The document summarizes key concepts about cellular metabolism and the digestive system. It describes how nutrients are broken down through metabolic pathways, producing energy molecules like ATP. Carbohydrates undergo glycolysis and the Krebs cycle to yield ATP. Lipids and proteins are broken down into smaller units that enter these cycles. Enzymes catalyze specific reactions in metabolic pathways. The document also lists common disorders of the digestive system like ulcers, IBS, and cancers.

1. Essentials of Anatomy and Physiology
Fifth edition
Seeley, Stephens and Tate
Slide 2.1
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Chapter 17: Cellular Metabolism

2. Processes of the Digestive System
Slide 14.46
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Figure 14.11

3. Control of Digestive Activity
Slide 14.47a
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 Mostly by reflexes via the
parasympathetic division
 Chemical and mechanical receptors
trigger reflexes

4. Control of Digestive Activity
Slide 14.47b
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 Stimuli include:
Stretch of the organ
pH of the contents
Presence of breakdown products

5. Control of Digestive Activity
Slide 14.47b
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 Reflexes include:
Activation or inhibition of glandular
secretions
Smooth muscle activity

6. Digestion and Absorption in the
Stomach
Slide 14.55
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 Proteases act on:
Pepsin –protein digestion
Rennin –milk protein digestion
 Absorption of:
Water, alcohol and aspirin

7. Digestion in the Small Intestine
Slide 14.57a
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 Pancreatic enzymes provide…
Complete digestion of starch
Amylase
Other carbohydrases
About half protein digestion (trypsin, etc.)

8. Digestion in the Small Intestine
Slide 14.57b
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 Pancreatic enzymes, cont…
Fat digestion (lipase)
Nucleic acid digestion (nucleases)
Alkaline content neutralizes acidic chyme

9. Stimulation of the Release of Pancreatic
Juice
Slide 14.58
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 Vagus nerve
 Local hormones
Secretin
Cholecystokinin
Figure 14.15

10. Absorption in the Small Intestine
Slide 14.59
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 Water
 Products of digestion
Most molecules absorbed by active
transport
Lipids absorbed by diffusion
 Nutrients transported to the liver

11. Nutrition
Slide 14.63
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 Nutrient – substance used by the body
for growth, maintenance, and repair
 Categories of nutrients
Carbohydrates
Lipids
Proteins
Vitamins
Mineral
Water

12. Cellular Metabolism
Slide 14.67
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 “All the chemical reactions necessary to
maintain life”
Anabolism: a constructive process during
which larger molecules are built from
smaller ones
Usually involves condensation
AKA dehydration synthesis

13. Cellular Metabolism, con’t…
Slide 14.67
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•Carbohydrates
•Monosaccharides = simple sugars
•Glucose, fructose
•Disaccharides = Combinations of
monosaccharides, removal of water
•Sucrose, lactose, maltose
• Polysaccharides: usually polymers of
glucose
•Starch, cellulose, chitin

14. Cellular Metabolism, con’t…
Slide 14.67
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•Lipids
•1 glycerol + 3 fatty acids
neutral fat + 3 H2O
•These are triglycerides
•Further modifications produce:
•Phospholipids (cell membrane)
•glycolipids (cell membrane)
•Lipoproteins (cell membrane,
blood)

15. Cellular Metabolism, con’t…
Slide 14.67
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•Proteins
•Two amino acids a dipeptide + H2O
•Covalent bond formed is a peptide
bond
•Unique to proteins
•Polypeptides: 2-100 amino acids
•Protein: >100 amino acids
•Require additional modification to
become functional

16. Cellular Metabolism, con’t…
Slide 14.67
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
•Proteins
•Modification occurs on four levels
•Primary: string of amino acids
•Secondary: helix or “pleat” structures
•Tertiary: 3-D folding
•Quarternary: two or more 3-D
proteins that act as a functional unit
•i.e., hemoglobin, collagen

17. Cellular Metabolism, con’t…
Slide 14.67
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
•Proteins
•Recall from Chemistry: 
•Proteins each have a unique 3-D
shape
•Shape determines function
•Loss of shape leads to loss of
function
•“denaturing” proteins with heat, pH
changes

18. Cellular Metabolism, con’t…
Slide 14.67
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
•Proteins
•May be structural or functional
•Structural:
•Play a role in cellular architecture
•Collagen, fibrin, actin, myosin, etc.
•Functional:
•Play a role in cell metabolism
•Enzymes, neurotransmitters,
antibodies, etc.

