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© 2012 Pearson Education, Inc.
25The Digestive System
PowerPoint® Lecture Presentations prepared bySteven BassettSoutheast Community College Lincoln, Nebraska
© 2012 Pearson Education, Inc.
Introduction
• The digestive system consists of:• The digestive tract• Accessory organs of digestion
• Digestive tract• Mouth• Pharynx• Esophagus• Stomach• Small intestine• Large intestine
© 2012 Pearson Education, Inc.
Introduction
• Accessory Organs of the Digestive Tract• Teeth• Tongue• Salivary glands• Pancreas• Liver• Gallbladder
© 2012 Pearson Education, Inc.
Figure 25.1 Components of the Digestive System
Mouth
Anus
Mechanical processing,moistening, mixing withsalivary secretions
Oral Cavity, Teeth, Tongue
Liver
Gallbladder
Pancreas
Large Intestine
Secretion of bile (importantfor lipid digestion), storage ofnutrients, many other vitalfunctions
Storage and concentration ofbile
Exocrine cells secrete buffersand digestive enzymes;endocrine cells secretehormones
Dehydration and compactionof indigestible materials inpreparation for elimination
Enzymatic digestion andabsorption of water, organicsubstrates, vitamins, and ions
Small Intestine
Stomach
Esophagus
Pharynx
Salivary Glands
Chemical breakdown ofmaterials via acidand enzymes; mechanicalprocessing through muscularcontractions
Transport of materials to thestomach
Muscular propulsion ofmaterials into the esophagus
Secretion of lubricating fluidcontaining enzymes thatbreak down carbohydrates
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Introduction
• Functions of the Digestive System (details)• Ingestion
• Bringing food and liquids into the mouth
• Mechanical processing• Chewing and swallowing food
• Digestion• Chemical breakdown of food into nutrient form
• Secretion• Secretion of products by the lining of the digestive tract• Secretion of products by the accessory organs of digestion
• Absorption • The movement of nutrients from the small intestine to the bloodstream
• Excretion • The removal of waste products from the digestive tract
• Compaction • Progressive dehydration of organic wastes
© 2012 Pearson Education, Inc.
An Overview of the Digestive System
Major layers of the digestive tract include Mucosa
Mucosa can be expanded by folds and microvilli to increase surface area for digestion and absorption.
Submucosa Submucosa is separated from mucosa by “Muscularis
Mucosa”, which is the nearest muscular layer the lumen.
Muscularis externa Made of inner circular and outer longitudinal muscle layers. In
between there is “Myenteric Plexus”.
Serosa
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Figure 25.2a Histological Structure of the Digestive Tract
Three-dimensional view of the histologicalorganization of the general digestive tube
Mesenteric artery and vein
Mesentery Plica
Mucosa
Submucosa
Muscularisexterna
Serosa(visceral
peritoneum)
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An Overview of the Digestive System
• Movement of digestive materials through the digestive tract
• The muscularis externa propels material through the digestive tract
• This is called peristalsis
• Material is churned and fragmented and at the same time is propelled through the digestive tract
• This is called segmentation
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Figure 25.3a Peristalsis and Segmentation
Peristalsis propels materials along the length of thedigestive tract by coordinated contractions of the circularand longitudinal layers.
Contraction incircular musclelayer forcesbolus forward
Contraction oflongitudinalmuscles aheadof bolus
Contraction
Contraction
ContractionContraction ofcircular musclesbehind bolus
Longitudinal muscle
Circular muscle
Frommouth
Toanus
INITIAL STATE
Peristalsis
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Figure 25.3b Peristalsis and Segmentation
Segmentation movements primarily involve the circular muscle layers. These activities churn and mix the contents ofthe digestive tract, but do not produce net movement in aparticular direction.
Segmentation
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An Overview of the Digestive System
• The Peritoneum• The serosa (visceral peritoneum) is
continuous with the parietal peritoneum• The abdominal organs lie in association with
the peritoneal membrane• Intraperitoneal organs• Retroperitoneal organs
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An Overview of the Digestive System
• Intraperitoneal Organs• Organs that lie within the peritoneal cavity• Organs are surrounded completely by the
visceral peritoneum• Examples:
• Stomach • Liver
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An Overview of the Digestive System
• Retroperitoneal Organs• Organs are covered by the visceral
peritoneum on their anterior surface• These organs lie deep to the visceral
peritoneum• Examples:
• Kidneys• Ureters• Abdominal aorta
© 2012 Pearson Education, Inc.
Figure 25.4d Mesenteries
The organization of mesenteries inthe adult. This is a simplified view;the length of the small intestinehas been greatly reduced.
Greateromentum (cut)
Transversemesocolon
Fusion fascia ofascending anddescendingcolons fusesto dorsalperitoneum
Descendingcolon
Sigmoidcolon
Lesseromentum
Mesenteryproper
(mesenterialsheet)
Ascendingcolon
Transversecolon
Smallintestine
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Figure 25.4b Mesenteries
Mesenteries of the abdominopelviccavity, as seen in a diagrammaticsagittal section
Lesseromentum
Stomach
Transversemesocolon
Transversecolon
Greateromentum
Parietalperitoneum
Smallintestine
Uterus
DiaphragmFalciformligament
Urinary bladder
Sigmoidmesocolon
Mesenteryproper
Duodenum
Pancreas
Rectum
Liver
© 2012 Pearson Education, Inc.
