1. Anatomy of the Digestive System
Exercise 38
Anatomy of the Digestive System

2. Objectives Overall function Organs of alimentary canal
Accessory digestive organs
General functions of organs/structures
Histological structure of alimentary canal wall
Stomach and small intestine specializations
Enzymes produced
Deciduous and permanent teeth

3. Digestive System
Provides body with nutrients, water, electrolytes essential for health
Organs ingest (take in),
digest (break down), &
absorb (take into bloodstream) food,
and eliminate the undigested remains

4. Alimentary Canal
Hollow tube extending from mouth to anus (gastrointestinal tract or GI tract)
Various accessory organs/glands empty into
“Disassembly Line”

5. Alimentary Canal Histology
Mucosa (mucous membrane)
Inner layer, lines lumen; secretion of enzymes, absorption of nutrients, protection
Surface epithelium: simple columnar
Lamina propria: areolar connective
Muscularis mucosa: smooth muscle—local movements of mucosa
Lacteals: in villi (small fingerlike projections) of small intestine, lymphatic capillaries—transport fatty acids to bloodstream
LUMEN
OUTER surface

6. Lacteals will be in here
ONE VILLUS
Fig. 24-3

7. Alimentary Canal Histology
Submucosa (superficial to mucosa; nutrition, protection)
Blood, lymph vessels, nerve fibers
Submucosal plexus is it’s intrinsic nerve supply
Fig. 24-3

8. Alimentary Canal Histology
Muscularis externa
Bilayer of smooth muscle:
Circular layer of muscle (deep)
Longitudinal layer of muscle (superficial)
Myenteric plexus = another intrinsic nerve plexus, controls these muscle layers  major controller of GI motility
Fig. 24-3

9. Alimentary Canal Histology
Serosa (visceral peritoneum)
Outermost tunic
Mesothelium, areolar connective tissue
Reduces friction as GI organs slide across one another and cavity’s walls, protects and anchors organs also
Fig. 24-3

10. Alimentary Canal Organs
Fig. 24-1

11. Alimentary Canal Organs
Oral cavity (mouth)
Labia (lips)
Hard palate (anterior roof of mouth)
Soft palate (posterior roof of mouth)
Uvula (fingerlike projection of soft palate)
Tongue (floor of oral cavity)

12. Fig. 24-6

13. Pharynx Nasopharynx (behind nasal cavity)
Oropharynx (behind oral cavity)
Laryngopharynx (epiglottis to larynx)
Fig. 24-6

14. Esophagus
From pharynx through diaphragm to gastroesophageal sphincter at esophagus-stomach junction, controls food passage into stomach

15. STOMACH (left side of abdominal cavity)
Cardiac region: upper region, through which food ENTERS stomach
Fundus: superior & lateral to cardiac
Body: middle portion, inferior to fundus
Pyloric region: terminal part of stomach, continuous w/small intestine
Pyloric sphincter: between stomach & small intestine

16. Alimentary Canal Organs
Stomach (left side of abdominal cavity)
Greater curvature: lateral, convex
Lesser curvature: medial, concave
Rugae: prominent folds in the mucosa when stomach’s empty

17. Fig

18. SMALL INTESTINE ~2m long
Duodenum: from pyloric sphincter around pancreas
Jejunum: umbilical region of abdomen
Ileum: terminal portion, joins lg intestine
Plicae circularis: like rugae, deep folds
Ileocecal valve: between small and large intestine

19. Fig

20. Fig

21. LARGE INTESTINE ~1.5m long Encircles the small intestine on 3 sides
Cecum: 1st region, expanded pouch
Appendix:  attached to cecum, ~3.5” long
Ascending colon: up the right side
Transverse colon: across the top
Descending colon: down the left side

22. Fig

23. LARGE INTESTINE
Sigmoid colon: S-shaped curve (behind bladder) between descending colon and
Rectum: last 6” of digestive tract
Anus: exit of the anal canal
Anal sphincter: muscle layers (2) surrounding the anus

24. Fig

25. LARGE INTESTINE
Teniae coli: 3 external longitudinal muscle bands of muscularis, shorter than rest of wall, cause it to pucker into
Haustra: small pocketlike sacs

26. Fig

27. ACCESSORY Digestive Organs
Teeth
Deciduous: appear 6 months-2.5 years; begin to lose teeth around 6 years old
20 teeth
2, 1, 0, 2 x 2 = 20
2, 1, 0, 2
Each SIDE of the jaw
Upper: 2I, 1C, 0 PM, 2M
Lower: 2I, 1C, 0 PM, 2M
SIDES of the jaw

28. TEETH Permanent: gradually replaces the 1st set to age 12 32 teeth
2, 1, 2, 3 x 2 = 32
2, 1, 2, 3
Each SIDE of the jaw
Upper: 2I, 1C, 2 PM, 3M
Lower: 2I, 1C, 2 PM, 3M

29. Permanent Teeth For biting For chewing Central incisors
Lateral incisors
Canines (cuspids)
1st premolars (bicuspids)
2nd premolars (bicuspids)
1st molars
2nd molars
3rd molars
For biting
For chewing

30. Fig 24-9

31. Fig. 24-8

32. Teeth Anatomical crown: entire area of tooth covered by enamel
Clinical crown: portion of tooth visible above the gum
Root: inferior portion (base) of the tooth (below the gum)

33. Fig. 24-8

34. Teeth Enamel: “white” mineral (calcium salt) outer covering of crown
Dentin: like bone, but no cells; under enamel, it’s most of the tooth
Pulp, pulp cavity: interior chamber of the tooth—has blood vessels & nerves

35. Fig. 24-8

36. SALIVARY GLANDS
Parotid glands: inferior to zyg. arch, lateral/posterior mandible
Submandibular glands: floor of mouth, along inside of mandible
Sublingual glands: floor of mouth, more anterior & under tongue

37. Fig. 24-7

38. LIVER
Right, left, caudate, quadrate lobes
Fig

39. LIVER
Falciform ligament: divides Rt/Lt lobes
Fig

40. LIVER Round ligament: thickened posterior part of falciform ligament
Fig

41. LIVER
Hepatic ducts: right, left—collect bile (secreted by liver) from all bile ducts of lobes, unite to form the
Common hepatic duct which leaves the liver…bile then flows to
Cystic duct which leads to the gallbladder (stores/concentrates bile) ….OR goes to the
Common bile duct which is formed by union of cystic and common hepatic ducts--empties into the duodenum (sm intest),

42. Fig

43. PANCREAS
Posterior to stomach, extends laterally off the duodenum toward the spleen
Secretes digestive enzymes and buffers via the
Pancreatic duct into the duodenum
Accessory pancreatic duct branches off the larger pancreatic duct, also empties into duodenum
Hepatopancreatic sphincter (muscle) controlling entrance of substances (from common bile duct, pancreatic duct) into duodenal ampulla

44. Fig

45. Fig

46. Microscope Work Stomach
Gastric pits: shallow depressions, open onto gastric surface; mucous cells at base of each one mitotically active—shed into chyme (acidic “soup” of stomach secretions and food)

47. Fig
Fig

48. Microscope Work One VILLUS Small intestine
Villi: fingerlike projections all over the plicae circulares
One VILLUS
Fig

49. Microscope Work Large intestine (no villi in colon)
Goblet cells (unicellular glands) abundant
secrete mucus to help GI motility
Fig