1. The Digestive System

2. Digestive System Built around an alimentary canal (one-way tube)
Includes
Mount, pharynx, esophagus
Stomach
Small intestine
Large intestine
Salivary glands, pancreas, liver

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The Digestive System
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4. Mouth Begins mechanical digestion with chewing
Teeth crush food to make a fine paste for swallowing
Begins chemical digestion with saliva
Digestive enzymes begin breakdown of carbohydrates into smaller molecules

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Your Mouth
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6. Teeth Anchored in jaw bones Protected by mineralized enamel
Used to cut, tear, and crush food into smaller fragments

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Tooth
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8. Saliva
Secreted by salivary glands in mouth to moisten food and make it easier to chew
Controlled by nervous system
Begins chemical digestion
Enzyme amylase breaks down starches and releases sugars
Lysozyme fights infection by digesting bacteria that may enter mouth with food

9. Esophagus
Food (called a bolus) from mouth is swallowed (forced from mouth into esophagus by combined action of tongue and throat muscles)
Bolus moved through esophagus by contractions (peristalsis) of smooth muscles to the stomach
Cardiac sphincter at the bottom of esophagus prevents food in stomach from moving back into esophagus

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Peristalsis
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11. Stomach Muscular sac that continues mechanical and chemical digestion
Three layers of smooth muscle thoroughly churn and mix food to help with digestion

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Stomach
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13. Chemical digestion in stomach
Glands in the stomach lining release lubricants (to protect the stomach wall), hydrochloric acid (HCl), and pepsin (enzyme)
Pepsin is activated by HCl to begin protein digestion to break protein into smaller pieces or amino acids
Other enzymes are denatured by HCl and stop carbohydrate digestion

14. Mechanical digestion in the stomach
Stomach muscles contract to churn and mix stomach contents
This makes chyme
After 1-2 hours the pyloric sphincter opens so chyme can pass into the small intestine

15. Small intestine
Chyme enters the first part of the small intestine called the duodenum
Digestive enzymes and fluids from the pancreas and liver also enter at the duodenum
Most chemical digestion and absorption of nutrients occurs in the small intestine

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Pancreas & Liver
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17. Effects of digestive enzymes
Salivary amylase (mouth)
Pepsin (stomach)
Amylase (sm. Int. from pancreas)
Trypsin (sm. Int. from pancreas)
Lipase (sm. Int. from pancreas)
Breaks down starch and disaccharides
Breaks down proteins into large peptides
Continues breakdown of starch
Continues breakdown of protein
Breaks down fat

18. Effects of digestive enzymes
Maltase, sucrase, lactase (sm. Int.)
Peptidase (sm. Int.)
Breaks down remaining disaccharides into single sugars
Breaks down dipeptides into amino acids

19. Accessory structures of digestion
Pancreas (behind the stomach) has 3 roles
Releases hormones to regulate blood sugar levels
Releases enzymes that break down carbohydrates, proteins, lipids, nucleic acids
Produces sodium bicarbonate that neutralizes stomach acids so the enzymes can function (without neutralization, enzymes denature and don’t function properly)

20. Accessory structures cont.
Liver-(above and to the left of the stomach) produces bile loaded with lipids and salts
Bile dissolves fats in fatty foods
Bile is stored in the gallbladder

21. Absorption in the small intestine
Last 2 parts of the small intestine are the jejunum and ileum, together are 6 meters long
When chyme enters these it is a mixture of medium and small nutrient molecules (most chemical digestion is competed in the duodenum)
Lining of the small intestine is covered with villi (fingerlike projections) each of which is covered with microvilli, both are needed to increase the surface area for absorption

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Villi
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23. Absorption in the small int. cont.
Cells of small intestine absorb nutrients
Products of carbohydrate and protein digestion are absorbed into capillaries in villi
Undigested fat and fatty acids are absorbed by lymph vessels
When food leaves small intestine and enters the large intestine it is nutrient free and contains only water, cellulose, and undigestible substances

24. The large intestine Also called the colon
Primary function is to remove water from undigestible material
Water is absorbed quickly through the wall of the colon
Colonies of bacteria produce useable compounds such as vitamin K
Concentrated waste that remains passes through the rectum to be excreted