1. Chapter 16 The Digestive System

2. Functions of the Digestive System
take in food
break down food
absorb digested molecules
provide nutrients
eliminate wastes

3. Two Divisions of the Digestive System
alimentary canal (digestive tract)
digests and absorbs
oral cavity to anus
accessory digestive organs

4. Organs of the Digestive System
Figure 14.1

5. Digestive Tract muscular tube approximately 9 M long open at both ends
Wall has 4 layers with some variation due to specific function.

6. Layers of Digestive Tract
innermost: mucosa
epithelial cells which line cavity
attached to connective tissue
surrounded by thin muscular layer
protects tissues of canal
carries out secretion and absorption

7. Layers of Digestive Tract
next: submucosa
thick layer of loose connective tissue housing blood vessels, lymph vessels, and nerves
nourishes surrounding layers of tract

8. Layers of Digestive Tract
next: muscular layer
inner: circular smooth muscle
outer: longitudinal smooth muscle
propels food through digestive tract
contains lots of nerves to control movement and secretion

9. Layers of Digestive Tract
outermost: serosa
visceral peritoneum
protects underlying tissue
secretes serous fluid to keep tract from sticking to other tissues of abdominal cavity

10. Layers of Alimentary Canal Organs
Figure 14.3

11. Mouth (Oral Cavity) Anatomy
teeth – 32 total in adults
incisors, premolars, molars, wisdom teeth
tongue – thick, muscular organ
functions in digestion, taste and speech
attaches to posterior part of mouth and by frenulum
covered by mucous membrane
houses taste buds within papillae
salty, sweet, sour, bitter

12. Mouth (Oral Cavity) Anatomy
tonsils
lingual and palatine
palate – roof of oral cavity
hard = bone
soft = muscle and connective tissue
separates oral and nasal cavities
uvula – fleshy projection of the soft palate

13. Salivary Glands produce saliva – mixture of mucous and serous fluids
keeps mouth moist
contains enzymes that aid in chemical digestion
3 pairs in oral cavity
parotid – located anterior to ears
secrete serous and mucous fluids
submandibular – base of jaw
ducts open below tongue
secrete more serous than mucous fluids
sublingual – smallest, below tongue
duct opens into floor of oral cavity
secretes thick, stringy mucous fluid

15. Saliva produce 1 liter a day
serous fluid: parotid and submandibular glands
contains amylase, enzyme to break down starches
lysozyme: reduces bacterial growth in mouth
mucous: contains mucin for lubrication
regulated by parasympathetic stimulation (involuntary nervous system)
increase in secretions with sight, smell, thought of food

16. Processes of the Mouth mechanical digestion
mastication (chewing) of food
mixing of food with saliva by tongue
chemical digestion
salivary amylase breaks down starches
allow for the sense of taste
NO food absorption occurs in mouth.

17. Swallowing tongue, soft palate, pharynx and esophagus
phase 1: voluntary (mouth)
Bolus (food mass) is forced into pharynx by tongue.
phase 2: involuntary (pharynx)
Pharynx connects mouth and esophagus.
Receptors in pharynx sense food which triggers swallowing reflexes.
Epiglottis covers larynx.
phase 3: involuntary (esophagus)
Esophagus connects pharynx to stomach.
Peristalsis moves food from esophagus to stomach.
Lower esophageal sphincter helps prevent regurgitation of food.

19. Stomach Anatomy located on the left side of the abdominal cavity
Food enters at the cardiac opening.
Slide 14.15a
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

20. Stomach Functions acts as a storage tank for food
site of food breakdown
start of protein digestion
very little absorption
delivers chyme (processed food) to the small intestine
Slide 14.18
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

21. Regions of the stomach Cardiac region – near the heart
Fundus – most superior part
Body
Pylorus – funnel-shaped terminal end
Food empties into the small intestine at the pyloric sphincter.
Slide 14.15b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

22. Stomach Anatomy Slide 14.17 Figure 14.4a
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

23. Muscles of the stomach different than rest of digestive tract 3 layers
outer longitudinal layer
middle circular layer
inner oblique layer
produce churning action – mechanical digestion

24. Specialized Mucosa of the Stomach
gastric glands – secrete gastric juice
3 types of cells
mucus cells – produce a sticky alkaline mucus which protects stomach lining
chief cells – secrete protein-digesting enzymes (pepsinogen which becomes pepsin)
parietal cells – secrete hydrochloric acid
rugae – internal folds of the mucosa
allows stomach to stretch when full

25. Other Stomach Secretions
gastrin – hormone that increases stomach secretions
intrinsic factor – aids in absorption of vitamin B12
cholecystokinin – hormone that stimulates gastric secretions
Production of gastric juices is regulated by hormones and the nervous system.
Humans produce about 2 L per day.

26. How Stomach Digests Food
As food enters digestive tract, gastrin is produced which causes production of gastric juices.
Food mixes with gastric juices and forms chyme which passes to pyloric region.
As food empties, secretions from stomach wall are inhibited by nervous system.

