1. Ch 23: The Digestive System
Section 1: Overview of the Digestive System (pp )

2. Digestive System Overview
Two groups of organs:
1) Alimentary canal
- also known as gastrointestinal or GI tract
- digests & absorbs food
Major organs:
- mouth, pharynx, esophagus, stomach, small intestine, & large intestine

3. Digestive System Overview
Two groups of organs:
2) Accessory digestive organs
- teeth, tongue, & gallbladder
Major digestive glands:
- salivary glands, liver, & pancreas

4. Digestive Processes Digestion
- the physical grinding & chemical breakdown of food
ALL digestive systems must accomplish the following:
Ingestion
- placing food into digestive tract
Mechanical breakdown
- food physically broken down into smaller pieces
- allows digestive enzymes to work more efficiently

5. Digestion Chemical breakdown Absorption Elimination
- particles exposed to digestive enzymes
- breaks large molecules into smaller subunits
Absorption
- subunits transported out of digestive system…into cells
Elimination
- indigestible material expelled from body

6. Histology of Alimentary Canal
Four basic layers of tissue:
1) Mucosa
- inner lining of canal
- secretes mucus, digestive enzymes, & hormones
- absorbs nutrients
- protects against infectious diseases

7. Histology of Alimentary Canal
Four basic layers of tissue:
2) Submucosa
- dense connective tissue under mucosal layer
- rich in blood supply, lymph tissue, & nerves
- elastic fibers allow stomach to regain normal shape after large meal

8. Histology of Alimentary Canal
Four basic layers of tissue:
3) Muscularis externa
- responsible for peristalsis (rhythmic muscular contractions that move food through the canal)
Composed of two layers:
a) Inner circular layer opens/closes canal
b) Outer longitudinal layer lengthens/shortens canal

9. Histology of Alimentary Canal
Four basic layers of tissue:
4) Serosa
- protective, outermost layer
- known as the visceral peritoneum

10. Ch 23: The Digestive System
Section 2: Functional Anatomy of the Digestive System (pp )

11. Mouth Mechanical & chemical breakdown of food: - begins in the mouth
- mouth lined with thick stratified squamous epithelium to withstand considerable friction
- breakdown of food carried out mostly by the teeth

12. Teeth Function of teeth: - to break food down into smaller fragments
- vastly improves rate & efficiency of chemical breakdown of food in stomach

13. Teeth Tooth “Timeline”: 1) Deciduous teeth (“baby teeth”)
- begin appearing at 6 months; complete by age 2
- 20 total
- between age 6-12, roots are reabsorbed; teeth fall out
2) Permanent teeth
- 32 total
- All except wisdom teeth appear by end of adolescence
- Wisdom teeth appear by age 25 (sometimes never)

14. Mouth Teeth 1) Incisors 2) Canines 3) Premolars & Molars
- front of mouth; snip off pieces
of food
2) Canines
- pointed; useful for tearing
3) Premolars & Molars
- back of mouth; flattened
surfaces used to grind food
into a paste

15. Tongue Functions of the tongue: - reposition & mix food during chewing
- initiates swallowing response
- provides ability to manipulate sounds to form words
- provides sense of taste

16. Tongue Features of the tongue: 1) Filiform papillae
- cone-shaped; provide friction for manipulating foods
- smallest & most numerous
- contain keratin; gives them a whitish appearance
2) Fungiform papillae
- scattered across surface of tongue
- contain blood vessels; gives them a reddish appearance

17. Super Tasters Tongue Features of the tongue: 3) Circumvalate papillae
- form V-shaped row on back of tongue
4) Foliate papillae
- located on the sides of the tongue; near the back
**Fungiform, Circumvalate, & Foliate papillae together form the taste buds**
Note: Foliate taste buds only function during infancy & early childhood
Super Tasters

18. Cancerous salivary gland
Salivary Glands
- provide first stage of chemical digestion
- pour out saliva in response smell, feel, & taste
- can even be activated by the THOUGHT of food
Cancerous salivary gland

19. Saliva Saliva Donuts…. - mixture of mucus & water
- contains Amylase (digestive enzyme that begins
breaking down starches into sugars)
- kills bacteria & lubricates food
- taste is a direct result of food dissolving in saliva
Donuts….

