The Digestive System

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The Digestive System

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• Digestion the processes that break down food.
• 4 main groups of food and the building blocks
• Carbohydrates monosaccharides
• Proteins amino acids
• Lipids glycerol fatty acids
• Nucleic acids - nucleotides

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Parts of the digestive system

• Mouth
• Pharynx
• Esophagus
• Stomach
• Small intestine
• Large intestine
• Rectum anus

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• Accessory organs organs that assist in
• the process of digestion, but food does not
• actually pass through them.
• Salivary glands
• liver
• Pancreas
• Cells in the digestive system secrete
• mucus to protect the tissues from the
• strongly acidic digestive juices

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mouth

• Food is mechanically / physically broken down by
  the teeth
• Food is mixed with saliva to begin chemical
  digestion
• Salivary amylase an enzyme that breaks down
  starch
• Food is formed into a bolus swallowed

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pharynx

• Food is swallowed into the pharynx
• The epiglottis blocks the trachea

Epiglottis
Pharynx
Trachea
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esophagus

• Food is moved along via peristalsis wave-like
  muscular contractions
• Better picture of peristalsis

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stomach

• Separated from the esophagus by the cardiac
  sphincter
• The stomach wall secretes gastric
  juices (pepsin HCL)
  mucus

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Functions of the stomach

• Storage many folds, can hold 2-4 liters
• Mixing food gastric juices chyme
• Physical digestion grinds food into smaller
  pieces, HCL kills pathogens
• Chemical digestion pepsin catalyses the
  breakdown of proteins into polypeptides
• Controlled release chyme leaves via the pyloric
  sphincter

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Small intestine

• 3 main parts duodenum, jejunum, ileum
• Walls are folded covered with villi
  finger-like projections
• Villi are covered with microvilli which greatly
  increase the surface area of the small intestines

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actions of the small intestine

• Food continues to move along via peristalsis
• Chemical digestion continues (proteases, maltase,
  lactase, phosphatases)
• The main site of nutrient absorption

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Large intestine / colon

• Main function reabsorption of water fecal
  formation
• Absorption of vitamin K B formed by bacteria
• Feces is stored in the rectum

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Pancreas

• An accessory organ that produces proteases,
  lipase, amylase
• Helps neutralize stomach acid as it passes into
  the small intestine

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Liver

• An accessory organ that produces bile
• Bile emulsifies fat
• Bile is stored in the gall bladder

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