2. Four General Functions
Ingestion
Digestion
Absorption
Excretion

3. Digestion
The breaking down of food by both chemical and mechanical means into usable forms.

4. Types of Digestion
Mechanical Digestion – Physically breaking down of food into smaller pieces:
- Grinding of teeth to soften food
- Churning of food by smooth muscles to mix with digestive enzymes
Chemical Digestion - series of catabolic reactions that break down large molecules into smaller molecules.

5. Absorption
The passage of digested food from the alimentary canal into the cardiovascular and lymphatic systems for transportation to body cells

6. Defecation (Excretion)
The elimination of indigestible substances from the alimentary canal

7. Taking food into the body (EATING)
Ingestion
Taking food into the body (EATING)

8. Processes of the Digestive System
Mastication – chewing
Movement of skeletal muscles to close the mandible or jaw to help move the teeth break down food.

9. Maceration
Muscular waves in the stomach which mix food with the gastric juice forming a liquid paste called chyme. Occurs in the stomach.

10. Segmentation
Short small mixing movements of the alimentary canal. Muscle contractions to mix the chyme with enzymes and other secretions. Some propulsion of the chyme also occurs.

11. Peristalsis
Involuntary wave like smooth muscle contractions to propel food chime & wastes through the alimentary canal.

12. Haustral Churning
Movement of wastes along the large intestine by the contraction of pouches (haustra).
Slow, segmental churning helps to facilitate water reabsorption.

13. Gastrointestinal Tract (Alimentary Canal)
A continuous tube extending through the ventral cavity extending from the mouth to the anus
Organs of the Alimentary Canal
mouth
- pharynx
- esophagus
stomach
small intestine
- large intestine

14. Diagram of the Alimentary Canal

15. Accessory Organs
Organs that help with digestion by secreting chemicals such as enzymes and bile.
salivary glands
liver
gallbladder
- pancreas

16. Accessory Organs

17. Oral Cavity – The Mouth

18. Mouth (Oral or Buccal Cavity)
Cheeks
Lips
Hard Palate
Soft Palate
Uvula
Tongue
Papillae
Lingual Frenulum

19. Salivary Glands
Paired accessory structures that lie outside the oral cavity
Secrete their contents (saliva) into ducts that empty into the mouth
Parotid Glands - underneath the ears
Submandibular Glands - under the mandible
Sublingual Glands - under the tongue

20. Salivary Glands Accessory structures of the digestive system
Deciduous teeth (baby teeth) - 20
Permanent teeth - 32
Incisors (8) - 4 on top, 4 on bottom
chisel shaped - front of mouth
Canines (4) - 2 on top, 2 on bottom
sharp pointed tearing teeth
Premolars (8) - 4 on top, 4 on bottom
Molars (12) - 6 on top, 6 on bottom
broad, flat, crushing teeth

21. Saliva and Salivary Amylase
Salivary glands produce saliva which includes 99.5 % water, mucin, bicarbonate ions, and the enzyme, salivary amylase.
Salivary amylase helps to chemically break down starch into the disaccharide maltose.

22. Digestion in the Mouth Mechanical Digestion
Chewing (Mastication)
Tongue manipulates the food
Teeth grind up the food and mix it with saliva
The result of mechanical digestion is a soft flexible mass of food called a bolus
Chemical Digestion
Salivary amylase initiates the breakdown of carbohydrates
Only chemical digestion in the mouth

23. Digestion of Starch by Salivary Amylase

24. Teeth

25. Tooth Structures

26. Anatomy of a Tooth
Crown - exposed portion of the tooth above the gum line
Neck - constricted junction line in the tooth between the crown and the root
Root - one to three projections of the tooth that are embedded in the sockets of the alveolar processes of the mandible and maxillae

27. Anatomy of a Tooth
Enamel - outermost portion of the tooth, protects the tooth from wear and tear
the hardest substance in the body
Dentin - calcified connective tissue that gives the tooth its basic shape and rigidity
Pulp – fleshy part of the tooth that is enclosed by the dentin. It contains the blood vessels and nerves.
Cementum - a bone-like substance that covers the dentin of the root

28. Anatomy of a Tooth
Gingiva – the gums or epithelial tissue that help to protect the root of the tooth.
Periodontal Ligament - dense fibrous connective tissue, anchor teeth in position. Serves as a shock absorber when chewing.

