1. Digestive System: Path of food
Page 3 : Notes
Digestive System: Path of food

2. Alimentary canal: Open at both ends
Irregular tube about 29 ft. (9m) long
Also called gastrointestinal tract or GI tract
Food travels: mouth -> pharynx -> esophagus -> stomach -> small intestine -> large intestine -> rectum
Food does not travel through: liver or pancreas

3. Two forms of digestion:
Mechanical – teeth tear food into smaller pieces and stomach churns
Chemical – enzymes break large molecules into smaller molecules (molecular level)
Foods undergo digestion, absorption and metabolism.

4. Digestive System:
Functions in altering food in to a form that can be absorbed by cells
Serves as a system that also eliminates wastes (feces)
Composed of main organs and accessary organs:
Main organs – food passes through
Accessary organs – can secrete into the GI tract (teeth, tongue, salivary glands, liver, gallbladder, pancreas & appendix)

5. Walls of the digestive tract:
Mucosa - lines inside of GI tract
Submucosa - connective tissue with blood vessels + nerves
Muscularis – circular and longitudinal muscle layers; perform peristalsis
Serosa – outermost covering connects to mesentery
Google; digestive tract + layers

7. Path of food: Mouth Where digestion begins!
Roof has hard and soft palates with the uvula (prevents food from entering nasal cavity)
Floor has tongue and muscles, attached by the frenulum
Tongue surface has papillae (bumps on tongue), largest is vallate

8. Accessory glands: Salivary glands: Produce saliva Three pairs:
Contains mucus and
digestive enzymes
Salivary amylase –
Carb. Digestion
Three pairs:
Parotid – largest, back of throat
Submandibular – under jaw
Sublingual – under tongue

9. Teeth: Incisors – sharp, cutting Canines (cuspids) – tear or pierce
Premolars (bicuspids)
And
Molars (tricuspids) – tricuspids
Both have large, flat surfaces for grinding or crushing

10. How many teeth? Deciduous teeth (baby teeth) 20 teeth
6 months: average age for first eruption
Complete set at about 2 years of age
Permanent teeth (adult teeth)
32 teeth
6 years: average age for first eruption
Complete set between years of age

11. Sections of a typical tooth
Crown
Neck
Root

12. Pharynx:
Tubelike structure made of muscle and lined with mucous membrane
Food is small rounded mass, called bolus
Three regions:
Nasopharynx
Oropharynx
Laryngopharynx

13. Esophagus: Muscular, mucus-lined tube Connects the pharynx to stomach
About 10 inches long
Cardiac sphincter:
Ring of muscle
tissue at end that
leads to stomach

14. Stomach: Pouch that stores food
Muscular walls mix food with gastric juice that contains hydrochloric acid and enzymes (produced by gastric glands)
Empty – folds line inside called rugae
Chyme – food is a semi-solid mixture when it exits
Pyloric sphincter – ring of muscle tissue

15. Muscularis of stomach:

16. Small intestine: 20 feet long 3 sections:
Duodenum – first section – 12 in.
Jejunum – middle section
Ileum – last section

17. Small intestine:
Internal – mucus lining has intestinal glands and circular folds called plicae
Covered by small projections called villi
Microvilli are small projections on villi
Increase surface area for absorption of nutrients

18. Villi and microvilli:

19. Liver: Largest gland in the body Secretes bile, yellowish-brown liquid
Emulsifies fats and eliminates cholesterol from body

20. Pancreas: Lies behind stomach
Secretes pancreatic juice that contains enzymes
Breaks down proteins, lipids, + carbs
Secretes sodium bicarbonate (alkaline substance that neutralizes HCl

21. The Ducts

22. Large intestine:
5 feet long with regions (cecum, ascending, transverse, descending, sigmoid and rectum)

23. Large intestine:
Undigested and unabsorbed food is acted on by bacteria
Absorbs vitamins (K + B-complex)
No villi here
Absorption of salts and water
Ileocecal valve is doorway in to the large intestine

24. Appendix: Wormlike tubular structure Contains lymphatic tissue
May be involved in immunity

25. Peritoneum: Large, moist slippery sheet of serous membrane
Lines abdominal cavity + covers organs
Has two extensions:
1. mesentery - giant, pleated fan that encloses the small intestine and attaches it to the posterior abdominal wall
2. greater omentum – pouchlike extension, shaped like an apron, hangs over the intestines (lace apron)