Digestive system anatomy

1. DIGESTIVE SYSTEM
Prepared By: Simranjeet Kaur
Assistant Professor
Pharmacology

2. 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

3. 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

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

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

6. Figure 23.1

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

8. Layers of GI Tract
•From deep to superficial:
•Mucosa
•Submucosa
•Muscularis
•Serosa

9. Figure 23.2

10. 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

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

12. Peritoneum
• Mesothelium
• Parietal peritoneum
• Visceral peritoneum
• Peritoneal cavity
• Retroperitoneal

13. Figure 23.3a

14. Figure 23.3b

15. Figure 23.3c

16. Figure 23.3d

17. Folds of Peritoneum
• Greater omentum
– Adipose tissue
• Falciform ligament
– Liver to anterior abdominal wall
• Lesser omentum
• Mesentery
– Small intestine to posterior abdominal wall
• Mesocolon

18. 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

19. 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

20. Figure 23.4

21. 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

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

23. 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

24. Figure 23.5

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

26. Figure 23.6

27. 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

28. Figure 23.7

29. Table 23.1

30. Concept 23.3
Swallowing

31. Pharynx
• Composed of skeletal muscle
• Lined by mucous membrane
• Nasopharynx
• Oropharynx
• Laryngopharynx

32. 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

33. Figure 23.8

34. Deglutition
• Stages of swallowing
• Voluntary
– Mouth to oropharynx
• Pharyngeal
– Deglutition center in medulla oblongata and pons
– Closing of epiglottis
– Involuntary
• Esophageal
– Involuntary
– Peristaltic contractions

35. Figure 23.9a,b

36. Figure 23.9c

37. Table 23.2

38. 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

39. Figure 23.10a

40. 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

41. Figure 23.11a

42. Figure 23.11b

43. Figure 23.11c

44. 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
-
)

45. Figure 23.12

46. 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

47. Table 23.3 pt 1

48. Table 23.3 pt 2

49. Liver
• Superficially has four lobes – right, left, caudate, and quadrate
• The largest gland in the body

50. Liver: Associated Structures
The falciform ligament:
– Separates the right and left lobes anteriorly
– Suspends the liver from the diaphragm and anterior abdominal
wall
The ligamentum teres:
– Is a remnant of the fetal umbilical vein
– Runs along the free edge of the falciform ligament

51. Liver: Associated Structures
• The Lesser omentum anchors the liver to the stomach
• The hepatic blood vessels enter the liver at the Porta hepatis
• Gallbladder - rests in a recess on the inferior surface of the right
lobe; stores bile for digestion of fats

52. Figure 23.14a

53. Figure 23.14b

54. Liver: Microscopic Anatomy
Lobules are hexagonal shaped and the structural and functional
units of the liver
– Composed of hepatocyte (liver cell) plates radiating outward
from a central vein
– Portal triads are found at each of the six corners of each liver
lobule
Portal triads consist of a bile duct and
– Hepatic artery – supplies oxygen-rich blood to the liver
– Hepatic portal vein – carries venous blood with nutrients
from digestive viscera

55. Microscopic Anatomy of the Liver
Figure 23.24c,
d

56. • Liver sinusoids – enlarged, leaky capillaries located between
hepatic plates
• Kupffer cells – hepatic macrophages found in liver sinusoids

57. 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

58. 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

59. Figure 23.15

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

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

62. 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

63. Figure 23.16a

64. Figure 23.16b

65. 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)

66. Figure 23.17a

67. Small Intestine
Structural modifications of the small intestine wall increase surface
area:
– Villi – fingerlike extensions of the mucosa
– Microvilli – tiny projections of absorptive mucosal cells’
plasma membranes

68. Small Intestine: Microscopic
Anatomy
Figure 23.21

69. Small Intestine: Histology
The epithelium of the mucosa is made up of:
– Absorptive cells and goblet cells
• Cells of intestinal crypts secrete intestinal juice
• Peyer’s patches are found in the submucosa and are collections of
lymphatic/wbc tissue
• Brunner’s glands in the duodenum secrete alkaline mucus

70. Pancreas
Posterior to great curvature of the stomach
1. head - enlarged portion in C-curve of the duodenum
2. body - tapers off beneath the stomach
3. tail - terminal part near the end
4. pancreatic duct - merges with bile duct to duodenum
a. hepatopancreatic ampulla (merging of both)
5. accessory duct - empties into duodenum, smaller

72. Pancreas - histology
• Made of glandular epithelial cells
• Pancreatic islets (of Langerhans) (1% of all cells)
a. hormones: glucagon, insulin, somatostatin
• Acini - (99% of the cells in pancreas)
a. mixture of enzymes called "pancreatic juice"

73. Figure 23.13a

74. Figure 23.13c

75. 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

76. 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

77. Bile
Bile leaves the liver via:
– Bile ducts, which fuse into the common hepatic duct
– The common hepatic duct, which fuses with the cystic duct
• These two ducts form the bile duct

78. Gallbladder and Associated Ducts

79. Hepatocytes
Hepatocyte functions include:
– Production of bile
– Processing bloodborne nutrients
– Storage of fat-soluble vitamins
– Detoxification

80. The Gallbladder
• Thin-walled, green muscular sac on the ventral surface of the
liver
• Stores and concentrates bile by absorbing its water and ions
• Releases bile via the cystic duct, which flows into the bile duct

81. Large Intestine
• Is subdivided into the cecum, appendix, colon, rectum, and anal
canal
• The saclike cecum:
– Lies below the ileocecal valve in the right iliac fossa
– Contains a wormlike vermiform appendix

82. Colon
Has distinct regions:
• ascending colon
• hepatic flexure
• transverse colon
• splenic flexure
• descending colon
• sigmoid colon

83. Large Intestine

84. Colon
• The transverse and sigmoid portions are anchored via mesenteries
called mesocolons
• The sigmoid colon joins the rectum
• The anal canal, the last segment of the large intestine, opens to
the exterior at the anus

85. Anus
• Internal sphincter - smooth muscle (involuntary)
• External sphincter - skeletal muscle (voluntary)

86. Mesenteries of Digestive Organs

87. Mesenteries of Digestive Organs

88. Mesenteries of Digestive Organs
Figure 23.30d