Download 6.1 Digestion 6.1.1 Explain why digestion of large food molecules is

6.1 Digestion
Eating starts the process that leads to your body cells gaining necessary nutrients. In General:
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Ingestion – eating the food
Digestion – Series of chemical evens that break food down into smaller molecular forms
Absorption – small molecules pass through digestive cells and into the blood stream/lymphatic
vessels
Transport – circulatory system delivers molecules to body cells to serve as nutrients
6.1.1 Explain why digestion of large food molecules is essential.
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Most ingested molecules are polymers and insoluble, must first be broken down so smaller soluble
molecules are can be absorbed into the blood.
Smallest components can then be used to build larger molecules, useful to organism.
6.1.2 Explain the need for enzymes in digestion. 3 The need for increasing the rate of digestion at
body temperature should be emphasized.
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Enzymes are biological catalysts
Digestive enzymes secreted into the lumen of the gut, and increase the rate of hydrolysis of insoluble
food molecules, breaking them down into soluble products.
Digestive enzymes increase the rate of reaction at body temp (37 C)
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6.1.3 State the source, substrate, products and optimum pH conditions for one amylase, one
protease and one lipase. Any human enzymes can be selected. Details of structure or mechanisms
of action are not required.
Salivary Amylase
Pepsin (a protease)
Pancreatic Lipase
Source
Substrate
Products
Optimum pH
6.1.4 Draw and label a diagram of the digestive system. (The diagram should show the mouth,
esophagus, stomach, small intestine, large intestine, anus, liver, pancreas and gall bladder. The
diagram should clearly show the interconnections between these structures.)
6.1.5 Outline the function of the stomach, small intestine and large intestine.
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Stomach – food brought to stomach by esophagus, using peristalsis, or a sequential series of smooth
muscle contractions
o Once in stomach, food is held for a period of time to mix it with a variety of secretions
known as gastric juice:
 Pepsin
 Hydrochloric Acid
 Mucus
o Lumen of stomach stores the food from a meal
o Gastric pits secret mucus, enzymes, and acid
o Mucus Secreting Cells – secret mucus to protect surface of stomach from auto digestion
o Parietal Cells produce HCL – kills microorganisms that enter digestive center and converts
inactive pepsinogen into active pepsin
o Chief Cells – produces pepsinogen
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Small Intestine – digestion is completed and the vast majority of absorption occurs
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In duodenum (first portion of small intestine) three different organs insert digestive juices
 Bile from liver and gall bladder
 Trypsin (protease), lipase, amylase, and bicarbonate from pancreas
Products of digestion absorbed into blood stream or lymphatic system
Villus – increases surface area for absorption of products
Microvilli – border epithelial cell (cells lining small intestine) increases surface area for
absorption
Lacteals – connect to the lymphatic system for transport of lipids
Capillary beds – connect to circulatory system for transport of products to body cells
Large Intestine – colon is responsible for the reabsorption of water from the gut
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Contains large number of bacteria, including E. coli, that serve a mutualistic relationship –
they receive nutrients, water, and a warm environment, we receive vitamin K and a healthier
overall environment
Undigested food is eliminated as feces
6.1.7 Explain how the structure of the villus is related to its role in absorption and transport of the
products of digestion.
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Villus increases surface area of digestive system
Each villus contains:
o Capillary bed – small blood vessels of circulatory system that absorbs most nutrients, except
fatty acids
o Lacteal – small vessel of lymphatic system that absorbs fatty acids.
Folds of small intestine increase SA:V ration by 3, Villi increase SA:V ratio by 10, Microvilli increase
SA:V ratio by 10
6.1.6 Distinguish between absorption and assimilation.
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Absorption – digested nutrients are absorbed through digestive cells into the blood stream of
lymphatic system
Assimilation – movement of nutrients into body cell to be used to produce energy or to build larger
molecules.