1. Chapter 3: Digestion, Absorption, and Transport

2. What Are…?
Digestion: The process of breaking down food into individual molecules small enough to be absorbed through the intestinal wall
Absorption: The process of moving nutrients from the gastrointestinal (GI) tract into the bloodstream
Transport: The process of moving absorbed nutrients throughout the body through the circulatory and lymph systems
Elimination: The excretion of undigested and unabsorbed food through the feces

3. Gastrointestinal Tract
A 23-foot-long muscular tube comprised of the organs of the digestive tract
Extends from the mouth through the esophagus, stomach, and small and large intestines to the anus
Sphincters allow food to pass from one organ to the next
Saliva
Dissolves small food particles
Contains the enzyme amylase, which begins to break down carbohydrate

4. Journey through the GI Tract: Ingestion
Figure 3.1

5. Sphincters at Work
Figure 3.3

6. Journey through the GI Tract: Digestion and Absorption
Figure 3.1

7. Anatomy of the Stomach
Figure 3.4

8. Small Intestine Most digestion occurs in the small intestines
Extends from the pyloric sphincter to the ileocecal valve
Contains three sections
Duodenum
Jejunum
Ileum
Takes 3 to 10 hours for food to traverse the small intestine

9. Anatomy of the Small Intestine
Villi require proper nutrients or will deteriorate and flatten causing malabsorption
Figure 3.5

10. Anatomy of the Large Intestine
Figure 3.6

11. Large Intestine
Site of water, sodium, potassium, and chloride absorption
Bacteria produces vitamin K, thiamin, riboflavin, biotin, and vitamin B12
Only biotin and vitamin K can be absorbed
In the large intestine, 1 liter of fluid material is gradually reduced to 200 grams of brown fecal material
Brown color is due to unabsorbed iron mixed with yellowish-orange substance called bilirubin
Greater the iron content, the darker the feces

12. Journey through the GI Tract: Elimination
Final stage of defecation is influenced by age, diet, prescription medications, health, and abdominal muscle tone
Figure 3.1

13. The Accessory Organs
Figure 3.7

14. The Accessory Organs Liver
Is the first organ to receive absorbed nutrients from the portal vein
Is essential in carbohydrate metabolism
Produces proteins
Manufactures bile salts that are used to digest fats
Is the site of alcohol metabolism
Removes and degrades toxins and excess hormones

15. The Accessory Organs Gallbladder
Receives bile from the liver via common hepatic duct
Releases bile into small intestine via common bile duct
Pancreas
Endocrine function – releases hormones to maintain blood glucose levels
Exocrine function – secretes digestive enzymes into the small intestine

16. Quick Review In the mouth, saliva mixes with and moistens food
Bolus of food mixes with gastric juices in the stomach, becoming chyme
The majority of digestion and absorption occur in the small intestine
Undigested residue enters the large intestine, where water is removed from the chyme
The remnants of digestion reach the anus and exit the body in the feces
Accessory organs include the liver, which produces bile, the gallbladder, which concentrates and stores it, and the pancreas, which produces enzymes and hormones.

17. Propelling Food through the GI Tract
Food is propelled through the GI tract by synchronized contractions of the diagonal, circular, and longitudinal muscles
Two primary contractions are
Peristalsis – Squeezes food through the GI tract
Segmentation – Shifts food back and forth along the GI tract
Allows contact with surface of small and large intestine and increase absorption
Dependent on coordination between muscles, nerves, and hormones

18. Peristalsis and Segmentation
Figure 3.8

19. Quick Review
Food is propelled through GI tract by strong muscular contractions
Peristalsis squeezes food and propels it forward
Segmentation shifts food back and forth along intestinal walls

20. Chemical Digestion of Food
Aided by digestive enzymes and other substances
Regulated by hormones
Completed by the time the food reaches the large intestine

21. Chemical Digestion of Food
Enzymes
Proteins
Catalyze hydrolysis
Compatible with a specific compound or nutrient
Optimal pH range for enzyme function
Optimal temperature for enzyme function
Reactions do not change them
Named by type of substrate plus suffix –ase
Example: sucrase and maltase
Exception: pepsin
Secreted along the GI tract
Majority produced by the pancreas

23. pH Concentration of hydrogen ions in a solution
The more hydrogen ions (H–) the more acidic
The more hydroxide ions (OH–) the more basic

