Metabolism P1 (BISC2016)

• Metabolism


  All of the chemical reactions in the body
• Systems involved in metabolism

  • Respiratory
  • Cardiovascular
  • Digestive
  • Urinary

  
• Metabolism answers the "why" for much of the systems
• Integrative Physiology


  Homeostasis - the why
• Metabolism


  1. Breakdown and build up

  2. Pathophysiology
• Metabolism is not a system - it has no defined organs, tissues, cells
• Nutrient pool


  Derived from the foods we ingest, including carbohydrates, lipids, amino acids, vitamins, minerals
• Cells obtain most of their ATP from the electron transport system, which is linked to the citric acid cycle where cells can break down any available substrate from the nutrient pool to obtain the energy they need
• Carbohydrates are usually the preferred substrates for catabolism and ATP production under resting conditions
• Lipids reach the bloodstream in chylomicrons, and the cholesterol is then extracted and released as lipoproteins
• An amino acid not needed for protein synthesis may be broken down or converted to a different amino acid to create energy
• Vitamins and minerals are essential to the function of many metabolic pathways
• Proper nutrition depends on eating a balanced diet in which the control of appetite is complex and involves both short-term and long-term mechanisms
• The pancreatic islets secrete insulin and glucagon and regulate glucose use by most cells
• If glucose regulation goes uncontrolled, metabolic disorders may result from inadequate nutrition, biochemical problems, or starvation
• Nutrients and energy form a balance where besides keeping the organs functioning, the body uses energy continuously to maintain a constant body temperature, and heat gain and heat loss must be in balance
• Thermoregulatory centers in the hypothalamus adjust heat loss and heat gain
• The Big Three macromolecules

  • Carbohydrates
  • Lipids
  • Proteins
• Carbohydrates


  Carbon, hydrogen, oxygen
• Lipids


  Fatty acids
• Proteins


  Amino acids
• Enzymes


  • Carbohydrases
  • Lipases
  • Proteases
• The three macromolecules are released into the bloodstream, absorbed by cells, and generate ATP to build back up complex carbs, proteins and lipids
• The nervous and endocrine systems control the storage and mobilization of the three macromolecules as needed
• The body obtains energy from these three stores in the form of ATP to support intracellular processes and building new products
• Appetite


  Behavioral state that drives eating
• Satiety


  Behavioral state that inhibits eating
• The hypothalamus contains feeding and satiety control centers
• Glucostatic theory


  Blood glucose levels are low, feeding center is dominant until it levels, satiety center depressed until glucose levels increase
• Lipostatic theory


  Fat stores increase, eating decreases. Obesity results from a disruption in this pathway. Leptin is a hormone acting as a negative feedback where fat stores increase, adipose cells secrete Leptin, food intake decreases
• Basal Metabolic Rate (BMR)


  Rate at which body expends energy while at rest to maintain vital functions. Minimum resting energy expenditure of an awake, alert person. Measured as kcal (kilocalories) and involves monitoring respiratory activity
• To maintain homeostasis indefinitely, the digestive tract must absorb fluids, organic nutrients, minerals, and vitamins, and the body's chemical reactions (metabolism) will determine what happens to the nutrients in the food - heat, muscle, adipose

  
• Nutrition


  Absorption of nutrients from food. Body's requirement for each nutrient varies

  
• Balanced diet


  Contains all ingredients needed for homeostasis
• Malnutrition


  Unhealthy state resulting from nutrient imbalance
• If nutrients are constantly being supplied in a balanced way, the body will figure out where and what quantity will be delivered

  
• Energy input and output

  • Energy input equals energy output
  • Total body energy = energy stored + energy intake + energy output
  • Energy output = work + heat
  • Three categories of work done by our cells: transport across membranes, mechanical work, chemical work
• We need energy to keep our parts active and this is where the metabolic rate comes into play
• Unregulated


  • Thermoregulation
• Work


  • Transport across membranes
  • Mechanical work
  • Movement
  • Chemical work
  • Synthesis for growth and maintenance
  • Energy storage
  • High-energy phosphate bonds (ATP, phosphocreatine)
  • Chemical bonds (glycogen, fat)