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Chapter 17 Digestive System

Functions of Digestive System •  ingestion •  mechanical digestion •  chemical digestion •  propulsion •  absorption •  defecation

Consists of the alimentary canal and accessory organs

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Alimentary Canal

About 8 meters long

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Movements of the Tube •  mixing movements •  segmentation •  peristalsis

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Mouth

•  ingestion •  mechanical digestion (mastication) •  prepares food for chemical digestion

• Parts • Cheeks • Lips • Tongue • Palate

• uvula

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Tongue

• Taste • Moves food • Forms bolus

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Palate

•  roof of oral cavity • uvula

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Primary Teeth

•  8 incisors •  4 cuspids •  8 molars

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Secondary Teeth

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Salivary Glands

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Secretions of Salivary Glands

• Major salivary glands •  Parotid glands •  Submandibular glands •  Sublingual glands

• Saliva • Moistens food particles • Helps bind the food particles together to form bolus • Begins chemical digestions of carbohydrates (salivary amylase) • Helps clean the mouth

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Pharynx

Connects nasal and oral cavities with the larynx and esophagus 3 parts •  Nasopharynx •  Oropharynx •  Layrngopharynx

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Swallowing Mechanism

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Esophagus

Straight, collapsible tube about 25 cm long Carries food from pharynx to stomach Lower esophageal sphincter (cardiac sphincter) - controls the opening to the stomach

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Stomach

J-shaped, pouchlike organ 25-30 cm long 3 regions •  Cardiac region •  Fundic region •  Body •  Pyloric region

Wall contain three layers of muscle

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Lining of Stomach

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Gastric Secretions

•  pepsinogen •  from chief cells •  inactive form of pepsin

•  pepsin •  from pepsinogen in presence of HCl •  protein splitting enzyme

•  hydrochloric acid •  from parietal cells •  needed to convert pepsinogen to pepsin

•  mucus •  from goblet cells and mucous glands •  protective to stomach wall

•  intrinsic factor •  from parietal cells •  required for vitamin B12 absorption

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Gastric Absorption

•  some water •  certain salts •  certain lipid-soluble drugs •  alcohol

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Mixing and Emptying Actions

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Pancreas

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Pancreatic Juice

•  pancreatic amylase – splits glycogen into disaccharides •  pancreatic lipase – breaks down triglycerides •  trypsin, chymotrypsin, and carboxypeptidase – digest proteins •  nucleases – digest nucleic acids •  bicarbonate ions – make pancreatic juice alkaline

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Regulation of Pancreatic Secretions

•  acidic chyme stimulates release of secretin •  secretin stimulate release of pancreatic juice

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Liver Largest internal organ

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Liver Functions

•  produces glycogen from glucose •  breaks down glycogen into glucose •  converts noncarbohydrates to glucose •  oxidizes fatty acids •  synthesizes lipoproteins, phospholipids, and cholesterol •  converts carbohydrates and proteins into fats •  deaminates amino acids •  forms urea •  synthesizes plasma proteins •  converts some amino acids to other amino acids •  stores glycogen, vitamins A,D, B12, iron, and blood •  phagocytosis of worn out RBCs and foreign substances •  removes toxins from blood •  produces and secretes bile

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Composition of Bile

•  water •  bile salts

•  emulsification of fats •  absorption of fatty acids, cholesterol, and fat-soluble vitamins

•  bile pigments •  cholesterol •  electrolytes

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Gallbladder Stores bile until it is released into the small intestine

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Regulation of Bile Release

•  fatty chyme entering duodenum stimulate gallbladder to release bile

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Three Parts of Small Intestine Tubular organ 5.5 - 6.0 m long

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Intestinal Villus

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Wall of Small Intestine

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Secretions of Small Intestine

•  peptidase – breaks down peptides into amino acids •  sucrase, maltase, lactase – break down disaccharides into monosaccharides •  lipase – breaks down fats into fatty acids and glycerol •  enterokinase – converts trypsinogen to trypsin •  somatostatin – hormone that inhibits acid secretion by stomach •  cholecystokinin – hormone that inhibits gastric glands, stimulates pancreas to release enzymes in pancreatic juice, stimulates gallbladder to release bile •  secretin – stimulates pancreas to release bicarbonate ions in pancreatic juice

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Absorption in the Small Intestine

•  monosaccharides and amino acids

•  through facilitated diffusion and active transport •  absorbed into blood

•  electrolytes and water •  through diffusion, osmosis, and active transport •  absorbed into blood

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Absorption in the Small Intestine

•  fatty acids and glycerol •  several steps •  absorbed into lymph and blood

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Movements of the Small Intestine

•  mixing movements •  peristalsis – pushing movements •  segmentation – ringlike contractions •  overdistended wall triggers peristaltic rush resulting in diarrhea

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Large Intestine

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Functions of Large Intestine •  little or no digestive function •  absorbs water and electrolytes •  secretes mucus •  houses intestinal flora

• Absorbs vitamins K, B12, thiamine and riboflavin produced by the bacteria

•  forms feces •  carries out defecation

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Movements of Large Intestine

•  slower and less frequent than those of small intestine •  mixing movements •  peristalsis •  mass movements usually follow meals

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Feces

•  water •  electrolytes •  mucus •  bacteria •  bile pigments altered by bacteria provide color •  smell produced by bacterial compounds

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Life-Span Changes

•  teeth become sensitive •  gums recede •  teeth may loosen or fall out •  heartburn more frequent •  constipation more frequent •  nutrient absorption decreases •  accessory organs age but the effects are less noticeable

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Clinical Application

Hepatitis •  inflammation of the liver •  most commonly caused by viral infection •  can be caused by reactions to drug, alcoholism or autoimmunity

Signs and Symptoms •  headache •  low fever •  fatigue •  vomiting •  rash •  foamy urine •  pale feces •  jaundice •  pain

Hepatitis A – not washing hands or eating raw shellfish Hepatitis B – chronic; serum Hepatitis C – serum Hepatitis D – very severe; only produces symptoms if infected with B; serum Hepatitis E, F, G – more rare

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Clinical Application

Ulcers •  Sores in the lining of stomach •  most commonly caused by helicobacter pylorus •  can be caused by reactions to drug and certain foods

Signs and Symptoms •  pain • Blood in feces

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Clinical Application

Gastric Reflux Disorder •  recurrent heartburn • Can cause the lining of the esophagus to wear away • Treat with acid reducers and/or surgery

Signs and Symptoms •  pain