Chapter 23

Transcript Chapter 23

The Digestive System

Chapter 23 – Lecture Notes to accompany

Anatomy and Physiology: From Science to Life

textbook by Gail Jenkins, Christopher Kemnitz, Gerard Tortora

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

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

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

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 System 1.

• Ingestion Secretion Mixing and propulsion Motility 4.

• Digestion Mechanical and chemical 5.

Absorption 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   1.

External regions Crown Root Neck 1.

Internal components Enamel  Dentin Cementum   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    1.

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

Figure 23.10a

Stomach Histology 1.

 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

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 (HCO 3 )

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   Paneth  Lysozyme Intestinal glands (crypts of Lieberk ühn)  S cells  Hormone secretin  Endocrine CCK cells  Hormone – cholecystokinin (CCK)