Download Digestion and Absorption

Chapter 3
Digestion, Absorption, and
Metabolism
Learning Objectives
• Describe the organization of life.
• Define “digestion” and “absorption” and list
organ systems involved in these
processes.
• Explain the roles of mucus, enzymes,
nerves, and hormones in the digestive
tract.
• Discuss the digestive processes that occur
in the entire digestive tract.
3-3
Learning Objectives
• Explain how food is propelled through the
gastrointestinal tract.
• Explain how the structure of the small
intestine enhances its function.
• Distinguish passive diffusion, facilitated
diffusion, and active transport.
3-4
Learning Objectives
• Contrast the absorption and transportation
of a water-soluble molecule with that of a
fat-soluble molecule.
• Discuss how the body uses carbohydrate,
protein, and fat to produce energy.
• List four ways that waste products are
eliminated from the body.
3-5
The Organization of Life
3-6
The Gastrointestinal Tract: An
Overview
3-9
The Role of
Body Organ
Systems
3-8
• A good way to learn
the digestive system
is to create a
narrative of “what
happens to the
hamburger when I eat
it.
• Follow the anatomical
steps as well as how
the nutrients in the
hamburger are being
broken down and
used.
Trace a Meal Through Digestion and
Absorption—Head and Mouth
• I thought I was
brilliant when I
came up with this
technique.
• But, your book does
it so I am more of a
3-19
First: An Overall View of
the Digestive Process
•
The GI tract is a
“disassembly” line
–
•
Nutrients become more
available to the body in
each step
There are six essential
activities:
1.
2.
3.
4.
5.
6.
Ingestion
Propulsion
Mechanical digestion
Chemical digestion
Absorption
Defecation
Trace a Meal Through
Digestion and Absorption—
Head and Mouth
• The cephalic response
– Sights, sounds, and smells of food prepare
the digestive system for the arrival of food.
• Mouth:
– Mechanical processing (chewing) of food
– Saliva plays many functions
– Partial digestion of carbohydrate by salivary
amylase
– Lysozyme inhibits growth of bacteria
3-19
How Important Is Saliva?
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How much should taste
determine what we eat?
Think about taste
• How many taste receptors have we
discussed?
• How many tastes do you think you can
sense?
• What do you think the mechanism for
sensing so many tastes with 5 receptors
be? Nobody really knows.
Think about taste
• Black vs. green olives
• I hate tomatoes but I am ok with spaghetti
sauce.
• I am not particular about taste, I have eaten
spaghetti thousands of times.
• Cold pizza, hot pizza, instant cold pizza.
• Wine gargle
• Meat substitutes
• Why do some people like salt with their food (fat)
• Sugar on cottage cheese. I ask Ella and Celi to
try all their foods, but I will never try this.
Influence of Other
Sensations on Taste
• Taste is 80% smell
• We also sense heat, texture,
and pain.
• Temperature and texture
enhance or detract
from taste
Taste
Interactions
• http://blog.khymos.org/2
007/05/01/practicalmolecular-gastronomypart-5/
• http://justjared.buzznet.
com/2010/09/23/sofiavergara-stirring-saltinto-chocolate-milkvideo/
http://www.foodpolitics.com/t
ag/salt/
http://www.newsrecord.org/nation-world/fda-moves-to-reduce-saltin-american-diet-1.2233061
•
http://www.tnr.com/article/75074/the-other-whitepowder?page=0,1&passthru=NDQ2NTNmNDQ1YWVkMmM2M2JmMGNiZj
Q0YzQ2N2Q4Njg
•
http://www.nytimes.com/2010/05/30/health/30salt.html?scp=2&sq=salt&st=cse
The Demise of Slow Cooking
• Are we
getting so
rushed we
need salt,
fat and
sugar to
make food
taste good.
Do You Eat For Taste?
• Or do you just scarf
down whatever you
have available.
• Does it matter?
Trace a Meal Through
Digestion and
Absorption—Pharynx
• Shared by the
digestive and
respiratory tracts
• Epiglottis blocks the
air passages during
swallowing.
3-20
Digestion Movie
•
•
http://www.youtube.com/watch?v=wRWZvhz2CfU
Basic Anatomy and Physiology Movie
Trace a Meal Through
Digestion and
Absorption—Esophagus
• Peristalsis
movement
propels food
• A sphincter
controls the
passage of
food to the
stomach
3-21
Trace a Meal Through
Digestion and
Absorption—Stomach
• A temporary storage place for food
• A “mixing bowl” of bolus and highly
acidic secretion—forming chyme.
