3. Slide 14.47a
Control of Digestive ActivityControl of Digestive Activity
⢠Mostly by reflexes via the
parasympathetic division
⢠Chemical and mechanical receptors
trigger reflexes
4. Slide 14.47b
Control of Digestive ActivityControl of Digestive Activity
⢠Stimuli include:
⢠Stretch of the organ
⢠pH of the contents
⢠Presence of breakdown products
5. Slide 14.47b
Control of Digestive ActivityControl of Digestive Activity
⢠Reflexes include:
⢠Activation or inhibition of glandular
secretions
⢠Smooth muscle activity
6. Slide 14.55
Digestion and Absorption in theDigestion and Absorption in the
StomachStomach
⢠Proteases act on:
⢠Pepsin âprotein digestion
⢠Rennin âmilk protein digestion
⢠Absorption of:
⢠Water, alcohol and aspirin
7. Slide 14.57a
Digestion in the Small IntestineDigestion in the Small Intestine
⢠Pancreatic enzymes provideâŚ
⢠Complete digestion of starch
⢠Amylase
⢠Other carbohydrases
⢠About half protein digestion (trypsin, etc.)
8. Slide 14.57b
Digestion in the Small IntestineDigestion in the Small Intestine
⢠Pancreatic enzymes, contâŚ
⢠Fat digestion (lipase)
⢠Nucleic acid digestion (nucleases)
⢠Alkaline content neutralizes acidic chyme
9. Slide 14.58
Stimulation of the Release of PancreaticStimulation of the Release of Pancreatic
JuiceJuice
⢠Vagus nerve
⢠Local hormones
⢠Secretin
⢠Cholecystokinin
Figure 14.15
10. Slide 14.59
Absorption in the Small IntestineAbsorption in the Small Intestine
⢠Water
⢠Products of digestion
⢠Most molecules absorbed by active
transport
⢠Lipids absorbed by diffusion
⢠Nutrients transported to the liver
11. Slide 14.63
NutritionNutrition
⢠Nutrient â substance used by the body
for growth, maintenance, and repair
⢠Categories of nutrients
⢠Carbohydrates
⢠Lipids
⢠Proteins
⢠Vitamins
⢠Mineral
⢠Water
12. Slide 14.67
Cellular MetabolismCellular Metabolism
⢠âAll the chemical reactions necessary to
maintain lifeâ
⢠Anabolism: a constructive process during
which larger molecules are built from
smaller ones
⢠Usually involves condensation
â˘AKA dehydration synthesis
13. Slide 14.67
Cellular Metabolism, conâtâŚCellular Metabolism, conâtâŚ
â˘Carbohydrates
â˘Monosaccharides = simple sugars
â˘Glucose, fructose
â˘Disaccharides = Combinations of
monosaccharides, removal of water
â˘Sucrose, lactose, maltose
⢠Polysaccharides: usually polymers of
glucose
â˘Starch, cellulose, chitin
15. Slide 14.67
Cellular Metabolism, conâtâŚCellular Metabolism, conâtâŚ
â˘Proteins
â˘Two amino acids a dipeptide + H2O
â˘Covalent bond formed is a peptide
bond
â˘Unique to proteins
â˘Polypeptides: 2-100 amino acids
â˘Protein: >100 amino acids
â˘Require additional modification to
become functional
16. Slide 14.67
Cellular Metabolism, conâtâŚCellular Metabolism, conâtâŚ
â˘Proteins
â˘Modification occurs on four levels
â˘Primary: string of amino acids
â˘Secondary: helix or âpleatâ structures
â˘Tertiary: 3-D folding
â˘Quarternary: two or more 3-D
proteins that act as a functional unit
â˘i.e., hemoglobin, collagen
17. Slide 14.67
Cellular Metabolism, conâtâŚCellular Metabolism, conâtâŚ
â˘Proteins
â˘Recall from Chemistry: ď
â˘Proteins each have a unique 3-D
shape
â˘Shape determines function
â˘Loss of shape leads to loss of
function
â˘âdenaturingâ proteins with heat, pH
changes
18. Slide 14.67
Cellular Metabolism, conâtâŚCellular Metabolism, conâtâŚ
â˘Proteins
â˘May be structural or functional
â˘Structural:
â˘Play a role in cellular architecture
â˘Collagen, fibrin, actin, myosin, etc.
â˘Functional:
â˘Play a role in cell metabolism
â˘Enzymes, neurotransmitters,
antibodies, etc.
