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Digestive System
Chap 38
Nutrients
• Water – most important nutrient!!!!
• Carbohydrates – main energy source for
the body
• Fats – essential fatty acids, energy stores
• Proteins – growth, structure, transport,
regulation, metabolism, essential amino
acids
• Vitamins – organic molecules that work
with enzymes, water soluble, fat soluble,
essential
• Minerals – inorganic, Ca, K, Fe
pp 972 - 975
Food Pyramid
Fats, Oils, and Sweets (use sparingly)
Soft drinks, candy, ice cream, mayonnaise, and
other foods in this group have relatively few
valuable nutrients.
Milk, Yogurt, and Cheese Group
(2-3 Servings)
Milk and other dairy products are rich in
proteins, carbohydrates, vitamins, and
minerals.
Vegetable Group
(3-5 servings)
Vegetables are a low-fat
source of carbohydrates,
fiber, vitamins, and minerals.
Fats
Sugars
Meat, Poultry, Fish, Dry Beans, Eggs, and
Nut Group
(2-3 servings)
These foods are high in protein.
They also supply vitamins and minerals.
Fruit Group
(2-4 servings)
Fruits are good sources of
carbohydrates, fiber, vitamins
and water.
Bread, Cereal, Rice
and Pasta Group
(6-11 servings)
The foods at the base of the
pyramid are rich in complex
carbohydrates and also
provide proteins, fiber,
vitamins, and some
minerals.
pg 976
The Digestive System
• Mouth – mechanical and chemical –
breaking down food
• Esophagus – mechanical
• Stomach – mechanical*, chemical, chyme
• Small intestine – mechanical, chemical*,
digest, absorb
• Large intestine – mechanical, H2O
absorption
The Digestive System
Mouth
Pharynx
Salivary glands
Esophagus
Liver
Gallbladder
(behind liver)
Stomach
Pancreas (behind
stomach)
Large intestine
Small intestine
Rectum
pg 979
Accessory Structures of
Digestion
Liver
Gallbladder
Duodenum
Bile duct
Pancreas
Pancreatic duct
To rest of small intestine
pg 981
Four Main Stages of Food
Processing
• Ingestion- act of eating.
• Digestion – process of breaking food
down into molecules that can be absorbed
by the body.
• Absorption – absorbing the nutrients into
the blood.
• Elimination – ridding the body of waste.
The Mammalian Digestive System
• Peristalsis is the rhythmic contractions of
smooth muscle along the digestive tract
that keep food moving along.
• Sphincters close off various parts of the
tube for regulation of the passage of food
between chambers.
The Oral Cavity
• Chewing physically breaking the food into
smaller pieces and exposing more surface
area for enzymes to act on.
• Salivary amylase breaks down starch.
Saliva also contains mucin with makes
food slippery.
• Salivary lysozyme
• Bolus is the ball of food that gets pushed
into the esophagus.
Oral stage
Pharyngeal stage
Esophageal stage
The Stomach
• Can accommodate about 2 liters of food.
• Chyme is what the bolus becomes in the
stomach after digestive juices are added.
• Ridges in the stomach called ruggae help churn
food.
• Pepsin in stomach breaks down proteins.
– Pepsinogen is the inactive form of pepsin and is
activated by HCl.
– HCl also helps denature proteins in the chyme.
Digestion in the Stomach
A Closer Look
• Gastric Pits in the stomach lining are
composed of specialized epithelial cells.
• Gastric pits create the gastric juices.
– Parietal Cells secrete HCl.
– Chief Cells secrete pepsinogen.
– Mucus Cells secrete mucus that protects the
stomach lining.
Digestive Feedback Systems
• Pepsin activates more pepsinogen.
• The sight of food creates a nervous
response that causes gastric juices to be
secreted.
• A drop in pH and distention of the stomach
creates a negative feedback response that
signals a need for secretion of gastric
juices.
Stomach “Problems”
• Gastric ulcers are lesions in the stomach lining.
• Can occur when the lining is eroded faster that it
is replaced (from excess HCL alone)
• Helibacter pylori can cause ulcers but can be
treated with antibiotics (bacteria based)
• Heartburn occurs when acidic chyme seeps
back through the cardiac sphincter between
the esophagus and stomach.
Enter the Small Intestine!
• The pyloric sphincter is between the small
intestine and the stomach.
• It takes 2 to 6 hours after a meal for the stomach
to empty.
• duodenum->jejunum->ileum
• The small intestine secretes bicarbonate to
neutralize the acid chyme coming from the
stomach.
