Digestive system

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Digestive system

• Al Mina, M.D.
• Erskine College

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Modified from

• Powerpoint Presentation for BG210-211 made by
• Dr. Nora Espinoza, Ph. D.
• Which was

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Modified from a PowerPoint Presentation made
to accompanyHoles Human Anatomy and
Physiology, 11/e byShier,
Butler, and LewisMcGraw-Hill - publisher
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Digestion

• Breakdown of foods into absorbable form
• Mechanical
• chemical

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Digestive system

• Alimentary canal
• Structures that food passes through directly
• Accessory organs
• Secrete substances into canal

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Alimentary canal

• 8 meters long
• Wall similar layers throughout (in different
  forms)
• Lumen
• Mucosa
• Submucosa
• Muscular
• serosal

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• Mucosa
• Epithelium, connective tissue
• Mucous secreting glands
• Function protection, secretion, absorption
• Submucosa
• Loose connective tissue, vessels, nerves, lymph
• Nourishment, removes absorbed substances

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• Muscular layer
• Two layers of smooth muscle
• Circular narrows lumen
• Longitudinal shortens tube
• Movement of tube and contents
• Serosa
• Visceral peritoneum
• Covers, lubricates tube

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Movement

• Mixing movement
• Rhythmic movement in small areas
• Example stomach
• Propelling movement
• Contraction relaxation downstream
• Wavelike contraction - peristalsis

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innervation

• Primarily muscular
• Parasympathetic increase activity
• Sympathetic decreases
• Submucosal plexus controls secretions
• Myenteric plexus motility
• Also has sensory neurons

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Mouth

• Receives food
• Begins digestion
• mastication

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Cheeks

• Lateral walls of mouth
• Muscles for chewing and expression

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Lips

• Sense temperature and texture of food

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Tongue

• Muscular organ
• Covered by mucous membrane
• Connected by lingual frenulum to floor of mouth
• Helps in mixing food, moves to back of mouth for
  swallowing
• Papillae friction, taste
• Connects to hyoid bone

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Palate

• Roof of oral cavity
• Hard palate anterior portion bone
• Soft palate posterior muscular
• During swallowing, soft palate elevates to keep
  food out of nasal cavity
• Palatine tonsils lymph tissue

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Teeth

• Hardest structures in body
• Primary set 20 teeth
• Shed when roots resorbed
• Secondary -4 sets of 8
• 2 incisors
• Canine
• 2 bicuspids (premolars)
• 3 molars

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Teeth
Figure 17.9
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Function

• Begin mechanical digestion
• Allows digestive enzymes to work more effectively

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Teeth
Figure 17.10
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• Crown above gumline
• Root below
• Enamel hardened calcium salts irreplaceable
• Dentin living tissue
• Central cavity contains vessels, nerves
• Root canals entry points for vessels

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• Cementum bonelike material enclosing root
• Periodontal ligament connects tooth to jaw

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Salivary glands

• Secrete saliva
• Moistens food
• Dissolves food for taste
• Begins digestion
• Contains amylase splits complex carbs into
  disaccharides
• Cleans teeth

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Contd

• Innervated by para/sympathetic
• Can activate at sight/smell/thought of food

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Salivary glands

• Parotid largest
• Cheek
• Secretes mosly amylase
• Submandibular
• Inside lower jaw
• Mixed amylase/mucous (lubricant)
• Sublingual
• Below tongue
• Mostly mucous secretions

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Figure 17.11
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Pharynx

• Important for swallowing

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Palate
Figure 17.7
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Swallowing
Figure 17.14
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Swallowing stage 2

• Soft palate elevates
• Larynx/hyoid bone elevate, epiglottis closes
• Tongue presses upward
• Longitudinal muscles contract, pulling pharynx
  upward
• Lower constrictor muscles relax
• Higher constrictor muscles contract, propelling
  food into esophagus

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Also step 2
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Step 3
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Figure 17.15
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esophagus

• Straight 25 cm tube
• Propels food through thoracic cavity to stomach
• Posterior to trachea
• Goes through diaphragm at esophageal hiatus to
  reach stomach.
• Secretions mucous (no digestion)

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Contd

• Lower esophageal sphincter (cardiac sphincter)
  prevents food in stomach from regurgitating into
  esophagus
• Weakness of this sphincter can lead to reflux of
  stomach acid into esophagus heartburn