chapter 24 lecture 9 is chemical digestion small intestine the carbohydrates are broken down into monosaccharides for absorption these are those monomer subunits and intestinal enzymes break starts just into maltose they are going to break down Alpha dextrins into glucose maltose to glucose laughs sucrose to glucose and fructose and lactose to glucose and galactose of these the most important enzymes that you know are pancreatic amylase that breaks down starch into um maltose and Maltese that breaks down maltose into two glucose monomers sucrase breaks down glucose and fructose into monomers breaks down sucrose into glucose and fructose monomers and lactose lactase breaks down lactase so carbohydrate digestion starts in the mouth with salivary amylase there is no carbohydrate digestion in the esophagus and stomach in the duodenum pancreatic amylase is added to the mixture and then this breaks it down into maltose breaks down starch into maltose and then we have the brush border enzymes that are going to break maltose down as well as sucrose and lactose and this is going to produce our monosaccharides people that suffer from lactose intolerance don't have lactase and so it goes through their lactose goes through their system without being broken down it causes water to be drawn into the small intestine which increases the volume causes diarrhea and when the bacteria in the large intestine ferment the sugar it produces gas the um as I said the bacterial fermentation of the undigested lactose produces gases gases and the symptoms of lactose intolerance include diarrhea gas bloating and abdominal cramps uh there are different types of things you can do for lactose intolerance you can buy lactase which is um the you can replace the enzyme that's missing through supplementation or you can buy products in which it's already broken down all of the lactose free milks and and dairy products that are available have already been treated with lactase so that you can digest it if you're lactose intolerant proteins digestion starts in the stomach the hydrochloric acid is going to denature or unfold the proteins and then pepsin turns the proteins into smaller proteins called peptides the pancreas the pancreatic enzymes are going to be the real important ones in terms of breaking down proteins those as well as the brush border enzymes the pancreatic enzymes are going to work on specific peptide bonds between specific amino acids and the brush border enzymes we have an amino peptidase and we have a dipeptidase the amino peptidase uh starts at the amino side of the amino acid and just plucks off amino acids one by one carboxy peptidases those come from the pancreas and they do the exact same thing but on the other terminal side at the carboxyl side the dipeptidases split dipeptides into amino acids the digestion of lipids starts in the mouth with lingual lipase but most lipid digest in an adult happens in the small intestine first we have the globules of triglycerides emulsified by bile and then pancreatic lipase so splits those into fatty acids and monoglycerides they are packaged in these micelles they are absorbed into the absorptive cells and then they're going to be repackaged as triglycerides with protein code around them they'll be called chylomicrons nucleic acids have to be broken down into nucleotides in order to be absorbed and the pancreatic juice has two nucleases ribonuclease which digests RNA it's also called rnase deoxyribonuclease also called dnase that digests DNA the nucleotides then are further broken down by brush border enzymes into the component parts of a nucleotide there are two enzymes they're called nucleosidease and phosphatase and they break it down into pentose sugar a phosphate and a nitrogenous base these are absorbed by active transport remember that means you're going against the gradient so you need to use ATP or the gradient of another Amino of another ion to drive it through things that regulate secretion and motility in the lar in the small intestine include the enteric reflexes these are going to respond to the presence of chyme kind of like the stretch receptors in the stomach this will increase the motility of the the intestine and it'll start moving things out if if you already have substances in the small intestine it will move those into the large intestine the uh also VIP which is vasoactive intestinal polypeptide that stimulates the production of intestinal juice segmentation that process where it sloshes back and forth and combines it with intestinal juice depends upon distension of the small intestine and that's going to set impulses to the enteric plexus as well as the central nervous system when there's distension there's going to be more vigorous peristalsis if you have sympathetic impulses currently coming in that is going to slow down the motility and decrease secretions the absorption in the small intestine occurs through diffusion facilitated diffusion osmosis and active transport if we look at glucose and galactose they TR they travel across using secondary active transport with sodium remember secondary active transport is involves some Porters and um anti-porters importers they both go the same way any Porters they go in different directions so this would be a Sim Porter sodium a sodium is moved in so is glucose and so are glucose or galactose fructose goes through through facilitated diffusion that means it has to bind to a protein when the protein binds it it changes shape and moves it dumps it in to the interior of the cell this is regulated this is a type of diffusion so this will only go down its concentration gradient the amino acids use either active transport or they're directly transported across by hydrolysis of the terminal bond in ATP or secondary active transport again using a symporter with sodium dipeptides and tripeptides can be transported across and they will use sim Porters hydrogen ions importers to do that the short acid short chain fatty acids can simply diffuse across because they're hydrophobic the long chain fatty acids remember they are going to be broken down by the pancreatic lipase packaged in these structures called my cells and then they can diffuse across once they're inside the cell they're going to be reassembled into triglycerides protein coat we'll put we put around them and the new structure is now called the chylomicron this is the only one that's going to go into the lacteal everything else is going to go into the blood capillaries so monosaccharides once they're absorbed are going to use facilitated diffusion to go into the blood capillary amino acids directly diffuse as do the short Change fatty acids following absorption of the sugars the small chain fatty acids and amino acids they go into the blood and the blood goes into the hepatic portal vein which goes to the liver there the liver can make modifications detoxifications and so forth before the blood goes to the hepatic vein and then the inferior vena cava and back to the heart the triglycerides on the other hand enter into the lacteal the lacteal is going to fuse and form lymphatic vessels and they are going to travel up and dump into the bloodstream at the level of left subclavian vein the lipid rich fluid that you find in a lacteal is called Kyle c-h-y-l-e Kyle