Transcript pancreatic duct

The Digestive System
Chapter 25
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Introduction
– Structure of the digestive system
• A tube that extends from mouth to anus
• Accessory organs are attached
– Functions include
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Ingestion
Movement
Digestion
Absorption
Defecation
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Overview of Digestive System
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Histological Organization
– The wall of the digestive tract has the same
basic arrangement of tissues from the
esophagus to the anal canal
– Four layers (from innermost to outermost)
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Mucosa
Submucosa
Muscularis
Serosa
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Layers of the Digestive Tract
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Layers of the Digestive Tract
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Movement & Mixing of Digestive Materials
– Peristalsis
• Coordinated motion of the two muscular layers
• Circular muscles contract, then longitudinal muscles
– Segmentation
• Mixing of food
• Circular muscles in two areas contract
• Longitudinal muscles alternately contract & relax
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Peristalsis & Segmentation
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The Oral Cavity
– Functions
• Take in food
• Prepare food for digestion
– Structure
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Lined with stratified squamous epithelium
Lips surround the opening
Roof is formed from the hard & soft palate
Tongue dominates the floor
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Oral Cavity
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Oral Cavity
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The Tongue
– Functions
• Maneuvers food
– Structure
• Skeletal muscle covered with mucosa
• The lingual frenulum connects the tongue to the
floor of the mouth
• Surface
– Papillae
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The Salivary Glands
– Found outside the mouth
– Ducts carry saliva to the mouth
– Saliva
• Functions
– Keeps mucous membranes moist
– Lubricates food
– Dissolves food
– Begins carbohydrate digestion
– 3 pairs
• Parotid glands
• Submandibular glands
• Sublingual glands
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Salivary Glands
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Teeth
– 2 sets
• Deciduous (20)
• Permanent (32)
– Held in sockets
– Gingiva surrounds the base of the teeth
– Structure
• Crown
• Root
• Neck
– Composition
• Dentin – primary substance in tooth
• Enamel – covers crown
• Cementum – covers root
– Tooth decay
– Wisdom teeth – 3rd molars
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A Tooth
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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
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The Esophagus
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The Stomach
– Has the 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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External Anatomy of the Stomach
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Anatomy of the Stomach
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Histology of the Stomach
– Mucosa is simple columnar epithelium with
goblet cells
– Mucosa is folded to form gastric pits
• Gastric glands secrete gastric juice
– Several kinds of cells in each gland produce substances
that form the gastric juice
» Mucus cells
» Chief cells
» Parietal cells
» Enteroendocrine cells
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The Stomach Wall
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Gastric Gland
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Functions of the Stomach
– Mechanical digestion
• Food reaches pylorus
– Chemical digestion
• Digestion of proteins
– Absorption
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No food
Water, electrolytes
Some drugs
Alcohol
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The Small Intestine
– About 18 feet long
– 3 regions
• The duodenum (= “12 fingers’ length”)
– About 8 inches long
– Common bile duct & pancreatic duct empty here
• The jejunum (= “empty”)
– About 8 feet long
– Most digestion occurs here
• The ileum
– About 9.5 feet long
– Most absorption occurs here
– Ends in the ileocecal valve
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Regions of the Small Intestine
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Histology of the Small Intestine
– The lining is folded into circular pleats called
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
(“hidden place” – like gastric pits) at the base
of villi
• Secrete intestinal juice
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Histology of the Small Intestine
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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
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The Large Intestine
– AKA colon
– About 4.5 feet long
– Mesocolon supports
– Begins with the cecum
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Appendix is attached
Ascending colon
Transverse colon
Descending colon
Sigmoid colon
– Colon connects to the rectum
– Rectum connects to the anal canal which empties to
the exterior through the anus
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The Large Intestine
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Histology & Functions of the Large Intestine
– Mucosa - simple columnar epithelium (thin)
• Completion of absorption
• Formation of feces
– Lots of mucus glands
– Expulsion of feces from the body
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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
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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
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Histology of the Large Intestine
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Accessory Organs
– Liver
– Pancreas
– Gall bladder
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The Liver
– Performs many life-sustaining functions,
digestive and other.
– Location – under the diaphragm on the left
• Connected to the diaphragm by the falciform
ligament
– Divided into lobes
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Right lobe
Left lobe
Caudate lobe
Quadrate lobe
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The Liver
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The Liver
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Histology of the Liver
- Outside is a capsule
- Composed of tiny lobules
– Each lobule is surrounded by liver cells and
sinusoids
– Bile ducts run between liver cells
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Histology and Blood Supply of the Liver
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Functions of the Liver
– Produces bile – the primary digestive function
• Composition
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Water
Bile salts
Cholesterol
Pigments
» Bilirubin
• Digestive function
– Emulsification of fats
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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
• Kupffer cells
– Produces plasma proteins
– Removes worn-out and damaged red blood
cells
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The Gallbladder
– Location – underside of the left lobe of the liver
– Function – to concentrate and store bile
– Gallstones
• Cholesterol in bile crystalizes, crystals fuse.
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The Gallbladder
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The Pancreas
- Location – in the curvature of the duodenum
– Connected to the duodenum by the pancreatic
duct
– Produces pancreatic juic
– Functions
• Exocrine - digestion of all the nutrient groups
• Endocrine – production of insulin & glucagon
– Control level of blood glucose
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The Pancreas
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