• Partial digestion of protein by pepsin
• Very little absorption
• Stomach emptying
– Determined by the size and composition of the meal
– Controlled by signals from the small intestine
• Milk challenge
3-22
The Structure of the Stomach
Determines Its Functions
3-23
Regulation of Gastric Secretion
• By nerves
• By hormones
• And……..
3-24
Regulation of Gastric Secretion
• Fat
content.
Go to
www.milkgallon.c
om to see plenty
of evidence and
some high quality
high-speed
photography.
3-24
He’s so cute.
Dibbs!!!
You Can Even Get Animations
Look
Away
if you are squeamish
Olive Oil
•
•
http://www.metacafe.com/watch/390028/oil_bubble_in_alcohol/
http://answers.yahoo.com/question/index?qid=20081012024305AAQ9pXv
Trace a Meal Through
Digestion and
Absorption—Small
Intestine
• SI is divided into 3 segments:
– Duodenum: first 12 inches
– Jejunum: middle 8 feet
– Ileum: last 11 feet
• The main site of digestion and
absorption
– Function determined by its structure
3-25
Movement of the Small Intestine
• Peristalsis propels
chyme through the
small intestine.
• Segmentation
mixes chyme with
digestive secretion.
3-26
Secretion in the Small Intestine
• Secretion aids digestion
– Pancreas
• Bicarbonate ion: neutralizes stomach acid
• Pancreatic enzymes: digest food
– Liver and gallbladder
• Produces (liver) and stores and secretes
(gallbladder) bile
• Bile helps lipases to digest fat
– Brush border enzymes
3-27
Hormonal Control of Secretions
Important
Hormones:
Secretin
Cholecystokinin
(CCK)
3-28
The Structures of SI Maximize
Absorption
Folds
Villi
Microvilli
Capillary
Lacteal
3-29
The Small Intestinal Villi, cont’d
• The surface area of the small intestine is
roughly the size of a tennis court.
Absorption Mechanisms in the
SI
3-30
Trace a Meal Through
Digestion and Absorption—
Large Intestine
• Includes the colon and rectum
• Growth of intestinal microflora
– Mircoflora can synthesize small amounts of
some B vitamins and vitamin K
– By-products: gas
• Compacts unabsorbed substances into
feces
• Rectum stores feces prior to defecation
through anus
3-31
The
Digestion
and
Absorption
of a Meal
3-32
Digestive Problems and
Solutions
3-33
Digestive Problems and
Solutions
3-34
Alternate Feeding Method
• Enteral or tube-feeding
– A liquid diet fed through a tube
• Total Parenteral Nutrition (TPN)
– Nutrients directly provided into the blood
3-35
Blood Carries Absorbed Nutrients in the
Body
• The
Cardiovascular
System
3-37
Hepatic Portal and Lymphatic Circulation
• Two routes for nutrients to enter the blood
circulation
3-38
Destination of the Nutrients:
The Cell
3-39
Making and Breaking Molecules
• Metabolism
– The sum of chemical
reactions in the body
• Anabolic
– Energy-requiring
processes that combine
simpler molecules to more
complex substances
• Catabolic
– Energy-yielding
processes that break
down substances into
simpler molecules
3-40
ATP is the Energy Molecule for Cells
• Mitochondrion
– The cellular catabolic organelle responsible for
generating energy
• Cellular respiration
– The reactions that break down nutrients in the
presence of oxygen to produce carbon dioxide,
water, and ATP
3-41
Producing Energy
3-42
Elimination of Metabolic Wastes
• The digestive tract excretes the
undigested, unabsorbed substances in the
feces.
• The lungs eliminate carbon dioxide and
water.
• The skin eliminates water, protein
breakdown products, and minerals.
• The kidney eliminates water, nitrogen, and
other dissolved waste products.
3-43
The 4
Systems are
Interrelated
3-44
Pathology: Colic
• What causes colic?
No one is really sure, but there are a few
suspected causes, such as intestinal gas,
food sensitivity or allergy, or an immature
nervous system.
Pathology: Peritonitis
• Inflammation
of the
peritoneum.
Pathology:
Coeliac/Crohn’sDisease
Pathology: Mumps
• A viral disorder infection of the
parotid salivary gland.
Iowa to launch mass clinics for mumps
shots
State to target young adults caught
up in growing epidemic (4/2006)
Pathology: Cranial Nerve
Lesions
• Cranial nerve
lesions can lead to
paralysis of the
tongue(11) or
pharynx (10).
Pathology: GERD
(gastroesophageal reflux disorder)
Gas is trapped in the
fundus of the stomach.
– This gas may
cause the pyloric
valve to become
misshapen and
open.
Either this alone will
allow acid access to the
sphinchter and
esophagus or the
escaping gas will carry
acid with it.
Jaundice
Unconjugated
Urobilinogen
Blood
Conjugated
Urobilinogen