• Bile is secreted by the gallbladder to emulsify
fats which are broken down by an enzyme called
lipase which is secreted by the small intestine.
The small intestine
Villus
Small Intestine
Circular folds
Epithelial cells
Villi
Capillaries
Lacteal
Vein
Artery
pg 983
Small Intestine Enzymes
• Carbohydrates
– Pancreatic amylase secreted by the pancreas breaks
down starch.
– Maltase, Sucrase, Lactase break down disaccharides
and are built into the intestinal epithelium.
• Protein Digestion
– Chymotrypsin, Trypsin,Carboxypeptidase,
Aminopeptidase, enteropeptidase.
• Nucleic Acids – Nucleases
• Lipids - Lipases
Absorption of Nutrients
• Villi and microvilli increase surface area(300m2) for
maximum absorption.
• Intestinal epithelium absorb nutrients either by diffusion
or active transport.
• Nutrients are carried away from the intestine by
capillaries at the core of the villi.
• Lacteals are lymphatic vessels that are surrounded by
capillaries in the core of the villi that absorb fats which
are combined with proteins.
– These lipid proteins are called chylomicrons.
– They travel from through the lymphatic system and eventually
drain back into the blood and travel to the heart.
• Capillaries and veins drain blood into the
hepatic portal vessel which carries
blood to the liver.
– Ensures that the liver has first access to the
nutrients in the blood.
– The nutrient balance of the blood leaving the
liver may be very different than it was when it
entered.
– One of the many functions the liver include
regulating glucose levels in the blood and
converting amino acids into carbohydrates.
– From the liver the blood travels to the heart to
be pumped to the rest of the body.
Hormonal Regulation of Digestion
Hormones released by the stomach and duodenal
wall ensure that digestive juices are only around
when they are needed.
The sight of food will stimulate the brain to tell the
stomach wall to release gastrin which in turn
stimulates gastric juices to be secreted.
Gastric juices cause more gastric juices to be
released.
A drop in pH inhibits gastrin.
Reabsorbing Water
• Most of the water from waste is absorbed in the
colon.
• The junction between the duodenum and the
colon is called the Cecum (first 2-3 inches).
• A fingerlike projection that extends from the
cecum is called the appendix. Function is
uncertain, but it may help with production of
flora (good bacteria) for the colon.
Colon Bacteria
• Flora are bacteria that live within the body
that are beneficial.
• E. coli live in the colon and produce
vitamins, K, B, biotin and folic acid as they
metabolize the remaining food waste.
• Also generate gases such as methane and
hydrogen sulfide as by-products of
microbial metabolism (flatus!)
Digestive Disorders
•
•
•
•
•
•
•
•
1. Diseases of salivary glands
2. Mumps
3. Tooth decay (dental caries)
4. Gingivitis
5. Periodontitis
6. Malocclusion
7. GERD
8. Ulcers
Digestive Disorders
• 9. Chrohn’s Disease (IBS of end of ileum and
beginning of colon, but can be anywhere in GI
tract.)
• 10. Pylorospasm
• 11. Pyloric stenosis
• 12. Appendicitis
• 13. Hemorrhoids
• 14. Stomach cancer
• 15. Diverticulitis
• 16. Ulcerative Colitis (IBS of colon)
Digestive Disorders
•
•
•
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17. IBS
18. Colon cancer
19. Pancreatitis
20. Pancreatic cancer
Hepatitis
• 21. Hepatitis
A: viral and spread by contact with infected stool
(restaurant, day care centers, infected water in
developing countries, etc.)
- Symptoms: (2-7 weeks after exposure)
tired, nausea, weight loss, liver pain, fever, sore
muscles, jaundice (increased levels of yellowish
pigment bilirubin found in bile increased in
blood), dark urine, clay-colored stools
- Diagnose with blood test for antibodies and/or
liver biopsy
Hepatitis
• B: viral (acute hepatitis) spread through contact
with blood and other body fluids (unprotected
sex, drug use, tattoos and piercings, razors,
toothbrushes, etc.), but not kissing, sharing food
or drink, etc. CAN be passed on during
childbirth.
• Symptoms: most people may be asymptomatic
or feel like the flu
• Diagnose with blood test and/or liver biopsy
Hepatitis
• C: virus that can lead to permanent liver
damage, cirrhosis, liver cancer or liver failure, it
is also blood-borne and most people are
asymptomatic until liver damage occurs
• Same symptoms and diagnosis as A and B, but
much more serious. Often diagnosed by
accident when donating blood or as part of a
routine check-up.
• More common if had blood transfusion or organ
transplant before 1992
- Not as likely to go away on own as A or B. Can
become chronic.