Digestive System

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Digestive System

• Central Texas College
• BIOL 2401
• Chelsea Barker, MS

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Organs of the Digestive System
See figure 17.1 in text
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Alimentary Canal

• 4 layers of the alimentary canal wall
• Mucosa epithelium in contact with the lumen
• Submucosa loose connective tissue, glands,
  nerves and vessels
• Muscular layer smooth muscle cells
• Circular fibers constricts the tube
• Longitudinal fibers shortens the length of the
  tube
• Serosa epithelium that makes up the visceral
  peritoneum

See figure 17.2 in text
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Digestion

• Mechanical digestion
• Does not alter chemical composition, only
  physical composition
• Accomplished by teeth, tongue, and churning
  movements
• Chemical digestion
• Alters the chemical composition, breaking them
  down into small chemicals that are easier to
  absorb
• Accomplished by enzymes such as lipase, amylase,
  trypsin to name a few

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Mouth

• Functions to ingest food, mechanical digestion,
  chemical digestion
• Contain
• Salivary glands
• Teeth
• Tongue
• Lingual glands that secrete mucus and lingual
  lipase
• Lips/cheeks
• Palate
• Soft palate
• Hard palate

See figure 17.5 in text
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Salivary Glands

• Secrete saliva containing salivary amylase to
  moisten food and begin chemical digestion
• Mucus helps to lubricate food for swallowing
• Parotid glands
• Secrete serous fluid (thin)
• Submandibular glands
• Secrete serous fluid and mucus (thicker)
• Sublingual glands
• Secretes mucus (thick)

See figure 17.11 in text
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Swallowing Mechanism

• Soft palate raises
• Hyoid and larynx elevate
• Epiglottis covers trachea
• Tongue elevates pushing the bolus back
• Pharynx moves upward with muscle contraction
• Upper esophageal sphincter relaxes
• Peristalsis waves begin to move food from the
  pharynx to the esophagus
• Peristalsis continues to move the bolus down the
  esophagus

See figure 17.14 in text
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Stomach

• Mucus lined
• Contains three layers of muscle in the wall to
  allow for churning of contents
• Circular fibers
• Longitudinal fibers
• Oblique fibers
• Gastric secretions mix with the food bolus to
  create chyme

See figure 17.17 in text
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Radiograph of Stomach
See figure 17.18 in text
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Gastric Secretions

• Gastric pits contain cells that contribute to
  gastric secretions
• Mucus
• Alkaline fluid secreted by mucous cells
• Pepsinogen
• Secreted by chief cells to be activated to pepsin
• Pepsin
• Activated from pepsinogen when it contacts HCl
  and used to split proteins
• Hydrochloric Acid
• Secreted by parietal cells to provide acidic
  environment and to activate pepsinogen
• Intrinsic Factor
• Secreted by parietal cells to help with vitamin
  B12 absorption

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Phases of Gastric Secretions

• Cephalic phase (30-50 of secretion)
• Gastric juices secreted in response to seeing,
  smelling, tasting, or thinking about food
• Parasympathetic response to prepare stomach for
  food
• Gastric phase(40-50 of secretion)
• Gastric juices secreted in response to food
  present in the stomach
• Gastric juices further secreted as pH rises with
  the presence of food
• Intestinal phase (5 of secretion)
• Gastric juices are secreted when food first
  enters the small intestine
• Can be influenced by the hormone intestinal
  gastrin

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Pancreas

• Exocrine function as an accessory organ of the
  digestive system
• Pancreatic acinar cells create enzymes
• Pancreatic amylase
• Pancreatic lipase
• Trypsin (active form of trypsinogen)
• Chymotrypsin
• Carboxypeptidase
• Nucleases
• Bicarbonate produced and secreted to neutralize
  pH
• Secretions released out the pancreatic duct and
  hepatopancreatic ampulla

See figure 17.23 in text
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Pancreatic Secretion Release
See figure 17.24 in text
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Liver

• Largest internal organ
• Many functions
• Carbohydrate metabolism
• Lipid metabolism
• Protein metabolism
• Storage
• Blood filtering
• Detoxification
• Secretion of bile

See figure 17.28 and table 17.7 in text
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Bile

• Produced in the liver
• Yellowish-green fluid made up of
• Water
• Bile salts formed from cholesterol and is the
  only part that plays a role in digestive function
• Bile pigments products of hemoglobin from RBC
  breakdown
• Cholesterol
• Electrolytes
• Stored by the gallbladder and eventually released
  through the hepatopancreatic ampulla
• Fat is emulsified to allow for easier digestion

See figure 17.26 and 17.29 in text
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Bile Release Regulation
See figure 17.30 in text
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Hepatic Portal Circulation
See figure 15.55 in text
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Small Intestine

• Small folded tube in the lower abdominal cavity
• Three regions
• Duodenum 25 cm long
• Jejunum 2.3 meters long
• Most vascular wall and larger diameter
• Ileum 3.5 meters long
• Suspended by mesentery that houses blood vessels,
  nerves, and lymphatic vessels
• Absorbs products of digestion over a large
  surface area
• Plicae circulares
• Villi
• Microvilli

See figure 17.31 in text
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Small Intestine
See figure 17.38 17.35 in text
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Small Intestine Secretions

• Alkaline mucus secreted by mucous-secreting cells
• Enzymes secreted to further digestion
• Peptidase breaks down peptides into amino acids
• Sucrase, maltase, lactase break down
  disaccharides into monosaccharides
• Intestinal lipase breaks down fats into fatty
  acids and glycerol
• Enterokinase converts trypsinogen to trypsin
• Hormones used to regulate secretion
• 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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Intestinal Absorption
See table 17.10 in text
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Large Intestine

• Large tube surrounding the abdominal cavity
• Responsible for absorbing water and electrolytes
• Undigestible material is condensed and formed
  into feces
• 4 Sections
• Ascending colon
• Transverse colon
• Descending colon
• Sigmoid colon
• Alimentary canal terminates at the rectum and the
  anus

See figure 17.43 in text
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Digestive System Disorders

• Acid reflux cardiac sphincter does not close
  completely
• Stomach ulcers stomach lining damaged due to
  acid and lack of mucus
• Diarrhea watery feces due to excessively rapid
  movement through the colon and water cannot be
  absorbed
• Colon Cancer
• Cirrhosis of the liver