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STEP Physiology > Homeostasis of Fluids > Flashcards

Homeostasis of Fluids Flashcards

1
Q

How much of normal body weight is water?

A

60% (42 L)- total body water is less in women than men, and decreases with age

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2
Q

Most of the body water is in tissue. Which tissues carry the most?Second %= percent of the tissue that is water

A

muscle- 43% (76%)skeleton- 16% (22% )adipose- 10% (75%)other- 6% (10%)

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3
Q

What is the relationship between % total body water (y) and fat content (x)?

A

inversely proportional- as the fat content increases, % total body water decreases linearly

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4
Q

What are the main sources of water intake?

A

-drink-water from food-oxidative metabolism (300ml/day)

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5
Q

What are the main sources of water output?

A

-urine-insensible water (perspiration and sweat)-feces

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6
Q

How much water is lost daily through insensible water?

A

perspiration (skin and lung)- 700 ml/day (up to 5L/day burn)sweat- 100 ml/day (up to 1-2L day exercise)

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7
Q

What is the minimum urinary output?

A

0.5L/day- this is the minimum requirement to excrete the metabolic waste products produced by our body daily

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8
Q

What important hormone is produced in the kidneys?

A

EPO

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9
Q

What other hormones are produced/processed in the kidneys?

A

-conversion of 25-hydroxyvitamin D is converted to 1,25-dihydrovitamin D3 -renin production-gluconeogenesis during fasting primarily for the brain

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10
Q

Intracellular fluid represents what percentage of our body wgt? Plasma? Interstitial fluid?

A

-25L (40% of body weight)-3L plasma -12L

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11
Q

Notes on composition of blood.

A

-8% of BW, 5L (ECF + ICF)-60% plasma and 40% RBC (hematocrit)

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12
Q

What separates plasma from interstitial fluid?

A

capillary walls (very permeable so their contents are very similar)

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13
Q

What does plasma have higher protein content and interstitial fluid have very low protein content?

A

capillary walls are impermeable to large proteins such as albumin and cells

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14
Q

What are the main contents of plasma and interstitial fluid?

A

Na+ is the major cation (very little K+ present) and Cl- is the major anion with some HCO3- present (and Protein in plasma)

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15
Q

Why is Na+ a little (2%) higher in plasma compared to interstitial fluid?

A

Because proteins which are negatively charged bind them to retain them in plasma while Cl-/HCO3- is propelled from the plasma and thus has a slightly higher content in interstitial fluid

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16
Q

What separates extracellular fluid from intracellular fluid?

A

impermeable cell membranes

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17
Q

What are the main contents of intracellular fluid?

A

Main cation is K+ with very little Na+ and the main anions are phosphates, Pr-, and some HCO3- with very little Cl- is present

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18
Q

Ratio of components of intracellular vs. extracellular fluids (mM).

A

Na+- 14:140K+- 140:4Ca2+- 0:1.3HCO3- 10:26Protein: 4:1 Mg2+ 20: 0.75PO4 11:2

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19
Q

How to measure volume of body fluid compartments.

A

volume= quantity of dye injected/concentration

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20
Q

What are the criteria for probe selection for body fluid measurements?

A

-non toxic -neither synthesized nor metabolized-disperses evenly and only in the compartment of interest-does not influence compartment volume

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21
Q

What probe is used to measure PLASMA volume?

A

131I-albumin, Evans blue dye (binds to plasma proteins well)Why is this a good probe?

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22
Q

Describe the process of determining plasma volume using a probe?

A

-IV injection of small, known amount-withdraw blood and prepare plasma-measure concentration of probe in plasma (Q/V)PV= Q/Q/V

23
Q

How can you calculate blood volume from PV?

A

BV= PV/(1-hematocrit)

24
Q

What probe is used to measure total extracellular volume?

A

Inulin, thiosulfate, Na+ (preferably radioactive-think why)

25
Q

How can you measure ISF from ECF?

A

ECF-PV= ISF

26
Q

How can you correct from probe lost in urine?

A

Inulin will be lost in urine in small amounts Eg. 1g of inulin was injected into a 70Kg individual. Sixty minutes later 100mg had been excreted in urine and the plasma concentration was 0.06mg/ml (60mg/L)normal: ECF= 1000 mg/ 0.06 mg/ml= 16.66L**correction: ECF= 1000-100mg/ 0.06 mg/ml= 15L

27
Q

What probe is used to measure total body water?

A

2H20, 3H20, antipyrene (lipid soluble)then use same process

28
Q

How can you measure ICF?

A

TBW- ECF

29
Q

What forces given movement of fluid between plasma and ISF?

A

-starling forces (hydrostatic and oncotic pressure)-not plasma osmolarity because the capillary wall is permeable

30
Q

What forces given movement of fluid between ECF and ICF?

