1. 23
P A R T A
The Digestive System

2. Digestive System: Overview
The alimentary canal or gastrointestinal (GI) tract digests and absorbs food
Alimentary canal – mouth, pharynx, esophagus, stomach, small intestine, and large intestine
Accessory digestive organs – teeth, tongue, gallbladder, salivary glands, liver, and pancreas

3. Figure 23.1

4. Figure 23.2

5. Gastrointestinal Tract Activities
1. Ingestion – taking food into the digestive tract
2. Propulsion – swallowing and peristalsis
Peristalsis – waves of contraction and relaxation of muscles in the organ walls
3. Mechanical digestion – chewing, mixing, and churning food

6. Gastrointestinal Tract Activities
4. Chemical digestion – catabolic breakdown of food
5. Absorption – movement of nutrients from the GI tract to the blood or lymph
6. Defecation – elimination of indigestible solid wastes

7. GI Tract
Regulation of digestion involves
Mechanical and chemical stimuli – stretch receptors, osmolarity (solute concentration) , pH of contents and presence of substrate in the lumen
Controls (Enteric Nervous System)
Extrinsic by CNS centers (ACh; nitric oxide)
Intrinsic by local centers- within the walls of the canal

8. Nervous Control of the GI Tract
Figure 23.4

9. Peritoneum and Peritoneal Cavity
Peritoneum – serous membrane of the abdominal cavity
Visceral – covers external surface of most digestive organs
Parietal – lines the body wall
Peritoneal cavity – fluid space between the two
Lubricates digestive organs
Allows them to slide across one another

10. Peritoneum and Peritoneal Cavity
Figure 23.5a

11. Peritoneum and Peritoneal Cavity
Mesentery – double layer of peritoneum that provides:
Vascular and nerve supplies to the viscera
Hold digestive organs in place and store fat
Retroperitoneal organs – organs outside the peritoneum (pancreas, parts of SI and LI)
Peritoneal organs (intraperitoneal) – organs surrounded by peritoneum (stomach)

12. Peritoneum and Peritoneal Cavity
Figure 23.5b

13. Blood Supply: Splanchnic Circulation
Arteries that branch from the abdominal aorta and the hepatic portal system
The hepatic, splenic, and left gastric branches of the celiac trunk: spleen, liver, and stomach

14. Blood Supply: Splanchnic Circulation
Hepatic portal circulation:
Collects venous blood from the digestive viscera and delivers to the liver for metabolic processing and storage

15. Histology of the Alimentary Canal
4 layers (tunics) of the AC
1.Mucosa
2. Submucosa
3. muscularis externa
4. serosa

16. Histology of the Alimentary Canal
Figure 23.6

17. Three major functions: Secretion of mucus
Mucosa
Three major functions:
Secretion of mucus
Absorption of end products of digestion
Protection against infectious disease

18. Mucosa: Other Sublayers
Submucosa –containing elastic fibers, blood and lymphatic vessels, lymph nodes, and nerves
Muscularis externa – responsible for segmentation and peristalsis
Serosa – the protective visceral peritoneum

19. Functional Anatomy of the
Digestive System

20. Mouth
Oral or buccal cavity:

21. Anatomy of the Oral Cavity: Mouth
Figure 23.7a

22. Have a core of skeletal muscles Lips: orbicularis oris
Lips and Cheeks
Have a core of skeletal muscles
Lips: orbicularis oris
Cheeks: buccinators
Vestibule
Oral cavity proper
Labial frenulum

23. Oral Cavity and Pharynx: Anterior View
Figure 23.7b

24. Palate
Hard palate
Soft palate

25. Tongue
Occupies the floor of the mouth and fills the oral cavity when mouth is closed

26. Superior surface bears three types of papillae
Tongue
Superior surface bears three types of papillae
Filiform
Fungiform
Circumvallate

27. Tongue
Figure 23.8

28. Moistens and dissolves food chemicals
Salivary Glands
Cleanses the mouth
Moistens and dissolves food chemicals
Aids in bolus formation
Contains enzymes that break down starch

29. Salivary Glands
Figure 23.9a

30. Saliva: Source and Composition
Secreted from serous and mucous cells of salivary glands
% water, hypo-osmotic, slightly acidic solution containing
Electrolytes – Na+, K+, Cl–, PO42–, HCO3–
Digestive enzyme – salivary amylase
Proteins – mucin, lysozyme, defensins, and IgA
Metabolic wastes – urea and uric acid

31. Primary and permanent dentitions have formed by age 21
Teeth
Primary and permanent dentitions have formed by age 21
Primary – 20 deciduous teeth that erupt at intervals between 6 and 24 months
Permanent – enlarge and develop causing the root of deciduous teeth to be resorbed and fall out between the ages of 6 and 12 years
All but the third molars have erupted by the end of adolescence
Usually 32 permanent teeth

32. Permanent Teeth
Figure

33. Dental Formula: Permanent Teeth
A shorthand way of indicating the number and relative position of teeth 2I 1C
2PM 3M X
2 (32 teeth)

34. Tooth Structure
Figure 23.11

35. Tooth and Gum Disease: Periodontitis
Gingivitis – as plaque accumulates, it calcifies and forms calculus, or tartar
Accumulation of calculus:
Disrupts the seal between the gingivae and the teeth
Puts the gums at risk for infection
Periodontitis – serious gum disease resulting from an immune response
Immune system attacks intruders as well as body tissues, carving pockets around the teeth and dissolving bone