1. Chapter 26 *Lecture Outline
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2. Chapter 26 Outline
General Structure and Functions of the Digestive System
Oral Cavity
Pharynx
General Arrangement of Abdominal GI Organs
Esophagus
The Swallowing Process
Stomach
Small Intestine
Large Intestine
Accessory Digestive Organs
Aging and the Digestive System
Development of the Digestive System

3. Introduction The digestive system includes organs that:
ingest the food
transport the ingested material
digest the material into smaller usable components
absorb the necessary digested nutrients into the bloodstream
expel waste products from the body

4. Introduction
The digestive system is composed of two separate categories of organs:
Digestive organs
collectively make up the gastrointestinal (GI) tract, also called the digestive tract or the alimentary canal
Accessory digestive organs

5. Digestive System
Figure 26.1

6. GI Tract Organs The GI tract organs are as follows: oral cavity
pharynx
esophagus
stomach
small intestine
large intestine

7. Accessory Digestive Organs
The accessory digestive organs are not part of the long GI tube, but often develop as outgrowths of that tube. They are as follows:
……….. teeth
……….. tongue
……….. salivary glands
………. liver
……….. gall bladder
……….. pancreas

8. Digestive System Functions
Ingestion
Digestion
Propulsion
Secretion
Absorption
Elimination of wastes

9. Peristalsis and Segmentation
Propulsion of food along the GI tube involves two types of movement:
peristalsis
segmentation
Peristalsis is the ripple-like wave of muscular contraction that forces material to move further along the GI tract.
Segmentation is the churning and mixing of material helping to disperse the material and mix it and combine it with digestive organ secretions.

10. Peristalsis and Segmentation
Figure 26.2

11. Oral Cavity Contains the following structural features:
cheeks, lips, and palate
tongue
salivary glands
teeth

12. Cheeks, Lips, and Palate
Cheeks form the lateral wall of the oral cavity and are comprised mainly of the buccinator muscles.
The cheeks end anteriorly as the lips.
The gingivae (gums) cover the alveolar processes of the teeth.
The internal surface of the upper and lower lips are attached to the gingivae by a thin, midline mucosa fold called the labial frenulum.

13. Cheeks, Lips, and Palate The palate forms the roof of the oral cavity.
The anterior two-thirds of the palate is called the hard palate because it is comprised of bone. The posterior one-third of the palate is soft and muscular and is called the soft palate.
Extending from the soft palate posteriorly is the uvula, which elevates during swallowing and closes off the posterior entrance to the nasopharynx.

14. Cheeks, Lips, and Palate
Figure 26.3

15. Cheeks, Lips, and Palate
The fauces represent the opening from the oral cavity to the oropharynx.
The fauces are bounded laterally by paired muscular folds:
palatoglossal arch
palatopharyngeal arch
The palatine tonsils (see Chapter 24) are housed between the two arches.

16. Tongue
The tongue manipulates and mixes ingested materials during chewing and helps compress the partially digested materials into a bolus.
A bolus is a globular mass of ingested materials that can be more easily swallowed.
The inferior surface of the tongue attaches to the floor of the oral cavity by a thin, midline mucous membrane called the lingual frenulum.

17. Tongue
Figure 26.3

18. Salivary Glands
Salivary glands produce and secrete saliva into the oral cavity.
Saliva serves the following functions:
moistens ingested materials to become a slick bolus
moistens, cleanses, and lubricates the structures of the oral cavity
chemical digestion of ingested materials
antibacterial action
dissolves materials so that taste receptors on the tongue can be stimulated

19. Salivary Glands
Three pairs of salivary glands are located external to the oral cavity:
parotid glands
submandibular glands
sublingual glands

20. Salivary Glands
Figure 26.4

21. Parotid Salivary Glands
Largest of the three salivary glands
Located anterior and inferior to the ear. Lateral side of face, under ears
Secrete 25–30% of total saliva
Parotid duct runs parallel to the zygomatic arch and pierces the buccinator muscle just opposite the second upper molar
Also secrete amylase

22. Parotid Salivary Glands
Figure 26.4

23. Submandibular Salivary Glands
Reside inferior/lateral to the body of the mandible
Produce the majority of the saliva (60–70%)
A submandibular duct transports saliva from each gland through a papilla in the floor of the mouth on the lateral sides of the lingual frenulum

24. Submandibular Salivary Glands

25. Sublingual Salivary Glands
Inferior/anterior to the tongue
Each gland extends multiple tiny sublingual ducts that open onto the inferior surface of the oral cavity just posterior to the submandibular duct papilla
Contribute only 3–5% of total saliva

26. Sublingual Salivary Glands
Figure 26.4

27. Salivary Gland Secretion
Two types of secretory cells are found in salivary glands:
Mucous cells—secrete mucin, which forms mucus upon hydration
Serous cells—secrete a watery fluid
containing ions, lysozyme, and salivary amylase

28. Salivary Gland Secretion
Figure 26.4

29. Salivary Gland Secretion

30. Teeth The teeth are collectively known as the dentition.
A tooth has an exposed crown, a constricted neck, and one or more roots that fit into dental alveoli.
Dentin forms the primary mass of the tooth. It is harder than bone.
Each root is covered with cementum.
The external surface of the dentin is covered with a layer of enamel that forms the crown of the tooth.

