a movement in which stationary ringlike constrictions appear at several places

A movement in which stationary ringlike constrictions

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a movement in which stationary ringlike constrictions appear at several places along the intestine and then relax as new constrictions form elsewhere Mixing/contact digestion When most nutrients have been absorbed and little remains but undigested residue, segmentation declines and peristalsis begins Peristalsis- The duodenum secretes a hormone called motilin that triggers a peristaltic wave beginning in the duodenum. The wave travels 10 to 70 cm and dies out only to be followed by another wave that begins a little farther down the tract than the first one Migrating motor complex- overlapping waves of contraction Movement through Small Intestine Carbohydrate Digestion - Pancreatic amylase digests starch into maltose and small oligosaccharides. Brush border enzymes (maltase, dextrinase, and glucoamylase) digest these to glucose, which is absorbed by the epithelial cells. Starch is digested first to oligosaccharides up to eight glucose residues long then into the disaccharide maltose finally to glucose, which is absorbed by the small intestine
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The Process Mouth- starts here Salivary amylase- breaks starch down into shorter segments (oligosaccharides) Stomach- the acid in the stomach Churning, mixing Small Intestine- 50% of the starch is digested before it gets here, Pancreatic Amylase Dextrinase and Glucoamylase Maltase, Sucrase, Lactase The end product of all of these is glucose, which is then absorbed Carbohydrate Absorption Glucose transported into absorptive cells Sodium-Dependent Glucose Transporter (SGLT) Secondary active transport coupled to sodium Galactose- monosaccharide sugar Uses SGLT as well Fructose Via facilitated diffusion using a separate carrier that doesn’t depend on Na + Inside the enterocyte fructose is converted into glucose All transported to liver by the hepatic portal system Protein Absorption Amino Acid absorption similar to monosaccharides Enterocytes have several sodium-dependent amino acid cotransporters for different classes of amino acids they leave the cell by facilitated diffusion, enter the blood capillaries of the villus, and are carried away in the hepatic portal circulation Dipeptides and tripeptides also absorbed they are hydrolyzed within the enterocytes before their amino acids are released to the bloodstream Lipid Digestion Small Intestine Emulsification droplets are promptly passed on to the duodenum and coated by certain components of the bile—lecithin and bile acids Lecithin and bile salts coat fat droplets Pancreatic Lipase- TRG into FFA and Monoglyceride when lipase acts on a triglyceride, it removes the first and third fatty acids from the glycerol backbone and usually leaves the middle one.
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