TP3 Osmosis & Body Water Flashcards
Describe passive transport (4pts)
- Doesn’t require energy
- Movement DOWN conc. gradient
- Includes simple and facilitated diffusion
- At equilibrium, movement still occurs, but no more conc. gradient
Describe simple diffusion
Molecules pass through the membrane
Describe facilitated diffusion
Molecules pass through membrane via membrane bound channels or carrier proteins
Describe net diffusion
Net diffusion = difference in no. of molecules moving side A to B, and side B to A
Describe active transport
Requires energy (ATP)
Movement UP conc. gradient
Describe Fick’s law of diffusion (6 pts)
- Magnitude of conc. gradient
- Permeability of membrane
- S.A. of membrane
- MW of substance
- Distance travelled
- Temp
Describe osmosis
Diffusion of water through a selectively permeable membrane (passive)
Movement is higher conc. of water to lower conc. of water (H2O moves to where there is greater amount of solute)
Describe an isotonic solution
Conc. of water is same on either side of cell membrane.
Describe a hypotonic solution
conc. of solute outside the cell membrane is lower.
H2O molecules higher outside and therefore, water moves into cell.
Describe a hypertonic solution
conc. of solute outside cell membrane is higher.
H2O molecules lower outside and therefore water moves out of cell.
Define osmolarity
conc. of all solutes in a solution by volume
Define tonicity
determined by non penetrating solutes only. Not quantifiable and describes the effect of a solution on volume of cell placed in it.
Describe extracellular fluid & intracellular fluid
ECF: Fluid surrounding cells
ICF: Fluid within cells
Approx % ECF & ICF
ECF ~20% and ICF ~40%
Then:
- Interstitial Fluid ~15% : lies outside cells and capillaries
- Intravascular Fluid ~5% : fluid in walls of blood vessels
- Transcellular Fluid ~v low % : synovial fluid and aqueous humour
What factors effect total body water?
- Species
- Age
- Nutritional state
- Body composition
How much H2O retained from 1g protein?
3-4g H2O
Four principles of fluid regulation?
- Homeostatic mechanisms respond to changes in ECF, not ICF.
- Receptors monitor plasma volume and osmotic conc.
- All H2O movement is passive
- Body’s H2O/electrolyte content will rise if dietary gains exceed losses to the environment.
3 inter-related processes in water balance?
- Fluid balance -> affects circulatory pressure.
- Electrolyte balance.
- Acid-base balance -> H+ ions (H3O+) due to water being at equilibrium.
How is Osmotic balance maintained?
Regulation of ECF volume and osmolarity - changes to ECF will influence ICF
What happens to ECF during dehydration?
ECF becomes hypertonic, cell shrinks
Describe the affects of dehydration?
Causes disturbance of fluid volume & osmolarity.
Initially, water lost from ECF, then ICF.
Can also lose electrolyte
What happens when ECF becomes hypotonic?
Overhydration, cells swell and may burst
Describe the acceptable pH in life
Only narrow pH compatible - due to effect on protein structures & enzyme activity.
What will happen to pH outside acceptable range?
Enzymes cannot work (denature) and cells die/animal dies
What regulates blood pH?
Buffers, respiration & renal excretion
Describe the process of thirst recognition
Thirst center in hypothalamus detects change in osmotic pressure -> posterior pituitary directs kidney to conserve water - limited as kidneys must excrete some water.
OR: less water drunk than lost = thirst