31. Teeth
The center of the tooth is a pulp cavity that contains connective tissue called pulp.
A root canal opens into the connective tissue through an opening called the apical foramen. Blood vessels and nerves pass through this opening and are housed in the pulp.

32. Teeth
Figure 26.5

33. Surfaces of the Teeth Teeth have several surfaces: mesial surface
distal surface
buccal surface
labial surface
lingual surface
occlusal surface

34. Teeth Two sets of teeth develop and erupt in a normal lifetime:
deciduous teeth—erupt between 6–30 months, 20 in number, and are often
called milk teeth
permanent teeth—replace the
deciduous teeth and are 32 in
number

35. a: © The McGraw-Hill Companies, Inc./Photo by Christine Eckel
Teeth
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Central incisor (7–9 mos)
Lateral incisor (9–11 mos.)
Canine (18–20 mos.)
1st molar (14–16 mos.)
Upper
teeth
Permanent teeth
2nd molar (24–30 mos.)
2nd molar (20–22 mos.)
Lower
teeth
Deciduous teeth
1st molar (12–14 mos.)
Canine (16–18 mos.)
Lateral incisor (7–9 mos.)
(a) Child’s skull
Central incisor (6–8 mos.)
(b) Deciduous teeth
Right Upper (Maxillary) Quadrant
Left Upper (Maxillary) Quadrant
Central incisor (7–8 yrs.)
Lateral incisor (8–9 yrs.)
Canine (11–12 yrs.)
1st premolar (10–11 yrs.)
2nd premolar (10–12 yrs.)
Upper teeth 7 8 9
1st molar (6–7 yrs.) 1 6 11 5 12
2nd molar (12–13 yrs.) 4 13 3
3rd molar (17–25 yrs.) 14
Hard palate 2 15 1 16 32 17
3rd molar (17–25 yrs.) 31 18 30 19
2nd molar (11–13 yrs.) 29 20 28 21
1st molar (6–7 yrs.)
Lower teeth 27 22 26 25 24 23
2nd premolar (11–12 yrs.)
1st premolar (10–12 yrs.)
Canine (9–10 yrs.)
(d) Teeth numbering
Lateral incisor (7–8 yrs.)
Figure 26.6
Central incisor (6–7 yrs.)
Right Lower (Mandibular) Quadrant
Left Lower (Mandibular) Quadrant
(c) Permanent teeth
a: © The McGraw-Hill Companies, Inc./Photo by Christine Eckel

36. Permanent Teeth
Incisors—most anteriorly placed, shaped like chisels, and have a single root
Canines—posterolateral to the incisors, pointed tips for puncturing and tearing
Premolars—posterolateral to canines, have flat crowns with prominent ridges called cusps for crushing and grinding
Molars—thickest and most posterior teeth, also adapted for crushing and grinding of ingested materials

37. Oral Cavity Structures

38. Pharynx Shared by the respiratory and digestive systems
Three skeletal muscle pairs of pharyngeal constrictors (superior, middle, and inferior) form the wall of the pharynx and participate in swallowing
CN X innervates most pharyngeal muscles
Branches of external carotid arteries supply the pharynx
Internal jugular veins drain the pharynx

39. Peritoneum
Abdominopelvic cavity is covered with moist serous membranes:
parietal peritoneum—lines the inside
surface of the body wall
visceral peritoneum—covers the surface
of internal organs within the cavity

40. Peritoneum
Organs that are completely surrounded by visceral peritoneum are called intraperitoneal organs. They include the stomach and most of the small intestines.
Organs that lie in direct contact with the posterior abdominal and pelvic walls and are only covered on their anterolateral surfaces with visceral peritoneum are called retroperitoneal organs. Examples are the pancreas, ascending and descending colon of the large intestines, and the rectum.

41. Peritoneum
Figure 26.7

42. Mesenteries
Folds of peritoneum that support and stabilize intraperitoneal GI tract organs
Blood vessels, lymphatic vessels, and nerves are sandwiched between the two folds and supply the digestive organs

43. Mesenteries
Figure 26.7

44. Mesenteries
The greater omentum extends inferiorly like an apron from the greater curvature of the stomach and covers most of the abdominal organs.
The lesser omentum connects the lesser curvature of the stomach and the proximal end of the duodenum to the liver.
The mesentery proper suspends most of the small intestines from the posterior abdominal wall.
The mesocolon is a peritoneal fold that attaches parts of the large intestine to the posterior abdominal wall.

45. Mesenteries
Figure 26.8

46. Mesenteries
Figure 26.8

47. The Wall of the Abdominal GI Tract
The wall of the GI tract from the esophagus to the large intestine is composed of four concentric layers called tunics. From deep (in contact with ingested materials) to superficial (the external covering) they are:
mucosa
submucosa
muscularis
adventitia or serosa