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
Fig. 26.1
–
–
–
–
–
–
–
Mouth or oral cavity
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Anus
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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
24-3
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)
Upper lip
– Orbicularis oris
Hard palate
• Cheeks
Soft palate
Uvula
Palatine tonsil
Tongue
Salivary duct orifices
Sublingual
Submandibular
Teeth
Lower lip
Fig. 26.3
– Buccinator
• Palate: Oral cavity roof
– Hard and soft
• Palatine tonsils
• Tongue
– Involved in speech,
taste, mastication,
swallowing
– Skeletal muscles
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Salivary Glands
• Produce saliva
– Prevents bacterial
infection
– Lubrication
– Contains salivary
amylase
• Breaks down starch
• Three pairs
Fig. 26.4
– Parotid: Largest
– Submandibular
– Sublingual: Smallest
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Pharynx and Esophagus
• Pharynx
Internal nares
Opening of auditory tube
Nasopharynx
Oropharynx
– Food passes through
the oropharynx and
laryngopharynx
Pharynx
Laryngopharynx
Esophagus
Trachea
Fig. 25.2
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Review Question
Food moves along the esophagus by
(a) Peristalsis
(b) Gravity alone
(c) Mass movement
(d) Force of swallowing
(e) Contraction of ribs
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Pharynx and Esophagus
• Esophagus
Oral cavity
Pharynx
Esophagus
– Transports food from pharynx
to stomach
– Passes through esophageal
hiatus (opening) of diaphragm
and ends at stomach
• Hiatal hernia
Liver
Stomach
– Sphincters
• Circular muscles
• Upper
• Lower
Fig. 26.1
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Stomach Anatomy
Fig. 26.12
Fundus
Esophagus
Pyloric
orifice
Cardia
Pyloric
sphincter
Duodenum
Longitudinal
layer
(outer)
Circular
layer
(middle)
Oblique layer
(inner)
Three layers of
smooth
muscle
Pylorus
Openings
Gastric folds Body
•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
24-12
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)
24-13
Questions?
24-14