Lab 8: Digestive System

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Lab 8 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

• Extract nutrients from food
• 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 into
  smaller 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
• Secretion
• Release of enzymes and hormones for chemical
  digestion and regulation
• 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 food
  particles 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 lips and 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 during swallowing

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Esophagus

• www.mywebmd.ca.com

• Straight muscular tube about 1 foot long
• Motility muscular contraction moves food
  towards stomach

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Heartburn and the Esophagus

• Heartburn, acid reflux, is caused by acid and
  food going from the stomach into the esophagus
• The diaphragm normally prevents acid reflux, in
  conjunction 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 with more food
• How do we vomit?

• http//arbl.cvmbs.colostate.edu/hbooks/pathphys/di
  gestion

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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/di
  gestion

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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)
• Receives stomach contents, pancreatic juice and
  bile
• Neutralizes stomach acid and pepsin
• Pancreatic enzymes and 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
Microvilli

• Motility smooth muscle contract
• Digestion chemical enzymes received from the
  pancreas, liver and gall bladder
• Nutrient reabsorption
• microvilli increase surface area

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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 Intestine

• Transverse 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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Anatomy of the Large Intestine

• Rectum straight down
• Anal Canal out the body
• Appendix hangs off cecum
• Important in Immunity

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Enzymes Involved in Chemical Digestion

• Saliva
• Amylase breaks down starch
• Lipase breaks down fats when it enters the
  stomach
• 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 Intestine

• Liver secretes bile that is active in the small
  intestine
• Bile aids in fat digestion and absorption
• Activates pancreatic enzymes
• Synthesized from cholesterol
• Bacteria 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
• Amylase breaks down starch
• Lipase breaks down fats
• Ribonuclease (RNAase) breaks down RNA
• Deoxyribonuclease (DNAase) breaks down DNA
• 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, the
  greater 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

• Review todays material
• Dynamic Human Overview
• Know cat anatomy
• Lab Practical II returned well done!
• Next week Endocrine!!!