1. 23
The Digestive System

2. I. Overview of the Digestive System
A. Organs are divided into two groups
1. Alimentary canal
► mouth, pharynx, and esophagus
► stomach, small intestine, and large intestine, rectum
2. Accessory digestive organs
► teeth and tongue
► gallbladder, salivary glands, liver, and pancreas
i. connected to the alimentary canal by ducts
ii. secretions contribute to breakdown of foodstuffs

3. 3 Mouth (oral cavity) Parotid gland Sublingual gland Tongue
Salivary glands
Submandibular gland
Pharynx
Esophagus
Stomach
Pancreas
(Spleen)
Liver
Gallbladder
Transverse colon
Descending colon
Duodenum
Small intestine
Jejunum
Ascending colon
Ileum
Large intestine
Cecum
Sigmoid colon
Rectum
Appendix
Anus
Anal canal 3

4. II. Abdominal Regions
A. Four lines divide abdominal wall into nine regions
1. Midclavicular lines - vertical lines of grid
2. Subcostal plane - superior horizontal line
3. Transtubercular plane - inferior horizontal line
B. Four quadrants – cross with point in the umbilicus
1. Right upper quadrant
2. Left upper quadrant
3. Right lower quadrant
4. Left lower quadrant

5. Right hypochondriac region Left hypochondriac region Epigastric region
Right lumbar region
Left lumbar region
Umbilical region
Right iliac (inguinal) region
Hypogastric (pubic) region
Left iliac (inguinal) region
Nine regions delineated by four planes 5

6. Transverse colon of large intestine Ascending colon of large intestine
Liver
Diaphragm
Gallbladder
Stomach
Transverse colon of large intestine
Ascending colon of large intestine
Small intestine
Descending colon of large intestine
Cecum
Initial part of sigmoid colon
Appendix
Urinary bladder
Anterior view of the nine regions showing the superficial organs 6

7. III. The Peritoneal Cavity and Peritoneum
A. Imagine the digestive organs surrounded by plastic wrap
1. some of it touches the surface of the organ (“visceral”)
2. some of it touches the outer area of the organ (“parietal”)
3. like a hose that is surrounded by plastic wrapping
B. Peritoneum - a serous membrane around the digestive organs
1. visceral peritoneum - surrounds digestive organs on surface
2. parietal peritoneum – part that touches the outside
a. peritoneal cavity – space between these two layers

8. 8

9. 9

10. C. Mesentery - a double layer of peritoneum
1. holds organs in place
2. sites of fat storage
3. provides a route for circulatory vessels and nerves
4. it is the “sheet” that envelopes the intestines
D. Ventral mesenteries
1. Falciform ligament - binds anterior part of liver to anterior abdominal wall; between lobes of the liver
2. Lesser omentum - attaches liver to lesser curvature of stomach

11. E. Dorsal mesenteries
1. Greater omentum - connects greater curvature of stomach to posterior abdominal wall
a. a “fatty apron” flapped over the digestive organs
2. Transverse mesocolon - holds transverse colon in place
3. Sigmoid mesocolon - connects the sigmoid colon to posterior pelvic wall
F. Retroperitoneal organs - behind the peritoneum
G. Peritoneal organs - digestive organs that keep their mesentery

12. Liver Gallbladder Lesser omentum Stomach Duodenum Transverse colon
Small intestine
Cecum
Urinary bladder 12

13. Greater omentum Transverse colon Transverse mesocolon Descending colon
Mesentery
Sigmoid mesocolon
Jejunum
Sigmoid colon
Ileum 13

14. Gastrosplenic ligament
Ligamentum teres
Gallbladder
Lesser omentum
Spleen
Liver
Gastrosplenic ligament
Transverse mesocolon
Pancreas
Stomach, pyloric part
Duodenum, superior part
Transverse colon
Duodenum, horizontal part
Duodenojejunal flexure
Greater omentum
Descending colon
Ascending colon
Mesentery (cut)
Sigmoid mesocolon
Rectum
Ileum
Cecum 14

15. Falciform ligament Liver Gallbladder Spleen Stomach Ligamentum teres
Greater omentum
Small intestine
Cecum 15

16. IV. Histology of the Alimentary Canal Wall
A. Same four layers from esophagus to anus
1. mucosa—innermost layer
a. epithelium
b. lamina propria
c. muscularis mucosae
2. submucosa—external to the mucosa
a. contains blood and lymphatic vessels, nerve fibers

