A journey of nutrition p. 454-485 Part II Ch. 16 Digestive System A journey of nutrition p. 454-485 Part II

Getting & Using Food Ingest taking in food Digest mechanical digestion breaking up food into smaller pieces chemical digestion breaking down food into molecules small enough to be absorbed into cells enzymes Absorb absorb nutrients across cell membranes diffusion active transport Eliminate undigested material passes out of body intracellular digestion extracellular digestion

Human digestive system After chewing and swallowing, it takes 5 to 10 seconds for food to pass down the esophagus to the stomach, where it spends 2 to 6 hours being partially digested. Final digestion and nutrient absorption occur in the small intestine over a period of 5 to 6 hours. In 12 to 24 hours, any undigested material passes through the large intestine, and feces are expelled through the anus.

Stomach Lesser Curve, Greater Curve Fundus Three layers of muscle Rugae Cardiac Phyloric

Gastric Glands Gastric pits : openings for glands along the mucosal surface of stomach 5 groups: Surface Mucous cells Mucous Neck cells Parietal cells: HCl and Intrinsic Factor Endocrine cells: regulatory hormones Chief cells: pepsinogen Surface Mucous Cells: mucus coating to protect stomach Neck cells: produce mucus Parietal cells: HCl and intrinsic factor (absorbs vitamin B12 in small intestine) Chief cells: pepsinogen (protein digesting enzyme)

Gastric Glands Gastric pits : openings for glands along the mucosal surface of stomach 5 groups: Surface Mucous cells Mucous Neck cells Parietal cells: HCl and Intrinsic Factor Endocrine cells: regulatory hormones Chief cells: pepsinogen Surface Mucous Cells: mucus coating to protect stomach Neck cells: produce mucus Parietal cells: HCl and intrinsic factor (absorbs vitamin B12 in small intestine) Chief cells: pepsinogen (protein digesting enzyme)

Hypertrophic Pyloric Stenosis Defect of stomach Thickened pylorus Food cannot enter small intestine Results in projectile vomiting, reduces nutrient uptake, infant fails to gain weight Surgery to correct the problem Possible connection to an antibiotic used by mother? ethromycin

Gastric Bypass Roux-en-Y: most common Small stomach pouch by stapling stomach together or by vertical banding Y-shaped section of small intestine

Phases of Stomach Secretion Regulation Cephalic phase: sensation of taste, smell, process of chew/swallow stimulate medulla oblongata Gastric secretions: mucus, HCl, pepsinogen, intrinsic factor Gastric Phase: Presence of food in stomach Greatest amount of secretion Distention in stomach stimulates Intestinal Phase: controlled by chyme entering intestine Secretin: inhibits gastric secretions

Movement in stomach Every 20 seconds contractions occur in stomach wall Mixing waves: mix food with stomach secretions, more solid food moves to center while fluid food towards pyloric sphincter Peristaltic waves: push chyme toward and through pyloric sphincter

Part III: Liver, Pancreas, Intestines Digestive System Part III: Liver, Pancreas, Intestines

Small Intestine

Small intestine ~ 6 meters long 3 parts: DUODENUM -25 cm JEJUNUM-2.5 m ILEUM-3.5 m

Small intestine Major site of digestion and absorption of food Large surface area due to 3 modifications : Circular folds Villi . Microvilli . Mucosa and submucosa form circular folds Fingerlike projections of mucosa = villi Cytoplasmic extensions = microvilli Blood capillary network and lacteal (lymphatic) inside each villi = important for trasnport of nutrients

Small intestine Mucosa and submucosa form circular folds Fingerlike projections of mucosa = VILLI Cytoplasmic extensions = MICROVILLI Blood capillary network and LACTEALS(lymphatic) inside each villi = important for transport of nutrients Mucosa and submucosa form circular folds Fingerlike projections of mucosa = villi Cytoplasmic extensions = microvilli Blood capillary network and lacteal (lymphatic) inside each villi = important for trasnport of nutrients

Cells of small intestine Absorptive cells: have microvilli, produce enzymes, absorb digested nutrients Goblet cells: produce a protective mucus Endocrine cells: regulatory hormones Granular cells (Paneth’s cells): may help protect against bacteria

Secretions of small intestine Peptidases: enzyme to break down proteins Disaccharidases: enzyme to break down sugar Lactase: specific disaccharidase that breaks down the sugar in dairy (lactose). Most mammal species experience a sharp decrease in lactase production after infancy. Worldwide, 60% of adults are lactose intolerant In some Asian countries, 90% of adults have lactose intolerance; in Americans, 10% of adults; in Spain & France, 50% of adults. http://evolution.berkeley.edu/evolibrary/news/070401_lactose

Duodenum Common bile duct (from liver) and Pancreatic duct (from pancreas) empty into this section of the small intestine

Liver

Liver 2 major lobes 2 major sources of blood Hepatic artery: brings oxygen rich blood from heart to liver Hepatic portal vein: brings oxygen poor but nutrient rich blood to liver from digestive tract

Liver: Bile Bile: produced by hepatocytes Transported by hepatic ducts out of liver Secretes 700 mL bile daily Dilutes & neutralizes stomach acid Bile salts: emulsify lipid globules Gallbladder: Small sac Inferior surface of liver Stores & concentrates bile

Liver: Detoxification Alters structure of harmful substances Example: Ammonia : a byproduct of amino acid metabolism Alcohol: removed from blood at a rate of ½ oz pure alcohol per hour How your Body processes Alcohol: http://www.dummies.com/how-to/content/how-your-body-processes-alcohol.html https://cws.auburn.edu/studentaffairs/healthandwellness/resources/ad/alcohol/?YourBody

Disorders of Liver Cirrhosis Viral Hepatitis Damage to liver causes scarring Inflammation of liver by 7 distinct viruses Most common A: poor sanitation B: body fluids C: chronic disease and possible cancer

Pancreas

EnZymes Of the Pancreas HCO3 neutralizes acidic chyme from stomach Protein Digestive enzymes: Trypsin Chymotrypsin Carboxypeptidase Lipid digestive enzymes: Lipases