Chapter 23C Digestive System Slides by Barbara Heard and W. Rose. HESC310 4/15/2017 Chapter 23C Digestive System Slides by Barbara Heard and W. Rose. figures from Marieb & Hoehn 9th ed. Portions copyright Pearson Education Axial Skeleton

Digestive System Introduction/Overview Functional Anatomy HESC310 4/15/2017 Digestive System Introduction/Overview Functional Anatomy Physiology of Digestion & Absorption Chemical Digestion Absorption Axial Skeleton

Digestion Digestion Enzymes Hydrolysis Catabolic; macromolecules  monomers small enough for absorption Enzymes Intrinsic and accessory gland enzymes break down food Hydrolysis Water is added to break bonds © 2013 Pearson Education, Inc.

Digestion of Carbohydrates Only monosaccharides can be absorbed Monosaccharides absorbed as ingested Glucose, fructose, galactose Digestive enzymes Salivary amylase, pancreatic amylase, and brush border enzymes (dextrinase, glucoamylase, lactase, maltase, and sucrase) Break down disaccharides sucrose, lactose, maltose; polysaccharides glycogen and starch © 2013 Pearson Education, Inc.

Digestion of Carbohydrates Starch digestion Salivary amylase (saliva)  oligosaccharides at pH 6.75 – 7.00 Pancreatic amylase (small intestine)  breaks down any that escaped salivary amylase  oligosaccharides Brush border enzymes (dextrinase, glucoamylase, lactase, maltase, sucrase)  oligosaccharides  monosaccharides © 2013 Pearson Education, Inc.

Starch and disaccharides Figure 23.32 Flowchart of digestion and absorption of foodstuffs. (1 of 4) Foodstuff Enzyme(s) and source Site of action Path of absorption Starch and disaccharides Glucose and galactose are absorbed via cotransport with sodium ions. Fructose passes via facilitated diffusion. All monosaccharides leave the epithelial cells via facilitated diffusion, enter the capillary blood in the villi, and are transported to the liver via the hepatic portal vein. Salivary amylase Mouth Pancreatic amylase Small intestine Oligosaccharides and disaccharides Carbohydrate digestion Brush border enzymes in small intestine (dextrinase, gluco- amylase, lactase, maltase, and sucrase) Small intestine Lactose Maltose Sucrose Galactose Glucose Fructose © 2013 Pearson Education, Inc.

Digestion of Proteins Source is dietary, digestive enzymes, mucosal cells; digested to amino acid monomers Begins with pepsin in stomach at pH 1.5 – 2.5 Inactive in high pH of duodenum Pancreatic proteases Trypsin, chymotrypsin, and carboxypeptidase Brush border enzymes Aminopeptidases, carboxypeptidases, and dipeptidases © 2013 Pearson Education, Inc.

Amino acids of protein fragments Figure 23.33 Protein digestion and absorption in the small intestine. Slide 1 Lumen of intestine Amino acids of protein fragments Brush border enzymes Pancreatic proteases Apical membrane (microvilli) Na+ Proteins and protein fragments are digested to amino acids by pancreatic proteases (trypsin, chymotrypsin, and carboxy- peptidase), and by brush border enzymes (carboxypeptidase, aminopeptidase, and dipeptidase) of mucosal cells. 1 Absorptive epithelial cell Na+ The amino acids are then absorbed by active transport into the absorptive cells, and move to their opposite side. 2 Amino acid carrier The amino acids leave the villus epithelial cell by facilitated diffusion and enter the capillary via intercellular clefts. 3 Capillary © 2013 Pearson Education, Inc.

Amino acids of protein fragments Figure 23.33 Protein digestion and absorption in the small intestine. Slide 2 Lumen of intestine Amino acids of protein fragments Brush border enzymes Pancreatic proteases Apical membrane (microvilli) Na+ Proteins and protein fragments are digested to amino acids by pancreatic proteases (trypsin, chymotrypsin, and carboxy- peptidase), and by brush border enzymes (carboxypeptidase, aminopeptidase, and dipeptidase) of mucosal cells. 1 Absorptive epithelial cell Na+ Capillary © 2013 Pearson Education, Inc. 9

Amino acids of protein fragments Figure 23.33 Protein digestion and absorption in the small intestine. Slide 3 Lumen of intestine Amino acids of protein fragments Brush border enzymes Pancreatic proteases Apical membrane (microvilli) Na+ Proteins and protein fragments are digested to amino acids by pancreatic proteases (trypsin, chymotrypsin, and carboxy- peptidase), and by brush border enzymes (carboxypeptidase, aminopeptidase, and dipeptidase) of mucosal cells. 1 Absorptive epithelial cell Na+ The amino acids are then absorbed by active transport into the absorptive cells, and move to their opposite side. 2 Amino acid carrier Capillary © 2013 Pearson Education, Inc. 10

