Unformatted text preview: Click the Key Concepts Button: The endocrine gstem controls whether the body stgg or w energy. Twp concepts controls whether nutrients are stored or used. )6 1) With food intake the body stores nutrients; between meals the body breaks down these stores. it? 2) The brain depends on a constant supply of glucose as its primary energy source. So, blood glucose levels must be
maintained at all times, even between meals. Wold-0M
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”hummer WEN Go to the next screen: You have already been introduced to catabolism and anabolism. Click on the Catabolic and
Anabolic Reaction buttons to review these concepts. An interestin ect of metabolism is that the same small
biomolecules that rovr e to s esize lgmgﬂinmnleeglgs. A good example is acetyl CoA, which can
be catabolized in the Krebs cycle for energy and is also a substrate for triglyceride and cholesterol synthesis. Because
carbohydrates, Epids and proteins can all be catabolized to acetyl CoA, they can all eventually be converted to lipids. Roll over the Catabolic and Anabolic Pathways Butto s for a
summary of these pathways. (“05“ u b5 f”"""‘} V) Krebs Cyctz
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(roams \> - “(Ulrich 5 ms .39 (W91) cholesterut SYWZ S G0 to the next screen: If anabolic and catabolic pathways have several of the same intermediates, whatgoxemsrhe ' of metabolism? When we eat, digestion in the gastrointestinal tract breaks down the large molecules in food
into smaller molecules what are then absorbed into the bloodstream. Click the See Digestion Overview Button: What follows is a brief overview of digestion and follows digestion
all the way to the processing by the liver. Digestion begins in the oral cavity by both the mechanical and chemical
breakdown of food. Chewing motion breaks down food particles and mixes food with saliva secreted from salivary glands. W contribute secretions to saliva — the 12mm contribute a serous ﬂuid rich in amylase, an enzyme that begins carbohydrate digestion. As food is swallowed it enters the esophagus and down to the cardiac
region of the stomach. The lining of the stomach secretes gastric juices that contain digestive enzymes. In the stomach the food is mixed with digestive juices. In the duodenum enzymes released from the bile and pancreatic ducts digest food further. The bile works to break down fats while the pancreatic enzymes continue the digestion of other food particles. In
the duodenum the food is prepared so that the small intestine can absorb as many nutrients from the food as possible.
Themmwmrwﬁm - “@t is about 1 meter
long. As the food have through the jejunum it is gradually broken down into smaller an smaller particles. golds line
the walls of the intestine that act to increase the absorptive surface area. The green nutrient particles and the yellow fat
particles get caught in the folds so they can be absorbed into the intestinal wall. Larger, less digestible particles are pushed on to the large intestine where much of the water they contain is reabsorbed before being expelled by the body.
The intestinal walls are covered with thousands of ﬁnger like villi. A network of tiny blood vessels called capillaries run just below the surface of each villus. These capillaries absorb the available nutrients in the intestine and transport them to the liver. The ymnuu'ients are absorbed into the [W that carry them to the circulatory system. Nutrients Page 2 of 4 ...
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- Spring '07