1. Structure and Function of the Digestive System
Chapter 38

2. Gastrointestinal Tract
Mouth
Esophagus
Stomach
Small intestine
Large intestine
Rectum
Anus

3. Gastrointestinal Tract

4. Gastrointestinal Tract
Ingestion of food
Propulsion of food and wastes from the mouth to the anus
Secretion of mucus, water, and enzymes
Mechanical digestion of food particles
Chemical digestion of food particles
Absorption of digested food
Elimination of waste products by defecation

5. Gastrointestinal Tract
Histology
Mucosa
Submucosa
Muscularis
Serosa or adventitia
Enteric plexus
Submucosal plexus
Myenteric plexus
Subserosal plexus

6. Gastrointestinal Tract

7. Mouth Reservoir for chewing and mixing of food with saliva Taste buds
Salty, sour, bitter, and sweet
Olfactory nerves
Teeth
32 permanent teeth

8. Salivary Glands Three pairs Saliva Submandibular Sublingual Parotid
Water with mucus, sodium, bicarbonate, chloride, potassium, and salivary α-amylase (carbohydrate digestion)
Controlled by sympathetic and parasympathetic fibers

9. Swallowing Esophagus Peristalsis Upper esophageal sphincter
Primary and secondary
Upper esophageal sphincter
Lower esophageal sphincter
Phases
Oral and pharyngeal phases
Esophageal phase

10. Stomach
The stomach is a hollow, muscular organ that stores food, secretes digestive juices, mixes food with the juices, and propels partially digested food (chyme)
Muscle layers
Longitudinal
Circular
Oblique

11. Stomach Boundaries Functional areas Cardiac orifice Pyloric sphincter
Pylorus
Functional areas
Fundus
Body
Antrum

12. Stomach

13. Gastric Motility Swallowing Gastrin Cholecystokinin Motilin Secretin
Gastric emptying

14. Gastric Secretion The stomach secretes large volumes of gastric juices
Mucus
Acid
Enzymes
Hormones
Intrinsic factor
Gastroferrin

15. Gastric Secretion Gastric pits Gastric glands Parietal cells
Hydrochloric acid and intrinsic factor
Chief cells
Pepsinogen
G cells
Gastrin

16. Gastric Secretion Gastric glands Enterochromaffin-like cells D cells
Histamine
D cells
Somatostatin

17. Gastric Pits and Gastric Glands

18. Gastric Secretion Phases of gastric secretion Cephalic phase
Gastric phase
Intestinal phase

19. Small Intestine 5 to 6 meters long Three segments Peritoneum Duodenum
Jejunum
Ileum
Ileocecal valve
Peritoneum
Peritoneal cavity

20. Small Intestine Muscle layers Mucosal folds (plica) Villi Microvilli
Outer—longitudinal
Inner—circular
Mucosal folds (plica)
Villi
Microvilli
Brush border
Lamina propria
Lacteal

21. Small Intestine

22. Intestinal Digestion and Absorption
Hydrochloric acid
Pepsin
Pancreatic enzymes
Intestinal enzymes
Bile salts

23. Intestinal Digestion and Absorption
Carbohydrates
Proteins
Fats
Water
Electrolytes

24. Intestinal Digestion and Absorption

25. Intestinal Digestion and Absorption

26. Intestinal Digestion and Absorption

27. Intestinal Motility
The movements of the small intestine facilitate both digestion and absorption
Segmentation
Peristalsis
Ileogastric reflex
Intestinointestinal reflex
Gastroileal reflex

28. Large Intestine Cecum Appendix Colon Rectum Anus Ascending Transverse
Descending
Sigmoid
Rectum
Anus

29. Large Intestine

30. Large Intestine Ileocecal valve O’Beirne sphincter
Internal anal sphincter
External anal sphincter
Taenia coli
Haustra

31. Gastrointestinal Absorption

32. Intestinal Bacteria
The environment of the stomach is relatively sterile because of secreted stomach acid
Bile acid secretion, motility, and antibody production keeps bacterial numbers in the duodenum to a minimum
There is a low concentration of aerobes in the jejunum
Anaerobic bacteria are distal to the ileocecal valve
Anaerobes are 95% of the fecal flora in the colon

33. Accessory Organs of Digestion

34. Accessory Organs of Digestion
Liver
Lobes
Separated and attached to the anterior abdominal wall by the falciform ligament
Right lobe
Caudate and quadrate lobes
Left lobe
Glisson capsule

35. Liver

36. Hepatic Portal Circulation

37. Liver Liver lobules Hepatocytes Lipocytes Sinusoids Bile canaliculi
Common bile duct
Major duodenal papilla (sphincter of Oddi)

38. Liver Lobules

39. Liver
Kupffer cells
Stellate cells
Pit cells
Disse space

40. Secretion of Bile
Bile is an alkaline, bitter-tasting, yellowish green fluid that contains bile salts, cholesterol, bilirubin, electrolytes, and water
Bile is formed by hepatocytes and secreted into the bile canaliculi
Enterohepatic circulation
Recycling of bile salts

41. Enterohepatic Circulation

42. Metabolism of Bilirubin
Bilirubin is a by-product of the destruction of aged red blood cells
Bilirubin gives bile a greenish black color and produces the yellow tinge of jaundice
Unconjugated bilirubin
Conjugated bilirubin
Urobilinogen

43. Metabolism of Bilirubin

44. Vascular and Hematologic Liver Functions
Blood storage
Bacterial and foreign particle removal
Synthesizes clotting factors
Produces bile to absorb fat-soluble vitamins
Metabolizes fats

45. Vascular and Hematologic Liver Functions
Metabolizes proteins
Metabolizes carbohydrates
Metabolic detoxification
Storage of minerals and vitamins

46. Gallbladder
The gallbladder is a saclike organ that lies on the inferior surface of the liver
The function of the gallbladder is to store and concentrate bile between meals
The gallbladder holds about 90 mL of bile

47. Exocrine Pancreas
The exocrine pancreas is composed of acini and networks of ducts that secrete enzymes and alkaline fluids to assist in digestion
Pancreatic duct
Ampulla of Vater

48. Exocrine Pancreas

49. Exocrine Pancreas Secretions Enzymes
Potassium, sodium, bicarbonate, magnesium, calcium, and chloride
Enzymes
Trypsinogen, chymotrypsinogen, and procarboxypeptidase
Trypsin inhibitor
Pancreatic α-amylase
Pancreatic lipase

50. Aging and the Digestive Function
Tooth enamel and dentin wear down
Teeth are lost
Periodontal disease
Gum recession
Osteoporotic bone changes

51. Aging and the Digestive Function
Number of taste buds decline
Sense of smell diminishes
Salivary secretion decreases
Decreased esophageal and gastric motility