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1. PURPOSE

  1. A large part of biochemistry, covered in the past few chapters, focuses on energy production and storage

  2. There are a few aspects of metabolism that don't fit strictly in one of the previous chapters, and are presented here as a way to start integrating information

  3. Beyond these pathways, nutrition also covers vitamins, which contain a lot of information

  4. Vitamin questions tend to focus less on biochemical pathways and more on clinical symptoms

  5. This is the most memorization-intensive chapter within biochemistry, so we will prioritize information as much as possible

2. KETONE BODIES

  1. Energy source derived from fatty acids and certain amino acids

  2. Ketones are used primarily in brain and muscle

    1. Muscle cells derive energy from ketones in addition to glucose, glycogen, and fat

    2. Brain uses mainly glucose, but under certain conditions switches to ketones → minimal glycogen use

  3. Not often tested on their own, but important background for related topics

  4. Clinical: Diabetic ketoacidosis results from poorly controlled diabetes (insufficient insulin, unopposed glucagon)

    1. Often first time diabetes is diagnosed: May recall previous polydipsia, polyuria (thirst and peeing)

    2. Sudden onset of vomiting, tachypnea, confusion, progressing to loss of consciousness

    3. Metabolic acidosis: Acidic ketones build up in the blood

    4. Breath has a fruity odor: Acetone from some ketone bodies released through the lungs

    5. Treatment: Insulin, hydration, and support

  5. The ketogenic diet aims to reduce carbohydrates in favor of fats

    1. In pyruvate dehydrogenase deficiency, pyruvate cannot be converted to acetyl-CoA

      • Shunt to lactic acid leads to acidosis with neurologic symptoms

      • Appears in infancy: Failure to thrive, developmental delay, seizures

    2. In general, epilepsy disorders can benefit from a ketogenic diet

      • Possibly due to changes in neurotransmitter synthesis, lactic acid, etc.

3. METABOLISM OVERVIEW

  1. We have now gone through the major arms of metabolism: Carbohydrates, protein, and lipids

  2. Putting them all together is important for understanding how energy is used by the body in different contexts

  3. Important for (1) daily activity and exercise and (2) starvation conditions

  4. Exercise energy sources

    1. Creatine phosphate

    2. Anaerobic metabolism (glycolysis only)

    3. Aerobic metabolism (using glucose, fatty acids, etc.)

  5. Daily energy usage

    1. Fed state: Glycolysis, aerobic respiration

    2. Hours–1 day fasting: Glycogenolysis, gluconeogenesis, lipolysis

    3. 2–3 days fasting: Adipose fatty acids, gluconeogenesis → muscle and liver fatty acids

    4. Weeks fasting: Fatty acids → protein

    5. Death: Protein degradation → organ failure

4. PROTEIN-ENERGY MALNUTRITION

  1. Severe acute malnutrition due to lack of protein and/or caloric intake

  2. Common in childhood when needs are great, and in resource-limited countries especially

  3. Classified based on presence of absence of edema

  4. Marasmus: No edema; very thin, muscle wasting

    1. Prolonged caloric deficit → muscle wasting and depleted fat stores cause emaciated appearance

    2. Serum protein levels diminished, but not severely

    3. Example in resource-rich countries: Anorexia nervosa

  5. Kwashiorkor: Edema; peripheral edema, ...

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