Download digestive system, nutrition

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
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Processes of the Digestive System
 Mechanical
propulsion
 Secretion
 Digestion mechanical and
chemical
breakdown
 Absorption
 Elimination
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Mechanical Processing
• Teeth break down food
molars
(12)
premolars
(8)
canines (4)
lower jaw
incisors
(8)
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upper jaw
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
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Chemical Digestion in the Small Intestine
Pancreatic enzymes
digest starch,
proteins, nucleic
acids, fats; reset pH.
Gall bladder Figure 14.6
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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
Amino acids, sugars
move by active transport
into blood vessels
Next stop: liver, where
glucose
glycogen
amino acids protein
Excess molecules
are converted to fats
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Figure 14.13
Absorption of Fats
Lipids are absorbed into lymph system, which drains into heart
Emulsified with bile salts
Digested into fatty acids, glycerol
With bile salts, diffuse into cells
Reassembled into fats, exocytosis
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Figure 14.14
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
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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
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Figure 14.16
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
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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
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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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