29. Anatomy of a Tooth
Root Canal – the openings in the root that allows for the passage of blood vessels and nerves.

30. Processes of the Digestive System
Deglutition – swallowing

31. Swallowing (Deglutition)
Moving food from the mouth to the stomach
Voluntary Stage - bolus is moved through the mouth into the oropharynx
Pharyngeal Stage - involuntary passage of the bolus through the pharynx and into the esophagus
Esophageal Stage - involuntary passage of the bolus through the esophagus and into the stomach

32. Pharynx Also called the throat.
Serves as a passageway for food and air.
Also helps in the formation of words.

33. Esophagus About 10 inches long. Located posterior to the trachea.
Does not participate in digestive processes – transportation of the bolus to the stomach by peristaltic action. Moves food down into the stomach
Esophageal hiatus - opening in the diaphragm for the esophagus
Joins the stomach at the cardiac opening.

34. Peristalsis

35. Lining of the Esophagus

36. Stomach
J-shaped enlargement of the digestive tract located just below the diaphragm
Superior portion - continuation of the esophagus
Inferior portion empties into the duodenum through the pylorus.
Position and size of the stomach varies from individual to individual

37. Histology of the Stomach
Composed of the same four tissue types as the other structures of the alimentary canal
When the stomach is empty the mucosa lie in large folds called rugae
Mucosa contains millions of tiny openings called gastric pits that open into gastric glands
Secretes digestive enzymes and a fluid called gastric juice (2-3 liter per day)

38. Anatomy of the Stomach
Cardiac Opening – where the stomach is connected to the esophagus. Is not a true sphincter as food can flow into and out of the stomach.
Fundus -The rounded superior part of the stomach that will expand. Acts as a temporary storage for food.
Body -The large central portion of the stomach below the fundus.
Pylorus- narrow, inferior region of stomach that connects it to the small intestine.

39. Anatomy of the Stomach, p.2
Rugae - Folds of the stomach that allow for stretching with the intake of food.
Pyloric Sphincter – the one way valve between the stomach and the duodenum
(first part of the small intestine)

40. Anatomy of the Stomach

41. Stomach Structures

42. Secretory Cells of the Gastric Glands
Chief Cells
Digestive enzymes
Pepsinogen activated by HCl and converted to
Pepsin which breaks down protein
Parietal Cells
HCl – Hydrochloric Acid
Goblet Cells
Secrete mucus to protect the stomach mucosa from the acidic environment

43. Histology of the Stomach

44. Gastric Gland

45. Mechanical Digestion in the Stomach
Several minutes after food enters, the stomach generates mixing waves that churns the food inside - maceration
Food mixes with gastric juices and is converted into a thin liquid called chyme

46. Chemical Digestion in the Stomach
Cephalic Phase - reflexes initiated by sensory receptors in the head. Gastric juices are excreted.
sight -smell - taste -thought of food
Gastric Phase - sensory receptors in the alimentary canal and stomach initiate nervous and hormonal chemical digestive processes
Intestinal Phase - secretion of stomach enzymes that removes nutrients from food
Can absorb water if dehydrated. Medication like aspirin, ethanol and caffeine.

47. Absorption in the Stomach
Does not participate in the absorption of food molecules into the blood
However, can absorb some substances through the stomach wall
Water
Weak glucose concentrations
Electrolytes
Certain drugs (aspirin)
Alcohol

48. Small Intestine The next part of the alimentary canal.
Divided into three sections – the duodenum, jejunum, and ileum.
In the duodenum, chemical digestion is completed.
The majority of nutrients are absorbed in the jejunum and ileum.

49. The Small Intestine
Duodenum - the beginning of the small intestine where it attaches to the stomach
First 6 inches
Jejunum - the portion of the small intestine right after the duodenum
Normally about 8 ft. long
Ileum - the final portion of the small intestine
About 12 ft. long
Ileocecal valve

50. The Small Intestine

51. Chemical Digestion of the Small Intestine
Complex series of chemical events that results in the breakdown of carbohydrates, fats, and proteins
Result of the collective effort of pancreatic juice, bile, and intestinal juice which contain digestive enzymes
Results in absorption - passage of digested nutrients into the blood or lymph

52. Plicae Circulares

53. Modifictions of the Small Intestine
Villi – Finger-like extensions of the mucosa to increase surface area for absorption of nutrients.
Lacteal – lymphatic vessel for lipid absorption.

54. Villi in Duodenum

55. Absorption in the Small Intestine
90% of absorption takes place within the small intestine
Remaining 10% occurs in the stomach and large intestine
Absorption of nutrients occurs through the villi by means of:
diffusion - facilitated diffusion
osmosis - active transport

56. Villi of Small Intestine

57. Villi with Lacteal

58. Small Intestine Absorption

59. Nutrient Absorption

60. Additional Components of the Small Intestine
Intestinal Juice - slightly alkaline secretion (pH 7.6) secreted by intestinal glands
rapidly absorbed by the villi and provides a mechanism for absorption of substances in chyme
Peyer’s Patches - lymphatic glands of the small intestine
Brunner’s Glands - mucus secreting glands of the small intestine

61. Mechanical Digestion of the Small Intestine
Segmentation - localized contraction of muscles of the small intestine in areas containing food
Rate of about contractions/minute
Sloshing of chyme back and forth within the intestinal lumen
Peristalsis - rhythmical contraction of muscles of the small intestines that propels chyme through the intestinal tract

62. Large Intestine The last part of the alimentary canal.
Responsible for the absorption of water, compaction of feces, and the production of Vitamin K.