19. Cellular Metabolism, con’t…
Slide 14.67
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
•Enzymes:
•Biological catalysts
•Highly specific for a substrate
•Substrate: substance upon which an
enzyme acts
• i.e., peptidases act only on
peptide bonds in small polypeptides
•Produced only in presence of substrate

20. Cellular Metabolism, con’t…
Slide 14.67
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
•Enzymes:
•Huge protein molecules
•Alter shape to conform to shape of
substrate (“wrap around” effect)
•Average 1500/cell (>5000 in liver cells)
•Most require co-enzymes

21. Cellular Metabolism, con’t…
Slide 14.67
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
•Enzymes:
•Recognize substrate by shape of
binding site
•Serve to lower energy required for
reaction to occur (activation energy)
•therefore speed up reactions
•Not changed or used up during reaction

22. Cellular Metabolism, con’t…
Slide 14.67
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
•Co-Enzymes:
•Required to activate enzymes
•Facilitate enzymatic reactions
•May be a metal ion (Zn++, Cu++, Fe++)
•May be a vitamin
•Vitamins are co-enzymes
•Only function if “their” enzyme is
available

23. Cellular Metabolism
 Catabolism: substances are broken down into
molecules
 “destructive” process
 Large molecules broken down into smaller
molecules
 Usually by hydrolysis
 “splitting with water”
 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
• All nutrient molecules are ultimately
degraded or converted to glucose
• Only glucose can be used to make
ATP
• Oxidation: cellular process of
chemically breaking apart a glucose
molecule to release energy

27. Cellular Energy
• Glucose oxidation occurs in 2 phases
• Anerobic metabolism
• Occurs in cytoplasm
• Without oxygen
• AKA glycolysis
• Splits glucose into two 3-Carbon
molecules: pyruvate

28. Cellular Energy
• Glycolysis
• Process also produces 2 ATPs
• In yeast, plant cells:
• Pyruvate can undergo alcoholic
fermentation
• In bacteria, animal cells:
• Pyruvate can produce lactic acid

29. Cellular Energy
• Aerobic metabolism
• Uses oxygen
• AKA Kreb’s Cycle or Citric Acid
cycle or Tricarboxylic Acid (TCA)
Cycle
• Occurs in mitochondria
• Makes more ATP than anerobic
processes

30. Cellular Energy
• Aerobic metabolism
• CO2 and H2O are waste products
• CO2:
• Diffuses out of cells
• Dissolves in plasma
• Produces HCO3
- in blood
• Exhaled from lungs

31. Cellular Energy
• Aerobic metabolism
• H2O:
• “metabolic” water
• Exhaled from lungs
• Final products of glucose oxidation:
• CO2, H2O, ATP

32. Cellular Energy
• Aerobic metabolism
• For each molecule of glucose:
• 2 ATP formed in glycolysis
• 36 ATP formed in TCA cycle
• Energy stored in phosphate
bonds
• A reversible reaction

33. Metabolic Pathways
• “A particular sequence of enzymatic
reactions”
• Such as glycolysis, TCA cycle
• Carbohydrate pathways
• Carbos should comprise most of
our diet (~ 50% complex carbs)
• Used as a primary energy source
• Produce 4kcal/gm

34. Metabolic Pathways
• Carbohydrate pathways
• Excess carbs converted to energy
storage forms
• Glycogen (muscle, liver)
• Adipose tissue (hips)
• Process is anabolism

35. Metabolic Pathways
• Lipid pathways
• Metabolism controlled by liver
• Should comprise <30% of calories
in diet
• Get 9 kcal/gm (more ATP!)
• Must be degraded into glycerol,
fatty acids, then pyruvate
• A reversible catabolic process

36. Metabolic Pathways
• Protein pathways
• Proteins should comprise ~30% of
diet
• Get 4 kcal/gm
• Catabolism is more complex
• Proteins contain nitrogen

37. Metabolic Pathways
• Protein pathways
• Deamination: removal of nitrogen
from amino acids
• Occurs in liver
• Nitrogen is converted to urea
» A nitrogenous waste product
• Sent to kidneys for excretion

38. Metabolic Pathways
• Protein pathways
• After deamination:
• amino acid “skeleton” is
processed
• in TCA cycle
• May produce CO2, H2O, ATP
• May form glucose or fat

39. Metabolic Pathways
• Protein pathways
• Glucose formed from amino acid
skeletons may be re-converted to
amino acids
• “Essential” amino acids:
• Body cannot make these
• Must obtain in the diet

40. Regulation of Metabolic
Pathways
• Enzyme “saturation”
• Too much substrate for number of
enzyme molecules
• Reaction rate cannot increase
• A single enzyme can control an
entire metabolic pathway
• “rate limiting” enzyme

41. Digestive System: Disorders
Slide 14.92b
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 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

42. Digestive System: Disorders
Slide 14.92b
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 IBS: irritable bowel syndrome
 Crohn’s disease (autoimmune)
 Constipation
 Diarrhea
 Colitis
 Colon polyps/cancers