The Digestive SystemChapter 23 – Lecture Notes

to accompany

Anatomy and Physiology: From Science to Life

textbook by

Gail Jenkins, Christopher Kemnitz, Gerard Tortora

Chapter Overview23.1 Gastrointestinal (GI) Tract23.2 Accessory Organs of the Head23.3 Swallowing23.4 Stomach23.5 Accessory Organs of the Abdomen23.6 Small Intestine23.7 Large Intestine23.8 Phases of Digestion 23.9 Food Molecules23.10 Metabolism

Essential Terms

digestion process of mechanically or chemically breaking

down foodabsorption passage of small molecules into blood and lymphdigestive system organs which carry out process of digestion and

absorptionmetabolism all the chemical reactions of the body

IntroductionDigestive 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

Concept 23.1

Gastrointestinal (GI) Tract

GI Tract / Alimentary Canal

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

Accessory Digestive Organs Provide mechanical and chemical mechanisms

to aid digestion Teeth Tongue Salivary glands Liver Gallbladder Pancreas

Figure 23.1

Functions of Digestive System1. Ingestion

2. Secretion

3. Mixing and propulsion• Motility

4. Digestion• Mechanical and chemical

5. Absorption

6. Defecation

Layers of GI Tract

Same in all areas of GI tract

From deep to superficial: Mucosa Submucosa Muscularis Serosa

Figure 23.2

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

Layers of GI Tract

Muscularis Skeletal and smooth muscle Neurons – myenteric plexus

Serosa Areolar and simple squamous epithelium Visceral peritoneum

Peritoneum

Mesothelium Parietal peritoneum Visceral peritoneum Peritoneal cavity Retroperitoneal

Figure 23.3a

Figure 23.3b

Figure 23.3c

Figure 23.3d

Folds of Peritoneum

Greater omentum Adipose tissue

Falciform ligament Liver to anterior abdominal wall

Lesser omentum Mesentery

Small intestine to posterior abdominal wall Mesocolon

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

Concept 23.2 Accessory Organs of the Head

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

Figure 23.4

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

Salivary Glands

Release saliva to oral cavity

3 pairs of salivary glands Parotid Submandibular Sublingual

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

Figure 23.5

Teeth

External regions1. Crown2. Root3. Neck

Internal components1. Enamel2. Dentin

Cementum

3. Pulp cavity PulpRoot canals Apical foramen

Figure 23.6

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

Figure 23.7

Table 23.1

Concept 23.3 Swallowing

Pharynx

Composed of skeletal muscle Lined by mucous membrane

Nasopharynx Oropharynx Laryngopharynx

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

Figure 23.8

Deglutition

Stages of swallowing Voluntary

Mouth to oropharynx Pharyngeal

Deglutition center in medulla oblongata and pons Closing of epiglottis Involuntary

Esophageal Involuntary Peristaltic contractions

Figure 23.9a,b

Figure 23.9c

Table 23.2

Concept 23.4 Stomach

Stomach

Serves as mixing chamber and storage area for ingested food

Rugae allow for increased volume 4 main regions1. Cardia2. Fundus3. Body4. Pylorus

Pyloric antrum and canal Pyloric sphincter Lesser and greater curvatures

Figure 23.10a

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 tissue3. Muscularis

3 layers of smooth muscle

4. Serosa

Figure 23.11a

Figure 23.11b

Figure 23.11c

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-)

Figure 23.12

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

Table 23.3 pt 1

Table 23.3 pt 2

Concept 23.5 Accessory Organs of the Abdomen

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)

Figure 23.13a

Figure 23.13b

Figure 23.13c

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

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

Liver and Gallbladder

Liver Largest gland at 1.4 kg (~3 lb)

Gallbladder Closely associated with liver

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

Histology of Liver

Lobule Hepatocytes radiating from central vein Sinusoids

Reticuloendothelial (Kupffer) cells Stationary phagocytes

Figure 23.14a

Figure 23.14b

Figure 23.14c

Figure 23.14d

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

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

Figure 23.15

Bile

800-1000 mL/day pH 7.6 – 8.6 Water Bile acids Bile salts

Emulsification Cholesterol Lecithin Bile pigments

Bilirubin Stercobilin

Liver Functions

Metabolism of: Carbohydrates Lipids Proteins

Process drugs and hormones Excrete bilirubin Synthesize bile salts Storage

Glycogen Vtamins Minerals

Phagocytosis Activate Vitamin D

Concept 23.6 Small Intestine

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

Figure 23.16a

Figure 23.16b

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)

Figure 23.17a