The human digestive system

1. The Digestive System
Chapter 23 – Lecture Notes
to accompany
Anatomy and Physiology: From Science to Life
textbook by
Gail Jenkins, Christopher Kemnitz, Gerard Tortora

2. Chapter Overview
23.1 Gastrointestinal (GI) Tract
23.2 Accessory Organs of the Head
23.3 Swallowing
23.4 Stomach
23.5 Accessory Organs of the Abdomen
23.6 Small Intestine
23.7 Large Intestine
23.8 Phases of Digestion
23.9 Food Molecules
23.10 Metabolism

3. Essential Terms
digestion
 process of mechanically or chemically breaking
down food
absorption
 passage of small molecules into blood and lymph
digestive system
 organs which carry out process of digestion and
absorption
metabolism
 all the chemical reactions of the body

4. Introduction
Digestive System
1. Composed of GI tract and accessory
organs
2. Breaks down ingested food for use by the
body
3. Digestion occurs by mechanical and
chemical mechanisms
4. Excretes waste products or feces through
process of defecation

5. Concept 23.1
Gastrointestinal (GI) Tract

6. GI Tract / Alimentary Canal
 Continuous tube from mouth to anus
 Mouth
 Pharynx
 Esophagus
 Stomach
 Small intestine
 Large intestine

7. Accessory Digestive Organs
 Provide mechanical and chemical mechanisms
to aid digestion
 Teeth
 Tongue
 Salivary glands
 Liver
 Gallbladder
 Pancreas

8. Figure 23.1

9. Functions of Digestive System
1. Ingestion
2. Secretion
3. Mixing and propulsion
• Motility
4. Digestion
• Mechanical and chemical
5. Absorption
6. Defecation

10. Layers of GI Tract
 Same in all areas of GI tract
 From deep to superficial:
 Mucosa
 Submucosa
 Muscularis
 Serosa

11. Figure 23.2

12. Layers of GI Tract
 Mucosa
 Epithelium
 Type varies
 Lamina propria – areolar connective tissue
 MALT – mucus-associated lymphatic tissue
 Muscularis mucosae – smooth muscle
 Submucosa
 Areolar connective tissue
 Blood and lymphatic vessels
 Neurons – submucosal plexus

13. Layers of GI Tract
 Muscularis
 Skeletal and smooth muscle
 Neurons – myenteric plexus
 Serosa
 Areolar and simple squamous epithelium
 Visceral peritoneum

14. Peritoneum
 Mesothelium
 Parietal peritoneum
 Visceral peritoneum
 Peritoneal cavity
 Retroperitoneal

15. Figure 23.3a

16. Figure 23.3b

17. Figure 23.3c

18. Figure 23.3d

19. Folds of Peritoneum
 Greater omentum
 Adipose tissue
 Falciform ligament
 Liver to anterior abdominal wall
 Lesser omentum
 Mesentery
 Small intestine to posterior abdominal wall
 Mesocolon

20. Neural Innervation of GI Tract
 Regulated by autonomic nervous system
 Enteric division
 Myenteric plexus / plexus of Auerbach
 Submucosal plexus / plexus of Meissner
 Able to function independently from rest of nervous system
 Linked to CNS by extrinsic sympathetic and parasympathetic
nerves
 Sympathetic nerves decrease GI secretions & motility
 Parasympathetic nerves increase GI secretion and motility

21. Concept 23.2
Accessory Organs of the
Head

22. Mouth Parts of Digestive System
 Mouth formed by several parts:
 Cheeks
 Lips / labia
 Labial frenulum
 Orbicularis
 Vestibule
 Oral cavity proper
 Fauces
 Hard and soft palate
 Uvula
 Palatoglossal and palatopharyngeal arch

23. Figure 23.4

24. Tongue
 Skeletal muscle and mucous membrane
 Helps form floor of oral cavity
 Extrinsic muscles
 Intrinsic muscles
 Lingual frenulum
 Papillae
 Fungiform
 Filiform
 Circumvallate
 Foliate
 Lingual glands
 Lingual lipase

25. Salivary Glands
 Release saliva to oral cavity
 3 pairs of salivary glands
 Parotid
 Submandibular
 Sublingual

26. Composition of Saliva
 99.5 % water
 0.5% other solutes
 Ions
 Mucus
 Immunoglobulin A
 Enzymes
 Salivation controlled by autonomic nervous
system
 Stimulated by various mechanisms

27. Figure 23.5

28. Teeth
 External regions
1. Crown
2. Root
3. Neck
 Internal components
1. Enamel
2. Dentin
 Cementum
3. Pulp cavity
 PulpRoot canals
 Apical foramen

29. Figure 23.6

30. Teeth
 Dentitions
 Deciduous teeth – first set
 Permanent teeth – secondary
 Carry out mechanical digestion by mastication
 Creates bolus
 Salivary amylase
 Breakdown starch
 Lingual lipase
 Breakdown triglycerides

31. Figure 23.7

32. Table 23.1

33. Concept 23.3
Swallowing

34. Pharynx
 Composed of skeletal muscle
 Lined by mucous membrane
 Nasopharynx
 Oropharynx
 Laryngopharynx

35. Esophagus
 Collapsible muscular tube through esophageal
hiatus of diaphragm
 Mucosa
 Submucosa contains areolar connective tissue
 Muscularis
 Skeletal muscle
 Upper and lower esophageal sphincter
 Adventitia
 Attaches esophagus to nearby structures
 Secrets mucus and transports food

