copyright © 2006 pearson education, inc., publishing as benjamin cummings the digestive system and...
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
The Digestive System and Body Metabolism Digestion
Breakdown of ingested food
Absorption of nutrients into the blood
Metabolism
Production of cellular energy (ATP)
Constructive and degradative cellular activities
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Processes of the Digestive System
Mechanical propulsion
Secretion
Digestion - mechanical and chemical breakdown
Absorption
Elimination
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
molars (12)
premolars (8)
canines (4)
incisors (8)
lower jaw upper jaw
Mechanical Processing
• Teeth break down food
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Stomach Functions Acts as a storage tank for food
Mechanical, chemical breakdown of protein begins
Delivers chyme to the small intestine
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Propulsion in the Stomach Food must first be well mixed
Rippling peristalsis occurs in the lower stomach
Figure 14.15
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Chemical Digestion in the Small Intestine
Figure 14.6
Pancreatic enzymes digest starch, proteins, nucleic acids, fats; reset pH.Gall bladder -
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Propulsion in the Small Intestine Peristalsis is the major
means of moving food
Segmental movements
Mix chyme with digestive juices
Aid in propelling food
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Absorption in the Small Intestine
Site of nutrient absorption into the blood
Villi = Fingerlike structures on the mucosa surface
Microvilli on cells
All increase surface area
Figure 14.7a
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Absorption of Proteins and Carbohydrates
Figure 14.13
Amino acids, sugars move by active transport into blood vessels
Next stop: liver, where glucose glycogenamino acids protein
Excess moleculesare converted to fats
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Absorption of Fats
Figure 14.14
Lipids are absorbed into lymph system, which drains into heart
Emulsified with bile saltsDigested into fatty acids, glycerolWith bile salts, diffuse into cellsReassembled into fats, exocytosis
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Food Breakdown and Absorption in the Large Intestine No digestive enzymes are produced
Resident bacteria digest remaining nutrients
Produce some vitamin K and B
Release gases
Water and vitamins K and B are absorbed
Undigested fiber keeps materials moving and is eliminated via feces
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Control of Digestive Activity
Regulation dependent on volume and content of food
Nervous system: sight, smell of food, stretch receptors in stomach
Hormones:
Gastrin: stimulates release of gastric juice
Secretin: stimulates pancreas to secrete water and bicarbonate
Cholecystokinin (CCK): signals pancreas to secrete digestive enzymes
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Nutrition Carbohydrates: major energy source, simple
or complex
Lipids: cell components and energy sources, saturated or unsaturated
Proteins: 20 amino acids
Vitamins: fat soluble and water soluble
Minerals: recommended daily allowance
Fiber
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Food Guide Pyramid
Figure 14.16
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Body Energy Balance Energy intake = total energy output (heat +
work + energy storage)
Energy intake from food oxidation
Energy output
Heat is usually about 60%
Storage energy is in the form of fat or glycogen
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Regulation of Food Intake
Mechanisms that may regulate food intake
Levels of nutrients in the blood
Hormones
Body temperature
Psychological factors
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Basal Metabolic Rate
BMR– amount of heat produced by the body per unit of time at rest
Factors that influence BMR
Surface area
Gender
Age – children and adolescents have a higher BMR
thyroxine from thyroid gland
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Total Metabolic Rate (TMR) Total amount of kilocalories the body must
consume to fuel ongoing activities
TMR increases with an increase in body activity
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