17. 3. muscularis externa - external to the submucosa
a. circular muscularis - inner layer
b. longitudinal muscularis - outer layer
4. serosa—the outermost layer – is the visceral peritoneum

18. Mucosa
Epithelium
Lamina propria
Muscularis mucosae
Submucosa
Muscularis externa
Circular layer
Longitudinal layer
Serosa
Epithelium
Connective tissue
Nerve
Lumen
Artery
Vein
Mesentery
Lymphatic vessel
Longitudinal and cross-sectional views through the small intestine 18

19. Mucosa
Submucosa
Muscularis externa
Serosa
Light micrograph cross section through the small intestine (85) 19

20. Longitudinal layer of smooth muscle (shows smooth muscle fibers in cross section, 215)
Small intestine
Mucosa
Location and plane of section shown in (b)
Cross section of the intestine showing the smooth muscle layers (one circular and the other longitudinal) running at right angles to each other
Circular layer of smooth muscle (shows longitudinal views of smooth muscle fibers, 215) 20

21. V. Nerve Plexuses A. Myenteric nerve plexus
1. lies between circular and longitudinal muscularis
2. controls peristalsis and segmentation
B. Submucosal nerve plexus
1. lies in submucosa
2. signals glands to secrete
C. Innervation - sympathetic and parasympathetic motor fibers

22. VI. The Mouth and Associated Organs
A. Borders of the mouth
► Lips anteriorly
► Cheeks laterally
► Palate superiorly
► Tongue inferiorly
► Fauces of oropharynx posteriorly
B. lips and cheeks - formed from orbicularis oris and buccinator
C. Mucosal layer - stratified squamous epithelium

23. Sagittal section of the oral cavity and pharynx
Soft palate
Uvula
Hard palate
Nasopharynx
Palatine tonsil
Tongue
Oropharynx
Lingual tonsil
Epiglottis
Hyoid bone
Laryngopharynx
Esophagus
Trachea
Sagittal section of the oral cavity and pharynx 23

24. Sagittal section of the oral cavity and pharynx
Uvula
Nasopharynx
Oropharynx
Laryngopharynx
Sagittal section of the oral cavity and pharynx 24

25. D. labial frenulum - connects lips to gum
E. palate - forms the roof of the mouth (hard and soft)
F. Boundaries of the fauces
► palatoglossal arches
► palatopharyngeal arches

26. Superior labial frenulum
Palatoglossal arch
Hard palate
Soft palate
Palatopharyngeal arch
Uvula
Lingual frenulum
Gingivae (gums)
Inferior labial frenulum
Anterior view 26

27. VII. The Tongue A. Interlacing fascicles of skeletal muscle
B. Grips food and repositions it
C. Helps form some consonants
D. Intrinsic muscles - within the tongue
E. Extrinsic muscles - external to the tongue
F. Lingual frenulum - secures tongue to floor of mouth
G. Papillae – different “bumps” on the tongue for taste, etc.

28. Medial sulcus of the tongue
Epiglottis
Terminal sulcus
Foliate papillae
Vallate papilla
Medial sulcus of the tongue
Dorsum of tongue
Fungiform papilla
Filiform papilla 28

29. VIII. The Teeth
A. Deciduous teeth – (20 teeth) - first appear at 6 months of age
B. Permanent teeth – (32 teeth) - by the end of adolescence
C. Types of teeth:
► Incisors (8)
► Canines (4)
► Premolars (8)
► Molars (12)

30. Incisors
Central (6–8 mo)
Lateral (8–10 mo)
Canine (eyetooth) (16–20 mo)
Molars
First molar (10–15 mo)
Deciduous (milk) teeth
Second molar (about 2 yr)
Incisors
Central (7 yr)
Lateral (8 yr)
Canine (eyetooth) (11 yr)
Premolars (bicuspids)
First premolar (11 yr)
Second premolar (12–13 yr)
Molars
First molar (6–7 yr)
Second molar (12–13 yr)
Third molar (wisdom tooth) (17–25 yr)
Permanent teeth 30

31. IX. Tooth Structure A. Crown - exposed surface B. Neck – at gum line
B. Root - in tooth socket
C. Enamel – outer layer
D. Dentin - underlies enamel
E. Pulp cavity - center of tooth
F. Periodontal ligament – attaches tooth to bone

