5 Fluid Compartments of the Body Flashcards
Q: Lean humans are typically what percentage water? Role?
A: 55% women, 60% men
key to normal physiology
Q: Describe the main fluid compartments and sizes in a lead 70kg man. Use a diagram. (5)
A: intracellular = 23L = 55% of body water
extracellular = 19L = 45% of body water
Out of the extracellular fluid in a person, the majority of it is interstitial fluid = 15L = 36%
A small proportion (3L = 7%) is blood plasma
An even smaller proportion (1L = 2%) is transcellular fluid e.g. cerebrospinal, ocular, synovial fluid
Q: What are the barriers between various fluids? (3)
A: plasma membrane: intra and extracellular fluid
extracellular fluids is separated by layers of cells that form junctions with eachother
- epithelial cells separate various interstitial spaces
- endothelial cells line blood vessels = main barrier separating the fluid of the blood (the plasma) and interstitial fluids
Q: What makes up the composition of the main fluid compartments? (7)
A: cations: Na+ and K+ and Ca2+
anions: Cl- and organic phosphates- and protein17-
pH
Q: What’s the difference between plasma and other interstitual fluids?
A: plasma has far more protein (other components are v similar in amount)
Q: Compare blood plasma (extracellular) and muscle cells (intracellular) in terms of cations. (4)
A: -Sodium is present in high concentrations outside cells
- Potassium is present in high concentrations inside cells
- Calcium is an important signalling ion - it is present in very low concentrations inside cells though there are some compartments which store calcium (e.g. ER)
-main one in plasma is Na+ (150mmol/l vs 10)
main one in muscle is K+ (150mmol/l vs 5)
-Ca2+ is 2mmol/l in plasma vs 10^-4
-Mg2+ another one present in significant amounts
Q: Compare blood plasma (extracellular) and muscle cells (intracellular) in terms of anions.
A: -Chloride is present in high concentrations outside cells
- Organic Phosphates are present in high concentrations inside cells
- PROTEINS are also anions which are present in LOW concentration but have a HIGH CHARGE.
- main one in plasma is Cl- (110mmol/l vs 5)
- main one in muscle is oraganic phosphates- (130mmol/l vs 5)
- protein17- is 1mmol/l in plasma vs 2 in muscle
Q: Compare blood plasma (extracellular) and muscle cells (intracellular) in terms of pH.
A: plasma= 7.4, muscle=7.1
almost twice as much
Q: Compare blood plasma (extracellular) and muscle cells (intracellular) in terms of osmolarity.
A: 285mosm/l for both (exception is some parts of kidney)
Q: What osmolarity?
A: CONCENTRATION OF A SOLUTION EXPRESSED AS THE TOTAL NUMBER OF SOLUTE PARTICLES PER LITRE
Q: What is diffusion?
A: spontaneous movement of solute to spread evenly in a compartment (down its concentration gradient until even distribution)
Q: What is osmosis? In terms for osmolarity? Whole story?
A: movement of water down its own concentration gradient
osmosis moves water toward area of higher osmolarity and can change cell volume
but membrane permeability of solutes is also crucial
Q: What occurs when intracellular osmolarity is higher than extracellular? Result?
A: 3 options in terms of volume change
- no change
- increase
- burst
therefore osmolarity alone is too simple term for biological systems because it doesn’t include cell permeability
Q: What’s a more useful concept than osmolarity?
A: tonicity
Q: What is tonicity? What does it depend on?
A: defines the ‘strength’ of a solution as it affects final cell volume
both cell membrane permeability and solution composition
Q: What occurs when intracellular osmolarity is higher than extracellular and the membrane is permeable to both water and a solute?
A: 1. Initially, Osmolarity OUTSIDE < INSIDE
- Osmosis: water moves down the concentration gradient into the cell
- Diffusion: solute moves down the concentration gradient out of the cell - reduces intracellular osmolarity
- OVERALL EFFECT: Water concentration and solute concentration is even inside and outside the cell - no further net diffusion of osmosis - no change in cell volume
Q: What occurs when intracellular osmolarity is higher than extracellular and the membrane is permeable to both water and one of 2 solutes? (other solute =impermeable)
A: 1. Water moves down the concentration gradient into the cell until the osmolarity is the same inside and outside the cell
- Solute 1 moves out of the cell down a concentration gradient and decreases intracellular osmolarity
- Impermeant solute can’t cross the membrane
- CELL SWELLS - increase in cell volume
Q: What occurs when intracellular osmolarity is higher than extracellular and the membrane is permeable to water and impermeable to a solute?
A: 1. Osmosis- water moves down the concentration gradient into the cell.
- Impermeant solute can’t move out
- CELL BURSTS - before Osmolarity outside can equal the osmolarity inside
Q: What are the 3 tonicity terms? describe.
A: HYPERTONIC
- Osmolarity of impermeant solutes: out > in
- Cell shrinks in solution
- Solution is hypertonic
HYPOTONIC
- Osmolarity of impermeant solutes: out < in
- Cell swells in solution
- Solution is hypotonic
ISOTONIC
- Osmolarity of impermeant solutes: out = in
- Cell volume is unchanged
- The solution is isotonic
Q: Real cells. Membrane permeability? Content? Burst? why? Maintaining?
A: -permeable to water
- impermeable solute concentration is higher inside > outside the cell
- but they DO NOT BURST
- because SODIUM-POTASSIUM PUMP maintains a lower concentration of sodium inside the cell than outside
- makes membrane permeable to sodium ions because any sodium ions which diffuse in are pumped back out
- no net movement of sodium ions across the membrane
The intracellular osmolarity of impermeant solutes (mainly high concentration of proteins and low concentration of Na+) balances the extracellular osmolarity of impermeant solutes (mainly high concentration of Na+).
-Cells must actively maintain this state
Q: Considering a synthetic lipid bilayer which doesn’t have any membrane proteins. How are these transported across it?
- Hydrophobic Molecules.
- Small Uncharged Polar Molecules.
- Large Uncharged Polar Molecules.
- Ions.
A: 1. can easily pass through the membrane
- some molecules will diffuse through but the majority do not
- almost all molecules don’t pass through the membrane
- do not pass through the membrane
Q: What are the methods of transporting solutes across a membrane? (7)
A: Passive - Down an Electrochemical Gradient
- Through Lipid bilayer
- Through Pores
- On Carriers
Active
- On Carriers - primary active transport
- On Carriers - secondary active transport
- Endocytosis
- Exocytosis
Q: Summarise exchange across a capillary wall. (4)
A: 1. lipid soluble substances through the endothelial cells
- small water soluble substances pass through the pores between cells
- exchangeable proteins are moved across by vesicular transport
- plasma proteins generally can not cross the endothelial cell membranes and can not get through the pores between cells
Q: What are the 2 forces acting on a normal capillary? Balance? Result? (2) More likely?
A: 1. osmotic pressure due to plasma proteins (colloid osmotic pressure (COP)): more proteins inside than outside the vessel = tends to pull water into vessle
2. hydrostatic pressure due to blood pressure = tends to push water out
Solute and fluid movement across a vessel wall is determined by the balance between the opposing pressures.
- Hydrostatic Pressure > COP = Plasma Leaks Out (usual)
- Hydrostatic Pressure < COP = Flow Into Vessel