20. Swallowing After chewing… Pharynx
- tongue (a muscle) presses food backward into pharynx
Pharynx
- muscular cavity connecting mouth w/ esophagus & larynx
- separates food/liquids from air that is being inhaled

21. Swallowing Epiglottis
- flap of cartilage that closes off the larynx when you
swallow…prevents food from going into lungs

22. Esophagus Once past the epiglottis… - Food travels into the esophagus
- Esophagus is collapsed when empty

23. Stomach Stomach Rugae Gastric pits
- Expandable bag…capable of holding 2-4 liters of food/liquid
- Located on left side of abdominal cavity
- Food enters at cardioesophageal sphincter & exits at pyloric
sphincter (both act as “clamps” on either end of stomach)
Rugae
- Internal folds of stomach…allow for expansion
Gastric pits
- Line inner wall…release HCl & various other enzymes

24. Stomach

25. Stomach

26. Stomach Stomach Functions:
Stores food gradually releasing it into small intestine
Continues mechanical breakdown of food
- 3 groups of muscles “churn” food
Major chemical breakdown of food begins
*Food gradually converted into thick, acidic liquid called chyme
Takes 2-6 hrs to empty stomach depending on size of meal…

27. Stomach Stomach functions:
- “Churning” action mixes food w/ digestive enzymes
- Peristalsis occurs in lower stomach

28. Stomach Stomach functions:
- Pyloric sphincter releases food 20-30mL at a time

29. Stomach Protection: - lined with a layer of bicarbonate-rich mucus
- bicarbonate is a base…helps to neutralize acid
- damaged epithelial cells are replaced quickly

30. Stomach Vomiting: Most commonly caused by:
- body’s attempt to rid itself of substances that are unsettling to the stomach
Most commonly caused by:
- extreme stretching (due to over-eating) of the stomach &/or small intestine
- bacterial toxins
- excessive alcohol
- spicy foods
- certain drugs

31. Small Intestine Small intestine 2 Major Functions
- Body’s major digestive organ
- Longest part of digestive tract…approximately 20ft
2 Major Functions
1) Use enzymes from liver & pancreas to break food
particles into small molecules
2) Absorb molecules into the bloodstream

32. Inflamed Small Intestine
3 Major Segments of Small Intestine
Duodenum
- Directly attached to stomach
Jejunum
Ileum
- Directly attaches to large intestine
Inflamed Small Intestine

33. Small Intestine Duodenum
- Mixes chyme from stomach with liver & pancreatic enzymes

34. Small Intestine Remember: Key structures: 1) Numerous folds 2) Villi
*In addition to being the major site for digestion, the small intestine is the main location for food absorption.
Key structures:
1) Numerous folds
- increase the total surface area by over 600 times that of a smooth tube that is same length
2) Villi
- Minute, fingerlike projections that line entire folded surface…further increase SA of intestinal wall

35. **Without these structures, absorption would be VERY inefficient!
Small Intestine
Key structures:
3) Microvilli
- Further divisions of villi…even more increased SA
*Together, these 3 structures give the intestinal wall the surface area of a tennis court!
**Without these structures, absorption would be VERY inefficient!

36. Small Intestine

37. Small Intestine Key structures: 4) Circular folds
- permanent folds; about 1cm deep
- forces chyme to slowly spiral as it moves through canal

38. Liver Liver Functions - Perhaps the most versatile organ
- Largest gland in the body
Functions
Storing fats & carbohydrates for energy
Regulating blood glucose levels
Synthesizing blood proteins
Storing iron & some vitamins
Detoxifying harmful substances we ingest

39. Liver Bile - Complex mixture of bile salts, water, & cholesterol
- Acts as a detergent or emulsifying agent that causes fat
particles to be dissolved into microscopic particles
that can be broken down by other enzymes
- Stored in gall bladder & released into small intestine
through tube called the bile duct
Normal Liver
Cirrhosis of the Liver
Fatty Liver

40. Pancreas
Pancreas
- Small organ sitting between stomach & small intestine
- Produces a “soup” of enzymes that can break down
the 3 major types of nutrients:
Carbohydrates
Lipids
Proteins
- Insulin is produced here

41. Composed of 2 Main Sections:
Large Intestine
Large Intestine
- Wider diameter, but only half as long as small intestine
- Does not participate in digestion
- Absorbs majority of water in food
- Eliminates indigestible food in form of feces
- Not essential for life
Composed of 2 Main Sections:
Colon
Rectum

