1. The Digestive System
Chapter 24

2. Introduction Structure of the digestive system Functions include
A tube that extends from mouth to anus
Accessory organs are attached
Functions include
Ingestion
Movement
Digestion
Absorption
Defecation

3. Overview of Digestive System
FG25_01.JPG
Title: Components of the Digestive System
Notes: This figure introduces the accessory organs and major regions of the digestive tract, together with their primary functions.
Keywords: digestive system, components, oral cavity, teeth, tongue, liver, gallbladder, large intestine, salivary glands, pharynx, esophagus, stomach, pancreas, small intestine
Human Anatomy, 3rd edition
Prentice Hall, © 2001

4. Histological Organization
Same basic arrangement of tissues from esophagus to anal canal
Four layers (from innermost to outermost)
Mucosa
Submucosa
Muscularis
Serosa
Human Anatomy, 3rd edition
Prentice Hall, © 2001

5. Movement and Mixing of Digestive Materials
Peristalsis
Coordinated motion of two muscular layers
Circular muscles contract, then longitudinal muscles
Segmentation
Mixing of food
Circular muscles in two areas contract
Longitudinal muscles alternately contract & relax
Human Anatomy, 3rd edition
Prentice Hall, © 2001

6. Human Anatomy, 3rd edition
The Oral Cavity
Structure
Lined with stratified squamous epithelium
Lips surround the opening
Roof is formed from the hard & soft palate
Tongue dominates the floor
Functions
Take in food
Prepare food for digestion
Human Anatomy, 3rd edition
Prentice Hall, © 2001

7. Human Anatomy, 3rd edition
The Tongue
Structure
Skeletal muscle covered with mucosa
The lingual frenulum connects the tongue to the floor of the mouth
Surface
Papillae
Functions
Maneuvers food
Human Anatomy, 3rd edition
Prentice Hall, © 2001

8. Human Anatomy, 3rd edition
Salivary Glands
Found outside mouth
Ducts carry saliva to mouth
3 pairs
Parotid glands
Submandibular glands
Sublingual glands
Saliva
Functions
Keeps mucous membranes moist
Lubricates food
Dissolves food
Begins carbohydrate digestion
Human Anatomy, 3rd edition
Prentice Hall, © 2001

9. Human Anatomy, 3rd edition
Teeth
2 sets
Deciduous (20)
Permanent (32)
Held in sockets
Gingiva = gums
Structure
Crown
Root
Neck
Composition
Dentin
Enamel
Cementum
Dental caries
Wisdom teeth
Human Anatomy, 3rd edition
Prentice Hall, © 2001

10. The Pharynx and Esophagus
Food enters the esophagus from the pharynx
The esophagus is a muscular tube behind the trachea
Food is moved by peristalsis from the pharynx to the stomach
Cardiac sphincter separates esophagus from stomach
Human Anatomy, 3rd edition
Prentice Hall, © 2001

11. External Anatomy of the Stomach
FG25_10A.JPG
Title: The Stomach and Omenta
Notes: (a) Surface anatomy of the stomach, showing blood vessels and relation to liver and intestines. (b)Radiograph of stomach and duodenum after swallowing barium solution to increase contrast. (c)Radiograph of pyloric region, pyloric valve, and duodenum.
Keywords: stomach, surface, lesser curvature, gastroepiploic artery, greater curvature, omentum, hepatoduodenal ligament, hepatogastric ligament, duodenum, pylorus, rugae, pyloric sphincter, fundus, body
Human Anatomy, 3rd edition
Prentice Hall, © 2001

12. Human Anatomy, 3rd edition
The Stomach
Same 4 basic layers
When the stomach is empty, the mucosa lies in large folds
Rugae
Pyloric sphincter separates stomach from small intestine
Human Anatomy, 3rd edition
Prentice Hall, © 2001

13. Histology of the Stomach
Mucosa is simple columnar epithelium with goblet cells
Mucosa is folded to form gastric pits
Gastric glands secrete gastric juice
Human Anatomy, 3rd edition
Prentice Hall, © 2001

14. Human Anatomy, 3rd edition
Gastric Gland
Several kinds of cells produce substances that form gastric juice
Mucus cells
Chief cells
Parietal cells
Enteroendocrine cells
Human Anatomy, 3rd edition
Prentice Hall, © 2001

15. Functions of the Stomach
Mechanical digestion
Food reaches pylorus
Chemical digestion
Digestion of proteins
Absorption
No food
Water, electrolytes
Some drugs
Alcohol

