5- Fluid Compartments Flashcards
(13 cards)
Describe the fluid composition of a 70kg man
Sixty percent of a person is water
o 55%ofthisisintracellular o 45%isextracellular
36% of body water is interstitial fluid, between cells (15L)
7% of body water is blood plasma (3L)
2% of body water is transcellular fluid for example CSF, synovial fluid etc (1L)
Compare fluid composition in plasma and muscle
in plasma*** in muscle (mmol/l) (mmol/l) \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ Na+ 150 10 K+ 5 150 Ca2+ 2 10-4 Cl- 110 5 Organic phosphates 5 130 Protein17- 1 2 pH 7.4 7.1 ---------------------------------------------------------------------- osmolarity 285 mosm/l 285 mosmol/l
What is osmolarity?
Osmolarity is a measure of all solute particles in a solution i.e. if [NaCl] = 150 mmol/L, the osmolarity is 300 mosm/L, because there are 150 mmol/L of both Na+ and Cl ions
How does osmolarity determine cell shrinkage?
o A hypertonic solution is when the osmolarity of the impermeant solutes outside is greater
than inside the cell. The cell shrinks
o Ahypotonicistheopposite.Thecellswells
o An isotonic solution is where the osmolarity of the impermeant solutes outside is equal to
those that are inside the cell. The cell remains the same
What is tonicity?
It defines the strength of a solution as it affects final cell volume. Thus is depends on BOTH cell membrane permeability and solution composition
What is oedema?
Caused by an imbalance of forces and sometimes increased permeability of the capillary walls to plasma proteins, hypertension
The hydrostatic pressure»_space;> osmotic pressure
This leads to the accumulation of fluid that cannot be drained in the interstitium
Caused by inflammation (makes capillaries leaky), trauma, hypertension
How can substances be transported across membranes?
Passivelydownanelectrochemicalgradient(lipids,oxygen,carbondioxideetc.)
o Passively via facilitation through channel proteins that are specific to their ligand. Some
are gated using voltage or by ligand (water, ions, urea etc.)
o Passively via carriers through carrier proteins that bind the ligand to the carrier and
instigate a conformational change e.g. facilitated diffusion
ActivelyupanelectrochemicalgradientviacarriersthatuseenergyviaATPhydrolysise.g.
sodium potassium pump
o Activelybyusingthedownhillmovementofonesolutetocoupletotheuphillmovementof
a different solute e.g. sodium diffuses in and glucose pumped out
o Viaendo/exocytosis
Why do normal cells not burst despite having a higher solute conc inside cells?
Because sodium potassium pump maintains lower sodium conc inside cell.
any Na+ that diffuses in down the Na + concentration gradient is pumped out again. Thus there is no net movement of Na+ across the membrane.
The intracellular osmolarity of impermeant solutes (mainly high conc proteins and low conc Na+) balances the extracellular osmolarlity of impermeant solutes (mainly high conc Na+).
Cells have to actively maintain this state.
The pump makes the membrane “effectively impermeable” to Na+
How are fluid used to preserve organs?
In transplantation, donated organs and tissues are commonly required to be transported to where the recipient is situated.
When any tissue loses its blood supply, ischaemic changes occur, but these can be significantly slowed by rapid cooling of the tissue/organ to 0 - +4°C.
Tissues are perfused with cold solutions via the arterial supply.
Even when cooled, tissues/organs deteriorate.
The composition of the perfusion solution can reduce the deterioration in hypothermia, prolonging the time available to transport and keep viable.
What makes up the university of Wisconsin solution?
no Na+ or Cl- (no influx possible)
•extracellular impermeant solutes (lactobionate ions, raffinose (a sugar))
• macromolecular colloid (starch)
Together, these factors reduce cell swelling in cooled tissues.
How much fluid leaks out capillaries each day?
Each day, 8L of plasma leaks out of blood vessels. Since the volume of blood plasma is ~3L, the entire plasma volume must pass into the interstitial space and back into the blood circulation every 9 hours!
Describe exchange across the capillary wall
Plasma proteins generally cannot cross the endothelial cell membranes & cannot get through the pores between cells
lipid-soluble substances pass through the endothelial cells
Small water-soluble substances pass through the pores between cells
Exchangeable proteins are moved across by vesicular transport
What is the colloid osmotic pressure
Hydrostatic pressure caused by plasma proteins
