1. The Digestive System
Chapter 14

2. I. Overview of Digestive System

5. A. Digestive System Organs
alimentary canal
also called gastrointestinal tract
mouth, pharynx, esophagus, stomach, small intestine, and large intestine

7. B. Digestive Processes 1. Ingestion: taking food in
2. Propulsion: move food through alimentary canal
swallowing
peristalsis: alternate waves of contraction & relaxation of muscles, squeezes food

9. 3. Mechanical digestion: physically prepares food for chemical digestion
mastication: chewing, mix with saliva
churning & mixing food in stomach
segmentation: rhythmic local constrictions of intestine

10. 4. Chemical digestion: large food molecules are broken down to their monomers
carbohydrates: monosaccharides
glucose, fructose, & galactose
proteins: amino acids
lipids: fatty acids & glycerol

11. 5. Absorption: transport of digested end products from lumen of GI tract to blood
occurs in small intestine
6. Defecation: elimination of indigestible substances from body via anus in form of feces

12. II. Anatomy of the Digestive System

13. A. Mouth & Associated Organs

15. 1. Tongue
movements required for speech, mixes food with saliva to form bolus, swallowing
papillae: taste buds
lingual tonsil

16. parotid, submandibular, sublingual
2. Salivary Glands
Saliva:
cleanses teeth, moistens food
dissolves food to release taste
enzymes for chemical breakdown of starch - amylase
parotid, submandibular, sublingual

17. 3. Teeth deciduous: 20 permanent: 32 incisors: cutting
canines: tearing
premolars: crushing
molars: crushing

18. B. Pharynx
passageway for food, fluids, & air

19. C. Esophagus muscular tube 25 cm long
goes through diaphragm at esophageal hiatus
joins stomach at gastroesophageal sphincter which is closed when food is not being swallowed

20. D. Stomach
temporary storage tank for food & site for mechanical & chemical breakdown of proteins
produces semifluid mass called chyme

22. 1. Gross Anatomy large longitudinal folds - rugae
pyloric sphincter: controls stomach emptying

23. 2. Microscopic Anatomy
four layers of muscle all running in different directions that allows food to be churned & mixed
chief cells: produce pepsinogen, inactive form of protein-digesting enzyme pepsin

24. parietal cells: secrete HCl
HCl needed for activation of pepsin & kills bacteria
mucous neck cells: produce sticky, alkaline mucus that protects stomach walls

25. E. Small Intestine 1. Gross Anatomy major digestive organ
convoluted tube extending from pyloric sphincter to ileocecal valve
6 m
most of water absorbed occurs here

26. duodenum jejenum ileum
ducts delivering bile to break down fat & pancreatic juice
jejenum
ileum

28. 2. Microscopic Anatomy modifications for absorption
increase surface area
plicae circulares: force chyme to move spirally to enhance mixing
villi: fingerlike projections
microvilli: tiny projection on villi increase surface area

29. Histology enteroendrocrine cells: secrete hormones
intestinal crypts: secrete intestinal juice
goblet cells secrete mucus to protect digestive organs

30. blood capillaries: absorption of nutrients
absorptive cells
lacteal: absorbs lipids
Peyer’s patches: kill bacteria
Brunner’s glands: produce an alkaline mucus that neutralize acidic chyme

32. F. Liver & Gallbladder store & concentrates bile - gall bladder
store vitamins
important role in detoxification of blood
produce bile

33. Acidic, fatty chyme
entering duodenum causes
release of cholecystokinin
and secretin from
duodenal wall
enteroendocrine cells
Cholecystokinin
and secretin enter the
bloodstream
(via bloodstream)
causes gallbladder
to contract and
hepatopancreatic
sphincter to relax;
bile enters
duodenum
Bile salts
and secretin
transported via
stimulate liver
to produce bile
more rapidly
Bile salts reabsorbed into blood
Vagal stimulation causes
weak contractions of
gallbladder 1 2 6 5 4 3

34. G. Pancreas Location Exocrine function
Lies deep to the greater curvature of the stomach
The head is encircled by the duodenum and the tail abuts the spleen
Exocrine function
Secretes pancreatic juice which breaks down all categories of foodstuff
Acini (clusters of secretory cells) contain zymogen granules with digestive enzymes
The pancreas also has an endocrine function – release of insulin and glucagon

35. Pancreatic Activation

36. Composition and Function of Pancreatic Juices
Water solution of enzymes and electrolytes (primarily HCO3–)
Neutralizes acid chyme
Provides optimal environment for pancreatic enzymes
Enzymes are released in inactive form and activated in the duodenum

