1. The Digestive System
Chapter 23

2. The Digestive System Structures of the Digestive Tract:
Alimentary canal - The continuous tube from mouth to anus whose organs perform various digestive functions
Accessory structures - the additional organs and glands that play a role in digestion
Figure 23.1

3. The Digestive System Functions of the Digestive System:
Ingestion - taking food into the alimentary canal at the mouth
Propulsion - the movement of food through the alimentary canal
Peristalsis – waves of muscle contraction that propel food
Mechanical digestion - physical breakdown of food into smaller pieces
Segmentation – contractions of the alimentary canal that mixes food
Chemical digestion - food molecules are broken down via enzymes
Absorption - transport of digested materials from lumen through an epithelium into the blood or lymph
Defecation – removal of indigestible materials through the anus
Figure 23.2

4. The Peritoneum
The Peritoneum - the serous membrane lining the abdominal/pelvic body cavity
Visceral layer - lines the surfaces of the organs in the cavity
Parietal layer – lines the inside of the body wall
Peritoneal cavity - serous fluid-filled space between the visceral and parietal layers
Figure 23.5

5. The Peritoneum
Mesentery - a double layer of serous membrane that suspends organs in the abdominal body cavity
Intraperitoneal – refers to organs that hang into the peritoneal cavity, suspended from mesenteries
Retroperitoneal – refers to structures behind parietal peritoneum
Figure 23.5

6. The Alimentary Canal Layers of the Alimentary Canal:
Mucosa - Innermost layer composed of epithelium, specialized for secretion and absorption
Submucosa - Connective tissue with glands, blood vessels, lymphatics, and nerves
Muscularis - Layers of smooth muscle
Circular layer – inner layer controlling lumen size
Longitudinal layer – outer layer controlling canal length
Serosa – serous membrane, also called the visceral peritoneum
Figure 23.6

7. The Oral Cavity
Oral cavity - start of the alimentary canal where ingestion occurs. Begins mechanical digestion via chewing (mastication) and chemical digestion via enzymes
Teeth - bony structures used in mastication
Tongue – skeletal muscle used to manipulate food and form a bolus
Palate – roof of the oral cavity, hard and soft regions
Uvula – extension of the soft palate, blocks the nasopharynx during swallowing
Figure 23.7a

8. Salivary Glands
Salivary glands – paired glands that secrete saliva into the oral cavity to moisten food and cleanse the mouth
Saliva – secretion containing salivary amylase which begins chemical digestion of starches. Also contains IgA antibodies and lysozymes to clear potential pathogens
Figure 23.9

9. The Pharynx
Pharynx - Begins propulsion, transporting food from the oral cavity to the esophagus, performing the act of deglutition (swallowing)
Only the oropharynx and laryngopharynx transport food
Figure 23.7a

10. The Esophagus
Esophagus - Transports food from the pharynx to the stomach
Esophageal Hiatus – Opening in the diaphragm, allowing passage of esophagus from thorax to abdomen
Figure 23.12

11. The Esophagus
Deglutition – when swallowing, the elevation of the larynx and uvula block the respiratory passages ensuring flood enters the esophagus
Figure 23.13a

12. The Esophagus
Gastroesophageal sphincter (cardiac sphincter) - circular muscle allowing passage into stomach and prevents regurgitation
Heartburn – burning when acidic gastric juices regurgitate into the esophagus
Figure 23.13d, e

13. The Stomach
Stomach – stores food, performing mechanical digestion via churning and chemical digestion via enzymes
Chyme – the acidic, paste-like substance passed to the small intestine after about 4 hours
Regions: The cardia is nearest to the esophagus, the fundus is the superior dome, the body is the central region, and the pylorus is nearest the small intestine
Figure 23.14

14. The Stomach
Curvatures: the lateral surface of the stomach is the convex greater curvature, while the medial surface is the concave lesser curvature
Rugae – large folds of the mucosa allowing expansion
Muscle layers – only organ in the alimentary canal with 3 layers, outer longitudinal, middle circular, and inner oblique
Pyloric sphincter – circular muscle regulating chyme movement into the small intestine
Figure 23.14

15. The Omenta
Omenta – the 2 mesenteries that attach to the surfaces of the stomach
Lesser omentum – mesentery from liver to the lesser curvature of the stomach
Greater omentum – largest mesentery draping from the greater curvature of the stomach
Figure 23.30d

16. The Stomach
Gastric pits/glands – invaginations of the stomach mucosa containing cells that produce the gastric juices
Chief cells – secrete pepsinogen that quickly becomes pepsin, a protein enzyme that works best in acidic pH
Parietal cells – secrete hydrochloric acid (HCl), to produce acidic environment
Mucous neck cells – produce mucus that with the mucous of goblet cells protects the mucosa
Enteroendocrine cells – secrete local hormones to regulate stomach activity
Figure 23.15