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The Oral Cavity
The oral cavity includes: The tongue Salivary glands
Parotid gland Sublingual gland Submandibular gland.
Teeth Mastication
Functions of the oral cavity: Analyzes material before swallowing Mechanical processing of food through the actions of teeth,
tongue, and palatal surfaces Lubrication Limited digestion of carbohydrates by a salivary enzyme
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Figure 25.5a The Oral Cavity
The oral cavity as seen in sagittal section
Soft palate
Pharyngeal tonsil
Entrance toauditory tube
Nasopharynx
Palatine tonsil
Lingual tonsil
Epiglottis
Hyoid bone
Laryngopharynx
Oropharynx
Palatopharyngealarch
Fauces
Uvula
Hard palate
Nasal cavity
Palatoglossalarch
Opening ofparotid duct
Dorsum oftongue
Body oftongue
Root oftongue
Vestibule
GingivaLower lip
Cheek
Upper lip
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Figure 25.5b The Oral Cavity
An anterior view of the oralcavity as seen through the open mouth
Uvula
Openings ofsubmandibular
ducts
Frenulumof lower lip
Frenulumof upper lip
Lingualfrenulum
Palatinetonsil
Palatopharyngealarch
Palatoglossalarch
Vestibule
Gingiva
Fauces
Soft palate
Hard palate
Tongue
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Figure 25.6a The Salivary Glands
Lateral view showing the relative positions of the salivaryglands and ducts on the left side of the head. Much of the left half of the body and the left ramus of the mandible have been removed. For the positions of the ducts inside the oral cavity, see Figure 25.5.
Parotid salivary gland
Parotid duct
Submandibularduct
Submandibularsalivary gland
Sublingualsalivary gland
Opening of leftsubmandibular
duct
Openings ofsublingual ducts
Lingual frenulum
© 2012 Pearson Education, Inc.
Figure 25.7a Teeth
Diagrammatic section through a typical adult tooth
Crown
Neck
Root
Enamel
Dentine
Pulp cavityGingiva
Gingival sulcus
Cement
Periodontal ligament
Root canal
Bone of alveolus
Apical foramen
Branches of alveolarvessels and nerves
© 2012 Pearson Education, Inc.
The Pharynx
Muscles involved in swallowing: Pharyngeal constrictors push the bolus toward
theesophagus. Palatopharyngeus and stylopharyngeus
muscles elevate the larynx. The palatal muscles raise the soft palate.
The swallowing process: Buccal phase Pharyngeal phase Esophageal phase
© 2012 Pearson Education, Inc.
Figure 25.8 The Swallowing ProcessBuccal Phase
Pharyngeal Phase
Esophageal Phase
Esophagus
Diaphragm
Stomach
Thoraciccavity
Peristalsis
Hard palate
Tongue
Epiglottis
Trachea
Bolus
Esophagus
Softpalate
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The Esophagus
Muscular tube that transports food and liquid to the stomachConnects the pharynx to the stomach Superior portion is skeletal muscle Inferior portion is smooth muscle
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Figure 25.9a Histology of the Esophagus
Low-power view of a section through the esophagus
LM 5
Muscularismucosae
Muscularisexterna
Mucosa
Submucosa
Adventitia
The esophagus
© 2012 Pearson Education, Inc.
The Stomach
Stomach is an intraperitoneal structure. Three major functions:
Stores bulk amounts of ingested food Mechanically breaks down ingested food Chemically digests ingested food
Parietal cells: HCL production Chief cells: pepsinogen production
Four regions: Cardia Fundus Body Pylorus
Three layers of muscle Highly specialized mucosa
© 2012 Pearson Education, Inc.
Figure 25.10a The Stomach and Omenta
Surface anatomy of the stomach showing blood vessels and relation to liver and intestines
Pylorus
Body
STOMACH
Fundus
Liver
Retractor
Right colicflexure
Right kidney
Duodenum
Gallbladder
Right gastroepiploicartery
Lesseromentum Hepatoduodenal ligament
Hepatogastric ligament
Esophagus
Diaphragm
Spleen
Left colic flexure
Greater omentum
Greater curvature
Lesser curvature
Left gastroepiploicartery
Cardia
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Figure 25.11a Gross Anatomy of the Stomach
External and internal anatomy of the stomach
Anterior surface
Pyloric antrum
Pylorus
Pyloric canal
Pyloricsphincter
Duodenum
Esophagus
Lesser curvature(medial surface)
Circularmuscle layer
Longitudinalmuscle layer
Cardia
Fundus
Left gastroepiploicvessels
Body
Oblique muscle layeroverlying mucosa
Greater curvature(lateral surface)
Rugae
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Figure 25.13bc Histology of the Stomach Wall
Colorized SEM of the gastric mucosa
Gastric mucosa
Mucousepithelialcells
Entrances togastric pits
SEM 35
Diagrammatic view of the organization of the stomachwall. This corresponds to a sectional view through thearea indicated by the box in part (b).
