1. The Digestive System
Dr. Holly Nash-Rule

2. Overview of the Digestive System
Organs are divided into two groups
Alimentary canal
Mouth, pharynx, and esophagus
Stomach, small intestine, and large intestine
Accessory digestive organs
Teeth and tongue (sort of)
Gallbladder, salivary glands, liver, and pancreas
Accessory organs are connected to the alimentary canal by ducts
Secretions contribute to breakdown of foodstuffs

3. Digestive Processes Ingestion—occurs in the mouth
Propulsion—movement of food
Peristalsis—major means of propulsion
Mechanical digestion—prepares food for chemical digestion
Chewing, churning food in stomach, segmentation
Segmentation is rhythmic local constrictions of intestine

4. Digestive Processes
Chemical digestion—complex molecules broken down to chemical components
Mouth
Stomach
Small intestine
Absorption—transport of digested nutrients
Small intestines, primarily jejunum
Defecation—elimination of indigestible substances as feces

5. Peristalsis & Segmentation
Major means of propulsion
Adjacent segments of the alimentary canal relax and contract
Segmentation
Rhythmic local contractions of the intestine
Mixes food with digestive juices
Peristalsis
Figure 23.3a

6. Abdominal Regions Four lines divide abdominal wall into nine regions
Midclavicular lines—vertical lines of grid
Subcostal plane—superior horizontal line
Connects inferior points of costal margin
Transtubercular plane—inferior horizontal line
Connects tubercles of iliac crests

7. Abdominal Quadrants
A simpler method of sectioning the anterior abdominal wall
Right upper quadrant
Left upper quadrant
Right lower quadrant
Left lower quadrant

8. The Peritoneal Cavity and Peritoneum
Peritoneum—a serous membrane
Visceral peritoneum—surrounds digestive organs
Parietal peritoneum—lines the body wall
Peritoneal cavity—a slit-like potential space
Retroperitoneal organs
Behind the peritoneum
Peritoneal organs
Digestive organs that keep their mesentery

9. 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

10. Mesenteries Lesser omentum attaches to lesser curvature of stomach
Greater omentum—a “fatty apron” of peritoneum
Greater omentum and transverse colon reflected
Mesenteric Arteries
Figure 23.6c

11. Intraperitoneal and Secondarily Retroperitoneal Organs
Initially formed within peritoneum
Become retroperitoneal
Fuse to posterior abdominal wall
Table 23.1

12. Histology of the Alimentary Canal Wall
Same four layers from esophagus to anus
The mucosa—innermost layer
Consists of
Epithelium
Muscularis mucosae
The submucosa—external to the mucosa
Contains blood and lymphatic vessels, nerve fibers

13. Histology of the Alimentary Canal Wall
The muscularis externa—external to the submucosa
Two layers
Circular muscularis—inner layer
Longitudinal muscularis—outer layer
The serosa—the outermost layer
Is the visceral peritoneum

14. Smooth Muscle Primarily found in walls of viscera Fibers elongated
Have one centrally located nucleus
Grouped into sheets
Longitudinal layer—parallel to long axis of organ
Circular layer—deeper layer, fibers run around circumference of organ

15. Nerve Plexuses Myenteric nerve plexus
Lies between circular and longitudinal muscularis
Controls peristalsis and segmentation
Submucosal nerve plexus
Lies in submucosa
Signals glands to secrete
Innervation
Sympathetic and parasympathetic motor fibers
Visceral sensory fibers

16. The Mouth and Associated Organs
The mouth—oral cavity
Mucosal layer
Stratified squamous epithelium
The lips and cheeks
Formed from orbicularis oris and buccinator muscles, respectively

17. The Tongue Interlacing fascicles of skeletal muscle
Grips food and repositions it
Helps form some consonants
Intrinsic muscles—within the tongue
Extrinsic muscles—external to the tongue
Lingual frenulum
Secures tongue to floor of mouth

18. The Superior Surface of the Tongue
Tongue papillae
Filiform papillae—no taste buds
Fungiform papillae
Circumvallate papillae
Sulcus terminalis
Marks border between mouth and pharynx
Posterior one-third of tongue lies in oropharynx
Lined with lingual tonsil
Tongue papillar

19. The Teeth Deciduous teeth—20 teeth First appear at ~6 months of age
Permanent teeth—32 teeth
Most erupt by the end of adolescence
Dental formula—shorthand
Way to indicate number and position of teeth
2I, 1C, 2P, 3M
Teeth

20. The Salivary Glands Produce saliva Parotid glands
Parotid duct—parallel to zygomatic arch
Submandibular glands
Lay along medial surface of mandible
Sublingual glands
Lay in floor of oral cavity

21. The Pharynx Oropharynx and laryngopharynx Passages for air and food
Lined with stratified squamous epithelium
External muscle layer
Consists of superior, middle, and inferior pharyngeal constrictors