Amino acids of protein fragments Figure 23.33 Protein digestion and absorption in the small intestine. Slide 4 Lumen of intestine Amino acids of protein fragments Brush border enzymes Pancreatic proteases Apical membrane (microvilli) Na+ Proteins and protein fragments are digested to amino acids by pancreatic proteases (trypsin, chymotrypsin, and carboxy- peptidase), and by brush border enzymes (carboxypeptidase, aminopeptidase, and dipeptidase) of mucosal cells. 1 Absorptive epithelial cell Na+ The amino acids are then absorbed by active transport into the absorptive cells, and move to their opposite side. 2 Amino acid carrier The amino acids leave the villus epithelial cell by facilitated diffusion and enter the capillary via intercellular clefts. 3 Capillary © 2013 Pearson Education, Inc. 11

Figure 23. 32 Flowchart of digestion and absorption of foodstuffs Figure 23.32 Flowchart of digestion and absorption of foodstuffs. (2 of 4) Foodstuff Enzyme(s) and source Site of action Path of absorption Proteins Amino acids are absorbed via cotransport with sodium ions. Some dipeptides and tripeptides are absorbed via cotransport with H+ and hydrolyzed to amino acids within the cells. Infrequently, transcytosis of small peptides occurs. Amino acids leave the epithelial cells by facilitated diffusion, enter the capillary blood in the villi, and are transported to the liver via the hepatic portal vein. Pepsin (stomach glands) in presence of HCl Stomach Large polypeptides Pancreatic enzymes (trypsin, chymotrypsin, carboxypeptidase) Small intestine Protein digestion Small polypeptides, small peptides Brush border enzymes (aminopeptidase, carboxypeptidase, and dipeptidase) Small intestine Amino acids (some dipeptides and tripeptides) © 2013 Pearson Education, Inc.

Pre-treatment—emulsification by bile salts Enzymes—pancreatic lipases Digestion of Lipids Pre-treatment—emulsification by bile salts Does not break bonds Enzymes—pancreatic lipases  Fatty acids and monoglycerides © 2013 Pearson Education, Inc.

with bile salts to form micelles which Figure 23.34 Emulsification, digestion, and absorption of fats. Slide 1 Fat globule Bile salts in the duodenum emulsify large fat globules (physically break them up into smaller fat droplets). 1 Bile salts Digestion of fat by the pancreatic enzyme lipase yields free fatty acids and monoglycerides. These then associate with bile salts to form micelles which “ferry” them to the intestinal mucosa. 2 Fat droplets coated with bile salts Micelles made up of fatty acids, monoglycerides, and bile salts Fatty acids and monoglycerides leave micelles and diffuse into epithelial cells. There they are recombined and packaged with other fatty substances and proteins to form chylomicrons. 3 Chylomicrons are extruded from the epithelial cells by exocytosis. The chylomicrons enter lacteals and are carried away from the intestine in lymph. 4 Epithelial cells of small intestine Lacteal © 2013 Pearson Education, Inc.

Figure 23.34 Emulsification, digestion, and absorption of fats. Slide 1 Fat globule Bile salts in the duodenum emulsify large fat globules (physically break them up into smaller fat droplets). 1 Bile salts Fat droplets coated with bile salts © 2013 Pearson Education, Inc. 15

with bile salts to form micelles which Figure 23.34 Emulsification, digestion, and absorption of fats. Slide 3 Fat globule Bile salts in the duodenum emulsify large fat globules (physically break them up into smaller fat droplets). 1 Bile salts Digestion of fat by the pancreatic enzyme lipase yields free fatty acids and monoglycerides. These then associate with bile salts to form micelles which “ferry” them to the intestinal mucosa. 2 Fat droplets coated with bile salts Micelles made up of fatty acids, monoglycerides, and bile salts © 2013 Pearson Education, Inc. 16