17. The Stomach Gastic Juice Secretion:
Cephalic phase – smell or thought of food begins limited gastric secretions
Gastric phase – stretch and chemicals in stomach trigger largest secretions
Intestinal phase – a balance of excitatory and inhibitory actions
Excitatory – movement of chyme into intestine triggers continued secretion
Figure 23.16

18. The Stomach Gastic Juice Secretion:
3. Intestinal phase – a balance of excitatory and inhibitory actions
Excitatory – movement of chyme into intestine triggers continued gastric secretion
Inhibitory – stretch of duodenum inhibits gastric secretion and motility (prevents overload of duodenum)
Figure 23.16

19. The Small Intestine
Small intestine – coiled digestive organ transporting food from stomach to large intestine. Completes digestion and performs all nutrient absorption. Receives secretions form liver, gall bladder, and pancreas.
Regions – divided into duodenum, jejunum, and ileum
Length: 6-7 meters (about 20 ft) in a living person (add 10ft in a cadaver)
Diameter: cm
Figure 23.1

20. The Small Intestine
Hepatopancreatic sphincter (of Oddi) – regulates the entrance of secretions from the liver, gall bladder and pancreas into the duodenum
Figure 23.20

21. The Small Intestine Specializations for absorption:
Circular folds – large folds of the mucosa and submucosa that help slow food movement
Figure 23.21a

22. The Small Intestine Specializations for absorption:
Villi– finger-like projections of the mucosa that increase surface area of the epithelium. Each villus contains a capillary bed and a lacteal for nutrient absorption.
Intestinal crypts – invaginations producing intestinal juices, a mucous secretion
Figure 23.21b

23. The Small Intestine Specializations for absorption:
Microvilli – finger-like extensions of the epithelial cell membranes with attached “brush border enzymes,” further increasing surface area
Figure 23.21b, c

24. The Liver
Liver – a 4-lobed gland whose digestive function is the production of bile
Hepatitis – inflammation of the liver, usually resulting from viral infection
Cirrhosis – chronic inflammation usually associated with alcohol abuse
Bile – a green, alkaline fluid containing bilirubin pigment and bile salts that perform emulsification of fats. Drains from the liver via the hepatic ducts
Figure 23.23a

25. The Liver
Emulsification – the physical breakdown of large fat globules into smaller fat droplets, thus increasing surface area for enzymatic digestion
bile salts are partially polar and partially nonpolar, thereby breaking up fat globules like a detergent
Figure 23.35

26. The Gall Bladder
Gall bladder - muscular sac on the posterior surface of the liver that stores and concentrates bile. The gall bladder is drained by the cystic duct
Gall stones - crystallization of bile that accumulate in the gall bladder, may be passed naturally or removed via ultrasound, drugs, or surgery
Figure 23.23b

27. The Pancreas
The Pancreas – gland whose acinar cells produces pancreatic juices containing digestive enzymes such as proteases, lipases, nucleases, and amylases.
Figure 23.26

28. The Pancreas
Pancreatic duct - drains pancreatic juices into the duodenum through the sphincter of Oddi
Accessory duct – alternate pathway that drains directly
Figure 23.20

29. Intestinal Hormones
Intestinal hormones - chemicals released by enteroendocrine cells when chyme enters the duodenum
Cholecystokinin (CCK) - triggers secretions of bile from the gall bladder and relaxation of hepatopancreatic sphincter
Secretin – triggers liver to increase bile production
Figure 23.25

30. Intestinal Hormones
Cholecystokinin (CCK) - triggers release of pancreatic juices rich in enzymes
Secretin – triggers release of pancreatic juices rich in bicarbonate
Figure 23.28

31. The Large Intestine
Large Intestine (Colon) - transports food from the small intestine to the anus while absorbing water and forming feces
Ileocecal valve – regulates movement of food from the small to the large intestine
Haustra – individual pouches of the large intestine wall
Teniae coli – thin longitudinal muscle layer forming the haustra
Figure 23.29a

32. The Large Intestine Regions:
Cecum - pouch-like region with the hanging vermiform appendix
Ascending colon – transports food up the right side of the abdomen, turning at the hepatic flexure
Transverse colon – transports food across the abdomen, turning at the splenic flexure
Descending colon – transports food down the left side of the abdomen
Sigmoid colon – s-shaped region
Figure 23.29a

33. The Rectum and Anus
Rectum – most distal region of the colon, where feces is stored until defecation
Rectal valves – projections that allow gases to pass around feces
Anus – end of the alimentary canal from which defecation occurs
Internal anal sphincter – smooth muscle regulating anal opening
External anal sphincter – skeletal muscle regulating anal opening
Figure 23.29b

34. The Defecation Reflex
Defecation reflex – series of impulses that trigger release of feces
Sensory fibers sense stretch of rectum wall due to filling
Parasympathetic fibers trigger contraction of rectum wall and relaxation of internal anal sphincter
External anal sphincter can allow defecation, or voluntarily contract to temporarily stop the reflex
Figure 23.32

35. Chemical Digestion Overview
Figure 23.33a

36. Chemical Digestion Overview
Figure 23.33b