Digestive System Part 3 PDF

Digestive System – Part 3 Accessory Digestive Organs Not part of the alimentary canal, but secrete into or perform accessory digestive functions Salivary glands Salivary Glands Pancreas Liver Liver...

Digestive System – Part 3 Accessory Digestive Organs Not part of the alimentary canal, but secrete into or perform accessory digestive functions Salivary glands Salivary Glands Pancreas Liver Liver Gallbladder Gallbladder Pancreas Pancreas Location and Secretions Lies behind the stomach, retroperitoneal Bile duct Exocrine function: Acinar cells secrete pancreatic juice into the duodenum a) Digestive enzymes: Duo- Pancreatic amylase (for carbs) denum Pancreatic lipase (for lipids) Pancreatic ducts Protein digesting enzymes are inactive to prevent damage to the pancreas Trypsinogen → Trypsin Chymotrypsinogen → Chymotrypsin Procarboxypeptidase → Carboxypeptidase b) Alkaline fluid (NaHCO3) secreted to neutralize acidic chyme from the stomach Histology of the Pancreas Pancreatic acini – Bile duct clusters of exocrine from liver Stomach cells producing the Duodenum Hormones pancreatic juices (insulin, glucagon) Pancreatic islet – Blood endocrine cells producing hormones insulin & glucagon Endocrine portion Duct cells Acinar cells of pancreas (islets of Langerhans) Exocrine portion To pancreatic duct of pancreas NaHCO3– and duodenum Duct cells (secrete aqueous NaHCO3– solution) Enzymes Acinar cells (secrete digestive enzymes)  Acid in Fat and protein duodenal products in lumen duodenal lumen Secretin CCK (Secretin carried (CCK carried Neutralizes by blood) Digests by blood) Pancreatic duct Pancreatic acinar cells cells Secretion of Secretion of aqueous pancreatic digestive NaHCO3 solution into enzymes into duodenal lumen duodenal lumen a) Control of pancreatic aqueous (b) Control of pancreatic digestive NaHCO3– secretion enzyme secretion Liver Large organ (~3 lbs), enclosed in rib cage Inferior to the diaphragm Over 200 functions! a) Digestive functions: produces bile for fat digestion detoxifies and processes blood from the digestive system nutrient storage (blood sugar regulation) b) Other main function: plasma protein production (e.g. albumin) When bile is not actively being secreted, it is stored in the gallbladder Liver Blood Flow - Summary Blood coming from Digestive System  Diagrammatic view of lobular organization of liver. Sinusoid Bile Branch of Portal area Triads: hepatic portal duct hepatic portal vein (triads) vein, hepatic artery proper, and bile duct Blood from hepatic portal veins and hepatic arteries empty into sinusoids Sinusoids supply hepatocytes hepatocytes produce bile (and much more)  Central Sinusoid vein Kupffer cells Hepatocytes (macrophages) Bile canaliculi Bile duct Branch of Branch of hepatic hepatic portal vein artery proper Bile Salts & Fat Digestion Bile salts are a component of bile necessary for fat digestion, they do NOT contain any enzymes Emulsification: bile salts physically separate large fat globules into small fat droplets suspended in aqueous solution Increases surface area for lipases to chemically breakdown fats Large fat droplet Lipid emulsion Micelles & Chylomicrons Micelles are water-soluble transport vesicles formed by bile salts (and lecithin) Micelles surround lipid-soluble substances to help them stay in solution and get absorbed: triglycerides fatty acids fat-soluble vitamins Cholesterol Chylomicrons are large particles of fat- soluble substances made from micelle contents that move from the small intestinal epithelium to the lacteals of the Lymphatic system  The Bile Duct System Left hepatic duct Right hepatic duct Cystic duct Common hepatic duct Gallbladder Common bile duct Liver Duodenum Stomach Pancreas  Duodenal (hepatopancreatic) ampulla Duodenal ampulla enters lumen of duodenum empties bile from the liver digestive enzymes from the pancreas Pancreatic Common duct bile duct Duodenal ampulla Pancreas Intestinal lumen A sectional view through a portion of the duodenal wall Role of CCK The liver secretes bile continuously —roughly 1 liter As it remains in the per day. gallbladder, bile becomes more concentrated. Liver Duodenum CCK The release of CCK by the In the lumen of the duodenum triggers dilation of the digestive tract, bile hepatopancreatic sphincter and salts break the lipid Lipid droplet contraction of the gallbladder. This droplets apart by ejects bile into the duodenum emulsification. through the duodenal ampulla. Regions of Large Intestine Cecum – first sac-like part TRANSVERSE Appendix – hangs from the COLON cecum (lymphatic organ) Ascending colon – travels up the right side Transverse colon –travels across the cavity ASCENDING DESCENDING COLON COLON Descending colon -travels down the left side Cecum Sigmoid – s-shaped portion, travels posteriorly into the SIGMOID pelvis Appendix Rectum COLON Rectum – anterior to the sacrum and coccyx Haustra & Taenia coli Taenia coli – incomplete longitudinal muscularis externa forms three thin bands Bands of taniae coli are shorter than the underlying circular layer of