GI Tract Lecure 5 - Digestion and Absorption

Starch

multiple glucose units joined in glycosidic bonds, most common

Starch consists of ___

amylose and amylopectin

Absorption of carbohydrates occur mainly in the ___

duodenum and jejunum

Carbohydrates are digested by ___

salivary amylase, pancreatic amylase, brush border membrane enzymes, glucoamylase

Carbohydrates are broken down into ___ during digestion

disaccharides, monosaccharides

The three locations of carbohydrate digestion are ___

saliva, pancreas, brush border of intestinal epithelial cells

The absorb-able monosaccharides derived from carbohydrates are ___

glucose, fructose, galactose

Glucoamylase breaks down the substrate(s) ___

maltose, maltotriose

Isomaltase breaks down the substrate(s) ___

alpha-limit dextrins, maltose, maltotriose

Lactase breaks down the substrate(s) ___

lactose

Sucrase breaks down the substrate(s) ___

maltose, maltotriose, sucrose

Glucoamylase aides in creating the product(s) ___

glucose

Isomaltase aides in creating the product(s) ___

glucose

Lactase aides in creating the product(s) ___

glucose, galactose

Sucrase aides in creating the product(s) ___

glucose, fructose

The small intestine absorbs glucose or galactose through the ___

SGLT symporter alongside Na+

GLUT2 serves to ___ of glucose or galactose

allow for exit

GLUT5 allows entry to ___ for absorption

fructose

Lactose intolerance is caused by ___

lactase deficiency

Lactose intolerance causes watery chyme due to ___

increased osmolarity due to undigested lactose

Proteins are held together by ___

peptide bonds

Digestion of proteins occurs in the ___

stomach, duodenum, jejunum

Protein digestion is initiated by ___

pepsin

Most proteins are digested by ___

pancreatic proteases

To absorb large proteins, they are ___

broken down into smaller peptides

Ultimately, ____ in the duodenum and jejunum are responsible for digesting peptides

cytosolic peptidases

Proteins are degraded into smaller peptides by ___

pancreatic peptidases, proteases, brush border pepsidases in small intestine

Absorption of peptides from the lumen is done via ___

Na+ linked transporters or H+ linked transporters (PepT1)

PepT1 can only absorb ___ alongside one H+ ion

dipeptides and tripeptides

Basolateral transporters for each amino acid are ___

specific to each amino acid

Defects of specific basolateral transporters cause ___

deficiencies in their associated amino acids

The kidney and small intestine often ___

share transporters for protein absorption

Dietary lipids are composed of ___

triglycerides (glycerol and free fatty acids)

Lipase and co-lipase break down tryglycerides into ___

monoglycerides and free fatty acids

Digestion of lipids requires secretions from ___

liver and pancreas

Lipids are emulsified by ___ in the duodenum and jejunum

bile salts

Bile insufficiency/pancreatic insufficiency can lead to malabsorption of ___

lipids

A, D, E, and K deficiencies can be caused by ___

lipid malabsorption due to fat soluability

The key enzymes of lipid digestion are ___

lipase/colipase, cholesterol esterase, (pro)phospholipase-A2

Celiac Disease is cause by ___

a malfunctioning immune response to gluten in the small intestine

Celiac effects on the small intestine include ___

blunting of villi, epithelial cell apoptosis, crypt hyperplasia, vacuolization, lymphocyte infiltration