Body Fluid Homeostasis SS - Rao

Question 1

Total body water (TBW) is what percent of a person’s weight?

Answer 1

60%

Question 2

What are the major sources of fluid intake in the body?

Answer 2

Drinking water, followed by water in food and oxidative metabolic production of water

Question 3

What are the major sources of fluid output?

Answer 3

Urine, ‘insensible’ water from skin/lung/sweat, and a little in feces

Insensible water loss is high in burn victims and fecal loss high in diarrhea

Question 4

What is the absolute minimum daily urine output?

Answer 4

500 mL

Question 5

What is the volume of ICF in an average person?

Answer 5

25L

Question 6

What is the volume of ECF in an average person?

Answer 6

15L

Question 7

What is the volume of fluid in interstitial space?

Answer 7

12L

Question 8

What is the volume in a person’s plasma and total blood?

Answer 8

3L in plasma; 5L total blood volume; blood is 60% plasma and 40% hematocrit

Question 9

What is the major cation and anion in the interstitium/plasma?

Answer 9

Na, Cl

Question 10

What is the major anion and cation in the intracellular fluid?

Answer 10

K+, Protein-

Question 11

What is the Gibbs-Donnan effect in relation to fluid compartments?

Answer 11

Explains the behavior of charged particles near a semi-permeable membrane; Na+ is greater in plasma by 2% and Cl- lower by 2% because the capillaries are more permeable than the cellular membranes, allowing negatively charged proteins to retain the Na+ through electrical interactions

Question 12

Where is bicarbonate in highest concentration

Answer 12

Plasma and interstitium

Question 13

Where is phosphate in highest concentration

Answer 13

intracellular

Question 14

Where is magnesium in highest concentration/

Answer 14

intracellular

Question 15

What are the criteria for probes that measure body fluid?

Answer 15

Non-toxic at used concentration
Neither synthesized or metabolized
Disperses evenly
Disperses only in compartment of interest
Doesn't influence volume itself

Question 16

What probes are used to measure plasma volume?

Answer 16

Iodinated albumin, Evans blue dye, both which bind avidly to plasma proteins

Question 17

What is the formula to measure volume of plasma?

Answer 17

Blood volume = plasma volume / (1-HCT)

Question 18

What is the formula for measuring concentration of a something in a fluid compartment?

Answer 18

Compartment volume = Q / (Q/V), where Q/V is the concentration of the probe and Q is the amount of probe injected

Applies to intra- and extracellular compartments

Question 19

What are the probes used to measure extracellular fluid volume?

Answer 19

Inulin, thiosulfate, and Na+

Question 20

ISF=

Answer 20

ECF-PV

Question 21

What are the probes used to measure total body water?

Answer 21

Radiolabelled water; antipyrene

Question 22

ICF=

Answer 22

TBW-ECF

Question 23

What forces determine the fluid movement between plasma and ISF?

Answer 23

Starling forces - hydrostatic and oncotic pressure

(Capillaries are more permeable than cell membranes)

NOT plasma osmolarity

Question 24

What forces determine the fluid movement between the intracellular and extracellular fluid?

Answer 24

Osmosis, mainly due to differences in sodium concentration causing water rearrangment

Question 25

How are osmoles different than moles?

Answer 25

Moles is amount of molecules; osmoles is amount of particles in solution

Question 26

Does osmotic pressure depend on molecule size?

Answer 26

One particle of albumin and one particle of glucose have the same osmotic pressure

Question 27

How do the osmolarities of different fluid compartments compare?

Answer 27

They are all the same, 295 mOsm/L, because water is freely permeable through barriers

Question 28

What happens to RBCs in hypotonic Na solution?

Answer 28

Swelling and lysis

Question 29

What happens to RBCs in hypertonic Na solution?

Answer 29

Shrink

Question 30

What happens to RBCs in the presence of a low Na and high urea environment?

Answer 30

Swelling, because urea is freely permeable across membranes

Question 31

Formula for estimating plasma osmolarity?

Answer 31

Plasma osmolarity = 2[Na+] + glucose + urea

Question 32

What are the steps for estimating how much fluid to give a patient?

Answer 32

Calculate ECF and ICF before depletion; calculate total mOsm in ECF and ICF now, calculate volume needed to achieve 280 mOsm, then calculate amount of fluid needed to add

Question 33

Giving isotonic saline to a normally hydrated person will change which compartments?

Answer 33

ECF only, maintain same osmolarity while increasing volume

Question 34

Gaining pure water through drinking or giving 5% glucose H20 will change which compartments?

Answer 34

Increase volume of all compartments; decrease osmolarity of all compartments

Question 35

What does excess gain of salt do to copartments?

Answer 35

Increase ECF osmolarity, draws water from ICF, increase ECF volume, decrease ICF volume, osmolarity of all compartments increased

Question 36

What does loss of NaCl do to compartments?

Answer 36

Decreases ECF osmolarity, flux of water into ICF, decrease volume of ECF, increase vol of ICF, osmolarity decreasd in all compartments This is why you should drink electrolyte-rich drinks like Gatorade after excessive sweating instead of pure water

Question 37

What does infusion of isotonic urea do to compartments?

Answer 37

Increases volume of all compartments (water retained everywhere) without changing osmolarity of anything