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Digestive System
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Announcements
Exams
Lab notes will be on reserve in library and
on the web
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Goals of the Digestive System
1. Extract nutrients from food
2. Transform nutrients into useful forms
Ex- oreo= glucose
3. Absorb nutrients and distribute them
where they are needed
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Functions of the Digestive
System Ingestion: intake of nutrients
Digestion: breakdown of large particles intosmaller ones
Absorption: uptake of nutrient molecules
Defecation: elimination of undigested residues
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Actions of the Digestive
System
1. Motility- Breaks up food
- Moves food through the GI tract (Peristalsis)
- Mixes with digestive enzymes
2. Secretion- Release of enzymes and hormones for chemical
digestion and regulation
3. Membrane Transport- Absorption of nutrients from the tissues by the
blood and lymph for transport
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Stages of Digestion
Mechanical: physical breakdown of food
Chemical: digestive enzymes hydrolyze foodparticles to break larger molecules into smaller
ones
Some nutrients are absorbed with out digestion
Vitamins, minerals, cholesterol, water
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Anatomy of the Digestive
System Oral Cavity
Pharynx
Esophagus
Stomach
Pyloric Sphincter
Small Intestine Large Intestine
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Accessory Organs
Teeth
Tongue
Salivary Glands
Liver Gall Bladder
Pancreas
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Oral Cavity Functions:
A. Ingestion: cheeks lipsand tongue mobilize food
B. Digestion: Mechanical
Mastication
Chemical
3 salivary glands
Digests some
starches and fat
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Pharynx
Motility: pharyngeal
constrictors force food
down duringswallowing
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Esophagus
Straight muscular tube
about 1 foot long
Motility: muscularcontraction moves
food towards stomach
www.mywebmd.ca.com
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Heartburn and the EsophagusHeartburn, acid reflux, is caused by acid and food
going from the stomach into the esophagus
The diaphragm normally prevents acid reflux, inconjunction with the lower esophageal sphincter.
When this fails, the burning sensation felt is known
as heartburn
May be linked to a rare type of cancer,adenocarcinoma
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Stomach
Muscular sac on the left
side of the peritoneal
cavity
Functions:
Food storage
Mechanical digestion Chemical digestion
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Rugae in the Stomach
Rugae- folds in the
stomach lining that
allow it to expand withmore food
How do we vomit?
http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion
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Pyloric Sphincter
Ring of smooth
muscle
Regulates the passage
of material from the
stomach into the
duodenum
http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion
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Digestion in the Stomach
Mechanical Digestion:
Muscular contraction
Chemical Digestion:
Secretes digestive enzymes and HCl
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Small Intestine
http://www.afns.ualberta.ca/bbo/1/ANATOMY/SI1.asp
2 meters long, 1 inch
in diameter, 5-6
meters in cadaver
Functions:
Chemical Digestion
Nutrient Absorption
Motility
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Anatomy of the Small Intestine
Duodenum (25 cm):
1. Receives stomach
contents, pancreaticjuice and bile
2. Neutralizes stomach
acid and pepsin
3. Pancreatic enzymesand bile take over
chemical digestion
Fig 25.22
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Anatomy of the Small Intestine
Jejunum (2.5m)
Ileum (3.6 m) Reabsorbs bile acids
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Functions of the Small
Intestine Motility: smooth muscle
contract
Digestion: chemicalenzymes received fromthe pancreas, liver and gall
bladder
Nutrient reabsorption:
microvilli increase surfacearea
Microvilli
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Dynamic Human: Microvilli
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Large Intestine
Functions
Motility
Reabsorbtion of Water and Electrolytes
Symbiotic bacteria Synthesis Vitamins B & K
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Anatomy of the Large
IntestineTransverse Colon: right to left
Ascending Colon: Descending Colon:
up the right side down the left side
Cecum: sac on Sigmoid Colon:
lower right side S-shaped
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Enzymes Involved in
Chemical Digestion Saliva:
Amylase: breaks down starch
Lipase: breaks down fats when it enters thestomach
Low pH of the stomach activates the enzyme
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Enzymes Involved in
Chemical Digestion Stomach:
Digestive chemicals-
HCL: activates enzymes, breaks up foods
Pepsin: digests proteins
Renin: digests milk
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Pepsin Formation
Interactions between Cells
Chief Cells make pepsinogen
Parietal Cells make HCl Pepsinogen is cleaved by HCl into Pepsin
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Dynamic Human: Pepsin
Formation
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Enzymes Involved in
Chemical Digestion Small Intestine
Two sources of
enzymes
Liver and Gall bladder
Pancreas
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Enzymes Involved in
Chemical Digestion in the
Small IntestineLiver secretes bile that is active in the small
intestine
Bile: aids in fat digestion and absorptionActivates pancreatic enzymesSynthesized from cholesterolBacteria in the small intestine use bilirubin to
make your feces brown
Gall bladder stores and concentrates bile
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Gall Stones
What is a gall stone?
How do they treat gall stones?
How is the gall bladder removed?
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Enzymes Involved in
Chemical Digestion in the
Small Intestine
Pancreas: secretes pancreatic juice
1. Amylase: breaks down starch2. Lipase: breaks down fats
3. Ribonuclease (RNAase): breaks down RNA
4. Deoxyribonuclease (DNAase): breaks downDNA
5. Zymogens: inactive enzymes that activate in the
small intestine
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Mechanism of Absorption
Membrane Transport:
Nutrients pass through membrane surface
The greater the membrane surface area, thegreater the amount of nutrients that can be
transported
Surface Area Rugae
Microvilli
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Final Destinations of Digestion
Products Starches bloodstream
Fats lymph vessels (lacteals)
Proteins bloodstream
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Dynamic Human:
Visualization
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Cat Dissection
Be able to locate and
identify
Esophagus Stomach
Small Intestine
Large Intestine
Ascending colon
Transverse colon
Descending colon
Also know accessory
organs
Tongue Teeth
Gall Bladder
Liver
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Conclusion