BIOL203 Lesson 9

• Osmosis


  Osmotic diffusion of water through a selectively permeable membrane

  • "Where ions go, water follows"
• Water content in the body

  • Adult body contains 40L of water
  • 2/3 is intracellular fluid, 1/3 is extracellular fluid (CV, lymphatic system, etc.)
  • Some cells (muscle, epithelial) contain 70-80% water
  • Others (fat, bone) contain <20% water
• Fluid compartments in the body

  • Extracellular fluid compartment (1/3 of water)
  • Includes CV system, lymphatic system, sweat, tears, gastric juices, spinal fluid, fluid between joints
• Water movement


  Water molecules move toward compartments with the highest concentration of solutes
• Electrolytes


  Minerals (K+, P, S, Mg, Na, Cl) that dissociate into ions when placed in water and help control volume of water within fluid compartments
• Functions of water in the body

  • Transports nutrients and waste
  • Participates in chemical reactions
  • Regulates body temperature
• Kidney function

  Kidneys control blood volume, blood pressure, solute concentration of body fluids
• Kidney regulation of water and electrolytes

  1. Pituitary gland secretes ADH to control water volume and blood pressure

  2. Adrenal gland secretes aldosterone to regulate sodium reabsorption and potassium elimination
• Increased potassium (K+) and magnesium (Mg) intake, reduced sodium (Na) intake


  Lowers blood pressure by withdrawing water from extracellular compartments into intracellular compartments
• Dehydration


  Fluid and electrolyte imbalance caused by water deficiency
• Hyponatremia


  Decreased concentration of sodium in blood, leading to severe headaches, confusion, seizures as water leaves intracellular and extracellular compartments and migrates into cells
• Water intoxication


  Excessive consumption of plain water or impaired kidney filtration, leading to hyponatremia, confusion, seizures, and coma
• Metabolism


  Sum total of all chemical reactions in living cells
• Anabolic reactions


  Small molecules are put together to build larger ones, requiring energy
• Catabolic reactions


  Large molecules are broken down into smaller ones, releasing energy
• ATP


  Energy currency of the cell, produced in mitochondria through breakdown of biological fuels

  • Contains around 40% of chemical energy stored in C-H bonds of glucose; the rest is lost as heat
• Sources of energy input

  • Carbohydrates (45-65%)
  • Fats (20-35%)
  • Proteins (10-35%)
• Energy balance

  Stable weight when energy in = energy out (30-50% physical activities, 50-65% basal metabolism, 10% thermic effect of food)
• Basal metabolic rate (BMR)


  • Rate of energy used for metabolism under specified conditions (after a 12-hour fast, restful sleep, no physical activity or emotional excitement and in a comfortable setting)
  • Liver: 27%
  • Brain: 19%
  • Skeletal muscle: 18%
  • Kidney: 10%
  • Heart: 7%
  • Other: 19%
• Factors affecting basal metabolic rate (BMR)

  • Body composition (the more muscle tissue you have relative to fat, the higher your BMR)
  • Sex (men and growing children have higher BMR)
  • Body surface area (larger surface area = higher BMR)
  • Environment (climate affects development of sweat glands)
• Fetal environment and low birth weight can increase risk of obesity in adults due to "thrifty gene" theory
• Quality of diet can play a role in gene expression (epigenetics)
• Daily intake of water

  • Metabolic water
  • Food
  • Water consumption
  • Total: around 2,500 mL/day
• Daily losses of water

  • Expired air
  • Insensible perspiration
  • Urine
  • Feces
  • Total: around 2,500 mL/day
• ADH hormone

  • Produced by pituitary gland in response to dehydration; stimulates kidneys to reabsorb more water and prevent water loss in urine
• Aldosterone

  • Hormone secreted by adrenal glands that regulates blood pressure by increasing reabsorption of sodium by kidneys; also regulates Cl and K concentrations
• DASH diet

  • Dietary approaches to stop hypertension
• Thermic effect of food (TEF)

  • Estimation of energy required to process food (digest, absorb, transport, metabolize, and store nutrients)
• Thrifty gene theory

  • Fetuses deprived of calories lower their BMRs because they predict an environment of food scarcity