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The Digestive System
Chapter 23
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Learning Objectives
• Describe the alimentary canal• Functions of alimentary canal• Digestive pathway!• Sphincters• Major Accessory Organs and
their functions• Digestion v Absorption
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Overview
• Digestive system deals with food, water, drugs, etc.
• Breaks down food (digestion) and absorbs the nutrients (absorption) and water in specific areas of GI tract
• Eliminates waste (non-digestible)• Accessory organs help break down
food mechanically and chemically
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Digestive System
• Alimentary canal or Gastrointestinal (GI) tract: continuous tube, mouth anus
• Key structures of the Alimentary Canal: mouth, pharynx (3 parts), esophagus, stomach, small and large intestine, rectum, and anus
• Digestion: process by which food is broken down into smaller molecules for absorption
• Absorption: bringing the small molecules from the GI tract into the blood
• *Digestion and absorption happen in key areas along the way*
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Digestive System
Alimentary CanalAccessory Organs
• Salivary glands
• Teeth• Liver• Gallbladder• Pancreas
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Layers to Alimentary CanalLayers to the Alimentary Canal:• Mucosa (Innermost)• Submucosa• Muscular, “peristalsis”
– rhythmic muscle movements
• Serosa (Outermost)Innervation? • Parasympathetic “Rest
and Digest”
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Draw it Out!
• Doodle our Digestive Pathway in your notes as we go• Pay attention to: • Enzymes• Absorption, Digestion, or both• Where will food go next?• Different names for food
depending on the area where its found!
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The Oral Cavity (Mouth)
Contains:• Teeth: mechanical
digestion – 20 deciduous teeth, – 32 permanent teeth– incisors, cuspids,
premolars, molars
• Tongue: – forms a bolus – contains taste buds
• Salivary glands
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Salivary Glands3 pairs of salivary glands:1. Parotid – anterior to
ears2. Submandibular –
located below the mandible
3. Sublingual – located below the tongue
Secretes saliva, contains Salivary Amylase, which digests carbohydrates
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The Pharynx (Throat)
Divided into 3 regions1. Nasopharynx:
“nasal part”2. Oropharynx: “oral
part”3. Laryngopharynx:
“near the Larynx” Which parts of the pharynx receives food? Air?
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Swallowing
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The Esophagus
• 10 inch muscular tube
• Connects pharynx to the stomach
• Transports food– Peristalsis – voluntary or
involuntary?
• No digestion or absorption—Just transportation
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The Stomach• “Pouch-like organ”• Turns food into
chyme• Regions of the
Stomach:a)Fundusb)Bodyc)Pylorus • Does Mechanical and
Chemical digestion– Churning and mixing
movements
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The Stomach
Stomach secretions:1.Mucus2.Hydrochloric
Acid3.Pepsin4.Intrinsic Factor
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The Small Intestine
Connects stomach to the large intestine3 regions:1. Duodenum2. Jejunum3. Ileum• “Dow Jones
Industrial”• “Don’t Judge It”
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The Small Intestine1. Duodenum:– Absorption and
Digestion– receives chyme -
digests carbs, proteins, and fats
2. Jejunum: – Absorption Either
into bloodstream or lymphatic system
3. Ileum: – immune function
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The Large IntestineMultiple segments:
1.Cecum: – has appendix
2.Ascending colon:– “going up”
3.Transverse colon: – “going across”
4.Descending colon:– “going down”
5.Sigmoid colon: – S-shaped
6.Rectum: – stores feces, passes
through anus
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Sphincters
• Muscle that “guards” opening of tube• 6 sphincters• 5 are made of smooth
muscle• 1 is made of skeletal muscle
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Sphincters1. UES: between pharynx and esophagus2. LES: between esophagus and stomach3. Pyloric: between the stomach and small
intestine4. Ileocecal Valve: between the small
intestine and large intestine5. Internal Anal Sphincter: between rectum
and anus = smooth muscle!6. External Anal Sphincter: between rectum
and anus = skeletal muscle (means what?)
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PRACTICE
Labelling
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Major Accessory Organs
Chapter 23
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The LiverFunctions:1. Produce bilirubin and
bile2. Converts ammonia to
urea. 3. Make plasma proteins4. Detox5. Glycogen6. Metabolism of carbs,
proteins, and fats• Location• Blood supplies?
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The Gallbladder• Location• Stores and releases bile into the
duodenum• What does bile do?a)Emulsify fats (think washing
dishes)b)This helps another enzyme digest
the fat
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The PancreasBoth exocrine and endocrine glands!• Releases the following into
the duodenum:1.Bicarb: neutralize chyme
coming from stomach2.Pancreatic Lipase: “fats”3.Pancreatic Amylase:
“carbs”4.Proteases: “proteins”
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Recap
• We digest: carbs, proteins, and fats. Remember where?
A.Oral cavityB.The StomachC.The Small
Intestine
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Final Digestion and Absorption
Make the small molecules even smaller• Table 23-1• Absorption happens
in the duodenum and jejunum
• Absorb monosaccharaides, amino acids, and fatty acids where?
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Group Activity