32. Pulp cavity (contains blood vessels and nerves)
Enamel
Dentin
Crown
Pulp cavity (contains blood vessels and nerves)
Neck
Gingiva (gum)
Cement
Root canal
Root
Periodontal ligament 32

33. Pulp cavity (contains blood vessels and nerves)
Gingiva (gum)
Cement 33

34. X. The Salivary Glands B. Parotid glands – in the cheeks
A. Produce saliva
B. Parotid glands – in the cheeks
C. Submandibular glands - along medial surface of mandible
D. Sublingual glands - lie in floor of oral cavity

35. 35 Parotid gland Ducts of sublingual gland Parotid duct
Submandibular duct
Submandibular gland
Mucous cells
Serous cells forming demilunes 35

36. XI. The Esophagus A. A long muscular tube – moves food by peristalsis
B. Begins as a continuation of the pharynx
C. Joins the stomach inferior to the diaphragm
D. Cardiac sphincter—closes lumen to prevent stomach acid from entering esophagus
E. Statified squamous epithelium
F. Skeletal muscle ---- mixed skeletal/smooth ---- smooth muscle

37. Mucosa (stratified squamous epithelium)
Esophagus- stomach junction
Submucosa (areolar connective tissue)
Lumen
Muscularis externa
Simple columnar epithelium of stomach
Circular layer
Longitudinal layer
Adventitia (fibrous connective tissue)
Cross section through esophagus (3)
Esophagus-stomach junction, longitudinal section (85) 37

38. XII. The Stomach A. Site where food is churned into chyme
B. Regions of the stomach
► cardiac region
► fundus
► body
► pyloric region
C. Muscularis has three layers
1. circular and longitudinal and oblique layers
D. Epithelium is simple columnar epithelium

39. Cardiac Region Fundus Body Lumen Lesser curvature Rugae of mucosa
Muscularis externa
Longitudinal layer
Circular layer
Body
Oblique layer
Lesser curvature
Lumen
Rugae of mucosa
Greater curvature
Pyloric sphincter
Pyloric region 39

40. E. Mucosa dotted with gastric pits with gastric glands
F. Pyloric sphincter – valve that leads to small intestine
G. Rugae – folds along the inner surface
H. Greater and Lesser curvatures

41. Cardiac Region Fundus Body Lumen Lesser curvature Rugae of mucosa
Muscularis externa
Longitudinal layer
Circular layer
Body
Oblique layer
Lesser curvature
Lumen
Rugae of mucosa
Greater curvature
Pyloric sphincter
Pyloric region 41

42. Fundus
Liver (cut)
Body
Spleen
Lesser curvature
Greater curvature 42

43. Mucosa layer of stomach
A gastric ulcer lesion
Bacteria
Mucosa layer of stomach
H. pylori bacteria 43

44. XIII. The Small Intestine
A. Longest portion of the alimentary canal
B. Site of most enzymatic digestion and absorption
C. Three subdivisions
► duodenum (1 foot)
► jejunum (next 8 feet)
► ileum (last 12 feet)
D. Innervation
1. parasympathetic fibers from vagus nerve
2. sympathetic from thoracic splanchnic nerves

45. E. Duodenum
1. receives digestive enzymes and bile
2. Main pancreatic duct and common bile duct enter duodenum
3. Sphincters control entry of bile and pancreatic juices

46. 46 Right and left hepatic ducts of liver Common hepatic duct
Cystic duct
Bile duct and sphincter
Accessory pancreatic duct
Pancreas
Gallbladder
Main pancreatic duct and sphincter
Hepatopancreatic ampulla and sphincter
Duodenum 46

47. F. Modifications for absorption
1. circular folds - transverse ridges of mucosa and submucosa
2. Villi - fingerlike projections of the mucosa
a. covered with simple columnar epithelium
3. microvilli - further increase surface area for absorption
4. lacteals – special lymphatic vessels of the intestine

48. Villi Microvilli 48 Lumen Circular folds Absorptive enterocytes
Goblet cells
Lacteal
Villi
Vilus
Intestinal crypt 48

49. XIV. The Large Intestine
A. Small amount of digestion by bacteria
B. Main functions - Absorb water and electrolytes
C. Mass peristaltic movements force feces toward the rectum
D. Subdivided into: cecum, appendix, colon, rectum, anal canal
E. Special features of large intestine
1. teniae coli - thickening of longitudinal muscularis layer
2. haustra - puckering created by teniae coli
3. epiploic appendages - fat-filled pouches of visceral peritoneum