Myentericplexus
Arteryand vein
Gastric pit(opening to
gastric gland)
Mucousepithelium
Lymphaticvessel
Laminapropria
Muscularismucosae
Submucosa
Obliquemuscle
Circularmuscle
LongitudinalmuscleSerosa
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The Small Intestine
Plays primary role in the digestion and absorption of food
Three anatomical regions: Duodenum— the “mixing bowl”, the first part of
small intestine that recieves stomach contents. Jejunum— where the bulk of digestion and
absorption occurs Ileum— materials flow through here into large
intestine. This is the longest portion of small intestine.
© 2012 Pearson Education, Inc.
Figure 25.14 Regions of the Small Intestine
Duodenum
Jejunum
Ileum
Cecum
Rectum
Sigmoidcolon
Descendingcolon
Transversecolon
Ascendingcolon
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Figure 25.15a Histology of the Intestinal Wall
Characteristic featuresof the intestinal lining
Plica circulares
Villi
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Figure 25.15bc Histology of the Intestinal Wall
The organization of villi and the intestinal crypts
Diagrammaticview of a singlevillus showingthe capillary andlymphaticsupply
Mucosa
Muscularismucosae
Muscularisexterna
Submucosa
Serosa
Villi LactealIntestinalcrypt
Lymphoidnodule
Submucosalartery and vein
Lymphaticvessel
Submucosalplexus
Circular layerof smoothmuscle
Myenteric plexus
Longitudinal layerof smooth muscle
Arteriole Venule Lymphaticvessel
Laminapropria
Capillarynetwork
Nerve
Lacteal
Columnarepithelialcell
Goblet cell
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The Large Intestine
Often called the large bowel Functions include:
Reabsorb water and compact feces Absorption of important minerals by bacteria Storage site for feces before defecation
Three regions: The cecum The colon The rectum
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Figure 25.17a The Large Intestine
Gross anatomyand regions of thelarge intestine
Rectum
SIGMOID COLON
Sigmoid flexure
Taenia coli
Rectal artery Sigmoid arteriesand veins
Left colic artery
Haustra
Inferiormesentericartery
Left colic vein
DESCENDINGCOLON
Intestinal arteriesand veins
Greateromentum (cut)
Left colic(splenic)flexure
Inferior mesenteric vein
Superior mesenteric arterySplenic vein
Ileum
Appendix
Cecum
Ileocecal valve
Omental appendices
ASCENDINGCOLON
Right colicartery and vein
Middle colicartery and vein
Right colic(hepatic) flexure
TRANSVERSECOLON Inferior vena cava
Hepatic portal veinAorta
Superiormesenteric vein
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Accessory Glandular Digestive Organs
Liver Bile production
Gallbladder Bile storage and concentration
Pancreas Enzyme production and secretion
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Table 25.1 Major Functions of the Liver
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Figure 25.21a Liver Histology
Diagrammatic view of lobular organization
Bileductules
Portalarea
Branch of hepatic portal vein
Bileduct
Interlobularseptum
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Figure 25.22ac The Gallbladder and Associated Bile Ducts
A view of the inferiorsurface of the livershowing the position of the gallbladder andducts that transport bile from the liver to the gallbladder andduodenum
A portion of the lesser omentum has been cut away tomake it easier to see the relationships among thecommon bile duct, the hepatic duct, and the cystic duct.
Round ligament
Right hepatic duct
Cystic duct
Gallbladder
Fundus
Body
Neck
Liver
Common bileduct
Duodenum
Pancreas
Stomach
Right gastricartery
Commonhepaticartery
Hepaticportal vein
Cut edge oflesseromentum
Commonhepatic duct
Left hepaticartery
Left hepaticduct
Common bile duct
Pancreaticduct
PancreasIntestinal lumen
Duodenalpapilla
Duodenalampulla
Hepatopancreaticsphincter
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Figure 25.23a The Pancreas
Gross anatomy of the pancreas. The head of the pancreas is tucked into a curve of the duodenum that begins at the pylorus of the stomach.
Superior mesentericartery
Inferior pancreatico-duodenal arteryPosterior branch
Anterior branch
Transversepancreatic artery
Body ofpancreas
Great pancreaticartery
Pancreatic duct(to greater duodenal
papilla) with commonbile duct
Accessory pancreaticduct (to lesser
duodenal papilla)
Superior pancreatico-duodenal artery
Superiorpancreatic artery
Common hepaticartery
Celiac trunk
Gastroduodenal artery
Head of pancreas
Splenic artery
Stomach
Abdominal aorta
Common bile duct
Duodenum
Tail ofpancreas
Caudalpancreatic
artery
Lobules
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Aging and the Digestive System
The rate of epithelial stem cell division declines. Smooth muscle tone decreases. The effects of cumulative damage become apparent. Cancer rates increase. Changes in other systems have direct or indirect effects on the digestive system.
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