1. Digestion, Absorption, and Transport
Chapter 3

2. Chapter 3 Objectives
Explain how foods move through the digestive system, describing the actions of the organs, muscles, and digestive secretions along the way.
List the segments of the digestive tract in order from the mouth to the colon.
Explain the mechanical processes of digestion in order of occurrence in the digestive tract.
List the five organs and their secretions which assist in the breakdown of food.
List the secretions that break down carbohydrates.
List the secretions that break down protein.
List the secretions that break down fat.
Describe the anatomical details of the intestinal cells that facilitate nutrient absorption.
Explain how nutrients are routed in the circulatory systems from the GI tract into the body and identify which nutrients enter the blood directly and which must first enter the lymph.
Describe how bacteria, hormones, and nerves influence the health and activities of the GI tract.
Identify the hormones involved in digestive and absorptive processes.
Outline strategies to prevent or alleviate common GI problems.
Apply the concepts presented in the chapter to explain common digestive tract problems.

3. Digestion Breaking down foods into nutrients Challenges of digestion
Prepare for absorption
Challenges of digestion
Tasks of the mouth (eat, breathe, drink)
Diaphragm (blockade)
Steady movement (pacing)
Lubrication of food (fluidity)
Digestive enzyme functions (surface area)
Excretion of waste (periodic)

4. Anatomy of the Digestive Tract
Gastrointestinal (GI) tract
Flexible and muscular tube
Path
Mouth → esophagus → stomach → small intestine → large intestine → rectum → anus
Lumen = inner space within the GI tract)
Continuous
Not “inside” the body

5. The Gastrointestinal Tract
Fig 3-1 (pg 71)

6. Anatomy of the Digestive Tract
Mouth
Process of digestion begins
Mastication
Four basic taste sensations
Sweet, sour, bitter, salty (savory/umami)
Aroma (75-95%), texture, and temperature
Must be in solution
Pharynx – digestion and respiratory tube
Bolus – swallowed food

7. Anatomy of the Digestive Tract
Esophagus
Two sphincters (each end)
Upper esophageal sphincter
Lower esophageal sphincter
Stomach
Movement of bolus
Chyme – semiliquid mass
Pyloric sphincter
Sphincter is circular muscle surrounding, and able to close, a body opening. Sphincters are found at specific points along the GI tract and regulate the flower of food particles.

8. Anatomy of the Digestive Tract
Small intestine
Common bile duct
Pancreas and gall bladder
Three segments (duodenum, jejunum, ileum)
Large intestine (colon)
Ileocecal valve
Withdrawal of water
Rectum and anus

9. Opening from small intestine to large intestine Descending colon
Transverse colon
Ascending colon
End of small intestine
Opening from small intestine
to large intestine
Figure 3-2 The Colon
The colon begins with the ascending colon rising upward toward the liver. It becomes the transverse colon as it turns and crosses the body toward the spleen. The descending colon turns downward and becomes the sigmoid colon, which extends to the rectum. Along the way, the colon mixes the intestinal contents, absorbs water and salts, and forms stools.
Descending colon
Appendix
Rectum
Sigmoid colon
Anus
Stepped Art
Figure 3-2 p72

11. Muscular Action of Digestion
Peristalsis
Circular and longitudinal muscles working together
Rate and intensity of contractions vary
Stress, meds, conditions may interfere with peristalsis
Stomach action
Strongest, thickest muscles – circular, longitudinal, and diagonal muscles
Timing the release of chyme (3x/min)

12. Stomach Muscles

13. Muscular Action of Digestion
Segmentation
Contraction of circular muscles in small intestine
Mix chyme
Promote contact with absorption cells
Sphincter contractions
Periodically open and close
Control pace of GI tract contents

14. An Example of a Sphincter Muscle

15. Secretions of Digestion
Five organs
Salivary glands
Stomach
Pancreas
Liver (gall bladder)
Small intestine
Secretions
Water
Enzymes

16. Secretions of Digestion
Enzymes
Protein that facilitates a chemical reaction
A catalyst – remains unchanged
Facilitate hydrolysis – addition of water to breakdown molecules
Look for –ase in the name

17. Secretions of Digestion
Salivary glands = Saliva
Moisten food for easy passage
Protective role
Carbohydrate digestion
Stomach = Gastric juice
HCl, along with water and enzymes
Protein digestion
Mucus to protect
pH units

18. The Salivary Glands

19. The pH Scale

20. Secretions of Digestion
Pancreas = Pancreatic juice
Released via ducts into duodenum
Enzymes act on all three energy nutrients
Sodium bicarbonate
Small Intestine = Intestinal enzymes
Liver/Gallbladder = Bile
Liver produces
Gallbladder excretes
Bile = emulsifier, not enzyme
Emulsifier – brings fats into suspension in water
so that enzymes can break them down into their component parts

21. Summary of Digestive Secretions & Their Major Actions

22. The Final Stage Undigested residues Colon
Fiber carries some minerals, bile acids, additives, contaminants out of the body
Exercise intestinal muscles
Fiber retains water  stool consistency
Colon
Intestinal bacteria ferment some fibers  gas
Recyclable materials retrieved
Water and dissolved salts

25. Absorption Small intestine Majority of absorption Ten feet long
Surface area – villi, microvilli
Absorption techniques
Simple diffusion – with gradient
Facilitated diffusion – carrier cell
Active transport – against gradient