25. Quick Review Foods are chemically digested by hydrolysis
Enzymes catalyze hydrolysis when
Correct substrate is available
pH is optimal
Temperature is optimal
Secretions of the GI tract help optimize the environment for digestion
Saliva
Gastric juices
Bile
Bicarbonate

26. Nutrient Absorption
Majority of absorption takes place in the small intestine
Nutrients are absorbed via
Passive diffusion – nutrients move from high concentration to low concentration; no energy is required
Facilitated diffusion – nutrients move from high concentration to low concentration with the help of a carrier protein; no energy is required
Active transport – nutrients move from low concentration to high concentration with the help of a carrier protein, energy is required
Endocytosis – cell forms a vesicle to surround and engulf a nutrient

27. Nutrient Absorption
Figure 3.10

28. Nutrient Absorption
Some absorption takes place in the stomach and large intestine
Water and salt are absorbed in the large intestine

29. Quick Review
Brush border of the small intestine is the major site of nutrient absorption
Water and salt not absorbed in the small intestine are absorbed in the large intestine
Nutrients are absorbed by
Passive diffusion
Facilitated diffusion
Active transport
Endocytosis

30. Hormones Affect Digestion
The GI tract releases hormones
Enterogastrones
Are produced and secreted by the cells lining the stomach and small intestine
Gastrin, secretin, cholesystokinin (CCK), and gastric inhibitory peptide (GIP)
Influence GI motility, stomach emptying, gallbladder contraction, intestinal absorption, and hunger
Release is stimulated by the types of food passing through the digestive tract

31. Hormones Affect Digestion
Regulate digestion by controlling
The release of gastric and pancreatic secretions
Peristalsis
Enzyme activity

32. How Does the Nervous System Affect Digestion?
Lets you know when you need to eat and drink
Extrinsic nerves originate in the brain and spinal cord
Intrinsic nerves are woven into the lining of the esophagus, stomach, and small and large intestine
Hormones work with nerves to communicate feelings of hunger and fullness
Ghrelin – hormone of hunger
Peptide YY – signals that you have eaten or are full

33. Quick Review
Enterogastrones regulate digestion by stimulating or inhibiting the release of stomach, small intestine, pancreas, and gallbladder secretions, and influencing GI motility
Gastrin, secretin, cholecystokinin, and gastric inhibitor peptide
Extrinsic and intrinsic nerves communicate and interpret changes in the GI tract
Affect gastric motility, release or inhibition of digestive juices, and hunger
Ghrelin and peptide YY communicate with the nervous system
Help decide when to eat and when to stop eating

34. Transportation of Nutrients Throughout the Body
Nutrients are absorbed into the circulatory or lymphatic system
Water-soluble nutrients are absorbed into the circulatory system
Carbohydrates, amino acids, and water-soluble vitamins
Hepatic Portal Vein
Water-soluble nutrients
Water-soluble nutrients
Water-soluble nutrients
GI tract Capillaries
Liver

35. Transportation of Nutrients Throughout the Body
Fat-soluble nutrients are absorbed into the lymphatic system
Fat-soluble vitamins, long-chain fatty acids, and proteins too large to be transported via the capillaries
Lymphatic vessels
Fat-soluble nutrients
Fat-soluble nutrients
Fat-soluble nutrients
Lymph Capillaries
Thoracic Duct

36. Quick Review
The circulatory and lymph system transport absorbed nutrients throughout the body and deliver them to the cells
Water-soluble nutrients are transported via the circulatory system
Carbohydrates, proteins, and water-soluble vitamins
Fat-soluble nutrients are transported via the lymph system
Fat-soluble vitamins and long-chain fatty acids

37. Common Digestive Disorders
Digestive disorders can range from annoying to serious in nature
The esophagus, stomach, gallbladder, and large and small intestines can all be affected by problems ranging from ulcers to cancer

38. Disorders Affecting the Esophagus
Heartburn, also known as indigestion or acid reflux
The lower esophageal sphincter doesn’t close properly, allowing HCl from the stomach to flow into the esophagus
Chronic heartburn and stomach acid reflux are typical of gastroesophageal reflux disease (GERD)
Certain foods and lifestyle factors are generally associated with GERD
Dietary changes, behavior modification, antacids, prescription drugs, or surgery may help

39. Disorders Affecting the Esophagus
Esophageal cancer
This is one of the most common cancers of the digestive tract
Sufferers are typically males over age 50 who smoke and drink heavily, living in urban areas
Treatment can include surgery, radiation, and chemotherapy