with bile salts to form micelles which Figure 23.34 Emulsification, digestion, and absorption of fats. Slide 4 Fat globule Bile salts in the duodenum emulsify large fat globules (physically break them up into smaller fat droplets). 1 Bile salts Digestion of fat by the pancreatic enzyme lipase yields free fatty acids and monoglycerides. These then associate with bile salts to form micelles which “ferry” them to the intestinal mucosa. 2 Fat droplets coated with bile salts Micelles made up of fatty acids, monoglycerides, and bile salts 3 Fatty acids and monoglycerides leave micelles and diffuse into epithelial cells. There they are recombined and packaged with other fatty substances and proteins to form chylomicrons. Epithelial cells of small intestine Lacteal © 2013 Pearson Education, Inc. 17

with bile salts to form micelles which Figure 23.34 Emulsification, digestion, and absorption of fats. Slide 5 Fat globule Bile salts in the duodenum emulsify large fat globules (physically break them up into smaller fat droplets). 1 Bile salts Digestion of fat by the pancreatic enzyme lipase yields free fatty acids and monoglycerides. These then associate with bile salts to form micelles which “ferry” them to the intestinal mucosa. 2 Fat droplets coated with bile salts Micelles made up of fatty acids, monoglycerides, and bile salts 3 Fatty acids and monoglycerides leave micelles and diffuse into epithelial cells. There they are recombined and packaged with other fatty substances and proteins to form chylomicrons. Chylomicrons are extruded from the epithelial cells by exocytosis. The chylomicrons enter lacteals and are carried away from the intestine in lymph. 4 Epithelial cells of small intestine Lacteal © 2013 Pearson Education, Inc. 18

Figure 23. 32 Flowchart of digestion and absorption of foodstuffs Figure 23.32 Flowchart of digestion and absorption of foodstuffs. (3 of 4) Foodstuff Enzyme(s) and source Site of action Path of absorption Unemulsified triglycerides Fatty acids and monoglycerides enter the intestinal cells via diffusion. Fatty acids and monoglycerides are recombined to form triglycerides and then combined with other lipids and proteins within the cells. The resulting chylomicrons are extruded by exocytosis. The chylomicrons enter the lacteals of the villi and are transported to the systemic circulation via the lymph in the thoracic duct. Some short-chain fatty acids are absorbed, move into the capillary blood in the villi by diffusion, and are transported to the liver via the hepatic portal vein. Lingual lipase Mouth Gastric lipase Stomach Emulsification by the detergent action of bile salts ducted in from the liver Small intestine Fat digestion Pancreatic lipases Small intestine Monoglycerides (or diglycerides with gastric lipase) and fatty acids © 2013 Pearson Education, Inc.

Digestion of Nucleic Acids Enzymes Pancreatic ribonuclease and deoxyribonuclease  nucleotide monomers Brush border enzyme nucleosidases and phosphatases  free bases, pentose sugars, phosphate ions © 2013 Pearson Education, Inc.

Figure 23. 32 Flowchart of digestion and absorption of foodstuffs Figure 23.32 Flowchart of digestion and absorption of foodstuffs. (4 of 4) Foodstuff Enzyme(s) and source Site of action Path of absorption Nucleic acids Units enter intestinal cells by active transport via membrane carriers. Units are absorbed into capillary blood in the villi and transported to the liver via the hepatic portal vein. Pancreatic ribo- nuclease and deoxyribonuclease Small intestine Nucleic acid digestion Brush border enzymes (nucleosidases and phosphatases) Small intestine Pentose sugars, N-containing bases, phosphate ions © 2013 Pearson Education, Inc.

~ All food; 80% electrolytes; most water absorbed in small intestine Absorption ~ All food; 80% electrolytes; most water absorbed in small intestine Most prior to ileum Ileum reclaims bile salts Most absorbed by active transport  blood Exception - lipids © 2013 Pearson Education, Inc.

Absorption of Carbohydrates Glucose and galactose Secondary active transport (cotransport) with Na+  epithelial cells Move out of epithelial cells by facilitated diffusion  capillary beds in villi Fructose Facilitated diffusion to enter and exit cells © 2013 Pearson Education, Inc.

Absorption of Carbohydrates Glucose and galactose Secondary active transport (cotransport) with Na+  epithelial cells Move out of epithelial cells by facilitated diffusion  capillary beds in villi Fructose Facilitated diffusion to enter and exit cells © 2013 Pearson Education, Inc. 24

Amino acids transported by several types of carriers Absorption of Protein Amino acids transported by several types of carriers Most coupled to active transport of Na+ Dipeptides and tripeptides actively absorbed by H+-dependent cotransport; digested to amino acids within epithelial cells Enter capillary blood by diffusion © 2013 Pearson Education, Inc.

