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BIO NOTES EXAM 2 - Digestion A Why do we Eat B What do we...

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Digestion A. Why do we Eat? B. What do we Eat? C. Human Digestive System A. Why Do we Eat??? 1. Energy –the ability to do work, we use energy to move things around. You need energy to do work- getting energy is not a minor problem – we need the atp! a) thermodynamics- the study of energy pg. 153-154, energy is used up as heat Chemical energy in the form of ATP First law of thermodynamics- energy cant be created or destroyed, it can only be converted. We as humans are heterotrophs must consume photoautotrophs to obtain our energy. Organisms cannot create the energy they require in order to live – instead they must capture energy from the environment and transform it to a form that can be used for biological work Second Law – any time you use energy you lose some of it as heat, no energy transfer will be 100% - this energy cannot be used to do work Cellular respiration – is only 30% efficient The energy in your car is only 20% efficient Pg. 153-154 (121-124 in old book) b) Controlling acquisition of energy – our bodies keep track of how much energy we have Hypothalamus – hunger center nucli – tells us amount of energy we have satiety center nucli- tells us how full are we Secrets hormone when energy levels are low – this makes you feel hungry Stomach – directly impacts if you need to eat or not secrets – ghrelin when nothing is in the stomach – you become hungrier it stimulates the hypothalamus which releases NPY (neuropeptide Y) – gives you hunger sensation 1. Short term After a meal your small intestine hormones tell us we are getting filled up – endocrine cells release 2 hormones 1) Cholecytoskinin (CCK)– affects how full you feel Satiety Center – also impacted by stomach stretch receptors as the stomach gets filled 2) PYY – causes reduction in NPY when carbohydrates and sugars hit small intestine – your pancreases releases insulin
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2. Long Term a. Good energy availability i. insulin levels rise high ii. Adipose tissue – secrets hormone Leptin – feeds back to hypothalamus- lowers NPY *after a period of time you will add adipose tissue if your eating normally b. Poor availability – does opposite effects – insulin levels low, no addition of adipose tissue C. Energy yield –what provides the most energy per gram? we consume 3 types of macromolecules - Carbs, Proteins, Lipids Lipids have the highest energy per gram (9Kcal) Proteins and Carbohydrates both have (4Kcal) We should have a dispersed diet (33% of each) but we love fats because they taste good so the average fat intake is 65% Fats – taste mad good, we evolved from creatures who were desperately in search for fats *if you eat too much protein and carbs they get stored as fat in your liver! 2. Biosynthesis -make things out of biological molecules -digestive-polymers-broken down into monomers – carbohydrates, proteins, and lipids =)!!!!
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BIO NOTES EXAM 2 - Digestion A Why do we Eat B What do we...

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