The Digestive System Chapter 23 Lecture Notes

1
The Digestive SystemChapter 23 Lecture Notes

• to accompany
• Anatomy and Physiology From Science to Life
• textbook by
• Gail Jenkins, Christopher Kemnitz, Gerard Tortora

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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

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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

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Introduction

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

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Concept 23.1Gastrointestinal (GI) Tract
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GI Tract / Alimentary Canal

• Continuous tube from mouth to anus
• Mouth
• Pharynx
• Esophagus
• Stomach
• Small intestine
• Large intestine

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Accessory Digestive Organs

• Provide mechanical and chemical mechanisms to aid
  digestion
• Teeth
• Tongue
• Salivary glands
• Liver
• Gallbladder
• Pancreas

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Figure 23.1
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Functions of Digestive System

• Ingestion
• Secretion
• Mixing and propulsion
• Motility
• Digestion
• Mechanical and chemical
• Absorption
• Defecation

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Layers of GI Tract

• Same in all areas of GI tract
• From deep to superficial
• Mucosa
• Submucosa
• Muscularis
• Serosa

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Figure 23.2
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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

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Layers of GI Tract

• Muscularis
• Skeletal and smooth muscle
• Neurons myenteric plexus
• Serosa
• Areolar and simple squamous epithelium
• Visceral peritoneum

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Peritoneum

• Mesothelium
• Parietal peritoneum
• Visceral peritoneum
• Peritoneal cavity
• Retroperitoneal

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Figure 23.3a
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Figure 23.3b
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Figure 23.3c
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Figure 23.3d
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Folds of Peritoneum

• Greater omentum
• Adipose tissue
• Falciform ligament
• Liver to anterior abdominal wall
• Lesser omentum
• Mesentery
• Small intestine to posterior abdominal wall
• Mesocolon

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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

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Concept 23.2 Accessory Organs of the Head
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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

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Figure 23.4
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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

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Salivary Glands

• Release saliva to oral cavity
• 3 pairs of salivary glands
• Parotid
• Submandibular
• Sublingual

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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

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Figure 23.5
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Teeth

• External regions
• Crown
• Root
• Neck
• Internal components
• Enamel
• Dentin
• Cementum
• Pulp cavity
• PulpRoot canals
• Apical foramen

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Figure 23.6
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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

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Figure 23.7
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Table 23.1
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Concept 23.3 Swallowing
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Pharynx

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

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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

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Figure 23.8
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Deglutition

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

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Figure 23.9a,b
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Figure 23.9c
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Table 23.2
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Concept 23.4 Stomach
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Stomach

• Serves as mixing chamber and storage area for
  ingested food
• Rugae allow for increased volume
• 4 main regions
• Cardia
• Fundus
• Body
• Pylorus
• Pyloric antrum and canal
• Pyloric sphincter
• Lesser and greater curvatures

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Figure 23.10a
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Stomach Histology

• Mucosa
• Surface mucous cells
• Lamina propria
• Muscularis mucosae
• Gastric glands and pits
• Parietal cells
• Chief cells
• G cells
• Submucosa areolar connective tissue
• Muscularis
• 3 layers of smooth muscle
• Serosa

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Figure 23.11a
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Figure 23.11b
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Figure 23.11c
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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-)

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Figure 23.12
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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

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Table 23.3 pt 1
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Table 23.3 pt 2
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Concept 23.5 Accessory Organs of the Abdomen
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Pancreas

• Produces secretions to aid digestion
• Head
• Body
• Tail
• Pancreatic duct /duct of Wirsung
• Hepatopancreatic ampulla
• Sphincter of the heatopancreatic ampulla
  (sphincter of (Oddi)
• Regulates passage of pancreatic juice and bile
• Accessory duct (duct of Santorini)

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Figure 23.13a
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Figure 23.13b
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Figure 23.13c
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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

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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

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Liver and Gallbladder

• Liver
• Largest gland at 1.4 kg (3 lb)
• Gallbladder
• Closely associated with liver

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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

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Histology of Liver

• Lobule
• Hepatocytes radiating from central vein
• Sinusoids
• Reticuloendothelial (Kupffer) cells
• Stationary phagocytes

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Figure 23.14a
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Figure 23.14b
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Figure 23.14c
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Figure 23.14d
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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

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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

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Figure 23.15
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Bile

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

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Liver Functions

• Metabolism of
• Carbohydrates
• Lipids
• Proteins
• Process drugs and hormones
• Excrete bilirubin
• Synthesize bile salts
• Storage
• Glycogen
• Vtamins
• Minerals
• Phagocytosis
• Activate Vitamin D

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Concept 23.6 Small Intestine
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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

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Figure 23.16a
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Figure 23.16b
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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)

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Figure 23.17a