Homeostatic Imbalance Whole proteins not usually absorbed Can be taken up by endocytosis/exocytosis Most common in newborns  food allergies Usually disappear with mucosa maturation Allows IgA antibodies in breast milk to reach infant's bloodstream  passive immunity © 2013 Pearson Education, Inc.

Absorption of Lipids Absorption of monoglycerides and fatty acids Cluster with bile salts and lecithin to form micelles Released by micelles to diffuse into epithelial cells Combined with lecithin, phospholipids, cholesterol, & coated with proteins to form chylomicrons Enter lacteals; transported to systemic circulation Hydrolyzed to free fatty acids and glycerol by lipoprotein lipase of capillary endothelium Cells can use for energy or stored fat Absorption of short chain fatty acids Diffuse into portal blood for distribution © 2013 Pearson Education, Inc.

Absorption of Nucleic Acids Active transport across epithelium  bloodstream © 2013 Pearson Education, Inc.

Absorption of Vitamins In small intestine Fat-soluble vitamins (A, D, E, and K) carried by micelles; diffuse into absorptive cells Water-soluble vitamins (vitamin C and B vitamins) absorbed by diffusion or by passive or active transporters. Vitamin B12 (large, charged molecule) binds with intrinsic factor, and is absorbed by endocytosis © 2013 Pearson Education, Inc.

Absorption of Vitamins In large intestine Vitamin K and B vitamins from bacterial metabolism are absorbed © 2013 Pearson Education, Inc.

Absorption of Electrolytes Most ions actively along length of small intestine Iron and calcium are absorbed in duodenum Na+ coupled with active absorption of glucose and amino acids Cl– transported actively K+ diffuses in response to osmotic gradients; lost if poor water absorption Usually amount in intestine is amount absorbed © 2013 Pearson Education, Inc.

Absorption of Electrolytes Iron and calcium absorption related to need Ionic iron stored in mucosal cells with ferritin When needed, transported in blood by transferrin Ca2+ absorption regulated by vitamin D and parathyroid hormone (PTH) © 2013 Pearson Education, Inc.

9 L water, most from GI tract secretions, enter small intestine Absorption of Water 9 L water, most from GI tract secretions, enter small intestine 95% absorbed in the small intestine by osmosis Most of rest absorbed in large intestine Net osmosis occurs if concentration gradient established by active transport of solutes Water uptake coupled with solute uptake © 2013 Pearson Education, Inc.

Malabsorption of Nutrients Causes Anything that interferes with delivery of bile or pancreatic juice Damaged intestinal mucosa (e.g., bacterial infection; some antibiotics) © 2013 Pearson Education, Inc.

Malabsorption of Nutrients Gluten-sensitive enteropathy (celiac disease) Immune reaction to gluten Gluten causes immune cell damage to intestinal villi and brush border Treated by eliminating gluten from diet (all grains but rice and corn) © 2013 Pearson Education, Inc.

Developmental Aspects Oral membrane  mouth opening Cloacal membrane  anus By week 5 alimentary canal continuous tube from mouth to anus Shortly after, accessory organs bud from mucosa © 2013 Pearson Education, Inc.

Figure 23.36 Embryonic development of the digestive system. Lung bud Stomodeum Brain Foregut Oral membrane Liver Stomach Heart Site of liver development Bile duct Yolk sac Midgut Spinal cord Gall- bladder Dorsal pancreatic bud Cloacal membrane Hindgut Cystic duct Duodenum Body stalk Ventral pancreatic bud Proctodeum Endoderm © 2013 Pearson Education, Inc.

Homeostatic Imbalance Cleft palate and cleft lip Tracheoesophageal fistula Opening between esophagus and trachea Cystic fibrosis Genetic disease  thick mucus  can block pancreatic duct © 2013 Pearson Education, Inc.

Developmental Aspects Fetal nutrition via placenta, but GI tract stimulated to mature by amniotic fluid swallowed in utero Newborn's rooting reflex helps infant find nipple; sucking reflex aids in swallowing Newborns double birth weight in six months; adult diet by 2 years Cholecystitis, ulcers – problems of middle age © 2013 Pearson Education, Inc.

Developmental Aspects During old age GI tract activity declines, less digestive juice, absorption less efficient, peristalsis slows  less frequent bowel movements Taste/smell less acute; periodontal disease often develops Diverticulosis, fecal incontinence, and cancer of GI tract fairly common © 2013 Pearson Education, Inc.

Stomach and colon cancers rarely have early signs or symptoms Metastasized colon cancers frequently cause secondary liver cancer Prevention Regular dental and medical examination © 2013 Pearson Education, Inc.