Transcript General anatomy of Digestive system

The Digestive System
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
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)
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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
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
• 2 sets
Teeth
– 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
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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
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
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Mucus cells
Chief cells
Parietal cells
Enteroendocrine
cells
Human Anatomy, 3rd edition
Prentice Hall, © 2001
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
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
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A Villus
Human Anatomy, 3rd edition
Prentice Hall, © 2001
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)
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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
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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
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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
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Accessory Organs
• Liver
• Pancreas
• Gall bladder
Human Anatomy, 3rd edition
Prentice Hall, © 2001
The Liver
• Performs many lifesustaining functions
• Location – under the
diaphragm on the right
– Connected to the
diaphragm by the
falciform ligament
• Divided into lobes
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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
Human Anatomy, 3rd edition
Prentice Hall, © 2001
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
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Other Functions of the Liver
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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
Human Anatomy, 3rd edition
Prentice Hall, © 2001