36. Figure 23.8

37. Deglutition
 Stages of swallowing
 Voluntary
 Mouth to oropharynx
 Pharyngeal
 Deglutition center in medulla oblongata and pons
 Closing of epiglottis
 Involuntary
 Esophageal
 Involuntary
 Peristaltic contractions

38. Figure 23.9a,b

39. Figure 23.9c

40. Table 23.2

41. Concept 23.4
Stomach

42. Stomach
 Serves as mixing chamber and storage area for
ingested food
 Rugae allow for increased volume
 4 main regions
1. Cardia
2. Fundus
3. Body
4. Pylorus
 Pyloric antrum and canal
 Pyloric sphincter
 Lesser and greater curvatures

43. Figure 23.10a

44. Stomach Histology
1. Mucosa
 Surface mucous cells
 Lamina propria
 Muscularis mucosae
 Gastric glands and pits
 Parietal cells
 Chief cells
 G cells
2. Submucosa – areolar connective tissue
3. Muscularis
 3 layers of smooth muscle
4. Serosa

45. Figure 23.11a

46. Figure 23.11b

47. Figure 23.11c

48. Mechanical and Chemical Digestion
 Mixing waves caused by peristaltic movement
 Chyme released in process of gastric emptying
 Proton pumps bring H+ into the lumen
 Carbonic anhydrase forms carbonic acid to
provide H+ and bicarbonate ions (HCO3
-)

49. Figure 23.12

50. Mechanical and Chemical Digestion
 Chemical digestion stimulated by nervous system
 Parasympathetic neurons release acetylcholine
 Works with gastrin
 HCl released in presence of histamine
 Pepsin begins digestion of proteins
 Stomach protected by alkaline mucus secretion
 Gastric lipase digests triglycerides
 Few molecules absorbed by stomach
 Water, ions, short-chain fatty acids, alcohol

51. Table 23.3 pt 1

52. Table 23.3 pt 2

53. Concept 23.5
Accessory Organs of the
Abdomen

54. Pancreas
 Produces secretions to aid digestion
 Head
 Body
 Tail
 Pancreatic duct /duct of Wirsung
 Hepatopancreatic ampulla
 Sphincter of the hepatopancreatic ampulla
(sphincter of (Oddi)
 Regulates passage of pancreatic juice and bile
 Accessory duct (duct of Santorini)

55. Figure 23.13a

56. Figure 23.13b

57. Figure 23.13c

58. Histology of Pancreas
 Glandular epithelial cells
 99% exocrine clusters
 Secrete pancreatic juice
 Fluid and enzymes
 Pancreatic islets (islets of Langerhans)
 1% endocrine cells
 Hormones
 Glucagon
 Insulin
 Somatostatin
 Pancreatic polypeptide

59. Pancreatic Juice
 1200-1500 mL/day
 pH 7.1-8.2
 Water
 Salts
 Sodium bicarbonate
 Enzymes
 Pancreatic amylase
 Trypsin
 Entereokinase
 Chymotrypsin
 Carboxypeptidase
 Elastase
 Pancreatic lipase
 Ribonuclease and deoxyribonuclease

60. Liver and Gallbladder
 Liver
 Largest gland at 1.4 kg (~3 lb)
 Gallbladder
 Closely associated with liver

61. Anatomy of Liver
 Right and left lobe separated by falciform
ligament
 Quadrate lobe
 Caudate lobe
 Round ligament (ligamentum teres)
 Remnant of umbilical vein
 coronary ligaments

62. Histology of Liver
 Lobule
 Hepatocytes radiating from central vein
 Sinusoids
 Reticuloendothelial (Kupffer) cells
 Stationary phagocytes

63. Figure 23.14a

64. Figure 23.14b

65. Figure 23.14c

66. Figure 23.14d

67. Bile Duct System
 Bile secreted by hepatocytes
 Bile canaliculi
 Bile ducts
 Right and left hepatic ducts
 Common hepatic duct
 Common bile duct
 Gallbladder for temporary storage of bile
 Cystic duct

68. Blood Supply of Liver
 Hepatic artery provides oxygenated blood
 Hepatic portal vein provides deoxygenated blood
 Nutrients, drugs, toxins, microbes
 Hepatic artery and vein carry blood to sinusoids
 Substances exchanged by hepatocytes
 Blood drains to central vein and eventually hepatic vein
 Portal triad
 Hepatic portal vein
 Hepatic artery
 Bile duct

69. Figure 23.15

70. Bile
 800-1000 mL/day
 pH 7.6 – 8.6
 Water
 Bile acids
 Bile salts
 Emulsification
 Cholesterol
 Lecithin
 Bile pigments
 Bilirubin
 Stercobilin

71. Liver Functions
 Metabolism of:
 Carbohydrates
 Lipids
 Proteins
 Process drugs and hormones
 Excrete bilirubin
 Synthesize bile salts
 Storage
 Glycogen
 Vtamins
 Minerals
 Phagocytosis
 Activate Vitamin D

72. Concept 23.6
Small Intestine

73. Small Intestine
 Adapted for digestion and absorption
 3 m (10 ft) living
 6.5 m (21 ft) without muscle tone
 Duodenum
 Jejunum
 Ileum
 Ileocecal sphincter
 Connection to large intestine

74. Figure 23.16a

75. Figure 23.16b

76. Histology of Small Intestine
 Mucosa
 Cell types
 Absorptive
 Goblet
 Endocrine
 Paneth
 Lysozyme
 Intestinal glands (crypts of Lieberkühn)
 S cells
 Hormone secretin
 CCK cells
 Hormone – cholecystokinin (CCK)

77. Figure 23.17a