Body Fluid and membrane function

• Major constituent of body comprising approximately 60% of total body weight

  Body water
• What percentage of body weight is water in a person with high body fat

  40%
• Percentage of body weight is water in a lean person

  80%
• 3 mechanism regulate body water content

  Hormonal mechanism

  Circulatory mechanism

  Renal mechanism
• Water contained inside cells

  Intracellular Fluid
• Fraction of total body water is ICF

  2/3
• Water located outside cells

  Extracellular fluid
• Fraction of total body water is ECF

  1/3
• 2 major compartments of ECF

  Interstitial fluid (80% of ECF)

  Plasma (20% of ECF)
• Fluid surrounding cells


  Interstital fluid
• Circulatory fluid containing blood components

  Plasma
• The total distribution of fluids between intracellular and extracellular compartments in the human body


  Body fluid distribution
• Volume of intracellular fluid

  27 Litres
• Volume of interstitial fluid

  11 litres
• Normal volume of plasma

  3 - 3.5l
• The regulation of water intake and output in the body

  Water balance
• How much metabolic water is produced daily

  200ml
• Normal daily water intake from food and drink?

  1.5 - 2.5l
• What are the four routes of water loss

  Kidneys (0.5 - 1.5L/day)

  Lungs (0.3 - 0.4L/day)

  Skin and sweat (0.2 - 1.0L/day)

  Faeces (0.1 - 0.2L/day)
• The barrier between blood vessels and interstitial fluid that regulates fluid and solute movement

  Capillary wall
• What can pass freely through capillary wall

  Ions
• Why are plasma and interstitial fluid similar in ionic composition

  Small ions can move freely across capillary walls
• What is retained within the plasma

  Large particles/proteins
• The osmotic pressure created by proteins in blood plasma

  Oncotic pressure
• What happens to fluid distribution when plasma protein levels fall

  Plasma osmotic pressure falls

  Fluid moves into interstitial space

  Oedema develops
• A membrane protein that actively transport sodium and potassium ions across cell membranes

  Sodium potassium pump
• What does sodium potassium pump out of the cells


  Sodium
• What does sodium potassium pump into the cells


  Potassium
• A biological barrier that selectively controls which substances can pass through

  Cell membrane
• What property allows it to control substance passage

  Semi permeable or selectively permeable
• What are the three major routes for substance to cross

  Diffusion through aqueous pores

  Dissolving in lipid portion

  Carrier mediated diffusion
• Water filled chanels in the cell membrane that allow certain substances to pass through

  Aqueous pores
• Process by which substances move across biological membrane

  Membrane transport
• Membrane proteins that facilitate the movement of specific substances across the cell membrane

  Carrier protein
• Channel in cell membrane approximately 10 angstroms wide that allows passage of water and polar molecules

  Membrane pore
• What type of molecules can pass through these

  Water and polar molecules
• What is the size limit for molecules passing through

  10 angstroms in diameter
• What defines a polar molecule

  Uneven charge distribution with positive and negative ends
• Hydrophobic barrier in cell membrane that allows passage of lipid soluble molecules


  Lipid membrane
• Carrier mediated transport that moves substances across membrane without using energy

  Facilitated diffusion