Fluid and Electrolytes

Question 1

Describe the major fluid compartments, including their ionic composition and relative size.

Answer 1

Total body water (60% of body weight BW) = ICF (40% of BW) + ECF (20% of BW)
ECF = ISF (80%) + Plasma (20%)

=> ICF, ISF, Plasma

Question 2

Blood volume is 7% of body weight.

Plasma volume = ______________

Answer 2

plasma volume = blood volume * (1-Hct)

Question 3

Distribution of water in the body by weight and by volume

Answer 3

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)

Question 4

Ionic composition of ICF and ECF

Answer 4

ICF: K+, Mg2+,
proteins, organic phosphates (ATP and ADP), organic anions

ECF: Na+, Ca2+
Cl-
Bicarbonates ion (HCO3-)

Question 5

Cellular proteins are usually _________ due to its amino acid composition

Answer 5

negatively charged

Question 6

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

Answer 6

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.

Question 7

Describe the external and internal balance fluid and electrolytes and the consequences of imbalance.

Answer 7

FLUID BALANCE
Input into ECF–>ICF:
Food, water, (metabolism)

Output from ECF

Question 8

Two types of fluid loss are sensible and insensible.

Answer 8

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.

Question 9

Fluid balance

Answer 9

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.

Question 10

Importance of fluid balance

Answer 10

1. Blood: fluid imbalance affects blood volume which then affects blood pressure.
2. Interstitium: fluid imbalance can be edematogenic.
3. Cells: Fluid imbalance compromises the environment for cells to function optimally – Swelling and shrinking

Question 11

Fluid shift

Answer 11

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.

Question 12

Fluid shift

Answer 12

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.

Question 13

Explain the fluid shift in saline injection

Answer 13

ICF

osmolarity: no change
volume: no change

ECF

osmolarity: no change
volume: increase

Question 14

Explain the fluid shift in diarrhea

Answer 14

ICF

osmolarity: decrease
volume: no change

ECF

osmolarity: no change
volume: decrease

Question 15

Explain the fluid shift in sweating

Answer 15

ICF

osmolarity: increase
volume: decrease

ECF

osmolarity: increase
volume: decrease

Question 16

fluid shift affected by changes in volume and in osmolarity.

can be of 6 types:

Answer 16

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!!

Question 17

Note2

Answer 17

: 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.

Question 18

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!!

Answer 18

and

ECF Na+ concentration is NOT synonymous with sodium balance!!! Therefore, the physiological systems that regulate these two parameters are different!!!

Question 19

Describe the relative importance and role of the kidneys in fluid and electrolyte balance.

Answer 19

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.