1 the digestive system. 6.1.1 why digest food? food consists of: –carbohydrates –lipids...
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The Digestive System
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6.1.1 Why digest food?Food consists of:
– Carbohydrates– Lipids– Proteins– Nucleic acids– Minerals– Vitamins – Water
These are large, insoluble polymer molecules. They must be digested into monomers small enough to pass through the cell membrane of the cells lining the digestive tract so they can be absorbed in to the blood stream
Can be absorbed directly (because of small size), so do not need to be “digested”
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6.1.2 Enzymes and digestion• Digestion involves hydrolysis of food
molecules breaking apart molecules by adding water
Hydrolysis of lactose (a disaccharide) into glucose and galactose (both monosaccharides) with the addition of water
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• Digestive enzymes catalyze the hydrolysis of insoluble food molecules to soluble end products
Increase the rate
The enzyme sucrase catalyzes the hydrolysis of sucrose (a disaccharide) into glucose and fructose (both monosaccharides) with the addition of water
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Digestive Enzymes
Break down complex substances into simpler substances that can be absorbed by the body
Digestive Enzymes
Complex proteins
Complex sugars
Fat molecules
Amino acids
Glucose
Fatty acids
6.1.2 Enzymes and digestion
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Digestive enzymes work best at 37 C ⁰(body temp)
• Reactions occur faster at higher temperatures, but the rate of denaturation of enzymes also increases at higher temperatures.
• High temperatures break the bonds important for the tertiary structure of the enzyme.
• This destroys the active sites and therefore makes the enzyme non-functional.
Rapid denaturation
Temperature (°C)
Enz
yme
act
ivity
Too cold for the enzyme to operate
Optimum temperature for enzyme
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6.1.3 Examples of digestive enzymes
Class of Enzyme
Example Source Substrate Product Optimal pH
Amylase digest carbohydrates
Salivary amylase
Salivary glands
Starch Maltose (disaccharide)
6.7
Proteasedigest proteins
Pepsin Stomach cells
polypeptides Shorter polypeptides
2-3
Lipasedigest fats
Gastric lipase
Stomach cells
triglyceride Glycerol and 3 fatty acids
2-3
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Parts of the Alimentary CanalThe Digestive System
Consists of the alimentary canal (the long tube) and several accessory organs.
Parts of the Alimentary Canal
mouth
pharynx
esophagus
stomach
anal canal
large intestine
small intestine
6.1.4 Digestive System
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Organs of the Digestive System
Organs of the Digestive System
Parotid salivary glandPharynx
Esophagus
Stomach
Pancreas
Small intestine
RectumAnal canal
Large intestine
DuodenumGall bladder
Liver
Submandibular salivary gland
Sublingual salivary gland
Tooth
TongueMouth
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Tracing Toastmouth pharynx epiglottis esophagus
stomach
duodenum
jejunum
ileum
cecumascendingcolon
transversecolon
descendingcolon
sigmoidcolon
rectum
anus feces
toast
Tracing a piece of toast through thealimentary canal
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Animation of digestive system
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6.1.5 Function of the Stomach
1. Mechanical Digestion• Muscle contractions
break apart and mix food
• bolus chyme
2. Chemical Digestion• Enzymes and HCl digest
chyme
Mass of solid food
Semi-fluid mass of partly digested food
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6.1.5 Function of the Small Intestine
1. Digestion by enzymes in the duodenum (first 50 cm)
2. Absorption of nutrients into the blood stream (see 6.1.7)
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6.1.5 Function of the Large Intestine
Removes water and minerals
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6.1.6 Absorption and Assimilation
ABSORPTION
Transport of molecules from the intestine to the blood stream
ASSIMILATION
Incorporation of molecules from the blood stream into cellular structures
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6.1.7 Structure of Villus
The small intestine has large folds which increase the surface area for absorption
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6.1.7 Structure of Villus
Each villus has a capillary bed that absorbs small molecules from the small intestine and transport the molecules in the blood stream
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6.1.7 Structure of Villus
Epithelial cells that line the villi have microvilli that also increase the surface area for absorption