42. Large Intestine Divisions of the Colon: 1) Cecum 2) Ascending
- Connection between sm. & lg. intestine
- Appendix (collection of lymph tissue) attached here
2) Ascending
3) Transverse
4) Descending
5) S-shaped sigmoid
**Goblet cells…part of lining of lg. intestine…produces mucous that acts as a lubricant

43. Large Intestine

44. Large Intestine Bacterial Flora:
- various bacteria colonize the large intestine
- ferment & break down indigestible carbohydrates
- help to synthesize Vitamins B and K

45. Ch 23: The Digestive System
Section 3: Physiology of Chemical Digestion/Absorption (pp )

46. Digestive System - Control
Digestion is controlled by:
1) the parasympathetic nervous system
2) hormones
Stimuli include:
1) stretch of the organ
2) pH of the stomach contents
3) presence of broken down food particles

47. Digestive Structures & Secretions
Overview of Digestion
Digestive Structures & Secretions
Site
Source
Secretion
Results
Mouth
Salivary glands
Amylase
Breaks down starch into disaccharides
Mucus, water
Lubricates, dissolves food
Stomach
Cells lining stomach
Small Intestine
Liver
Pancreas
Intestine

48. Digestive Structures & Secretions
Overview of Digestion
Digestive Structures & Secretions
Site
Source
Secretion
Results
Mouth
Salivary glands
Amylase
Breaks down starch into disaccharides
Mucus, water
Lubricates, dissolves food
Stomach
Cells lining stomach
Hydrochloric acid
Kills bacteria, dissolves minerals
Pepsin
Breaks down proteins into peptides
Mucus
Protects stomach lining
Small Intestine
Liver
Pancreas
Intestine

49. Digestive Structures & Secretions
Overview of Digestion
Digestive Structures & Secretions
Site
Source
Secretion
Results
Mouth
Salivary glands
Amylase
Breaks down starch into disaccharides
Mucus, water
Lubricates, dissolves food
Stomach
Cells lining stomach
Hydrochloric acid
Kills bacteria, dissolves minerals
Pepsin
Breaks down proteins into peptides
Mucus
Protects stomach lining
Small Intestine
Liver
Bile
Emulsifies lipids
Pancreas
Sodium bicarbonate
Neutralizes acidic chyme from stomach
Protease
Lipase
Breaks down lipids
Intestine
Peptidase
Breaks down peptides into amino acids
Disaccharidase
Converts disaccharides into monosaccharides

50. Overview of Digestion

51. Ch 23: The Digestive System
Section 3: Homeostatic Imbalances

52. Homeostatic Imbalances
Dental cavities:
- gradual demineralization of tooth enamel
- caused by dental plaque (sugar, bacteria, & other debris) that sticks to teeth
- bacteria secrete acid that dissolves calcium in teeth

53. Homeostatic Imbalances
Gingivitis:
- caused when plaque begins to calcify & harden
- calcified plaque separates teeth from gums
- bacteria enter separation site & infect gums

54. Homeostatic Imbalances
Periodontitis:
- autoimmune disorder that destroys ligament holding tooth in socket
- accounts for 80-90% of tooth loss in adults

55. Homeostatic Imbalances
Gastritis:
- inflammation that is caused by anything that interferes
with the mucus layer on the inside of the alimentary canal
Gastric ulcers:
- erosion of the stomach wall
- usually caused by bacterial infection or hypersecretion of digestive enzymes

56. Homeostatic Imbalances
Heartburn:
- burning sensation caused when digestive chemicals escape the stomach & move up into the esophagus
- usually the result of eating or drinking too much
- causes frequent problems in people who have a weak cardioesophageal sphincter

57. Homeostatic Imbalances
Gall stones:
- crystals that develop in the gallbladder
- often the result of too much cholesterol or too little bile
- stones can possibly be dissolved by using ultrasound
- often requires surgical removal

58. Homeostatic Imbalances
8) Hepatitis:
- inflammation of the liver caused by viral infection
Cirrhosis:
- chronic inflammation of the liver often caused by excessive alcohol consumption
- liver transplant is the only effective treatment for patients with severe cirrhosis

59. Homeostatic Imbalances
Bruxism:
- grinding or clenching of teeth; especially when sleeping
- can wear down or crack teeth over time
- usually a sign of stress
Dysphagia:
- difficulty in swallowing
- usually due to obstruction or physical trauma to esophagus