Fluid and Electrolytes Flashcards
Describe the major fluid compartments, including their ionic composition and relative size.
Total body water (60% of body weight BW) = ICF (40% of BW) + ECF (20% of BW)
ECF = ISF (80%) + Plasma (20%)
=> ICF, ISF, Plasma
Blood volume is 7% of body weight.
Plasma volume = ______________
plasma volume = blood volume * (1-Hct)
Distribution of water in the body by weight and by volume
TBW=60%of BW
of BW => WICF:ECF = 40:20
of ECF => ISF:plasma = 80:20
Blood volume about 7% of body weight
volume of blood=> plasma:bloodcells = 60:40
Percentage of blood volume occupied by red blood cells is called hematocrit (40% or 0.4)
Ionic composition of ICF and ECF
ICF: K+, Mg2+,
proteins, organic phosphates (ATP and ADP), organic anions
ECF: Na+, Ca2+
Cl-
Bicarbonates ion (HCO3-)
Cellular proteins are usually _________ due to its amino acid composition
negatively charged
Plasma and ISF have similar composition = high Na Cl Ca and HCO3-.
The interstitial fluid is an ultrafiltrate of plasma.
Both have the same composition except for plasma proteins and blood cells.
Only main difference is that
However, plasma has plasma proteins whose negative charge retain other small cations such as sodium and potassium ions, resulting in the plasma having more cations than the interstitial fluid.
On the other hand, plasma proteins repel small anions such as chloride and bicarbonate ions, resulting in the plasma having lesser anions than the interstitial fluid.
Describe the external and internal balance fluid and electrolytes and the consequences of imbalance.
FLUID BALANCE
Input into ECF–>ICF:
Food, water, (metabolism)
Output from ECF
Two types of fluid loss are sensible and insensible.
sensible - can be perceived. sweat 100 ml per day. feces 100 ml per day. urination 1.5L per day.
insensible - which cannot be perceived. skin 300-400 ml per day. lung 300-400 ml per day.
Fluid balance
Fluid intake = fluid loss at steady state important in preventing drastic changes in body fluid volume. Fluid balance balance of water and the ionic composition in ECF and ICF.
Importance of fluid balance
- Blood: fluid imbalance affects blood volume which then affects blood pressure.
- Interstitium: fluid imbalance can be edematogenic.
- Cells: Fluid imbalance compromises the environment for cells to function optimally – Swelling and shrinking
Fluid shift
𝑷𝒍𝒂𝒔𝒎𝒂 𝒐𝒔𝒎𝒐𝒍𝒂𝒓𝒊𝒕𝒚 = (𝟐×𝑷𝒍𝒂𝒔𝒎𝒂 𝑵𝒂)+𝑮𝒍𝒖𝒄𝒐𝒔𝒆+𝑩𝒍𝒐𝒐𝒅 𝒖𝒓𝒆𝒂 𝒏𝒊𝒕𝒓𝒐𝒈𝒆𝒏
𝑷𝒍𝒂𝒔𝒎𝒂 𝒐𝒔𝒎𝒐𝒍𝒂𝒓𝒊𝒕𝒚= 𝟐𝟗𝟑.𝟔 𝒎𝑶𝒔𝒎/𝑳
𝑰𝑪𝑭 𝒐𝒔𝒎𝒐𝒍𝒂𝒓𝒊𝒕𝒚 =𝟐𝟖𝟎 𝒎𝑶𝒔𝒎/𝑳
𝑬𝑪𝑭 𝒐𝒔𝒎𝒐𝒍𝒂𝒓𝒊𝒕𝒚=𝟐𝟖𝟏 𝒎𝑶𝒔𝒎/𝑳
Note: At steady state, both compartments are assumed to have the same osmolarity.
Fluid shift
Fluid shift is the balancing of water by osmosis
eg. if you increase salt intake = ECF change, lots of salt meaning osmolarity increase. H2O moves from inside to outside. so osmolarity inside increase, volume decrease.
Explain the fluid shift in saline injection
ICF
osmolarity: no change
volume: no change
ECF
osmolarity: no change
volume: increase
Explain the fluid shift in diarrhea
ICF
osmolarity: decrease
volume: no change
ECF
osmolarity: no change
volume: decrease
Explain the fluid shift in sweating
ICF
osmolarity: increase
volume: decrease
ECF
osmolarity: increase
volume: decrease
fluid shift affected by changes in volume and in osmolarity.
can be of 6 types:
Hyperosmotic volume expansion Hyperosmotic volume contraction Isosmotic volume expansion Isosmotic volume contraction Hyposmotic volume expansion Hyposmotic volume contraction
Note1: Volume expansion and contraction refers to the ECF volume only!! The change in osmolarity also refers to ECF osmolarity only!!
Note2
: The purpose of fluid shift is to balance the final osmolarity in both compartments. So, always remember that the final osmolarity in both compartments will be the SAME, just that it could be lower, the same or higher than the starting osmolarity.
Remember: since osmolarity (which is concentration) is the target to be regulated, and that solutes are assumed to be not moving, water shift becomes very important in determining the eventual osmolarity and volume!!
and
ECF Na+ concentration is NOT synonymous with sodium balance!!! Therefore, the physiological systems that regulate these two parameters are different!!!
Describe the relative importance and role of the kidneys in fluid and electrolyte balance.
1) Hypothalamic osmosensing:
1. water balance
2. osmoregulation
3. [Na+]
by release of ADH from ppg
2) Na balance –> RAAS
- *Osmoregulation is the regulation of ECF osmolarity.
- *Disturbance to the water balance will affect the other two components and hypothalamic osmosensing will be involved in stimulating the release of ADH from the posterior pituitary gland.
- *Disturbance to the sodium balance involves the renin-angiotensin-aldosterone (RAAS) family of hormones.