27. Stomach Movement
2 types resulting from stomach wall muscle contractions
mixing – from weak contractions
mix ingested food with stomach secretions to form chyme
peristalsis – from stronger contractions
force chyme toward and through pyloric sphincter

28. Structure of the Stomach Mucosa
Figure 14.4b, c
Slide 14.20b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

29. Small Intestine absorbs products of digestion
receives secretions from pancreas and liver
transports remaining residue to large intestine
6 meters long
ileocecal junction – joins ileum and large intestine
Ileocecal sphincter and ileocecal valve keep materials moving in right direction.

30. Subdivisions of the Small Intestine
Duodenum
attached to the stomach
curves around the head of the pancreas
25 cm long
Common bile duct from liver and pancreatic duct join each other and empty into duodenum.
Jejunum
2.5 meters; attaches anteriorly to the duodenum
Ileum
3.5 meters, extends from jejunum to large intestine
Slide 14.22
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

31. Subdivisions of the Small Intestine
Duodenum, jejunum and ileum have same structure except:
there is a gradual decrease in diameter
decrease in thickness of the walls
decrease in # of circular folds
decrease in # of villi
Slide 14.22
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

32. Chemical Digestion in the Small Intestine
3 modifications to increase surface area up to 600 times
circular folds – run perpendicular to long axis of tract
villi – tiny finger-like projections formed by mucosa
microvilli – extensions of villi found in absorptive cells

34. Mucous Lining of Small Intestine
composed of simple columnar epithelium
absorptive cells
have microvilli
produce digestive enzymes
absorb digested food
goblet cells
produce protective mucus
granular cells
protect intestinal epithelium from bacteria
endocrine cells
produce regulatory hormones

35. Secretions of the Small Intestine
lubricate and protect intestinal wall from acidic chyme and digestive enzymes
keep chyme in liquid form
produced by mucosa, pancreas, liver
peptidases – break proteins into amino acids
disaccharidases – break down complex sugars into monosaccharides
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

36. Absorption in the Small Intestine
major function of small intestine
most in duodenum and jejunum
monosaccharides – absorbed through active transport or facilitated diffusion by villi
amino acids – absorbed through active transport by villi and carried away in blood
fatty acids – dissolve into cell membranes of villi and carried away by lymphatic vessels
water – absorbed through osmosis into villi
electrolytes – absorbed by active transport by villi

37. Movement in the Small Intestine
mixing and propulsion – mechanical breakdown
peristaltic contraction – causes chyme to move along tract; occur along entire digestive tract
segmental contraction – short movements to mix contents

38. Large Intestine
larger in diameter, but shorter than the small intestine
1.5 meters
extends from ileocecal valve to anus
major functions:
absorption of water, electrolytes, vitamins K and B
elimination of indigestible food (feces)
production of mucus for lubrication
No digestion of food occurs here.
Bacteria produce vitamin K and B.

39. Divisions of the Large Intestine
cecum – saclike first part of the large intestine
appendix
accumulation of lymphatic tissue
hangs from the cecum
colon
ascending
transverse
descending
S-shaped sigmoid (in pelvis)
rectum
anus
external body opening
contains 2 sphincters

40. Large Intestine Slide 14.28 Figure 14.8
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41. Structures of the Large Intestine
3 bands of longitudinal muscle
arranged in teniae coli
create haustra (pocket like sacs in wall)
large numbers of goblet cells

42. Absorption in the Large Intestine
no digestive enzymes
absorption of water and electrolytes and vitamins K and B

43. Propulsion in the Large Intestine
mass movements
slow, powerful contractions
move contents toward anus
occur two to three times per day
cover more distance than peristaltic contractions
Presence of feces in the rectum causes a defecation reflex.
Internal anal sphincter is relaxed.
Defecation occurs with relaxation of the voluntary (external) anal sphincter.

44. Pancreas located behind the stomach
produces digestive enzymes that break down all categories of food
trypsin – protein digestion
pancreatic amylase – starch digestion
lipidase – fat digestion
secreted into the duodenum
Alkaline fluid introduced with enzymes neutralizes acidic chyme.

46. Liver located on the right side of the body under the diaphragm
consists of four lobes
capable of regeneration
connected to the gall bladder via the common hepatic duct
metabolizes carbohydrates, lipids, proteins
stores glycogen, vitamins A,D and B12, iron and blood
filters blood, removes toxins and damaged blood cells
secretes bile

48. Bile yellowish, green liquid
includes water, bile salts, bile pigments, cholesterol and electrolytes
Bile salts
emulsify fats.
aid in absorption of fatty acids, cholesterol and some vitamins

49. Gall Bladder sac found beneath liver stores bile from the liver
releases bile into the duodenum in the presence of fatty food
release controlled by sphincter muscles
Crystallized bile causes gallstones.

50. Processes of the Digestive System
Figure 14.11