1. Overview of the Digestive System
Digestive Tract:
Mouth, pharynx, and esophagus, stomach, small intestine, and large intestine (colon)
Accessory Organs:
Teeth, tongue, salivary glands, pancreas, liver, and gallbladder

2. Functions of the Digestive System
Ingestion
Mechanical processing
Chemical digestion
Secretion
Absorption
Excretion

3. Histology of the Digestive Tract
Mucosa
Submucosa
Muscularis Externa
Serosa

4. Mucosa (Innermost Layer)
Epithelium
Connective Tissue (Blood vessels, lymphatic vessels, lymphatic nodules)
Smooth Muscle

5. Submucosa
Connective tissue
Blood vessels
Lymphatic vessels
Nerve plexus
May have glands and lymphatic tissue

6. Muscularis Externa Smooth or Skeletal Muscle
If smooth muscle, usually 2 layers (circular and longitudinal)

7. Adventitia or Serosa Adventitia (organs superior to diaphragm)
Serosa = visceral peritoneum

8. Small Intestine: Peyer’s Patches

9. Components of the Digestive System
GI Tract:
Oral Cavity
Pharynx
Esophagus
Stomach
Small Intestine
Large Intestine

10. Oral Cavity

11. Oral Cavity

12. The Pharynx
Nasopharynx
Oropharynx
Laryngopharynx

13. The Esophagus

14. The Esophagus Stratified squamous epithelium Mucous glands
Muscularis externa – skeletal muscle first third of length

15. Peristalsis in Esophagus
LE 21-8
Muscles contract
Muscles
contract,
constricting
passageway
and pushing
bolus down
Muscles relax
Bolus of
food
Muscles relax,
allowing
passageway
to open
Muscles contract
Muscles
relax
Stomach

16. Stomach
Site where food is churned into chyme
Protein digestion begins

17. Stomach

18. Stomach

19. Stomach – Microscopic Anatomy

20. Stomach – Microscopic Anatomy

21. The Stomach – Microscopic Anatomy

22. Ulcers in stomach
Helicobacter pylori

23. Small Intestine – Gross Anatomy
Longest portion of the alimentary canal
Site of most enzymatic digestion and absorption
Three subdivisions
Duodenum, jejunum, and ileum

24. Duodenum and Related Organs
LE 21-11a
Duodenum and Related Organs
Liver
Bile
Gall-
bladder
Stomach
Bile
Pancreas
Acid chyme
Intestinal enzymes
Pancreatic
juice
Duodenum of
small intestine

25. Duodenum and Related Organs

26. Enzymes in Small Intestine

27. Small Intestine – Microscopic Anatomy

28. Amino acids and sugars Fatty acids and glycerol
LE 21-11b
Lumen of intestine
Nutrient
absorption
Vein
with blood
en route to
the liver
Nutrient absorption
into epithelial cells
Microvilli
Epithelial
cells
Amino
acids
and
sugars
Fatty
acids
and
glycerol
Muscle
layers
Lumen
Fats
Blood
capillaries
Large
circular folds
Villi
Blood
Lymph
vessel
Nutrient
absorption
Lymph
Epithelial cells
Villi
Intestinal wall

29. Small Intestine: Duodenum
Br = Brunner glands
V = Villus
G = Goblet cells
Cr = Intestinal glands
MM = Muscularis
Mucosae
LP = Lamina Propria

30. The Small Intestine – Structural Features

31. Gross Anatomy of Large Intestine
Cecum
Appendix
Ascending
Transverse
Descending
Sigmoid colon
Rectum
Anus

32. Large intestine (colon) Sphincter Small intestine End of small
LE 21-12
Large
intestine
(colon)
Sphincter
Small
intestine
End
of small
intestine
Rectum
Anus
Nutrient
flow
Appendix
Cecum

33. Gross Anatomy of Large Intestine
Rectum – descends along the inferior half of the sacrum
Anal Canal – the last subdivision of the large intestine

34. Gross Anatomy of Large Intestine

35. Microscopic Anatomy of Large Intestine
Villi are absent
Contains numerous goblet cells
Intestinal crypts – simple tubular glands
Lined with simple columnar epithelial tissue
Epithelium changes at anal canal
Becomes stratified squamous epithelium

36. Microscopic Anatomy of Large Intestine

37. Teeth

38. Salivary Glands

39. Pancreas

40. Exocrine Pancreas: Histology

41. Liver Largest gland in the body Performs over 500 functions
Digestive function – bile production
Performs many metabolic functions

42. Visceral Surface of the Liver

43. Microscopic Anatomy of Liver

44. Microscopic Anatomy of Liver

45. Gallbladder Stores and concentrates bile Expels bile into duodenum
Bile emulsifies fats

46. Gallbladder

47. Enzymes in Small Intestine

48. The Peritoneal Cavity and Peritoneum
Mesentery – a double layer of peritoneum
Holds organs in place
Sites of fat storage
Provides a route for circulatory vessels and nerves

49. Mesenteries
Superficial view of the abdominal organs

50. Mesenteries
Greater omentum and transverse colon reflected

51. Mesenteries
Sagittal section through the abdominopelvic cavity

52. Segmentation
Rhythmic local contractions of the intestine
Mixes food with digestive juices

53. Disorders of the Digestive System
Intestinal obstruction
Mechanical obstructions
Adhesions, tumors, or foreign objects
Nonmechanical obstruction
Halt in peristalsis
Trauma
Intestines touched during surgery

54. Disorders of the Digestive System
Inflammatory bowel disease
Inflammation of intestinal wall
Crohn’s disease
Ulcerative colitis
Viral hepatitis – jaundice and flu-like symptoms
Major types – A, B, C, and G
Cystic Fibrosis and the Pancreas

55. The Digestive System in Later Life
Middle age – gallstones and ulcers
Old age – activity of digestive organs decline
Fewer digestive juices and enzymes produced
Absorption is less efficient
Dehydration of fecal mass leads to constipation
Diverticulosis and cancer of digestive organs