1. Ingestion and Digestion

2. Ingestion and other Mouth Events
3 important events take place in your mouth (oral cavity):
mechanical digestion starts the teeth cut, tear, crush, and grind the food
chemical digestion starts salivary amylase begins the hydrolytic digestion of starch
the food is moistened and lubricated for the journey through the esophagus (saliva is mainly water, water is a good lubricant!)

4. Incisors: cutting & biting
Canines: tearing
Premolars: grinding
Molars: crushing

5. The tongue
Moves food around for chewing proper type of tooth can be utilized
Taste buds are located here important for determining if food is spoiled
forms chewed food into a bolus for swallowing
a giraffe’s tongue is up to 50 cm in length and can be used to clean the inside of its own ears!

8. Saliva and the salivary glands
there are 3 pairs of salivary glands
salivary glands are exocrine glands, they are under the control of the nervous system
there are 2 types of glands in the body: exocrine and endocrine
exocrine: secretes product onto an epithelial surface (e.g. lining of digestive tract, skin, mouth) may have a duct
endocrine: secretes hormone directly into blood

9. 4 important ingredients of saliva and their functions
salivary amylase (also called ptyalin)begins the break down of cooked starch molecules produces maltose
water  moistens food which aides in movement through the esophagus (swallowing)
mucin slippery lubricant that also aides in movement of food
bicarbonate ions buffer the pH of the oral cavity so that it remains near neutral even when you eat acidic food

10. A Spitacular Saliva Fact:
An adult produces from 1 to 2 litres of saliva in a day

11. Starch molecule
Remember that starch is a polymer of glucose

12. Amylase causes the hydrolysis of starch to maltose two glucose molecules joined together

13. From mouth to stomach
Tongue pushes food to the pharynx (fancy term for throat)the food has been shaped into a ball called a bolus at this point
air and food both pass through here  air on its way from oral or nasal cavity to the lungs via the trachea
food to the stomach via the esophagus  swallowing
Breathing and swallowing must be separated—even a small amount of water or food in breathing passages can cause blockage “café coronary”

17. The Specifics of Swallowing
Swallowing is a reflex action  you don’t have to think about it
When bolus is swallowed the soft palate (uvula) is forced upwards  sealing off the nasal passageway
Nerves in the pharynx sense contact with the bolusstimulates glottis to close and the movement of the bolus down the throat pushes the epiglottis over the glottis to protect it further from the entry of food or H2O

18. Uvula, Glottis, Epiglottis
This person has a bifid uvula (unusual but not uncommon)
This is the glottis  (opening to the larynx)

19. The Glottis is bounded by the vocal cords

20. The Specifics of Swallowing Continued…
Food bolus passes from the pharynx to the esophagus  usually collapsed but opens when swallowing occurs
Peristalsis pushes the food down the esophagus (peristalsis is important in other areas of the digestive system too)
Esophagus passes through chest (thoracic) cavity and diaphragm to the stomach
The food is not changed in anyway by the esophagus—its just a tube

21. The Particulars of Peristalsis
Involves two layers of muscle—circular muscles (inner) and longitudinal muscles (outer)
Circular muscles in front of bolus relax while those behind it contract

22. It takes approximately 8 seconds for a peristaltic wave to reach the stomach peristalsis continues here

23. Reverse Peristalsis is also possible…
Drinking is very bad boys and girls…

25. Before the Food Enters the Stomach There Is One More Obstacle…
The food must pass through the cardiac sphincter (although not considered a “true” sphincter by some sphincter snobs)
Sphincters are circular muscles that acts as valves
Contract: close
Relax: open
There is also a sphincter at the other end of the stomach the pyloric sphincter

26. Of Course fans of Wayne’s World know the location of another sphincter in the body…

27. The Stomach…more physical and chemical digestion
An Empty Stomach
Rugae:
folds that allow the stomach to expand as it fills with food

28. Physical digestion in the stomach:
Peristalsis: the rhythmic muscular contractions of the muscular walls of the stomach mix the food with gastric juice
Capacity of the stomach is approximately 1 litre
Gastric juice is made by the gastric glands which line the walls of the stomach

29. Contents of Gastric Juice
HCl (hydrochloric acid) gives stomach its low pH (2--very acidic)
pepsin an enzyme that begins the breakdown of proteins
mucus made by Goblet cells in the lining of the stomach

31. What the HCl does and does not do...
Does activate pepsin pepsin only works at low pH (acidic conditions)
the chief cells make pepsinogen (inactive) converted to pepsin by HCl
Does kill most bacteria that may have been in the food
Does breaks down connective tissue in meat/bone
Does not digest food!!!

32. A pH of 2 and a enzyme that digests proteins How do the stomach walls survive?
The thick layer of mucus that lines the walls produced by the goblet cells
A gastric ulcer results when the wall is not protected by mucus
we know now that most ulcers are caused by a bacterium  Helicobacter pylori

34. Summary of the 4 main functions of the stomach
Physical digestion of food: the churning of the stomach is like a blender liquefies solid food surface area increased even further!
Partial chemical digestion of proteins
kill bacteria in food
storage of food

35. The food leaves the stomach in spurts as chyme a thick soupy liquid
Digestion will be finished in the first section of the small intestine  the duodenum: approximately the first 25 cm of the small intestine
mainly chemical digestion take place here but there is one nutrient that will still need to be physically broken down after the pulverizing in the stomach fats

36. Bile is released into the duodenum and emulsifies fats
Increased surface area of fats
Big glob of fat

37. A Whack of Digestive Enzymes are active in the Duodenum...
Specific enzymes for: fats
disaacharides
starch
proteins
nucleic acids
Bile is not an enzyme

38. Did you get that??? BILE IS NOT AN ENZYME!!!
Bile is involved in the physical breakdown of fats emulsification is not a chemical change it is a physical change

39. Digestion finishes in the duodenum portion of the small intestine --the other function of the small intestine is absorption
Absorption is the movement of water, nutrients, and other substances (toxins, poisons, synthetic pesticide residues) from the digestive system into the circulatory system