16. Human Anatomy, 3rd edition
The Small Intestine
About 18 feet long
The duodenum
About 8 inches long
Common bile duct & pancreatic duct empty here
The jejunum
About 8 feet long
Most digestion occurs here
The ileum
About 9.5 feet long
Most absorption occurs here
Ends in the ileocecal valve
Human Anatomy, 3rd edition
Prentice Hall, © 2001

17. Histology of the Small Intestine
The lining is folded into circular pleats
Plicae circulares
The mucosal surface is folded into villi
The epithelial cell membranes are highly folded into microvilli
Intestinal glands are found in the crypts at the base of villi
Secrete intestinal juice
Human Anatomy, 3rd edition
Prentice Hall, © 2001

18. Human Anatomy, 3rd edition
A Villus
FG25_15C.JPG
Title: The Intestinal Wall
Notes: (a) Characteristic features of the intestinal lining.(b) The organization of villi and the intestinal crypts.(c) Diagrammatic view of a single villus. (d)Panoramic view of small intestine wall. (e)Villi photomicrographs from jejunum.
Keywords: villi, intestinal crypts, mucosa, muscularis mucosae, submucosa, muscularis externa, serosa, lacteal, lymphoid nodule, intestinal glands, submucosal plexus, lymphatic vessel, myenteric plexus, plica, goblet cell, lacteal, brush border
Human Anatomy, 3rd edition
Prentice Hall, © 2001

19. Functions of the Small Intestine
Chyme is further broken down
Proteins
Carbohydrates
Fats
Most absorption is in the small intestine

20. The Large Intestine (Colon)
About 4.5 feet long
Mesocolon supports
Begins with the cecum
Appendix is attached
Ascending colon
Transverse colon
Descending colon
Sigmoid colon
Colon connects to rectum
Rectum connects to anal canal
Empties to the exterior through the anus
Human Anatomy, 3rd edition
Prentice Hall, © 2001

21. Histology and Functions of the Large Intestine
Mucosa - simple columnar epithelium
Completion of absorption
Formation of feces
Lots of mucus glands
Expulsion of feces from the body
Human Anatomy, 3rd edition
Prentice Hall, © 2001

22. Digestion in the Large Intestine
Mechanical
Regulated by the ileocecal valve
Mixing and peristalsis
Mass peristalsis
Chemical
Mucus secreted
No enzymes
Bacteria – prepare chyme for elimination
Human Anatomy, 3rd edition
Prentice Hall, © 2001

23. Feces Formation & Defecation
Chyme is now solid or semi-solid - feces
Large intestine absorbs any more water and electrolytes from feces
Defecation
Mass peristalsis pushes fecal material into rectum
Rectum stretches
Defecation reflex
Human Anatomy, 3rd edition
Prentice Hall, © 2001

24. Accessory Organs
Liver
Pancreas
Gall bladder

25. Human Anatomy, 3rd edition
The Liver
Performs many life-sustaining functions
Location – under the diaphragm on the right
Connected to the diaphragm by the falciform ligament
Divided into lobes
Right lobe
Left lobe
Caudate lobe
Quadrate lobe
Human Anatomy, 3rd edition
Prentice Hall, © 2001

26. Human Anatomy, 3rd edition
Histology of the Liver
Outside is a capsule
Composed of tiny lobules
Each lobule is surrounded by liver cells and sinusoids
Hepatocytes
Kupffer cells
Bile ducts run between liver cells
Human Anatomy, 3rd edition
Prentice Hall, © 2001

27. Functions of the Liver Produces bile – the primary digestive function
Composition
Water
Bile salts
Cholesterol
Pigments
Bilirubin
Digestive function
Emulsification of fats

28. Other Functions of the Liver
Absorbs and stores iron, vitamins A, D, E, B7, K
Detoxifies toxins and hormones
Metabolizes proteins, carbohydrates, and lipids
Removes bacteria from the blood
Produces plasma proteins
Removes worn-out and damaged red blood cells

29. Human Anatomy, 3rd edition
The Gallbladder
Location – underside of right lobe of liver
Function – concentrate and store bile
Collected from liver
Hepatic ducts
Adds bile to duodenum
Cystic duct
Common bile duct
Gallstones
Human Anatomy, 3rd edition
Prentice Hall, © 2001

30. Human Anatomy, 3rd edition
The Pancreas
Location – in the curvature of the duodenum
Connected to the duodenum by the pancreatic duct
Produces pancreatic juice
Functions
Exocrine - digestion of all nutrient groups
Endocrine – control blood glucose level
Human Anatomy, 3rd edition
Prentice Hall, © 2001