Digestion of Lipids and Vitamins Flashcards
1
Q
villi vs. crypts
A
- absorptive cells are located in vill: removing substances from the lumen
- secretory cells located in crypts: adding substances to the lumen
2
Q
Small intestine
A
Villi (absorptive cells)
crypts (secretory cells)
Columnar epithelial cells
3
Q
Large intestine
A
Surface epithelium (absorptive cells) colonic crypts (gland cells) Columnar epithelial cells
4
Q
Progenitor cells
A
- Found at the base of crypts in both small and large intestine
- Cell turnover is about 48-96 hours and results in cell being sloughed into lumen of intestine
- Cell turnover decreases during starvation and vice versa
5
Q
3 classes of dietary lipids
A
- Triaglycerols (TAGs)
- Phospholipids
- Cholesterol (unesterified)
6
Q
secreted lipids?
A
bile - contains phospholipids (Lecithin and unesterified cholesterol)
- amount secreted usually equals the amount of lipids being absorbed.
7
Q
emulsification
A
process we undergo in order to digest dietary lipids
- formation of oil droplets within water
- accomplished through chewing, gastric chewing, peristalsis, movement between pyloric sphincter and duodenum. With each mechanical process size of oil decreases resulting in an increased SA.
- emulsions are stabilized by a monolayer at the interface formed by dietary and secreted lipids
8
Q
Lipolysis
A
(Digestions of lipids) - accomplished by lipases
- lipases = enzymes responsible for hydrolysis of lipids, present in aqueous lumen at oil-water interfaces.
9
Q
Gastric lipase
A
- only active and stable at pH 4
- resistant to Pepsin
- secreted by Chief cells
- Inactivated by pancreatic proteases in bile salts in small intestine
- cleaves FA’s from TAG’s resulting in one FFA and one diacylglycerol at center of oil droplet.
- medium and short chain GGa’s can move through gastric mucosa
10
Q
Pancreatic lipase
A
- ** major enzyme of lipolysis***
- secreted into duodenum, by acinar cells
- created by pancreas and dependent upon: presence of Colipase, alkaline pH of small intestine, Ca2+, bile salts (allow enzymes to get close to miscelles), fatty acid substrate
Action:
- hydrolyzes all TAG’s
- at oil-water interface - Colipase helps reduce inhibition from phospholipids or proteins on micelle surface
- liberates 2 FFA and liberates 1MAG which moves to the surface of the miscelle
11
Q
Alli and Xenical
A
- drugs that inhibit pancreatic lipase
- most dietary lipids are ingested as TAG’s, which must be degraded into FFA’s and MAG’s by pancreatic enzyme to be taken up….
- this drug results in higher concentration of TAG’s in stools
12
Q
Phospholipiase A2
A
- secreted by pancreas and requires bile salts and alkaline pH
- Action: cleaves one FFA from a glycerophospholipid
- leaves lysophospholipid - no middle fatty acid
13
Q
Carboxyl Ester Hyrdolase
A
- not substrate specific
- hydrolyzes all ester residues, seen in glycerol containing molecules (MAG’s and TAG’s)
- releases free cholesterol and free glycerol
- Action: same action as bile-salt stimulated milk lipase. not active until it hits the duodenum where it is activated by alkaline pH
14
Q
CCK
A
Lipid absorption
- release stimulated by presence of FFA’s in duodenum
- stimulates bile flow into duodenum
- stimulates secretion of pancreatic enzymes: pancreatic lipase and esterases.
15
Q
Lipids in stools
A
- intact acylglycerols are rarely found in stools even in severe malabsorption.
- bacteria likes to digest them, so normally digested by bacteria
- Sudan III staining will show oil droplets that are present in stools.
- short chain and long chain FA’s can be used if patient has problem breaking down long chain FA’s
16
Q
emulsion droplets
A
- larger glycerols in core, smaller glycerols on outside.
- in beginning the vessels can have large arrangment of surface lipids: multilamellar: multiple layers
- as mixing continues the micelle will be formed - micelle contains a lipid monolayer with tails facing the hydrophobic core. results in increased SA and shorter distance for enzymes to reach substrates located in core
- MAGs are hydrolyzed on the surface by lipases and FFA’s released. DAGs and TAGs from the core replace the surface MAGs. the droplet decreases in size, thereby increasing its SA and facilitating more hydrolytic digestion by surface lipases
