Lecture 18 Flashcards
Villi?
Folds of mucosa/submucosa increase SA for absorption (microvilli increase SA further)
Secretion of intestinal juices?
Contains water/mucous/enzymes, secretion regulation by reflex when chyme present (CCK /secretin also stimulate juice secretion)
Digestion of carbohydrate?
Starch -> disaccharides (by pancreatic amylase)
Disaccharides (maltose, sucrose)-> monosaccharide (glucose, fructose) (by glycosidase)
Monosaccharide absorbed
Digestion of proteins?
Polypeptides from stomach catabolised (broken down) by pancreatic trypsin/chymotrypsin
Digestion completed by peptidases released from glandular epithelium
Peptidases = cleave peptides: carboxypeptidases act at carboxyl end, aminopeptidases act on amino end, dipeptidases convert dipeptides to amino acids
Digestion of fats?
Fat globules in duodenum coated in bile salts -> create emulsion + disperse large fat globules into smaller entities. Emulsion facilitates breakdown of triglycerides -> increases SA for water soluble pancreatic lipases to act upon + produce monoglycerides/free fatty acids
Breakdown products of small intestine?
Monosaccharides (from carbs)
Peptides and amino acids (from proteins)
Monoglyceride and free fatty acids (from fats)
Diffusion?
Random movement of molecules from higher to lower concentration. No energy input required.
Facilitated diffusion?
Use of a transporter protein to move molecules from higher to lower concentration. No energy required.
Active transport?
Use of a transporter protein that is coupled to ATP to move molecules against the electrochemical gradient.
Absorption of glucose/galactose?
Absorbed into epithelial cell by co-transport with Na+ via sodium-glucose transporters, leave epithelial cell and enter blood by facilitated diffusion via glucose transporters (GLUTs)
Absorption of fructose?
Absorbed into and leave cells by facilitated diffusion via GLUTs
Absorption of peptides?
Uptake into epithelial cell thought to be linked to H+ influx, broken down to constituent amino acids inside epithelial cell (only amino acids absorbed into blood, leave epithelial cell)
Absorption of amino acids?
Uptake into epithelial cells by Na+-dependent co-transport (active), leave epithelial cell by facilitated diffusion
Absorption of fats?
Monoglycerides/free fatty acids associate with bile salts to form micelles/emulsion, diffuse passively into epithelial cells
Lipids (triglycerides) accumulate in vesicles of smooth ER of epithelial cells to form chylomicrons (transport). These leave the cell by fusing with the plasma membrane.
Chylomicrons leave intestine in lymph since they are too large to enter the circulation immediately. They are eventually delivered into venous circulation
Lymphatic system?
Absorbs nutrients/electrolytes/fluids/protein from interstitial spaces (between cells, between organs)
Chylomicrons too large to enter capillaries but lacteals (lymphatic vessels of small intestine) have large pores.
