Chapter 25: Chemical Digestion and Absorption

most digestible dietary carbohydrate is...

starch

steps of starch breakdown

starch-oligosaccharides-disaccharide maltose-glucose-absorbed by small intestine

what hydrolyzes oligosaccharides

dextrinase and glucoamylase

what hydrolyzes maltose

maltase

what hydrolyzes sucrose and lactose

sucrase and lactase

what is immediately absorbed

monosaccharides

proteases

enzymes that digest proteins

location of proteases

not in saliva, begin in the stomach

pepsin

hydrolyzes any peptide bond and is inactivated in the duodenum and reactivated in the small intestine

carboxypeptidase

pancreatic secretion, removes amino acids from -COOH end of the chain

aminopeptidase

brush boarder enzyme, removes amino acids from -NH2 end

dipeptidase

brush boarder enzyme, splits dipeptides in the middle to release two free amino acids

lipases

fat-digesting enzymes

lingual lipase

secreted by intrinsic salivary glands of the tongue and digest small amount of fat while food is in the mouth, most active in stomach

antral pumping

vigourous pumping in the stomachs antrim that breaks up globs of fat

emulsification droplets

Produced in the duodenum by breakup of dietary fat globules

micelles

little droplets in the bile

nucleases

in pancreatic juice, hydrolyze DNA and RNA into nucleotides

nucleosidases and phosphatases

in brush border, split them into further ions: phosphate, ribose and nitrogenous bases

vitamins

not digested and absorbed unchanged

Fat-solube vitamins

A,D,E,K and absorbed with other lipids

Water-soluble vitamins

B and C, absorbed by simple diffusion or intrinsic factor binding to b12

minerals

absorbed all along the small intestine

diarrhea

occurs when large intestine absorbs too little water and feces pass through too quickly if intestine is irritated

constipation

occurs when fecal movement is slow, too much water gets reabsorbed, and feces become hardened