40. Disorders Affecting the Stomach
Belching
Generally caused by swallowing amounts of air
It usually happens as a result of eating too fast, drinking carbonated beverages, or anxiety

41. Disorders Affecting the Stomach
Stomachache can occur for a number of reasons
Gastroenteritis (stomach flu) is the inflammation of the stomach or intestines
It can be caused by a variety of viruses
Symptoms can include nausea, vomiting, diarrhea, and abdominal cramping
Treat symptoms through rest, rehydration, and eating soft foods
Consuming food or drink fluid contaminated with a pathogenic microbe can cause vomiting, abdominal cramps, diarrhea, and fever

42. Disorders Affecting the Stomach
Ulcers
Helicobacter pylori, a bacterium, is often involved in the creation of ulcers
Common symptoms are vomiting, fatigue, bleeding, general weakness, and burning pain
Treatment can include prescription drugs, dietary recommendations, and/or surgery
An untreated ulcer can result in peritonitis, scar tissue that can obstruct food and cause vomiting and weight loss, and greater risk for stomach cancer

43. Disorders Affecting the Gallbladder
Gallbladder disease
Diagnosed most frequently in women, older Americans
Obesity and rapid weight loss are contributing factors
An unhealthy gallbladder can create gallstones
Treatment includes surgery for gallbladder removal, prescription medication, shock-wave therapy, or a combination of therapies
The body eventually adapts to the removal of the gallbladder by secreting bile directly into the duodenum

44. An Ulcer and a Large Gallstone

45. Disorders Affecting the Intestines
Flatulence
Intestinal gas, which needs to be released 10 to 20 times a day
Caused by:
foods high in fiber and starch
eating quickly
drinking carbonated beverages
lack of exercise
smoking

46. Disorders Affecting the Intestines
Diarrhea: the passage of watery, loose stools more than three times a day
Generally the result of bacterial, viral, or parasitic infections that cause food and fluids to pass too quickly through the colon
Chronic diarrhea may be the sign of a more serious problem
Untreated diarrhea can lead to malnutrition
Diarrhea can lead to dehydration and potentially death, particularly in children and the elderly

47. Disorders Affecting the Intestines
Constipation: infrequent passage of dry, hardened stools
Often due to insufficient fiber or water intake.
Exercise, normal eating patterns, and proper rest can help resolve constipation
Laxatives should be used sparingly as they can cause dehydration, salt imbalances, and laxative dependency
Colon cleansing (enema) is not recommended as a treatment

48. Disorders Affecting the Intestines
Hemorrhoids: swelling of the veins of the rectum and anus
Can lead to bleeding, itching, and/or pain
Caused by a variety of factors, including diarrhea and constipation
Treatment includes increased dietary fiber and fluid intake
Some symptoms (itching and pain) can be relieved through use of creams, ice packs, and soaking in a warm bath
Severe cases may require surgery

49. Disorders Affecting the Intestines
Irritable bowel syndrome (IBS): changes in colon rhythm
Those with IBS experience an overresponse to colon stimuli, resulting in alternating patterns of diarrhea, constipation, and abdominal pain
The exact cause is not known
Treatment includes increased dietary fiber, stress management, and prescription drugs

50. Disorders Affecting the Intestines
Ulcerative colitis: a chronic inflammation of the large intestine, resulting in ulcers in the lining of the colon
Tends to run in families
Afflicts both men and women, beginning between the ages of 15 and 30
There is no known cause or cure
Treatment includes drug therapy and surgery

51. Disorders Affecting the Intestines
Crohn’s disease
Similar to ulcerative colitis, but ulcers can occur throughout the GI tract
There is no known cause or cure
Treatment includes drug therapy and possibly surgery
Celiac disease
Consuming foods containing gluten leads to damage of the small intestine

52. Sample Celiac Disease Serum Test

53. Disorders Affecting the Intestines
Colon cancer
The third-leading cause of cancer death
One of the most curable cancers if detected early
It begins with polyps on the lining of the colon that are often small, benign, and can be surgically removed
Polyps can develop into cancerous tumors if not detected early
Treatment includes radiation, chemotherapy, or surgery
Survival rates vary depending on age, treatment response, stage of cancer diagnosis

54. Quick Review

55. Putting It All Together
Eat food
Digest to food to nutrients in the GI tract
Absorb into circulation
Deliver nutrients to the cells
The digestive process