A

osmosis mediated (cell membrane is impermeable to sodium and potassium and other solutes, but is permeable to urea, water, and glycerol to some degree)only changes in components that are impermeable generate osmotic pressure

31
Q

Note on osmolarity vs. molarity

A

1 mole glucose in L solution= 1 Osmole glucose in L1 mole NaCl in L solution= 2 Osmole salt in L1 mole Na2SO4 in L solution- 3 Osmole salt in L

32
Q

Note on osmolarity vs. osmolality

A

1 Osmole glucose per kg of water= 1 Osmolal glucose1 Osmole glucose per L of solution= 1 Osmolar glucose

33
Q

What is osmotic pressure?

A

the amount of pressure required to prevent osmosis

34
Q

T or F. Osmotic pressure depends on the number of molecules present, not the size

A

T. One particle of albumin (70K daltons) and one particle of glucose (180 daltons) have the same osmotic pressure

35
Q

T or F. Osmolarity in all fluid compartment types is the same

A

T.

36
Q

What happens if you place an RBC in a hypotonic solution?

A

RBC swelling

37
Q

T or F. Infants can become dehydrated easily

A

T.

38
Q

What happens during dehydration?

A

loss of water from ECF initially, resulting in increased osmolarity of the ECF which draws water out of the ICF. Thus, volume is decreased in all compartments but osmolarity is increased in all compartments

39
Q

How can plasma osmolarity be estimated?

A

[plasma Na+ x 2] + glucose + ureaNormal- 286 mOsmDehydrated- 320 mOsm

40
Q

How can you estimate the fluid infusion volume needed for treatment?

A

-Know or predict patients original BW prior to dehydration and calculate TBW and therefore total mOsmoles of solutes-Calculate the patients TBW using new osmolarity and normal total mOsmoles-Calculate the difference in TBW to estimate fluid volume necessary to achieve concentration of 280mOsm Correct for excreted fluids (not infused all at one- should be titrated)

41
Q

How is osmolality of plasma measured in the clinic?

A

Osmol-meter

42
Q

What is osmolality gap? What is considered abnormal?

A

The difference between measured osmolality (MO) using an Osmol-meter and calculated osmolality (CO) using the plasma equation is known as the osmolar gap (OG). A large positive (>15) osmolar gap can help identify the presence in plasma of substances such as ethanol, methanol, isopropanol, ethylene glycol, propylene glycol (found as a diluent for some intravenous medications such as lorazepam), and acetone. The specific agent(s) responsible can be identified by the gas chromatographic assays for ethanol, methanol, isopropanol, acetone, propylene glycol, and ethylene glycol.Approximately 97% of osmolar gaps in patients are between -10 and +10.

43
Q

What changes occur following infusion of isotonic salt solution?

A

-increase in ECF volume without change in osmolarity-NO CHANGE in volume or osmolarity of ICF

44
Q

What changes occur following intake of a lot of water?

A

-increase in ECF volume and decrease ECF osmolarity-Flux of water into ICF-Increase in volume in ICF and decreased osmolarity as well

45
Q

What changes occur following intake of a lot of salt?

A

Increase in ECF osmolarity, draws water from ICF leading to an increase in volume of ECF and an increase in osmolarity of the ICF along with decreased volume levels

46
Q

What things cause a loss of NaCl?

A

drinking water after profuse sweating (hypoatriemia)

47
Q

What changes occur following loss of NaCl?

A

Decrease in ECF osmolarity causes flux of water in ICF, decreasing osmolarity in all compartments and an increase of volume in ICF

48
Q

What changes occur following infusion of isotonic urea?

A

urea is freely and rapidly permeable through all cell membranes leading to increased volume in all compartments without changing osmolarity

49
Q

What is the best thing to give after a patient loses only large amounts of water?

A

hypotonic saline with glucose or isotonic glucose isotonic saline will introduce more salt into the body and will take longer equilibrate

50
Q

What is the best thing to give after a patient loses large amounts of water and salt (vomit or diarrhea)?

A

isotonic saline

51
Q

What are some non-toxic causes of elevated osmolality gap?

A

Non-toxic examples of an elevated osmolar gap include hyperlipidemia (less plasma water), chronic renal failure, and myeloma (increased plasma proteins).

52
Q

Osmolality gap example

A

A sixty-seven year old white male was found pulseless and resuscitated; then brought to the emergency room. He had been reported to be drinking in a bar all afternoon, and had then fallen from a ten foot balcony to snow covered ground. He arrived in the emergency room with a fractured occiput and was unresponsive.Admission Data:NA=143 mEq/l BUN=4 mg/dLpH=7.30CL=105 mEq/l GLU=104 mg/dLMO=356 mOsm/kgHCO3=19 mEq/l KETO=Neg AG = NA - CL- HCO3= 143 - 105- 19 = 19CO = 2 x NA + 1.15 *GLU/18 + BUN/2.8 = 286+ 1.15 104/18 + 4/32.8 = 2940G = MO - CO= 356 - 294 =62If we assume OG is due to ethanol, then ethanol concentration (see table) would be approximately 623.8 = 236 mg/dL

53
Q

What is methanol found in?

A

anti-freeze (its contribution to osmolality gap is OG*3.2)

STEP Physiology (68 decks)

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