1. Beyond Ingestion….
Digestive system (2)

2. Review: Parts of Digestion
Ingestion – taking in of nutrients
Digestion – breakdown of complex molecules into smaller components by enzymes
Absorption- transport of digested nutrients to the tissue of the body
Egestion – removal of waste food material from the body

3. Review: Food has been: mechanically chewed by the teeth
moistened and partially digested by saliva
Saliva contains the enzyme AMYLASE that breaks down starch into simple sugars
The bolus is swallowed and………

4. And digestion is beginning…….
The bolus goes through the pharynx, closes the epiglottis (so food doesn’t enter the trachea)
and enters the esophagus…

5. Esophagus
Food and fluids move through the esophagus NOT because of gravity but because peristalsis.
Peristalsis = rhythmic, wavelike muscle contractions

6. Peristalsis is why we can drink while standing on our head!

7. Sphincters
Is a ring-shaped muscle that relaxes or tightens to open or close a passage or opening in the body.
Examples are the anal sphincter (around the opening of the anus) and the pyloric sphincter (at the lower opening of the stomach).

8. There is a sphincter at the top and the bottom of the esophagus.

9. “do not try this at home”!!

10. So, the food has now passed through the esophagus, thru the lower esophageal sphincter and into the stomach…

11. Functions of the stomach
Bulk storage (capacity of approx 1.5L) of undigested food
Mechanical breakdown of food (muscular contractions of the stomach)
Disruption of chemical bonds via acids and enzymes

12. Structure of stomach
Millions of cells line the inner wall of the stomach
These cells secrete gastric fluids

13. Gastric Juices:
Mucus: protects stomach against digestion and corrosion
HCl: hydrochloric acid kills harmful substances ingested with food
Pepsinogen: is activated to pepsin in the presence of HCl, the enzyme pepsin digests protein

14. Problems: ulcers and heartburn

15. Endoscopy:

16. So far, chemical digestion
Part
Enzyme
Digests
Example
Mouth
Amylase
Carbs
Bread
Stomach
Pepsin
Proteins
Meat
HCl (hydrochloric acid) allows pepsin to do its digestion and kills pathogens that come into the stomach.

17. Mechanical digestion Mouth Teeth Stomach Muscular contractions
Physically breaking food into smaller pieces so there is more surface area for chemical digestion.
Mouth
Teeth
Stomach
Muscular contractions

18. Next stop on the digestive bus: thru the pyloric sphincter to the small intestine…
Just something to look forward to……