Ch 23 Digestive System
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Two groups of organs
1. Alimentary canal (gastrointestinal or GI tract)
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2. Accessory digestive organs
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Digestive Processes
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Six essential activities
1. Ingestion
2. Propulsion
3. Mechanical breakdown
4. Digestion
5. Absorption
6. Defecation
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Peritoneum - serous membrane of abdominal cavity
1. Visceral peritoneum
2. Parietal peritoneum
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Peritoneal cavity
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Mesentery - double layer of peritoneum
1.
2.
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Homeostatic Imbalance
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Peritonitis
1.
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Blood Supply: Splanchnic Circulation
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Branches of aorta serving digestive organs
1. Hepatic, splenic, and left gastric arteries
2. Inferior and superior mesenteric arteries
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Hepatic portal circulation
1. Drains nutrient-rich blood from digestive organs
2. Delivers it to the liver for processing
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Histology of the Alimentary Canal
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Four basic layers (tunics)
1. Mucosa
2. Submucosa
3. Muscularis externa
4. Serosa
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Oral (buccal) cavity
1.
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Lips and Cheeks
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Vestibule -
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Oral cavity
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Labial frenulum -
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Hard palate -
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Soft palate -
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Tongue
1. Skeletal muscle
2. Functions include:
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Lingual frenulum: attachment to floor of mouth
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Surface bears papillae
1. Filiform—
2. Fungiform—
3. Circumvallate (vallate)—
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Lingual lipase
1.
2.
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Salivary Glands
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Extrinsic salivary glands
1.
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Intrinsic salivary glands
1.
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Function of saliva
1.
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Parotid gland
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Submandibular gland
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Sublingual gland
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Two types of secretory cells
1. Serous cells
2. Mucous cells
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Composition of Saliva
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Control of Salivation
1. 1500 ml/day
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Teeth
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20 deciduous teeth erupt (6–24 months of age)
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32 permanent teeth
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Classes of Teeth
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Incisors
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Canines
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Premolars (bicuspids)
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Molars
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Tooth Structure
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Crown –
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Root -
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Cement - calcified connective tissue
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Periodontal ligament
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Gingival sulcus - groove where gingiva borders tooth
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Dentin - bonelike material under enamel
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Pulp cavity -
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Root canal
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Dental caries (cavities) –
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Tooth and Gum Disease
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Gingivitis
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Periodontitis (from neglected gingivitis)
Digestive Part B
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Pharynx
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Esophagus
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Gastroesophageal (cardiac) sphincter
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Homeostatic Imbalance
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Heartburn
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Esophagus
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Digestive Processes: Mouth
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Ingestion
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Mechanical digestion
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Propulsion
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Deglutition (swallowing)
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Chemical digestion (salivary amylase and lingual lipase)
Mastication
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Deglutition
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Buccal phase
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Pharyngeal-esophageal phase
Stomach: Gross Anatomy
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Cardial part (cardia)
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Fundus
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Body
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Pyloric part
Stomach: Gross Anatomy
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Greater curvature - convex lateral surface
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Lesser curvature - concave medial surface
Mesenteries tether stomach
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Lesser omentum
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Greater omentum – contains fat deposits & lymph nodes
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ANS nerve supply
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Blood supply
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Gastric Glands
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Cell types
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Mucous neck cells (secrete thin, acidic mucus of unknown function)
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Parietal cells
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Chief cells
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Enteroendocrine cells
Parietal cell secretions
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Hydrochloric acid (HCl)
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Intrinsic factor
Chief cell secretions
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Pepsinogen -
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Lipases
Enteroendocrine cells
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Hormones
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Serotonin and histamine
Somatostatin (also acts as paracrine) and gastrin
Mucosal Barrier
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Homeostatic Imbalance
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Gastritis
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Peptic or gastric ulcers
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Digestive Processes in the Stomach
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Physical digestion
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Only stomach function essential to life
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Secretes intrinsic factor for vitamin B12 absorption
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Regulation of Gastric Secretion
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Hormonal control largely gastrin
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Three phases of gastric secretion
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Cephalic (reflex) phase
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Gastric phase –
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Gastrin  enzyme and HCl release
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Response of the Stomach to Filling
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Stretches to accommodate incoming food
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Gastric Contractile Activity
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Distension and gastrin increase force of contraction
Chyme is either
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Regulation of Gastric Emptying
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As chyme enters duodenum
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Carbohydrate-rich chyme moves quickly through duodenum
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Fatty chyme remains in duodenum 6 hours or more
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Homeostatic Imbalance
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Vomiting (emesis) caused by
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Small Intestine: Gross Anatomy
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Major organ of digestion and absorption
Subdivisions
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Duodenum (retroperitoneal)
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Jejunum (attached posteriorly by mesentery)
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Ileum (attached posteriorly by mesentery)
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Structural Modifications
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Increase surface area of proximal part for nutrient absorption
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Circular folds (plicae circulares)
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Villi
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Microvilli
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Homeostatic Imbalance
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Chemotherapy targets cancer cells
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Kills rapidly dividing GI tract epithelium  nausea, vomiting, diarrhea
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Mucosa
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Intestinal Juice
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The Liver and Gallbladder
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Liver
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Many functions; only digestive function  bile production
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Gallbladder
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Bile – fat emulsifier
Chief function  bile storage
Liver
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Falciform ligament
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Round ligament (ligamentum teres)
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Bile ducts
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Common hepatic duct leaves liver
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Cystic duct connects to gallbladder
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Bile duct formed by union of common hepatic and cystic ducts
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Liver: Microscopic Anatomy
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Liver lobules
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Liver: Microscopic Anatomy
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Portal triad at each corner of lobule
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Kupffer cells (hepatic or stellate macrophages) in liver sinusoids remove debris & old RBCs
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Hepatocytes – increased rough & smooth ER, Golgi, peroxisomes, mitochondria
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Hepatocyte functions
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Regenerative capacity
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Homeostatic Imbalance
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Hepatitis
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Cirrhosis
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Liver transplants successful, but livers scarce
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Bile
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Yellow-green, alkaline solution containing
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Bile salts -
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Bilirubin •
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Bile
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Enterohepatic circulation
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The Gallbladder
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High cholesterol; too few bile salts  gallstones (biliary calculi)
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Ch 23 Part C
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Pancreas
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Location
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Endocrine function
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Exocrine function
Pancreatic Juice
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Enzymes
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Digestion in the Small Intestine
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Chyme from stomach contains
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3–6 hours in small intestine
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Motility of the Small Intestine
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Segmentation
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Peristalsis
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From duodenum  ileum ~ 2 hours
Ileocecal sphincter relaxes, admits chyme into large intestine when
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Ileocecal valve flaps close when chyme exerts backward pressure
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Large Intestine
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Regions
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Cecum
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Appendix
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Colon
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Rectum
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Anal canal
Sphincters
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Internal anal sphincter—smooth muscle
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External anal sphincter—skeletal muscle
Large Intestine: Microscopic Anatomy
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Bacterial Flora
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Intestinal Flora
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Viruses and protozoans
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Digestive Processes in the Large Intestine
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Residue remains in large intestine 12–24 hours
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Major functions - propulsion of feces to anus; defecation
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Most contractions of colon
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Haustral contractions
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Gastrocolic reflex
Homeostatic Imbalance
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Diverticulosis
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Diverticulitis
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Irritable bowel syndrome
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Defecation
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Parasympathetic signals
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Assisted by Valsalva's maneuver
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Chemical Digestion
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Digestion, Enzymes, Hydrolysis