GI: Digestion and Absorption 2 Flashcards
How is carbohydrate digested?
Mouth- salivary alpha amylase
Stomach- salivary alpha amylase trapped in the bolus
Small intestine- pancreatic alpha amylase and oligosaccharidases (isomaltose, maltose, sucrase, lactase, maltase)
What bond does amylase break?
Internal alpha 1. 4 glycosidic bond
Cannot break aplha 1, 6 or beta 1, 4 bonds as in cellulose
ENDOENZYME
produces ogliosaccarhides
What are the final products of carbohydrate digestion?
Glucose
Galactose
Fructose
How is glucose and galactose absorbed?
Secondary active transport
How is fructose reabsorbed?
facilitated diffusion
How is fructose transported from the lumen into the enterocyte?
GLUT 5
How is glucose or galactose transported from the lumen?
SGLT1
How are glucose, galactose and fructose transported into the blood?
GLUT 2
How are amino acids absorbed?
Passive diffusion- hydrophobic amino acids
Active transport and facilitates transport
At brush border- five sodium dependant, 2 indepentandt
At basolateral border- Sodium dependant
How are di and tripeptides absorbed?
proton dependant mechanism at brush border (co-transport)
What happens to peptides within the enterocyte?
Hydrolysed furthur to amino acids
How do the amino acids then leave the enterocyte and enter the lumen?
Sodium independent systems at basolateral border
facilitatd transport
How are lipids digested?
Lingual lipase
Gastric lipase
Bile emulsifies
Pancreatic lipase
What is the products of fat digestion?
Fatty acids and monglycerides
What is the role of bile salts?
Deteregents to emulsify large lipid droplets
Decribe the structure of a bile salt.
Amphipathic
Hydrophilic outer surface
Hydrophobic inner
What can result from failure to secrete bile salts?
Lipid malabsoption and thus steatorrheoa
Secondary vitamen deficiency
What is colipase?
An amphipathetic polypeptide secreted with lipase by the pancreas - binds to bile salts and lipase allowing access of the lipase to tri and di-glycerides which are trapped in the core of lipid droplets
What are the products of digestion of a triglyceride by pancreatic lipase?
2-monoglyceride
Free fatty acids
How are the products of lipid digestion stored in the duodenum?
Micelles
How are free fatty acids and monoglyceride absopbed?
Transfer between mixed micelles and the apical mebrane of enterocytes enterying by passive diffusion
What happens to long chain fatty acids?
They are resynthesized back into triglycerides and stores as chylomicrons
What happens to chylomicrons after leaving the entericyte
Transported to subclavan vein via the thoracic duct
What enzyme metabolises chylomicrons in the capillaries?
Lipoprotein lipase
What happens to the free fatty acis and glycerol release from the chylomicrons?
Binds to albumen and taken up into tissues
What happens tot he chylomicron remenant
Endocytosed by hepatocytes to be stored, secreted or oxidised to bile salts
How is cholesterol absopbed from the blood into hepatocytes?
Niemann -Pick C1 like 1 protein
What does ezetimibe do?
Binds to PPC1L1 and prevents internalisation and cholesterol absorption
Used in hypercholesterolaemia along with statins