smooth muscle colon Haustra bunches up into sac like pouches: Haustra Taenia coli Haustral contractions: ring-like contractions at a rate of 1 every 30 minutes Mass movements are contractions of large segments of the colon at a rate of 3-4 per day, driving defecation Triggered by gastrocolic reflex (food enters stomach) to make room for incoming food Large Intestine: “Good” Bacteria Bacteria accumulate in the large intestine because the motility is slow enough 500 – 1000 species of bacteria estimated in colon, some beneficial functions: Prevent pathogenic bacterial growth Breakdown dietary fiber (produces gas) Promote motility Maintain mucosa Synthesize Vitamin K (for blood clotting and bone health)  Digestive Dietary Input Secretions Food and drink Saliva 2000 mL 1500 mL Gastric secretions 1500 mL 5000 mL Liver (bile) 1000 mL Pancreas (pancreatic juice) 1000 mL Water Reabsorption 9000 Intestinal secretions Small intestine mL 2000 mL reabsorbs 7800 mL 1200 mL Colonic mucous secretions Colon reabsorbs 200 mL Final water 1250 mL 1400 mL absorption in large intestines 150 mL lost in feces Anal Canal Anal canal – last 3 cm of the rectum, opens to the exterior Rectum Internal involuntary sphincter: smooth muscle External voluntary sphincter: skeletal muscle Anal canal Internal anal sphincter External anal sphincter Anus Anatomy of the rectum and anus Large Intestine: Defecation Defecation reflex: rectum wall stretched, internal anal sphincter relaxed Voluntary control of external anal sphincter to release contents  Digestion - Summary The Processing and Absorption of Nutrients Breaks down physical structure of food Disassembles component molecules (e.g. protein – amino acids) Molecules released into bloodstream Absorbed by cells Broken down to provide energy for ATP synthesis Used to synthesize carbohydrates, proteins, and lipids  CARBOHYDRATES REGION and Hormonal Controls ORAL CAVITY Salivary amylase salivary glands ESO PHAG US STOMACH Stimu lus: Ant icipation or arriva l of f ood Horm one: Ga strin Source : G cells of stoma ch Dis accharides Trisac cha rides Proenz ym e rel eased: Pepsinogen by chie f c ells, act iva ted to pe psin by HCl Stimu lus: Arrival of chyme in duodenum Pancreatic SMALL INTESTINE Horm one: CCK Proenz ym es rel eased: Chy motry psinogen, procar- box ype ptidase, proelasta se, alpha-amylase trypsinogen. Enteropeptidase Dis accharides Trisac cha rides act iva tes tryps in, w hich act iva tes ot her enzym es Enzymes rel eased: Pancreatic am yla se, pancreatic lipase, nuc lea se, enteropeptidase Lactas e Maltase, Sucrase Brush border FACILITATED Lactase, maltase, sucrase DIFFUS IO N AND COTRANSPORT INTESTINAL Monosacc haride s MUCOSA Cell body FACILITATED DIFFUS IO N ROUTE TO BLO ODSTREAM Carbohydrates and amino acids are absorbed and transported by intestinal capillaries. Lipids form chylomicrons that diffuse into lacteals and are delivered to the left Monosaccharides subclavian vein by the thoracic duct.  LIPIDS REGION and Hormon al Co ntrols ORAL CAVITY tongue ESO PHAG US STOMACH Stimu lus: Ant icipation or arriva l of f ood Horm one: Ga strin Source : G cells of stoma ch Proenz ym e rel eased: Pepsinogen by chie f c ells, act iva ted to pe psin by HCl Stimu lus: Arrival of chyme in duodenum Pancreatic SMALL INTESTINE Horm one: CCK Proenz ym es rel eased: Chy motry psinogen, procar- Monoglyc erides, lipase and bile salts box ype ptidase, proelasta se, Fatty acids in trypsinogen. Enteropeptidase micelles act iva tes tryps in, w hich act iva tes ot her enzym es Enzymes rel eased: Pancreatic am yla se, pancreatic lipase, nuc lea se, enteropeptidase DIFFUS IO N Brush border Monoglyc erides, Fatty acids INTESTINAL MUCOSA Cell body Trigly cerides Chy lomicrons EXO CY TO SIS ROUTE TO BLO ODSTREAM Lacteal Carbohydrates and amino acids are absorbed and transported by intestinal capillaries. Lipids form chylomicrons that diffuse into lacteals and are delivered to the left Monoglycerides and subclavian vein by the thoracic duct. fatty acids  PROTEINS REGION and Hormonal Controls ORAL CAV ITY ESO PHAG US STOMACH Stimu lus: Ant icipation or Pepsin arriva l of f ood Horm one: Ga strin Source : G cells of stoma ch Polype ptides Proenz ym e rel eased: Pepsinogen by chie f c ells, act iva ted to pe psin by HCl Trypsin Stimu lus: Arrival of chyme SMALL INTESTINE in duodenum Horm one: CCK Chymotrypsin Pancreas Proenz ym es rel eased: Carboxypeptidase Chy motry psinogen, procar- box ype ptidase, proelasta se, Short peptides, Elastase trypsinogen. Enteropeptidase Amino acids act iva tes tryps in, w hich act iva tes ot her enzym es Enzymes rel eased: Pancreatic am yla se, pancreatic lipase, nuc lea se, enteropeptidase Brush border Dipeptidase FACILITATED DIFFUS IO N AND COTRANSPORT INTESTINAL MUCOSA Cell body Amino acids FACILITATED DIFFUS IO N AND COTRANSPORT ROUTE TO BLO ODSTREAM Carbohydrates and amino acids are absorbed and transported by intestinal capillaries. Lipids form chylomicrons that diffuse into lacteals and are delivered to the left Amino acids subclavian vein by the thoracic duct.