body fluids

Water

  • A cell’s operations rely on water as a diffusion medium for the distribution of gases, nutrients and wastes

  • The ability to produce energy is fundamental to life 


ATP to ADP

  • Adenosine triphosphate is the primary compound that provides energy to drive many process in living cells

  • It consists of an adenosine molecule and 3 inorganic phosphates

  • After breaking down ATP to ADP, the energy released from the breaking of a molecular bond is the energy used for life

  • ATP ←→ ADP + Pi + energy 


Levels of organisation

  1. Chemical

  2. Cellular

  3. Tissue

  4. Organs

  5. Systems

  6. Organism 


Distribution of water in the body

  • %water varies between sex and age and different organs

  • Babies/ children > adult men > adult women > obese people

  • Brain > lungs > skin > bones (blood excluded - lungs has more if blood is included)


Distribution of water in and out the cell

  • Total body water (TBW) = ~60% of total body weight = ICF + ECF


Fluid balance: water gains and losses

  • ICF = ECF

  • Fluid balance: when amounts of water gained and lost each day are equal 

  • Water gains

  • ~2500 ml/day required to balance water loss from drinking 1.2, eating 1.0 and metabolic generation 0.3 within cells which result from oxidative phosphorylation in mitochondria  

  • Water losses

  • ~2500 ml/day from urine 1.2, feces 0.15 and insensible perspiration 1.15

  • Sensible perspiration (sweat) varies with activities and can cause significant water loss

  • Fever can increase water loss 


Plasma (cell) membrane


Function 

  • Physical isolation

  • Barrier separating cytoplasm from ECF

  • Semipermeable to regulate exchange with environment 

  • Ions and nutrients enter (O2 and CO2)

  • Wastes eliminated

  • Cellular products released

  • Degree of permeability depends on size, electrical charge, shape and lipid solubility 

  • Sensitivity to environment

  • Anchors cells and tissues


  • The exchange of ions between ICF and ECF takes place across plasma membranes by osmosis, diffusion, and carrier-mediated transport


Phospholipid bilayer

  • Hydrophilic head

  • Hydrophobic tail

  • Barrier to ions and water-soluble compounds

  • Protein molecules are inserted into the bilayer

  • Simple diffusion occurs

  • Lipid soluble compounds (alcohols, fatty acids, steroids)

  • Dissolved gases (O2 and CO2)

  • Water molecules

  • Channel-mediated diffusion occurs 

  • Water soluble compounds and ions

  • Affected by size, change and interaction with channel walls 


Diffusion 

  • Net movement of a substance from area of higher concentration to area of lower concentration

  • Ions and molecules are constantly in motion 

  • Concentration gradient is created 


Tonicity 

  • Effect of diffusion and osmosis on cells

  • Isotonic: same concentration creates dynamic equilibrium

  • Hypotonic: movement of water from high water concentrated (low solute) extracellular environment into low water concentrated (high solute) intracellular environment caused cell to swell/ lyse/ rupture

  • Hypertonic: movement of water from low water concentrated (high solute) extracellular environment into high water concentrated (low solute) intracellular environment caused cell to shrivel


Fluid balance 

  • Water can move between ECF and ICF in osmotic equilibrium

  • WRITE IN LECTURE


Electrolytes 

  • Inorganic ions released when inorganic compounds dissociate

  • Can conduct electrical currents in solution

  • Imbalance seriously disturbs vital body functions 

  • Eg. NaCL, KCl, CaPO4


Electrolytes composition of body fluid compartments

  • Osmolarity (osmotic concentration) is the total solute concentration in a solution

  • Although there is a lot more proteins inside the cell than outside

  • BUT: ICF and ECF osmolarity is similar, thus, osmotic pressure is negligible. Problems occur when osmotic balance is disturbed


Diffusion via channels and carriers

  • Carrier proteins are integral proteins that transport substances across the membrane both down (no energy needed) and up (need energy) the concentration gradient - does not require any energy.

  • They undergo a series of conformational changes to transfer the bound solute across the membrane - slow

  • Transport both water soluble and insoluble molecules.


  • Channel proteins are proteins that create hydrophilic holes in cell membranes, facilitating the transport of substances down the concentration gradient (no energy required) - fast

  • Only transport water-soluble molecules


Diffusion and osmosis

  • Transport through plasma membrane can involve

  • Passive processes (no energy required)

  • Active processes (requiring energy)

  • Diffusion and osmosis (passive)

  • Osmosis: Diffusion of water across a selectively permeable membrane

  • Water molecules diffuse across a membrane toward the solution with more solutes

  • Carrier-mediated transport (passive or active)

  • Vesicular transport (active)

  • Osmosis occurs more rapidly than solute diffusion because water can cross a membrane through abundant water channels (aquaporins) and aquaporins outnumber solute channels

Facilitated diffusion/ carrier mediated transport

  • Carrier proteins transport molecules too large to fit through channel proteins (glucose, amino acids)

  • Molecule binds to receptor site

  • Protein changes shape, molecule passes through

  • Receptor site is specific to certain molecules