Meyers' A&P
March 25, 2015
Unit 9
The
Digestive
System
I. Functions of the Digestive System
• Ingestion: The taking in of food.
• Propulsion:
Movement caused by force.
• Digestion: The breakdown of foodstuffs
> Mechanical:
> Chemical:
• Absorption:
• Defecation:
Physical breakdown of food stuff.
Chemical breakdown of food stuff.
Intake of nutrients from food.
Elimination of indigestible waste.
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Meyers' A&P
March 25, 2015
II. Organs of the Alimentary Canal (GI Tract)
A. Oral Cavity: Mechanical & Chemical Digestion
> Tongue
– Mixes food with saliva, initiates swallowing, has taste buds
> Salivary Glands
– Create saliva, mixture of mucus & serous fluids
« contains Salivary Amylase (digests starch)
« creates a BOLUS, helps dissolve food for taste
> Taste
– Mastication/Chew food (mechanical digestion)
> Epiglottis
– cartilage blocks trachea opening not allowing food to enter
during swollowing
> Hard & Soft Palate
– Separates oral & nasal cavities
– When swallowing, soft palate rises to close nasal
passageway
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Meyers' A&P
March 25, 2015
II. Organs of the Alimentary Canal (GI Tract)
B. Pharynx: divided into 3 parts
> Nasopharynx: respiratory passageway
> Oropharynx: most posterior part of oral cavity
> Laryngopharynx: most superior part of esophagus
C. Esophagus: muscular tube for transport (peristalsis)
II. Organs of the Alimentary Canal (GI Tract)
D. Stomach: Mechanical & Chemical Digestion
> Regions: Cardia, Fundus, Body & Pylorus
Churn
> Rugae: Folds in the walls of the stomach
> Mucosa: lined with simple columnar epithelium and gastric
pits which create gastric juice
– Chief cells: produce pepsinogen
– Parietal cells: produce HCl
» Pepsinogen + HCl = Pepsin (breaks down proteins)
– Mucous Neck cells: produce alkaline mucus
> Sphincter Muscles: on both ends of the stomach, regulate
entry and exit of food stuffs
> Stomach does aid in the small amount of absorption of fats
and alcohol
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Meyers' A&P
March 25, 2015
II. Organs of the Alimentary Canal (GI Tract)
E. Small Intestine: Chemical
Digestion & Absorption
> Regions:
– Duodenum
– Jejunum
– Ileum
> Mesentery: Webbing
Filled with blood Vessels
> Pancreatic juices and bile enter small intestine (duodenum)
– help with complete break down of food particles
> Structural modifications:
– Microvilli: Cellular projections
– Villi: Fold in Epithelial Tissue
– Plicae Circulares: Fold in Intestinal Wall
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Meyers' A&P
March 25, 2015
II. Organs of the Alimentary Canal (GI Tract)
F. Large Intestine: Water
Absorption & Waste Excretion
> Regions:
– Cecum (Appendix)
– Colon
» Ascending
» Transverse
» Descending
» Sigmoid
– Rectum
– Anal Canal
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Meyers' A&P
March 25, 2015
III. Anatomy of the Alimentary Canal (GI Tract)
• From the Esophagus to the Large Intestine,
the wall of the GI Tract is composed of...
– Mucosa: innermost layer of epithelial
tissue
» Lined with goblet cells
producing mucus
– Submucosa: connective tissue
containing...
» Blood vessels, nerves &
lymphatic tissue
– Muscularis Externa: Layers of
smooth muscles
» Varies between the organs
– Serosa: Outermost layer
» Peritoneum & Mesentery
IV. Accessory Digestive Organs
A. Pancreas: Flat gland, extends from spleen to duodenum
> Produces pancreatic juice consisting of enzymes that aid
in chemical digestion
– Protease: Proteins -> smaller peptides
– Pancreatic Amylase: Complex Sugars -> Dissacharides
– Lipase: Fats -> Glycerol & Fatty Acids
– Nuclease: Cleaves nucleic acids (DNA/RNA)
> Secreted in alkaline solution
> Emptied into duodenum
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Meyers' A&P
March 25, 2015
IV. Accessory Digestive Organs
B. Liver: Large lobed (4) organ, located just inferior to diaphragm
> Produces bile
– yellow-green fluid containing bile salts, pigments,
cholesterol, phospholipids & electrolytes
> Emulsification: Bile salts break large fat globules into
smaller ones
– increases surface area of lipids for lipase
> Exits liver via hepatic duct
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Meyers' A&P
March 25, 2015
IV. Accessory Digestive Organs
C. Gallbladder: sac-like organ
imbedded on underside of liver
> bile leaving liver backs up
into gallbladder via cystic
duct
> bile is concentrated in
gallbladder
– secrete into duodenum via
bile duct when fatty food
present
D. Salivary Glands: Parotid, Sublingual, Submandibular
> Produce and secrete saliva into oral cavity
– Mucus to moisten food
– Salivary Amylase for starch digestion
– Lysozyme & Antibodies to fight infection
– Dissolves food chemicals for taste
V. Chemical Digestion & Absorption
Carbohydrates
Starch
Oral Cavity
Salivary Amylase
Proteins
Proteins
Pepsin
Stomach
large
polypeptides
Nucleic
Acids
Fats/lipids
DNA/RNA
Triglycerides/Fats
Lumen of
Small
Intestine
Pancreatic
Amylase
disaccharides
Pancreatic
Proteases
small
polypeptides
Epithelium of
Small
Intestine
brush border
enzymes
brush border
enzymes
brush border
enzymes
amino acids
nucleotides
monosaccharides
Pancreatic
Nucleases
Pancreatic
Lipases
glycerol &
fatty acids
*all (except some lipids) absorbed in blood...to liver...to
rest of body
*some lipid breakdown products absorbed in blood, some in
lymph...all end up in liver...then to rest of body
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Meyers' A&P
March 25, 2015
VI. Metabolism
• All reactions that help maintain life
A. Anabolism: reactions that build molecules
B. Catabolism: reactions that breaks down molecules
– digestion is a catabolic process
– chemical digestion utilizing enzymes (hydrolysis)
1. Carbohydrate metabolism:
2. Fat Metabolism:
3. Protein Metabolism:
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