37. Composition and Function of Pancreatic Juices
Examples include
Trypsinogen is activated to trypsin
Procarboxypeptidase is activated to carboxypeptidase
Active enzymes secreted
Amylase, lipases, and nucleases
These enzymes require ions or bile for optimal activity

38. Regulation of the Pancreas
Secretin and CCK are released when fatty or acidic chyme enters the duodenum
CCK and secretin enter the bloodstream
Upon reaching the pancreas:
CCK induces the secretion of enzyme-rich pancreatic juice
Secretin causes secretion of bicarbonate-rich pancreatic juice
Vagal stimulation also causes release of pancreatic juice

39. Acidic chyme entering
duodenum causes the
enteroendocrine cells of
the duodenal wall to release
secretin, whereas fatty,
protein-rich chyme induces
release of cholecystokinin.
During cephalic and gastric
phases, stimulation by
vagal nerve fibers causes
release of pancreatic juice
and weak contractions of
the gallbladder.
Upon reaching the
pancreas, cholecystokinin
induces the secretion of
enzyme-rich pancreatic juice;
secretin causes copious
secretion of bicarbonate-rich
pancreatic juice.
Cholecystokinin
and secretin enter
bloodstream. 1 2 3

40. H. Large Intestine ileocecal valve to anus
dry out indigestible food residues by absorbing water
eliminate residues as feces
mass peristalsis
absorption of vitamins & some electrolytes

42. III. Physiology of Digestion

43. A. Mouth
Ingestion: food placed in oral cavity
Mechanical: mastication by teeth & mixing movements by tongue

44. Chemical: breakdown of starch by salivary amylase produced by salivary glands
Propulsion: tongue propels food into pharynx

46. B. Pharynx & Esophagus
Propulsion: peristaltic waves move food bolus to stomach

47. C. Stomach
Mechanical & Propulsion: peristaltic waves mix food with gastric juice & propel chyme into duodenum

49. Chemical: digestion of proteins begun by pepsin
Absorption: absorbs a few fat-soluble substances
(aspirin, alcohol, some drugs)

50. D. Small Intestine & Associated Accessory Organs
Mechanical: segmentation by smooth muscle of small intestine continually mixes contents with digestive juices & moves food along tract & through ileocecal valve at a slow rate allowing time for digestion & absorption

51. Chemical: bile produced by liver emulsifies fats & enhances fat digestion & absorption of fatty acids, monoglycerides, cholesterol, phospholipids, & fat-soluble vitamins

52. alkaline mucus produced by intestinal glands & bicarbonate-rich juice ducted in from pancreas help neutralize acidic chyme & provide proper pH for enzymes

53. Absorption: breakdown products of carbohydrate, protein, fat & nucleic acid digestion
vitamins, electrolytes, & water

54. E. Large Intestine
Chemical: some remaining food residues are digested by bacteria (also produce vitamin K & B)

55. Absorption: absorbs most remaining water, electrolytes (NaCl), & vitamins produced by bacteria

56. Propulsion: propels feces toward rectum by peristalsis, haustral churning, & mass movements; mucus produced by goblet cells eases passage of feces through colon

57. Defecation: reflex triggered by rectal distention; eliminates feces from body

59. IV. Homeostatic Imbalances
Peritonitis – infection in the peritoneum
Impacted teeth – when teeth are embedded in the jaw bone (exert pressure and cause pain – surgical removal)
Gallstones – crystallized cholesterol in the gall bladder due to bile being stored in the gallbladder for too long (pain)
heartburn – gastric juice backs up into the esophogus through the cardioesophogeal sphincter
Hiatal hernia – structural abnormality where superior part of stomach protrudes above the diaphram

60. Peptic Ulcer – erosion of mucosa of any part of GI tract
Peptic Ulcer – erosion of mucosa of any part of GI tract. Cause – thought to be stress though some are caused by acid-resistant bacteria Helicobacter pylori
Diverticulitis – mucosa protrudes through colon walls and becomes inflamed – caused by lack of bulk in diet.
Diarrhea – result of any condition that speeds food through large intestine before water can be absorbed.
Hyperthyroidism – produces excessive metabolic rate causing body to catabolize fats and proteins - weight loss and weak bones/atrophy of muscles including heart.

61. Hypothyroidism – slowed metabolism – obesity – diminished thought processes.
Cleft palate/lip – congenital defect where palate/lip are unfused
Phenylketonuria (PKU) – cells cannot use phenylalanine (amino acid found in all protein foods). May cause brain damage – must eat diet low in phenalalanine.