Transcript Absorption

The Digestive System
Chapter 15
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
• Ingestion
• Movement
• Digestion
• Absorption
• Defecation
Overview of Digestive System
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Histological Organization
– Same basic arrangement of
tissues from the esophagus
to the 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
the two muscular layers
• Circular muscles
contract, then
longitudinal muscles
contract
Human Anatomy, 3rd edition
Prentice Hall, © 2001
The Oral Cavity
– Functions
• Take in food
• Prepare food for
digestion
– Structure
• Lined with stratified
squamous epithelium
• Lips surround the
opening
• Roof is formed from the
hard & soft palate
• Tongue dominates the
Human Anatomy, 3rd edition
floor
Prentice Hall, © 2001
Salivary Glands
– Found outside the
mouth
– Ducts carry saliva
to the mouth
• Keeps mucous
membranes moist
• Lubricates and
dissolves food
• Begins
carbohydrate
digestion
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Salivary Glands
– 3 pairs
• Parotid glands
• Submandibular
glands
• Sublingual
glands
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Teeth
– 2 sets
• Deciduous (20)
• Permanent (32)
– Held in sockets
– Gingiva
surrounds the
base of the teeth
– Structure
• Crown
• Root
• Neck
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Teeth
– Composition
• Dentin – primary
substance in tooth
• Enamel
– Covers crown
• Cementum
– Covers root
– Dental caries
– Wisdom teeth
• 3rd molars
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
Human Anatomy, 3rd edition
Prentice Hall, © 2001
External Anatomy of the Stomach
Human Anatomy, 3rd edition
Prentice Hall, © 2001
The Stomach
– Has the same 4
basic layers
– When the stomach
is empty, the
mucosa lies in
large folds
– 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
– Chyme
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Gastric Gland
• Substances that
form gastric juice
– Mucus
– Hydrochloric
acid
– Pepsinogen
• Digestion of
proteins only
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Functions of the Stomach
– Mechanical digestion
• Food reaches pyloric valve
– 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
• Functions
– Most digestion and
absorption occurs
here
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Histology of the Small Intestine
– The mucosal
surface is folded
into villi
– Intestinal glands are
found at the base of
villi
• Secrete intestinal
juice - digests all
nutrient groups
except nucleotides
Human Anatomy, 3rd edition
Prentice Hall, © 2001
A Villus
Human Anatomy, 3rd edition
Prentice Hall, © 2001
The Large Intestine
– AKA colon
– About 4.5 feet long
– Begins with the
cecum
• Appendix is
attached
– Colon connects to the
rectum
– Rectum connects to
the anal canal which
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 with lots
of mucus glands
– Functions
• Completion of
absorption
• Formation of
feces
• Expulsion of feces
from the body
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Digestion in the Large Intestine
– Mechanical
• Mixing and peristalsis
• Mass peristalsis
– Chemical
• Mucus secreted
• No enzymes
• Bacteria – prepare chyme for elimination
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
Human Anatomy, 3rd edition
Prentice Hall, © 2001
The Liver
– Performs many life-sustaining functions
– Location – under the diaphragm on the left
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
– Bile ducts run
between liver
cells
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Digestive Function of the Liver
– Produces bile
• Composition
– Water
– Bile salts
– Cholesterol
– Pigments
» Bilirubin
– Digestive function of bile
• Emulsification of fats
Other Functions of the Liver
– Absorbs and stores iron, several vitamins
– 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
the left lobe of the liver
– Function – concentrate
and store bile
• Collected from liver
– Hepatic ducts
• Adds bile to small
intestine
– Common bile duct
– Gallstones
• Cholesterol in bile
crystalizes, crystals fuse.
Human Anatomy, 3rd edition
Prentice Hall, © 2001
The Pancreas
– in the
curvature between
stomach and small
intestine
– Connected to the
small intestine by the
pancreatic duct
– Produces pancreatic
juice
– Location
• Digestion of all the
nutrient groups Human Anatomy, 3rd edition
Prentice Hall, © 2001