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 Digest Absorb Eliminate 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 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