the digestive system - cabrillo collegepdarcey/bio 4/fall 2011/class notes... · 1 the digestive...
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The Digestive System
Chapter 24
Introduction • Structure of the digestive system
– A tube that extends from mouth to anus – Accessory organs are attached
• Functions include – Ingestion – Movement – Digestion – Absorption – Defecation
Human Anatomy, 3rd edition Prentice Hall, © 2001
Overview of Digestive System
Human Anatomy, 3rd edition Prentice Hall, © 2001
Histological Organization
• Same basic arrangement of tissues from esophagus to anal canal
• Four layers (from innermost to outermost) – Mucosa – Submucosa – Muscularis – Serosa
Human Anatomy, 3rd edition Prentice Hall, © 2001
Movement and Mixing of Digestive Materials • Peristalsis
– Coordinated motion of two muscular layers
– Circular muscles contract, then longitudinal muscles
• Segmentation – Mixing of food – Circular muscles in
two areas contract – Longitudinal muscles
alternately contract & relax
Human Anatomy, 3rd edition Prentice Hall, © 2001
The Oral Cavity • Structure
– Lined with stratified squamous epithelium
– Lips surround the opening
– Roof is formed from the hard & soft palate
– Tongue dominates the floor
• Functions – Take in food – Prepare food for
digestion
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Human Anatomy, 3rd edition Prentice Hall, © 2001
The Tongue • Structure
– Skeletal muscle covered with mucosa
– The lingual frenulum connects the tongue to the floor of the mouth
– Surface • Papillae
• Functions – Maneuvers food
Human Anatomy, 3rd edition Prentice Hall, © 2001
Salivary Glands • Found outside mouth • Ducts carry saliva to
mouth • 3 pairs
– Parotid glands – Submandibular glands – Sublingual glands
• Saliva – Functions
• Keeps mucous membranes moist
• Lubricates food • Dissolves food • Begins carbohydrate
digestion
Human Anatomy, 3rd edition Prentice Hall, © 2001
Teeth • 2 sets
– Deciduous (20) – Permanent (32)
• Held in sockets • Gingiva = gums • Structure
– Crown – Root – Neck
• Composition
– Dentin – Enamel – Cementum
• Dental caries • Wisdom teeth Human Anatomy, 3rd edition
Prentice Hall, © 2001
The Pharynx and Esophagus • Food enters the
esophagus from the pharynx
• The esophagus is a muscular tube behind the trachea – Food is moved by
peristalsis from the pharynx to the stomach
– Cardiac sphincter separates esophagus from stomach
Human Anatomy, 3rd edition Prentice Hall, © 2001
External Anatomy of the Stomach
Human Anatomy, 3rd edition Prentice Hall, © 2001
The Stomach • Same 4 basic layers • When the stomach is
empty, the mucosa lies in large folds – Rugae
• Pyloric sphincter separates stomach from small intestine
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Human Anatomy, 3rd edition Prentice Hall, © 2001
Histology of the Stomach
• Mucosa is simple columnar epithelium with goblet cells
• Mucosa is folded to form gastric pits – Gastric glands
secrete gastric juice
Human Anatomy, 3rd edition Prentice Hall, © 2001
Gastric Gland
• Several kinds of cells produce substances that form gastric juice – Mucus cells – Chief cells – Parietal cells – Enteroendocrine
cells
Functions of the Stomach • Mechanical digestion
– Food reaches pylorus • Chemical digestion
– Digestion of proteins • Absorption
– No food – Water, electrolytes – Some drugs – Alcohol
Human Anatomy, 3rd edition Prentice Hall, © 2001
The Small Intestine • About 18 feet long • The duodenum
– About 8 inches long – Common bile duct &
pancreatic duct empty here • The jejunum
– About 8 feet long – Most digestion occurs here
• The ileum – About 9.5 feet long – Most absorption occurs here – Ends in the ileocecal valve
Human Anatomy, 3rd edition Prentice Hall, © 2001
Histology of the Small Intestine
• The lining is folded into circular pleats – Plicae circulares
• The mucosal surface is folded into villi
• The epithelial cell membranes are highly folded into microvilli
• Intestinal glands are found in the crypts at the base of villi – Secrete intestinal
juice Human Anatomy, 3rd edition Prentice Hall, © 2001
A Villus
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Functions of the Small Intestine
• Chyme is further broken down – Proteins – Carbohydrates – Fats
• Most absorption is in the small intestine
Human Anatomy, 3rd edition Prentice Hall, © 2001
The Large Intestine (Colon) • About 4.5 feet long • Mesocolon supports • Begins with the cecum • Appendix is attached • Ascending colon • Transverse colon • Descending colon • Sigmoid colon • Colon connects to rectum • Rectum connects to anal
canal • Empties to the exterior
through the anus
Human Anatomy, 3rd edition Prentice Hall, © 2001
Histology and Functions of the Large Intestine
• Mucosa - simple columnar epithelium – Completion of
absorption – Formation of feces
• Lots of mucus glands • Expulsion of feces
from the body
Human Anatomy, 3rd edition Prentice Hall, © 2001
Digestion in the Large Intestine • Mechanical
– Regulated by the ileocecal valve – Mixing and peristalsis – Mass peristalsis
• Chemical – Mucus secreted – No enzymes – Bacteria – prepare chyme for elimination
Human Anatomy, 3rd edition Prentice Hall, © 2001
Feces Formation & Defecation • Chyme is now solid or semi-solid - feces • Large intestine absorbs any more water and
electrolytes from feces • Defecation
– Mass peristalsis pushes fecal material into rectum – Rectum stretches
• Defecation reflex
Accessory Organs
• Liver • Pancreas • Gall bladder
5
Human Anatomy, 3rd edition Prentice Hall, © 2001
The Liver • Performs many life-
sustaining functions • Location – under the
diaphragm on the right – Connected to the
diaphragm by the falciform ligament
• Divided into lobes – Right lobe – Left lobe – Caudate lobe – Quadrate lobe
Human Anatomy, 3rd edition Prentice Hall, © 2001
Histology of the Liver
• Outside is a capsule • Composed of tiny
lobules • Each lobule is
surrounded by liver cells and sinusoids – Hepatocytes – Kupffer cells
• Bile ducts run between liver cells
Functions of the Liver • Produces bile – the primary digestive function
– Composition • Water • Bile salts • Cholesterol • Pigments
– Bilirubin – Digestive function
• Emulsification of fats
Other Functions of the Liver
• Absorbs and stores iron, vitamins A, D, E, B7, K • Detoxifies toxins and hormones • Metabolizes proteins, carbohydrates, and lipids • Removes bacteria from the blood • Produces plasma proteins • Removes worn-out and damaged red blood cells
Human Anatomy, 3rd edition Prentice Hall, © 2001
The Gallbladder
• Location – underside of right lobe of liver
• Function – concentrate and store bile – Collected from liver
• Hepatic ducts – Adds bile to
duodenum • Cystic duct • Common bile
duct • Gallstones
Human Anatomy, 3rd edition Prentice Hall, © 2001
The Pancreas • Location – in the
curvature of the duodenum
• Connected to the duodenum by the pancreatic duct
• Produces pancreatic juice
• Functions – Exocrine - digestion
of all nutrient groups – Endocrine – control
blood glucose level