorbed?
Ingested in food
Salivary glands secret Haptocorin
Stomach release Vitamin B 12 from food.
Haptocorin binds Vitamin B 12 in the stomach
Pancreatic proteases release intrinsic factor
Pancreatic proteases digest haptocorin in small intestine
Vitamin B 12 binds to intrinsic factor in the small intestine
Vitamin B 12- instrinsic factor complex absorbed in the terminal Ileum
What are the fat soluble vitamins?
Vitamin A,D,E and K