1. The Digestive System Ingestion — taking in food
Digestion — breaking food down physically and chemically
Absorption — movement of nutrients into bloodstream
Defecation — rids body of indigestible waste
Figure 14.1

2. Organs of the Digestive System
Two main groups
Alimentary canal (gastrointestinal or GI tract) — continuous coiled hollow tube
Accessory digestive organs – tear and crush food (teeth) or secrete enzymes into lumen

3. Organs of the Alimentary Canal, i.e. the tube…
Mouth
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Anus

4. Accessory Digestive Organs
Teeth – mash up food mechanically
Salivary glands
Pancreas
Liver
Gallbladder
Secrete stuff into ‘the tube’

5. Mouth (Oral Cavity) Entrance to digestive system
Food moistened w/ saliva and masticated (chewed)
bolus = ball of moistened food
Starch (polysaccharide) digestion starts
Figure 14.2a

6. Baby (deciduous) and Permanent Teeth
Teeth: incisors bite; canines tear; molars grind
(32 adult; 20 juvenile)
Figure 14.9

7. Participating…
How many baby (deciduous teeth) do we start out with? How many potential permanent teeth do we end up with? What 2 parts of the GI tract follow the oral cavity?
20…32…pharynx, esophagus

8. Salivary glands secrete saliva into oral cavity…
Saliva = mix of mucus and serous fluids
Contains enzymes that digest starch
Dissolves chemicals for taste
binds and lubricates food (bolus)
…back to ‘the tube’!!

9. Deglutition (Swallowing) keep your eye on the epiglottis!
Bolus travels to stomach
I can breath again!
Figure 14.14a–b

10. Pharynx has 3 sections bolus Passageway for air and food
Food propelled by peristalsis to esophagus
Peristalsis – alternating contractions of smooth muscle layers
bolus
Figure 14.2a

11. Esophagus also moves food (bolus) by peristalsis
Connects pharynx to stomach through diaphragm (about 10”)

12. From esophagus on, alimentary canal has 4 layers
Mucosa – innermost lubricating layer
Submucosa – second layer supplies blood and nerves
Muscularis externa – circular and longitudinal smooth muscle for peristalsis
Serosa – visceral layer of double serous membrane (suspends and lubes)
All surround the internal cavity = lumen

13. Autonomic nerves control peristalsis and gland secretions
Gut brain = more neurons than spinal cord!
Figure 14.3

14. Participating…
How many layers are found in most of the alimentary canal? (____) The muscle layer moves the moistened ball of food known as the ________ down the GI tract by means of coordinated contractions known as ____________ 4
bolus
peristalsis

15. The Stomach is bordered by 2 sphincters
Bolus enters at cardioesophageal sphincter
Exits (as chyme) into small intestine at pyloric sphincter (valve)

16. Some Stomach Anatomy Fundus = expanded, upper portion of stomach
Rugae = folds of mucosa, expand for more food
3rd muscle layer helps churn food
Figure 14.4a

17. Some Stomach Physiology
Temporary storage tank for up to 1 gallon of food
Initiates protein digestion
Very acidic contents aid protein digestion, kill microbes
Delivers acidic chyme (processed food) to small intestine

18. Mucous secreted by stomach epithelium = alkaline…why?
Stomach mucosa has millions of gastric pits leading to acid/enzyme secreting glands
Gastric glands—secrete gastric juice (highly acidic w/ protein-digesting enzymes)
Enteroendocrine cells—produce hormones that control stomach activity
Mucous secreted by stomach epithelium = alkaline…why?

19. Few substances absorbed in stomach aside from alcohol and aspirin…
Stomach releases chyme slowly: hours to empty depending on fat content
Few substances absorbed in stomach aside from alcohol and aspirin…
Figure 14.15a–c

20. Small Intestine is the major absorption organ
Receives digestive secretions (enzymes, etc.) from liver, gallbladder, and pancreas
Most nutrients and water absorbed here

21. Participating…
The stomach environment is highly _______ to aid protein digestion and kill microbes. Absorption is limited to aspirin and ________ in the stomach. Partially digested food known as ________ is released into the small intestine. Where are most nutrients from food absorbed?
acidic
alcohol
chyme
small intestine

22. Virtually all nutrients enter blood from small intestine!!
3 regions…
Duodenum
1st part joining stomach, most digestion AND absorption
Jejunum
middle
Ileum
Last joining large intestine

23. Chemical Digestion begins in earnest in Small Intestine
Enzymes produced by Intestinal cells and Pancreas
Pancreatic ducts carry enzymes to small intestine
Bile = fat breakdown; made by liver, stored in gall bladder, enters from bile duct
Gallstones = cholesterol in bile crystallizes
Need lots of surface area to absorb all those precious nutrients…

24. So, luckily we have it…
Circular folds (plicae circulares)—deep folds of mucosa and submucosa
Villi—fingerlike structures formed by mucosa
Microvilli—tiny projections of the plasma membrane (form brush border)

25. Large Intestine mainly absorbs water (some vitamins and minerals)
Larger diameter, shorter length than small intestine
Little nutrient absorption – no villi or enzymes
Concentrates and stores undigested matter (feces)
Appendix = finger-like sac of large intestine; prone to infection (appendicitis)

26. Anus held closed by 2 sphincters
Internal involuntary sphincter—opens when rectum full (smooth muscle)
External anal sphincter— under voluntary control (skeletal muscle - phew!)
Where ‘the tube’ ends… (I’m sad, too)
Figure 14.8

27. Back to the Pancreas for a moment…
Produces enzymes that breakdown everything (fats, carbs, proteins, nucleic acids)
Also secretes bicarbonate to neutralize acidic chyme
Remember the hormones?
Insulin
Glucagon
Thank goodness for the pancreas!
Figure 14.1

28. Liver manages the distribution and storage of nutrients
Blood from stomach and intestines goes directly to liver.
Largest gland in the body
Makes bile for emulsifying fat

29. Participating…
The lining of the small intestine has enormous surface area due to circular folds, ______, and __________. The large intestine absorbs mainly _______, but also some valuable _________ and minerals. The largest gland of the body that manages nutrient distribution is the ________.
villi
microvilli
water
vitamins
liver

30. Functions of the Digestive System
Figure (1 of 3)

31. Functions of the Digestive System
Figure (2 of 3)

32. Functions of the Digestive System
Figure (3 of 3)

33. Nutrition Nutrient—substance used for growth, maintenance, and repair
Major nutrients
Carbohydrates
Lipids
Proteins
Water
Minor nutrients
Vitamins
Minerals

34. Regulation of Pancreatic Juice Secretion
Figure 14.16

35. Hormones and Hormonelike Products that Act in Digestion
Table 14.1 (1 of 2)

36. Hormones and Hormonelike Products that Act in Digestion
Table 14.1 (2 of 2)

37. A. D. B. E. F. C.