50. External anal sphincter
Epiploic appendages
Transverse colon
Descending colon
Haustrum
Ascending colon
Teniae coli
Sigmoid colon
Appendix
Rectum
Anal canal
External anal sphincter 50

51. External anal sphincter51

52. F. Cecum - beginning of large intestine
G. Appendix - contains lymphoid tissue; neutralizes pathogens
H. Colon - Divided into distinct segments
► ascending colon
► transverse colon
► descending colon
► sigmoid colon
I. Rectum - descends along the inferior half of the sacrum
J. Anal canal - the last subdivision of the large intestine
1. lined with stratified squamous epithelium

53. Left colic (splenic) flexure
Right colic (hepatic) flexure
Epiploic appendages
Transverse colon
Superior mesenteric artery
Descending colon
Haustrum
Ascending colon
Ileocecal valve
Teniae coli
Sigmoid colon
Cecum
Appendix
Rectum
Anal canal
External anal sphincter 53

54. 54

55. K. Vessels of the Large Intestine
1. superior mesenteric artery – first half
2. inferior mesenteric artery- second half
3. NOTE: hepatic portal vein to the liver
L. Vagus Nerve (X) – supplies parasympathetic innervation
M. Microscopic Anatomy
1. villi are absent
2. contains numerous goblet cells that secrete mucus
3. intestinal crypts - simple tubular glands
4. lined with simple columnar epithelial tissue

56. Goblet cells
Intestinal crypt
Muscularis mucosae 56

57. 57

58. 58

59. XV. The Liver
A. Largest gland in the body - performs over 500 functions
B. Production of bile to digest fats
C. Stores and distributes nutrients for the body
D. Four lobes: right, left, caudate, quadrate
E. Falciform ligament - divides right and left lobes
F. Ligamentum teres (round ligament) – at the base

60. G. Hepatic PORTAL vein – from intestines to the liver
H. Hepatic vein – from liver to inferior vena cava
G. Common hepatic duct – from liver to gall bladder
H. Cystic duct – from gall bladder to common bile duct

61. Round ligament (ligamentum teres) Gallbladder
Sternum
Nipple
Liver
Falciform ligament
Right lobe of liver
Left lobe of liver
Round ligament (ligamentum teres)
Gallbladder 61

62. Caudate lobe of liver Left lobe of liver Quadrate lobe of liver
Right lobe of liver
Gallbladder
Ligamentum teres 62

63. !!! NOTE !!! Hepatic portal vein Hepatic veins Caudate lobe Left lobe
Cystic duct
Common hepatic duct
Gallbladder
Fissure
Right lobe
Falciform ligament
Quadrate lobe
Ligamentum teres 63

64. 64

65. I. Microscopic Anatomy of the Liver
1. hepatocyte—functional cells of the liver
2. lobule – hexagonal component of the liver
3. portal triad composed of
► bile duct tributary
► branch of hepatic portal vein
► branch of hepatic artery
4. hepatic macrophages - destroy bacteria

66. A Lobule 66 Lobule Central vein Connective tissue septum
Interlobular veins (to hepatic vein)
Central vein
Sinusoids
Bile canaliculi
A Lobule
Plates of hepatocytes
Bile duct (receives bile from bile canaliculi)
Fenestrated lining (endothelial cells) of sinusoids
Bile duct
Portal venule
Portal triad
Stellate macrophages in sinusoid walls
Portal arteriole
Portal vein 66

67. XVI. The Gallbladder A. Stores and concentrates bile
B. Expels bile into duodenum - bile emulsifies fats

68. XVII. The Pancreas A. Has both exocrine and endocrine functions
1. Endocrine function - produces insulin and glucagon
2. Exocrine function – produces most digestive enzymes
a. delivered to duodenum via pancreatic duct
B. Head of the pancreas – circled by the duodenum
C. Tail of the pancreas – short extension

69. 69 Right and left hepatic ducts of liver Common hepatic duct
Cystic duct
Bile duct and sphincter
Accessory pancreatic duct
Tail of pancreas
Pancreas
Gallbladder
Main pancreatic duct and sphincter
Hepatopancreatic ampulla and sphincter
Duodenum
Head of pancreas 69