63. The Large Intestine About 1.5 m (5 ft) in length
Cecum - beginning of the large intestine
Vermiform appendix
Colon - large tube-like portion of large intestine
Ascending colon Transverse colon
Descending colon Sigmoid colon
Rectum
Anal Canal
Anus

64. Functions of the Large Intestine
Completion of absorption
Reabsorption of water
Manufacture of certain vitamins (K)
Formation of feces
Expulsion of feces from the body

65. Histology of the Large Intestine
Walls of the large intestine contain no villi or permanent circular folds in the mucosa layer
Epithelial tissue layer contain numerous goblet cells (secretes mucus)
Lubricates the colonic contents as it passes through the large intestine

66. Haustra - series of characteristic pouch like structures that run the entire length of the colon
Taenia Coli - bands of smooth muscle that are arranged longitudinally along the length of the colon
Anal Columns - parallel ridges of mucosa in the anal canal which reduces friction with feces during defecation

67. Large Intestine Histology

68. Large Intestine Structures

69. Mechanical Digestion in the Large Intestine
Haustral Churning - the relaxation and contraction of the individual segments of the colon
Peristalsis - rhythmical contraction of the colon that moves the contents along through the length of the colon
Mass Peristalsis - a strong peristaltic wave that begins about the middle of the transverse colon and drives the colonic contents into the rectum

70. Chemical Digestion in the Large Intestine
Last stage of digestion
Due to bacterial action in the large intestine
Bacteria ferment any remaining carbohydrates and release hydrogen, carbon dioxide, and methane gas
Also converts any remaining proteins into amino acids
Absorbs any remaining water and electrolytes

71. Feces Formation in the Large Intestine
By the time chyme has remained in the large intestine for hours it has become a solid or semi-solid and is known as feces
Consists of water, inorganic salts, sloughed off epithelial cells, products from bacterial decomposition, and indigestible parts of food

72. Defecation The emptying of the rectum
Diarrhea - frequent defecation of liquid feces
Constipation - infrequent or difficult defecation

73. Diagram of Accessory Organs

74. Pancreas
Oblong gland that lies posterior to the greater curvature of the stomach
Connected by the pancreatic duct to the duodenum
Composed of clusters of glandular epithelial cells.
Pancreas is the only organ classified as both an endocrine AND an exocrine gland.

75. Pancreas

76. Pancreas Two main types of Pancreatic Cells:
Pancreatic Islets-Islets of Langerhans (1%)
Hormones: insulin, glucagon, somatostatin
Acini Cells (99%)
Digestive pancreatic enzymes

77. Pancreatic Juice
Alkaline mixture of fluid and digestive enzymes from the acini cells
Pancreatic digestive enzymes:
Pancreatic amylase - carbohydrate digestion
Pancreatic lipase - fat digestion
Chymotrypsin-Trypsin-Carboxypeptidase - protein digestion
Nucleases - nucleic acid digestion
Regulated by the intestinal hormones secretin and cholecystokinin

78. Liver and Pancreas

79. Liver Located inferior to the diaphragm on the right side of the body
Largest organ of the abdominopelvic cavity
Weighs about 1.4 kgs (3 lbs)
Completely covered by the peritoneum and a dense layer of connective tissue beneath the peritoneum
Responsible for MANY regulatory functions for the body.

80. Lobules of the Liver Smaller functional units of the liver
Hepatocytes in the lobules produce bile which is a yellowish, brownish, or olive green liquid (1 quart daily)
Composed of bile salts and pigments, lecithin, and several ions
pH of
Excretory product and digestive secretion
Assists in the breakdown of fat molecules (emulsification)
Principle bile pigment is bilirubin

81. Functions of the Liver Metabolism of carbohydrates, fats, and proteins
Removal of drugs and hormones
Synthesis and excretion of bile
Storage of vitamins, minerals, and food molecules
Phagocytosis of old worn out red and white blood cells
Activation of Vitamin D
Storage of glucose and glycogen

82. The Gallbladder A pear shaped sac about 7 - 10 cm long
Located on the inferior surface of the liver
Stores and concentrates bile until it is needed by the small intestine for the emulsification of fat