22. The Esophagus Gross anatomy—muscular tube
Begins as a continuation of the pharynx
Joins the stomach inferior to the diaphragm
Cardiac sphincter (lower esophageal sphincter) — closes lumen to prevent stomach acid from entering esophagus

23. The Stomach Site where food is churned into chyme
Secretion of pepsin begins protein digestion
Functions under acidic conditions
Food remains in stomach approximately 4 hours
Regions of the stomach
Cardiac region
Fundus
Body
Pyloric region
Healthy stomach

24. Microscopic Anatomy of the Stomach
Muscularis has three layers
Circular and longitudinal layers and oblique layer
Epithelium is simple columnar epithelium
Mucosa dotted with gastric pits
Gastric glands—deep in gastric pits

25. Microscopic Anatomy of the Stomach
Gastric glands of fundus and body
Mucous neck cells
Secrete a special mucus
Parietal cells
Secrete hydrochloric acid and gastric intrinsic factor
Chief (zymogenic) cells
Secrete pepsinogen
Pepsinogen is activated to pepsin when it encounters acid in the gastric glands

26. The Small Intestine—Gross Anatomy
Longest portion of the alimentary canal
Site of most enzymatic digestion and absorption
Three subdivisions
Duodenum
Jejunum
Ileum
Innervation
Parasympathetic fibers from vagus nerve
Sympathetic from thoracic splanchnic nerves

27. The Duodenum Receives chyme, digestive enzymes and bile
Main pancreatic duct and common bile duct enter duodenum
Sphincters control entry of bile and pancreatic enzymes

28. The Small Intestine—Microscopic Anatomy
Modifications for absorption
Circular folds
Transverse ridges of mucosa and submucosa
Villi
Finger-like projections of the mucosa
Covered with simple columnar epithelium
Microvilli
Further increase surface area for absorption

29. Histology of the Intestinal Wall
Absorptive cells
Uptake digested nutrients
Goblet cells
Secrete mucus that lubricates chyme
Enteroendocrine cells
Secrete hormones
Intestinal crypts
Epithelial cells secrete intestinal enzymes

30. The Large Intestine Digested residue contains few nutrients
Small amount of digestion by bacteria
Main functions
Absorb water and electrolytes
Mass peristaltic movements force feces toward the rectum

31. Gross Anatomy of Large Intestine
Subdivided into
Cecum, vermiform appendix, colon, rectum, anal canal
Cecum
Blind pouch
Beginning of large intestine
Vermiform appendix
Contains lymphoid tissue
Neutralizes pathogens
Appendix

32. Gross Anatomy of Large Intestine
Colon
Divided into distinct segments
Ascending, transverse, descending, and sigmoid
Rectum
Descends along the inferior half of the sacrum
Anal canal
The last subdivision of the large intestine
Lined with stratified squamous epithelium

33. Vessels and Nerves of the Large Intestine
First half of large intestine
Arterial supply—superior mesenteric artery
Innervation
Sympathetic innervation—superior mesenteric and celiac ganglia
Parasympathetic innervation—vagus nerve

34. Vessels and Nerves of the Large Intestine
Distal half of large intestine
Arterial supply—inferior mesenteric artery
Innervation
Sympathetic innervation—inferior mesenteric and hypogastric plexuses
Parasympathetic innervation—pelvic splanchnic nerves

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

36. The Liver Largest gland in the body Performs over 500 functions
Digestive function
Bile production
Performs many metabolic functions

37. Microscopic Anatomy of the Liver
Hepatocyte—functional cells of the liver
Portal triad composed of
Bile duct tributary
Branch of hepatic portal vein
Branch of hepatic artery
Kupffer cells—destroy bacteria

38. Microscopic Anatomy of the Liver
Some functions of hepatocytes
Rough ER manufactures blood proteins
Smooth ER produces bile salts, detoxifies poisons
Peroxisomes detoxify poisons (alcohol)
Golgi apparatus packages secretory products
Mitochondria provide energy for liver processes
Glycosomes store sugar
Great capacity for regeneration

39. The Gallbladder Stores and concentrates bile Expels bile into duodenum
Bile emulsifies fats
Cholecystokinin—released from enteroendocrine cells in response to fatty chyme
Gallbladder

40. The Pancreas Exocrine function
Acinar cells make, store, and secrete pancreatic enzymes
Enzymes are activated in the duodenum
Endocrine function
Produces insulin and glucagon
Regulates blood sugar

41. Peptic Ulcers
Are erosions of the mucosa of a region of the alimentary canal
Gastric ulcers
Occur in pyloric region of the stomach
Duodenal ulcers
Occur in duodenum of the small intestine

42. Peptic Ulcers Caused by Helicobacter pylori H. pylori Acid-resistant
Binds to gastric epithelium
Induces oversecretion of acid and inflammation

43. 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

45. The End
Dr. Holly Nash-Rule