Anatomy and Physiology of the Digestive System

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Anatomy and Physiology of the Digestive System

• Chapter 14

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Groups of Organs

• Alimentary canal ingests, digests, absorbs and
  defecates
• Accessory digestive organs-

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GI Tract or Alimentary Canal

• Continuous coiled, hollow, muscular tube
• Includes mouth, pharynx, esophagus, stomach,
  small intestine, large intestine, anus

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Mouth

• Oral Cavity mucous membrane-lined cavity
• Lips (labia)
• Cheeks
• Hard palate
• Soft palate
• Uvula
• Vestibule and oral cavity proper
• Tongue

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Pharynx

• Nasopharynx, oropharynx and the laryngopharynx
• Peristalsis occurs here

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Esophagus

• Gullet
• Consists of 4 tissue layers or tunics
• Mucosa
• Submucosa
• Muscularis externa- circular and longitudinal
  muscles
• Serosa

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Stomach- external

• Cardioesophageal sphincter
• Fundus
• Body
• Pylorus
• Pyloric sphincter
• Rugae
• Greater and Lesser Curvature
• Greater and lesser omentum (peritoneum)
• Longitudinal, circular and the oblique muscularis
  externa- churning and mixing

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Stomach - internal

• The lining of the stomach is dotted with gastric
  pits leading into gastric glands that secrete
  gastric juice
• Some cells secrete intrinsic factor (needed for
  Vit B12 absorbtion)
• Chief cells produce pepsinogens (protein
  digestion)
• Parietal cells produce HCl
• Food processed by the stomach is called chyme
• http//www.peterjurek.com/rbv_site/web_pages/stoma
  ch.html

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Small Intestine

• Bodys major digestive organ
• Starts at the pyloric sphincter and ends at the
  ileocecal valve
• Average length of 6-13 feet

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3 divisions

• Duodenum-contains pancreatic ducts and bile duct
• Jejunum
• Ileum
• Nearly all food absorption occurs in the small
  intestine

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Internal Anatomy

• Microvilli- tiny projections (brush border)
• Villi- fingerlike projections, contain rich
  capillary bed
• Circular folds- deep folds of mucosa and
  submucosa layers
• Peyers patches- lymphatic tissue found in the
  submucosa

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Large Intestine

• About 5 feet long
• Extends from the ileocecal valve to the anus
• Frames the small intestine on 3 sides

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Divisions

• Cecum
• Appendix
• Colon- distinct regions
• Ascending colon, transverse colon and descending
  colon, sigmoid colon
• Rectum
• Anal canal

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Accessory Digestive Organs

• 3 pairs of salivary glands
• Teeth
• Pancreas
• Liver
• Gallbladder

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Salivary Glands

• Parotid glands- anterior to the ears
• Submandibular glands- floor of mouth
• Sublingual glands- floor of mouth
• Produce salivary amylase- starts starch
  digestion, contains lysozyme and IgA, dissolves
  food chemicals enhancing taste

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Teeth

• Mastication
• Deciduous teeth/permanent teeth
• Wisdom teeth- 3rd set of molars
• Impacted teeth
• 32 permanent teeth is a full set

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Classification of Teeth

• Based on shape and function
• Incisors-cutting
• Canines-tearing or piercing
• Premolars-grinding
• Molars-grinding

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Anatomy of the Tooth

• Crown- visible
• Enamel
• Dentin- bone-like material
• Root- below the gingiva (gum)
• Cementum attaches the tooth to the periodontal
  membrane (ligament that holds tooth in place)
• Neck- connects the crown and the root

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Pancreas

• Produces hormones insulin and glucagon and
  digestive enzymes

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Liver

• Largest organ
• 4 lobes
• Produces bile which leaves via the common hepatic
  duct

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Gallbladder

• Stores bile
• Enters via the cystic duct
• Eating fatty foods stimulates the gallbladder to
  contract and spurt out stored bile

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Disease

• Gallstones, gallbladder attack
• Jaundiced
• Hepatitis- inflammation of the liver
• Cirrhosis of the liver hard and fibrous

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Functions of the Digestive System

• Ingestion
• Propulsion- peristalsis and segmentation
• Mechanical digestion
• Chemical digestion
• Absorption
• Defecation

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Food ingestion and breakdown

• Physical- mastication
• Tongue helps form bolus
• Chemical- salivary amylase
• Pharynx and esophagus

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Food Propulsion

• Swallowing
• Buccal phase-food enters pharynx
• Pharyngeal-esophageal phase
• Tongue blocks off mouth
• Soft palate closes off nasal passages
• Larynx rises and epiglottis blocks respiratory
  tract
• Pressure on cardioesophageal sphinctor

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Stomach

• Gastric juice
• Gastrin- hormone that stimulates stomach
• 2-3 liters of gastic juice daily
• Mucus- ulcers
• Chemical- pepsinogen, Rennin
• Physical- churning

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Food Propulsion

• The pylorus of the stomach holds about 30ml of
  chyme
• The pyloric sphincter squirts about 3ml or less
  into the sm. Int.
• This process takes 4-6 hours

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Small Intestine

• Chemical- 3-6 hours for food to travel through
  the sm int
• Brush border enzymes
• Pancreatic juice- pancreatic amylase, trypsin,
  chymotrypsin, carboxypeptidase, lipases,
  nucleases, bicarbonate (brings pH up to 8)
• Hormonal control- secretin and cholecystokinin
  (CCK)
• Mechanical- bile
• Propulsion- peristalsis

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Large Intestine

• 12-24 hours
• About 500ml of flatus is produced daily
• Resident bacteria make vitamin K and some B
  vitamins
• Absorbtion is only vitamins, some ions, water
• Feces
• Peristalsis and mass movements

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Disease

• Heartburn
• ulcers