83. Gallbladder

84. Summary of Digestion Mouth Ingestion
Mastication – form a bolus as food mixes with saliva.
Digestion of carbohydrates with amylase (starch to maltose)
Deglutition

85. Summary of Digestion
Pharynx
Peristalsis
Esophagus

86. Summary of Digestion Stomach
Maceration and formation of chyme as the bolus mixes with gastric juices.
Digestion of proteins to dipeptides by the enzyme, pepsin.
Peristalsis continues

87. Summary of Digestion Small Intestine Segmentation
Digestion of carbohydrates, lipids, and proteins is completed (mostly in the duodenum)
Nutrient absorption (mostly in the ileum and jejunum)
Peristalsis

88. Summary of Digestion Large Intestine Peristalsis Haustral churning
Absorption of some vitamins
Absorption of water
Formation and compaction of feces.
Excretion

89. Digestive System Diseases and Homeostatic Imbalances

90. Appendicitis Inflammation of the vermiform appendix
Can be caused by an obstruction of the lumen of the appendix by fecal material, a foreign body, stenosis, kinking of the organ, or carcinoma

91. Cirrhosis of the Liver
Distorted or scarred liver tissue due to chronic inflammation
Commonly caused by hepatitis, chemical exposure, parasites, and alcoholism
Symptoms include: jaundice, bleeding, edema, and increased sensitivity to drugs and chemicals

92. Cirrhosis of the Liver

93. Effects of Cirrhosis

94. Colorectal Cancer
Can occur in all areas of the digestive system. 3rd most common cause of cancer for both males and females. Can be benign or malignant.
Overall mortality rate is over 60%
Factors contributing to colorectal cancer include genetic predisposition, diet high in fat, protein, insufficient dietary fiber, and low calcium and selenium in the diet

95. Colorectal Cancer

97. Gall Stones Crystallization of bile in the gallbladder
Medical Term -- Cholelithiasis
Can block the bile duct causing intense pain
Usually treated with gall stone dissolving drugs, lithotripsy, or surgery

98. Gallstones

99. Gallstones

100. Hepatitis Inflammation of the liver
Can be caused by viruses, drugs, and certain chemicals including steroids and alcohol
Many different types of Hepatitis including:
Hepatitis A (Infectious Hepatitis)
Hepatitis B (Serum Hepatitis)

102. Hepatitis A Infectious hepatitis Caused by Hepatitis A virus
Spread by fecal contamination of food, clothing, toys, eating utensils, etc.
Generally a mild disease of children and young adults
Characterized by anorexia, malaise, jaundice, nausea, diarrhea, fever, and chills

103. Hepatitis B Serum hepatitis Caused by the Hepatitis B virus
Transmitted by sexual contact, contaminated syringes, transfusion equipment, saliva, tears, and puncture wounds in the skin
Can produce cirrhosis and possibly cancer of the liver

104. Hepatitis

105. Obesity Clinically classified as obese if: Body Mass Index >30
Females greater than 30% of normal body weight
Males greater than 20% of normal body weight

106. A serious risk factor for:
U.S. surgeon general has said obesity is a serious threat to the health of Americans
A serious risk factor for:
Heart Disease
- Diabetes
Hypertension
- Cancers
Respiratory Disorders
Endocrine Disorders
Gastrointestinal Disorders
Urinary and Reproductive System Disorders

107. Obesity

108. Ulcers Crater like lesions that develop in the gastrointestinal tract
Gastric Ulcers ---> Stomach
Duodenal Ulcers ---> Duodenum
Commonly caused by hypersecretion of gastric juices and acids
Contributing factors include: stress, cigarette smoking, certain foods, some medications, and bacterial infections

109. Ulcers

110. Ulcers

111. Celiac Disease
A digestive and autoimmune disorder that results in damage to the lining of the small intestine when foods with gluten are eaten. Gluten is a protein found in some grains. The damage to the intestine makes it hard for the body to absorb nutrients, especially fat, calcium, iron, and folate.

112. Celiac Disease

113. Celiac Disease

114. Crohn’s Disase
Crohn's disease is a chronic disease that causes inflammation—irritation or swelling—in the gastrointestinal (GI) tract.
Most commonly, Crohn's affects the ileum of the small intestine and the beginning of the large intestine.

115. Crohn’s Disease

116. Crohn’s Disease

117. Irritable Bowel Syndrome
Irritable bowel syndrome commonly causes cramping, abdominal pain, bloating, gas, diarrhea and constipation.
IBS is a chronic condition.
IBS does not cause changes in the tissues of the intestine.

118. Irritable Bowel Syndrome

119. Bile Pathway