Fluid Compartments and Solutes Flashcards
What cations are found in molecules?
Sodium is most plentiful cation in plasma
Potassium is most plentiful cation in cells
What anions are found in molecules?
Organic phosphate is the main intracellular anion and is a key metabolite with roles in ATP production and cell signalling
How does the pH inside a cell compare to plasma?
Inside a cell is slightly more acidic than plasma
How does osmolarity compare between in a cell to plasma?
Osmolarity between blood and intracellular compartment is identical- there’s not really an osmotic effect
One exception is regions of the kidney where fluids are concentrated
What is osmosis?
Movement of water towards an area of high osmolarity
Define osmole
The number of moles of solute that contribute to the osmotic pressure of a solution
What is tonicity?
Defines the strength of a solution as it affects the final cell volume
It depends on both cell membrane permeability and solution composition
What is a hypertonic solution?
In a hypertonic solution, osmolarity of impermeant solutes outside cell are greater than those inside cell
Therefor cell shrinks in solution
What is a hypotonic solution?
Osmolarity of impermeant solutes outside cell are less than those in the cell
Cell swells in solution
What is an isotonic solution?
Same osmolarity inside and outside cell
Why don’t cells bursts?
Cells don’t burst because of the Na+/K+/ATPase pump - maintains a low conc. of Na+ in cells
Na+ is actively pumped out so there’s no net movement of Na across cell
What methods are used by solutes to cross membranes?
Active transport: uses ATP hydrolyse
Passive transport: transporter-mediated, channel-mediated,
How are tissues/ organs preserved?
In transport of tissues and organs they are perfused with cold solutions via arterial supply to rapidly cool the tissue/ organ to 4 deg. C- sows ischaemia
Na+/K+/ATPase stops functioning below 15 deg. C- little ATP to fuel pump
This means reactions need to be taken to stop Na and water entering cells and K+ exiting- could cause cells to burst
What precautions are taken to prevent cell death in organs being transported or transplantation?
Perfuse organs with University of Wisconsin solution (UW)- formulated to reduce hypothermic cells shrinking and enhance preservation
UW infused tissue has:
-lack of Na+ or Cl-
-presence of extracellular impermeant solutes
-presence of macromolecular colloid
What is the importance of exchange between blood and tissue?
Each day 8L of plasma leaks out of blood vessels
Since volume of blood plasma is 3L entire plasma volume must pass into interstitial space and back into circulation blood every 9 hours
How do molecules leave plasma?
Plasma proteins are too big to pass through endothelium
Lipid-soluble substances pass through endothelial cells
Exchange proteins are moved across by vesicular transport
Small water-soluble substances pass though pores between cells
Why are molecules pushed through capillary pores?
In a normal capillary there’s a higher conc. of plasma proteins inside capillary than outside, this generates an osmotic press known as colloid osmotic pressure
Flow of blood through the vessel also generates a hydrostatic pressure inside the vessel which is greater that in the tissue its passing
Thus there’s a tendency to push molecules through capillary pores
How does a normal capillary differ from a leaky one?
Solute and fluid movement across a vessel wall is determined by the balance between these opposing pressures (Colloid osmotic pressure and hydrostatic pressure)
In a normal capillary, although COP draws solute and fluid into the vessel, slightly greater hydrostatic pressure results in net leakage from the capillary under normal circumstances
What is oedema?
Accumulation of fluid within tissues
Its due to an imbalance in normal cycle of fluid exchange in tissues causing fluid to accumulate in interstitial space
What is a common cause of oedema?
Increased permeability of capillary walls
What happens in a leaky capillary?
Proteins are lost through an increase in pore size which reduces COP so fluids are more readily pushed out of capillary
What is the role of lymphatic capillaries?
To combat loss of plasma fluids of tissues, lymphatic capillaries collect interstitial fluid thats destined for return to the blood circulation
Fluids are constantly being lost from blood vessels and passed into interstitum bro be drained by lymphatic vessels
How does lymph fluid return to circulation?
Via lymphatic ducts in subclavian regions or via lymph nodes
When does oedema occur in relation to lymphatics?
When leakage of plasma in interstitum exceeds capacity of lymphatics to collect and return it to circulation
What is inflammatory oedema?
Oedema is one of the first signs of inflammation
What is hydrostatic oedema?
High blood pressure can lead to increased hydrostatic pressure in vessels
This pushes more fluid out of vessels and can lead to accumulation of interstitial fluid
What is elephantiasis?
Parasitic worms can block lymphatic vessels therefor preventing drainage of the lymph
How do you calculate osmolarity?
Multiply the concentrations (mmol/l) of each molecule by the number of ions in it
e.g. in NaCl there are 2 ions (1x Na and 1x Cl)
Glucose counts as 1 molecule
What is the units of osmolarity?
Mosmol/l