26. FACILITATED DIFFUSION
Carrier loads nutrient on outside of cell . . .
Carrier loads nutrient on outside of cell . . .
Outside cell
Energy
Cell membrane
. . . and then releases it on inside of cell.
. . . and then releases it on inside of cell.
Inside cell
Some nutrients (such as water and small lipids) are absorbed by simple diffusion. They cross into intestinal cells freely.
SIMPLE DIFFUSION
FACILITATED DIFFUSION
Some nutrients (such as the water-soluble vitamins) are absorbed by facilitated diffusion. They need a specific carrier to transport them from one side of the cell membrane to the other. (Alternatively, facilitated diffusion may occur when the carrier changes the cell membrane in such a way that the nutrients can pass through.)
ACTIVE TRANSPORT
Some nutrients (such as glucose and amino acids) must be absorbed actively. These nutrients move against a concentration gradient, which requires energy.
Figure 3-8 A bsorption of Nutrients
Absorption of nutrients into intestinal cells typically occurs by simple diffusion, facilitated diffusion, or active transport. Occasionally, a large molecule is absorbed by endocytosis—a process in which the cell membrane engulfs the molecule, forming a sac that separates from the membrane and moves into the cell.
Stepped Art
Figure 3-8 p77

27. Anatomy of the Absorptive System
Villi
Select and regulate nutrients absorbed
Microvilli
Enzymes and “pumps”
Crypts
In the “valleys”
Secretion of intestinal juices
Goblet cells
Mucus secretion

29. A Closer Look at the Intestinal Cells
Villi cells
Regulate nutrient absorption based on needs
Microvilli
Enzymes and ‘pumps’
Specialized cells
Duodenum not the same as ileum
Food combining
Enhanced use in the body
Ex: vit C and iron

30. A Closer Look at the Intestinal Cells
Once in villus, divergent transport pathways
Bloodstream
Water-soluble nutrients and smaller products of fat digestion
Liver
Lymphatic system
Larger fats and fat-soluble vitamins
Chylomicrons (ch 5)
Bypass liver at first

32. The Vascular System Closed system of vessels Blood Heart pump
Delivers oxygen and nutrients
Removes carbon dioxide and wastes
Blood flow
Special routing for digestive system
Liver

33. The Vascular System

34. The Liver

35. The Lymphatic System One-way route Entry into bloodstream
No pump
Circulation between cells
Entry into bloodstream
Subclavian vein (near heart)
Nutrients in lymphatic vessels
Bypass liver at first

37. Health and Regulation of the GI Tract
Gastrointestinal bacteria – flora
Most are not harmful
Benefits of gastrointestinal bacteria
Factors influencing bacteria presence
Diet – probiotics
Prebiotics
Digestion of fibers and complex proteins
Vitamin production

38. Gastrointestinal Hormones and Nerve Pathways
Homeostatic regulation
Endocrine system
Nervous system
Feedback mechanisms
Examples
GI hormones
Gastrin  stimulates HCl secretion
Secretin  stimulates bicarb secretion
Cholecystokinin (CCK)  stimulates bile secretion

39. An Example of a Negative Feedback Loop

40. The Primary actions of Selected GI Hormones

41. The System at Its Best Sensitive and responsive to environment
Immunity against intestinal diseases
Defense against foreign invaders
Health of digestive system
Healthy supply of blood
Lifestyle factors
Types of foods eaten
Balance, moderation, adequacy, and variety

43. Common Digestive Problems
Highlight 3

44. Choking Food slips into trachea International sign for choking
Cuts off breathing
International sign for choking
Heimlich maneuver
Foods commonly associated with choking
Prevention of choking

45. Normal Swallowing and Choking

46. First Aid for Choking

47. Vomiting Vomiting Adaptive mechanism of the body Medical treatment
Dehydration
Self induced

48. Diarrhea Diarrhea Symptom of medical conditions & treatments Treatment
Irritable bowel syndrome (IBS)
Colitis
Treatment

49. Irritable Bowel Syndrome and Colitis
Characterization
Cause
Unknown
Triggers
Colitis
Inflammation of large intestine

50. Celiac Disease Autoimmune disease Gluten-containing foods Symptoms
Inflammation of small intestine
Gluten-containing foods
Symptoms
Treatment
Rehydration

51. Constipation Not a disease Symptoms of constipation Causes Prevention
Lifestyle
Side effect of medications
Prevention
Fiber and water
Physical activity

52. Constipation Hemorrhoids Diverticulosis Laxatives Harmful practices
Colonic irrigation

53. Belching and Gas Belching Intestinal gas Swallowed air Prevention
Consumption of certain foods
Individually determined

54. Heartburn and “Acid Indigestion”
Gastroesophageal reflux (heartburn)
Causes
Prevention
Indigestion
Antacids and acid controllers
Damage to esophagus
Barrett’s esophagus

55. Gastroesophageal Reflux

56. Ulcers Peptic ulcers Causes Ulcer treatment regimen Gastric ulcers
Duodenal ulcers
Causes
Bacterial infection
Anti-inflammatory drugs
Excessive gastric acid secretion
Ulcer treatment regimen

57. Strategies to Prevent or Alleviate Common GI Problems