Digestive System I

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Lecture 21

• Digestive System I

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Digestive System Anatomy

• Digestive tract
• Alimentary tract or canal
• Gastrointestinal (GI) tract
• Accessory organs
• Primarily glands
• Liver, gallbladder, pancreas, salivary glands
• Regions
• Mouth or oral cavity
• Pharynx
• Esophagus
• Stomach
• Small intestine
• Large intestine
• Anus

Fig. 26.1
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Functions

• Ingestion Introduction of food into mouth
• Mastication Chewing
• Propulsion
• Peristalsis Moves material through digestive
  tract
• Mass movements Moves material through large
  intestine

Fig. 26.2
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Functions

• Segmentation Segmental contraction that occurs
  in small intestine
• Secretion Lubricate, liquefy, digest
• Digestion Mechanical and chemical
• Absorption Movement from tract into circulation
  or lymph
• Elimination Waste products removed from body

Fig. 26.2
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Oral Cavity

• Mouth or oral cavity
• Lips (labia)
• Orbicularis oris
• Cheeks
• Buccinator
• Palate Oral cavity roof
• Hard and soft
• Palatine tonsils
• Tongue
• Involved in speech, taste, mastication,
  swallowing
• Skeletal muscles

Upper lip
Hard palate
Soft palate
Uvula
Palatine tonsil
Tongue
Salivary duct orifices
Sublingual
Teeth
Submandibular
Lower lip
Fig. 26.3
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Salivary Glands

• Produce saliva
• Prevents bacterial infection
• Lubrication
• Contains salivary amylase
• Breaks down starch
• Three pairs
• Parotid Largest
• Submandibular
• Sublingual Smallest

Fig. 26.4
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Pharynx and Esophagus

• Pharynx
• Food passes through the oropharynx and
  laryngopharynx

Internal nares
Opening of auditory tube
Nasopharynx
Oropharynx
Pharynx
Laryngopharynx
Esophagus
Trachea
Fig. 25.2
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Review Question

• Food moves along the esophagus by
• Peristalsis
• Gravity alone
• Mass movement
• Force of swallowing
• Contraction of ribs

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Pharynx and Esophagus

• Esophagus
• Transports food from pharynx to stomach
• Passes through esophageal hiatus (opening) of
  diaphragm and ends at stomach
• Hiatal hernia
• Sphincters
• Circular muscles
• Upper
• Lower

Oral cavity
Pharynx
Esophagus
Liver
Stomach
Fig. 26.1
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Stomach Anatomy
Fundus
Fig. 26.12
Esophagus
Longi- tudinal layer (outer)
Cardia
Pyloric orifice
Pyloric sphincter
Three layers of smooth muscle
Circular layer (middle)
Oblique layer (inner)
Duodenum
Pylorus
Body
Gastric folds

• Openings
• Gastroesophageal to esophagus
• Pyloric to duodenum
• Parts
• Cardia
• Fundus
• Body
• Pyloric

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Stomach Histology

• Layers
• Three layers of muscles
• Outer longitudinal
• Middle circular
• Inner oblique

Fig. 26.13
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Stomach Histology
Fig. 26.12

• Rugae Folds in stomach when empty
• Gastric pits Openings for gastric glands
• Contain cells
• Mucous cells Mucus along surface and in pits
• Parietal cells Hydrochloric acid
• Chief cells Pepsinogen

Fig. 26.13
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Points to Remember

• Digestive system consists of digestive tract and
  accessory organs (primarily glands)
• Functions include mechanical and chemical
  breakdown of food, absorption of nutrients and
  elimination of wastes
• Mechanical and chemical breakdown start with oral
  cavity
• Food transported through pharynx and esophagus to
  rest of digestive tract
• Stomach
• Mixes food
• Protein digestion
• Limited absorption (aspirin)

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Questions?