19. Slide 14.67
Cellular Metabolism, conâtâŚCellular Metabolism, conâtâŚ
â˘Enzymes:
â˘Biological catalysts
â˘Highly specific for a substrate
â˘Substrate: substance upon which an
enzyme acts
⢠i.e., peptidases act only on
peptide bonds in small polypeptides
â˘Produced only in presence of substrate
20. Slide 14.67
Cellular Metabolism, conâtâŚCellular Metabolism, conâtâŚ
â˘Enzymes:
â˘Huge protein molecules
â˘Alter shape to conform to shape of
substrate (âwrap aroundâ effect)
â˘Average 1500/cell (>5000 in liver cells)
â˘Most require co-enzymes
21. Slide 14.67
Cellular Metabolism, conâtâŚCellular Metabolism, conâtâŚ
â˘Enzymes:
â˘Recognize substrate by shape of
binding site
â˘Serve to lower energy required for
reaction to occur (activation energy)
â˘therefore speed up reactions
â˘Not changed or used up during reaction
22. Slide 14.67
Cellular Metabolism, conâtâŚCellular Metabolism, conâtâŚ
â˘Co-Enzymes:
â˘Required to activate enzymes
â˘Facilitate enzymatic reactions
â˘May be a metal ion (Zn++
, Cu++
, Fe++
)
â˘May be a vitamin
â˘Vitamins are co-enzymes
â˘Only function if âtheirâ enzyme is
available
23. Cellular Metabolism
⢠Catabolism: substances are broken down into molecules
⢠âdestructiveâ process
⢠Large molecules broken down into smaller molecules
⢠Usually by hydrolysis
⢠âsplitting with waterâ
⢠Adds H2O back into molecule
⢠Breaks covalent bonds
24. Cellular Metabolism
⢠Catabolism
⢠Energy is released when bonds break
⢠Reverse of dehydration synthesis
(condensation)
⢠Hydrolysis = chemical digestion
⢠Occurs simultaneously (and
continuously) with anabolism
⢠Processes controlled by enzymes
25. Cellular Energy
⢠Cellular energy is chemical energy
⢠Derived from breaking chemical
bonds
⢠~ ½ Energy is stored as ATP
⢠~ ½ Energy is released as heat
⢠Helps maintain body temperature
⢠Enzymes control in the process
26. Cellular Energy
ďľAll nutrient molecules are ultimately
degraded or converted to glucose
ďľOnly glucose can be used to make
ATP
ďľOxidation: cellular process of
chemically breaking apart a glucose
molecule to release energy
27. Cellular Energy
ďľGlucose oxidation occurs in 2 phases
ďľAnerobic metabolism
ďľOccurs in cytoplasm
ďľWithout oxygen
ďľAKA glycolysis
ďľSplits glucose into two 3-Carbon
molecules: pyruvate
28. Cellular Energy
ďľGlycolysis
ďľProcess also produces 2 ATPs
ďľIn yeast, plant cells:
ďľPyruvate can undergo alcoholic
fermentation
ďľIn bacteria, animal cells:
ďľPyruvate can produce lactic acid
29. Cellular Energy
ďľAerobic metabolism
ďľUses oxygen
ďľAKA Krebâs Cycle or Citric Acid
cycle or Tricarboxylic Acid (TCA)
Cycle
ďľOccurs in mitochondria
ďľMakes more ATP than anerobic
processes
30. Cellular Energy
ďľAerobic metabolism
ďľCO2 and H2O are waste products
ďľCO2:
ďľDiffuses out of cells
ďľDissolves in plasma
ďľProduces HCO3
-
in blood
ďľExhaled from lungs
32. Cellular Energy
ďľAerobic metabolism
ďľFor each molecule of glucose:
ďľ2 ATP formed in glycolysis
ďľ36 ATP formed in TCA cycle
ďľEnergy stored in phosphate
bonds
ďľA reversible reaction
33. Metabolic Pathways
ďľâA particular sequence of enzymatic
reactionsâ
ďľSuch as glycolysis, TCA cycle
ďľCarbohydrate pathways
ďľCarbos should comprise most of
our diet (~ 50% complex carbs)
ďľUsed as a primary energy source
ďľProduce 4kcal/gm
35. Metabolic Pathways
ďľLipid pathways
ďľMetabolism controlled by liver
ďľShould comprise <30% of calories
in diet
ďľGet 9 kcal/gm (more ATP!)
ďľMust be degraded into glycerol,
fatty acids, then pyruvate
ďľA reversible catabolic process
39. Metabolic Pathways
ďľProtein pathways
ďľGlucose formed from amino acid
skeletons may be re-converted to
amino acids
ďľâEssentialâ amino acids:
ďľBody cannot make these
ďľMust obtain in the diet
40. Regulation of Metabolic Pathways
ďľEnzyme âsaturationâ
ďľToo much substrate for number of
enzyme molecules
ďľReaction rate cannot increase
ďľA single enzyme can control an
entire metabolic pathway
ďľârate limitingâ enzyme
41. Slide 14.92b
Digestive System: DisordersDigestive System: Disorders
⢠Ulcers: bacterial infection with H. pylori
⢠Vomiting: controlled by center in medulla
oblongata
⢠Activity of tract slows in old age
⢠Fewer digestive juices
⢠Peristalsis slows
⢠Diverticulosis and cancer more common