1. Do Now
What do you already know about the digestive system? List 3 things!
What would happen if you were tied upside down, would you still be able to eat? Explain.
List the components of the alimentary canal.

2. The Digestive System!
Chapter 15

3. Objectives To compare and contrast chemical vs. mechanical digestion.
To explain the general characteristics of the alimentary canal.
To explain the process of swallowing and peristalsis.
To identify the structures of the mouth and explain their function.
To understand the necessity of salivary glands and name each type.

4. Digestion
Chemical digestion- complex molecules are broken down into smaller molecules
Mechanical digestion- physical movement of food that breaks it down into smaller pieces
Ex. Chewing, grinding, mashing
Chewing is called “mastication”

5. Components of Digestive System
Alimentary Canal
“digestive tract”
Mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum and anus
Accessory Structures:
Salivary glands, liver, gallbladder, & pancreas

6. Alimentary Canal
Muscular tube that passes through the body’s ventral cavity
About 9 meters long
Contains 4 layers

7. Alimentary Canal 1) Mucosa (innermost): 2) Submucosa:
Protects the tissues beneath it & carries out secretion and absorption
Consists of epithelium, underlying CT, and a little bit of smooth muscle
2) Submucosa:
Nourishes surrounding tissue and carries away absorbed materials
Consists of loose connective tissue, blood vessels, glands.

8. Alimentary Canal 3) Muscular Layer: 4) Serosa:
Layer which moves the tube
Contains two coats of smooth muscle tissue & nerves (plexus)
Fibers of the inner coat (circular) surround the tube
When they contract the tube’s diameter decreases
Fibers on the outer muscular coat (longitudinal) run lengthwise
When they contract the tube shortens
4) Serosa:
Protects underlying tissues and secrete serous fluid

9. Alimentary Canal

10. Movements of the Alimentary Canal
Mixing Movement
Occurs when smooth muscle in small units of the tube contract rhythmically
Mixes food with digestive juices secreted by the mucosa
Propelling Movement
Known as peristalsis

11. Do Now
-Which layer of the alimentary canal is responsible for moving the tube? What type of tissue is this layer?
- List the 3 macromolecules found in your food and what they’re broken down into.
P.3

12. Alimentary Canal Length

13. Organs of the Digestive System
The Mouth
Receives food and begins digestion mechanically
Reduces the size of solid particles and mixes them with saliva
Oral cavity - Lips, cheeks, tongue & palate
Vestibule - Narrow space between teeth, cheeks, & lips

14. Salivary Glands Secrete saliva Contain 2 types of secretory cells:
Serous cells: produce salivary amylase (breaks down carbs)
Mucous cells: produce mucus to bind to food and lubricate during swallowing
*Major glands:
Parotid
Submandibular
Sublingual

15. Pharynx Connects nasal and oral cavities with larynx and esophagus
Contains 3 parts:
Nasopharynx
Oropharynx
Laryngopharynx

16. Swallowing Mechanism
1. Food is chewed and mixed with saliva,tongue rolls this into a mass or bolus and forces it into the pharynx
2. Food stimulates sensory receptors around the pharyngeal opening, triggering the swallowing reflex
3. Momentarily inhibits breathing, peristalsis transports food into the esophagus and to the stomach

17. Esophagus Connects pharynx to the stomach
Separated from the stomach by the cardiac sphincter
Contracts and closes the sphincter to prevent regurgitation

18. Stomach J shaped with about a 1 liter capacity
Contains rugae, which allow it to expand
Divided into 4 regions
Cardiac
Fundic
Body
Pyloric
Contains cardiac and pyloric sphincters

19. Stomach Juices “Gastric Juice” consists of: HCl Mucus
Viscous alkaline secretion that coats the stomach
Enzymes:
Proteases such as Pepsin- digests protein (starts as pepsinogen and when mixed with HCl makes pepsin)
P.6

20. Stomach Juices
The mixture of gastric juice and the bolus gives us chyme
Chyme pushed into the small intestine
Type of food can affect rate of emptying:
Fatty food 3-6 hrs. in stomach
Proteins move more quickly
Carbs go through the fastest!

21. Gastric Absorbtion The stomach mostly breaks things down
Can absorb only small amounts of water, certain salts, alcohol, and some lipid- soluble drugs.
EX: Aspirin

22. Pancreas Secretes pancreatic juice into the duodenum
Pancreatic enzymes:
Pancreatic amylase
Digests carbs
Pancreatic lipase
Digests fats
Nucleases
Digests nucleic acids
Proteases:
Digest protein

23. Liver Effects carbohydrate, lipid, and protein metabolism
Produces bile:
Contains bile salts, bile pigments (bilirubin and biliverdin)
**bile salts emulsify fats and also increase absorption of fat-soluble vitamins (A,D,E, & K)

24. Liver Also involved in… Blood sugar regulation
Storage of iron, vitamins A, D, B12
Detoxifies blood (ex: removes alcohol, H202)

25. Small Intestine 3 sections: Duodenum, Jejunum, Ileum
Receives secretions from pancreas and liver
Contain intestinal “villi”- increase surface area for absorption
*Most of the absorption occurs here!

26. Large Intestine
Contains cecum (appendix attached), colon, rectum, anal canal
Main function is to absorb water and electrolytes from remaining chyme, and forms and stores feces.

27. Feces Contains materials not digested or absorbed Water Electrolytes
Mucus
Shed intestinal cells
Bacteria (makes it smell!)

28. Review What is the process that occurs after swallowing?
What is the scientific name for the digestive tract?
How many layers is this tract?
What are the 3 parts of the pharynx?
What is absorbed in the stomach?
What does the pancreas do?
Why are bile salts important?