1. DIGESTION
© 2016 Paul Billiet ODWS

2. Processes associated with feeding
Ingestion
Digestion
Absorption
Excretion
Urine, breath, sweat
Egestion
Faeces
Assimiliation
© 2016 Paul Billiet ODWS

3. Digestion The breakdown of polymers into monomers for absorption
Polymers are usually insoluble and too large to pass across cell membranes.
© 2016 Paul Billiet ODWS

4. Physical digestion & movement
Mastication: using jaws and specialised teeth
Peristalsis: circular and longitudinal smooth muscles of the gut wall producing waves of contraction
muscles contract
Food
Food moves down the gut
© 2016 Paul Billiet ODWS

5. Tissue layers
TS Small Intestine
© 2016 Paul Billiet ODWS

6. Esophagus wall Circular muscle Longitudinal muscle
© 2016 Paul Billiet ODWS

7. Physical digestion Chewing reduces the food to small particles
Increasing the surface area exposed to the enzymes
Peristalsis moves the food along the gut & mixes the foods with digestive juices
Soluble compounds dissolve Large molecules exposed to digestive enzymes.
© 2016 Paul Billiet ODWS

8. Chemical digestion Using a range of specialised enzymes…
that work in different conditions…
in different compartments of the organ-system
All these enzymes have an optimum temperature of 37°C.
© 2016 Paul Billiet ODWS

9. Chemical digestion - Carbohydrates Polysaccharides
Starches
& glycogen
Amylases
Salivary & pancreatic
pH 8
Maltose
Cellulose
No enzymes
Undigested
© 2016 Paul Billiet ODWS

10. Chemical digestion - Lipids
Fats & oils
Lipase
Pancreatic
pH8
Fatty acids & Glycerol
© 2016 Paul Billiet ODWS

11. Chemical digestion - Proteins
Pepsin
Stomach
pH 1
Peptones
Endo-petidase
Pancreatic
pH 8
Amino acids
© 2016 Paul Billiet ODWS

12. Chemical digestion – Nucleic acids
DNA & RNA
Nucleases
Pancreatic
pH8
Nucleotides
Evidence suggests that pepsin, in the stomach, can also
digest nucleic acids though much more slowly than it
digests proteins.
© 2016 Paul Billiet ODWS

13. Absorption The uptake of nutrients from the gut into the blood stream
Most takes place in the small intestine
Water is absorbed by the colon
Alcohol, some minerals and water are absorbed by the stomach lining.
© 2016 Paul Billiet ODWS

14. Absorption across membranes
Diffusion Water, gases, alcohol, lipids
Facilitated diffusion Water, glucose & amino acids
Active transport Na+/K+ also glucose & amino acids
Endocytosis Proteins e.g. antibodies.
© 2016 Paul Billiet ODWS

15. The Digestive System Mouth Salivary glands Oesophagus Liver Stomach
Gall bladder
Pancreas
Small intestine
Large intestine
Appendix
Anus
© 2016 Paul Billiet ODWS

16. The Stomach Endoscope view inside stomach Stomach diagram
© 2016 Paul Billiet ODWS

17. Stomach Transit: 0 to 3h Capacity: 1.5dm3
Muscular sack (Circular, longitudinal & diagonal muscles)
Churning food into chyme
Gastric Pits:
HCl
Acidic pH: Enzyme activation & bacteriocidal
Pepsinogen (inactive)  Pepsin (active)
Protease
Mucus epithelium  mucus
Protection of stomach from acid and protease enzymes
Cardiac sphincter & pyloric sphincter (muscular valves)
Hold food in stomach for digestion
© 2016 Paul Billiet ODWS

18. TS Small Intestine
© 2016 Paul Billiet ODWS

19. The villus Mouse intestinal villi Microvilli of the epithelium
Microvilli of the epithelium
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© 2016 Paul Billiet ODWS

20. Small intestine FEATURES FUNCTIONS Intestinal Glands: Enzymes
(e.g. lactase)
Pancreas and Liver also secrete bile and pancreatic juice
Disaccharide digestion
Bile – HCO3- and salts for lipid digestion
Pancreatic juices HCO3- and enzymes
Length (3 5m long), Rugae (folds), Villi & Microvilli
Large surface area 200m2
(a) Digestion
(b) Absorption
Capillaries
Transport of digested food.
Lacteals (lymph vessels)
Fatty acids + monoglycerides.
Hepatic portal system
All absorbed food is first taken to the LIVER
Gut flora (bacteria)
Mutualistic & vitamin synthesis
© 2016 Paul Billiet ODWS

21. Large intestine Endoscope view Large intestine
© 2016 Paul Billiet ODWS

22. Large intestine CAECUM/ APPENDIX
Transit up to 96h Length 1,5m
CAECUM/ APPENDIX
Sack at the beginning of the large intestine
Bacterial fermentation cellulose (non ruminants)
Vestigial in humans
COLON
No villi but rugae (folds)
Water absorption
Bacterial activity
Mutualistic
RECTUM
Anal sphincter
Holding area for faeces before egestion
© 2016 Paul Billiet ODWS