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Medical Physiology > Body Fluid Homeostasis > Flashcards

Body Fluid Homeostasis Flashcards

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USMLE® Step 1 flashcards
1
Q

What is the physiological blood glucose range for homeostasis?

A

70-99 mg/dL

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2
Q

What is the physiological range for pH in homeostasis?

A

7.35 -7.45

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3
Q

What is the physiological range for sodium concentrations to maintain homeostasis?

A

135 - 145 mEq/L

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4
Q

What is the physiologic range for Potassium to maintain homeostasis?

A

3.5 - 5.5 mM/L

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5
Q

How does the brain regulate fluid concentrations in the blood?

A
  • Magnocellular neurons of the hypothalamus receive information about ECF osmolality and blood pressure and will produce & release vasopressin (ADH) into the blood vessels of the posterior pituitary to help maintain osmolality within a narrow physiological range
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6
Q

What is the osmolality of a
100 mM glucose solution?

A.100 mOsmol/Kg
B.200 mOsmol/Kg
C.300 mOsmol/Kg
D.400 mOsmol/Kg

A

A.100 mOsmol/Kg

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7
Q

What is the osmolarity of a 100 mM sodium chloride solution?

A.100 mOsmol/L 
B.188 mOsmol/L 
C.200 mOsmol/L 
D.300 mOsmol/L 
E.400 mOsmol/L
A

C.200 mOsmol/L

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8
Q

What are the main actions of Vasopressin?

A
  • Increased Water reabsorption
  • decrease in EC fluid osmolality
  • More concentrated Urine
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9
Q

What are the main actions of the RAAS?

A
  • Vasoconstriction
  • Increased Na+ reabsorption
  • Water retention
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10
Q

Which cells of the kidney are stimulated by the SNS (EP/NP) to release renin?

A

Juxtaglomerular cells

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11
Q

What affect does the SNS have on the proximal convoluted tubule?

A

Increases Na+ reabsorption

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12
Q

What is the approximate total body water volume of a 70 kg, 25 year-old normal healthy male?

A. 22 L 
B. 32 L 
C. 42 L 
D. 52 L 
E. 62 L
A

C. 42 L

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13
Q

What is the approximate intracellular fluid volume of a 70 kg, 25 year-old normal healthy male?

A. 18 L 
B. 28 L 
C. 42 L 
D. 38 L 
E. 8 L
A

B. 28 L

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14
Q

What is the body fluid percentage of intracellular fluid volume?

A

40%

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15
Q

What percentage of body weight is water?

A

60%

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16
Q

What are the percentages of fluid weight are IF, Plasma, and adipose?

A

IF -> 16 % (10 L)

Plasma -> 4% (2.5 L)

Adipose -> 3-30%

17
Q

What is the osmolality of blood?

A

300 mOsmol/Kg

18
Q

What are the 3 main ions in plasma and interstitial fluid?

A

Na+, Cl-, and HCO3-

19
Q

What are the 3 most abundant ions in intracellular fluid?

A

K+, Phosphates, and Proteins

20
Q

How is osmolality estimated?

A

2* [Na+] + [glucose] + [Urea] (molecules/L)

*Clinical labs often give glucose and Urea in mg/dL which you must convert to molecules/ L

21
Q

Which 2 of the following are true statements? [select all that apply]
A. Total body water as a % of body weight
increases with age.
B. The extracellular fluid volume is greater
than the intracellular fluid volume.
C. The extracellular fluid osmolality is
equal to the intracellular fluid osmolality.
D. Plasma osmolality is equal to the plasma
tonicity.
E. [Na+] is greater in extracellular fluid than
intracellular fluid.

A

C. The extracellular fluid osmolality is
equal to the intracellular fluid osmolality.

E. [Na+] is greater in extracellular fluid than
intracellular fluid.

22
Q

Why is Urea not included int he toxicity calculation?

A
  • Urea is freely permeable
  • A solute does not create a lasting osmotic
    effect if it is freely permeable to the
    membrane and will equilibrate across the
    membrane
23
Q

How is plasma tonicity calculated?

A

Tonicity = 2 * [Na+] + [glucose] (molecules/L)

24
Q

Which type of solution will cause cells to crenate?

A

Hypertonic

25
Q

What is the osmality of a Na+ isotonic solution?

A

154 mmol/Kg

26
Q

What is the osmolality of an isotonic NaCl solution?

A

154 + 154 = 308 mOsm/ Kg

27
Q

Which of the following would you expect from the IV infusion of 1 L isotonic saline into a patient? [disregard urine output] [select all that apply]

A. Total body water increases ~ 1 L.
B. Extracellular fluid (ECF) volume increases ~ 500 mL and the intracellular fluid (ICF)
volume increases ~ 500 mL.
C. ECF volume increases ~ 333 mL and the ICF volume increases ~ 666 mL.
D. ECF volume increases ~ 666 mL and the ICF volume increases ~ 333 mL.
E. ECF volume increases ~ 1 L.

A

A. Total body water increases ~ 1 L.

E. ECF volume increases ~ 1 L.

28
Q

What is RVD and what are it’s long term effect?

A
  • Activated by cell swelling caused by hypotonic ECF
  • Typically caused by hyponatremia
  • Causes activation of regulatory mechanisms to compensate resulting in net movement of K+ and Cl- out of cell.
  • End result can be osmotic demyelination syndrome or other harmful CNS effects
29
Q

What is RVI, it’s causes, and it’s long term effects?

A
  • Activaetd by cell shrinkage due to hypertonic ECF
  • Caused by hypernatremia, hyperglycemia, etc.
  • Acute response: Increase Intracellular K+/Cl-, Na/H exchanger causes alkalinizing of cytoplasm, activation if Cl-/HCO3- transporter
  • Chronic: generation of Diogenes osmoles; cells produce taurine, glycine, glutamine, sorbitol. And inositol
30
Q

What is the importance of correction speed for osmotic imbalances?

A

Correction of disorders of Na+ and water balance should be done slowly to avoid serious neurological complications

Can cause cerebral edema, seizures, neurological damage, CPM, and the zombie apacolypse

31
Q

What is Bulk Flow?

A

hydrostatic pressure differences

moving molecules in the same direction much faster than can be accounted for by diffusion

32
Q

What is ultrafiltration?

A

separation by size of solutes in a

solution achieved by forcing the solution through a filter

33
Q

What is Oncotic pressure?

A

Oncotic pressure is the osmotic
pressure generated by large
molecules in solution, and is an important force
keeping fluid inside blood vessels

34
Q

How is CFR calculated?

A

CFR = Kf [(Pc-Pisf) - σ(πc - πisf)]

Kf= Ultrafiltration coefficient (product of permeability and surface area)

PC = Hydrostatic pressure in capillary

Pisf= Hydrostatic pressure in interstitial fluid

σ= Reflection coefficient for protein

πC= Oncotic pressure in capillary (primarily plasma proteins)

πisf = Oncotic pressure in interstitial fluid

35
Q

What are the forces moving fluid at the arterial end of a capillary?

  • Some of these aren’t in the lecture, but were gathered from outside sources to be more accurate
A

Capillary Pressure: 30 mmHg

Negative interstitial free fluid pressure: 3 mmHg

Interstitial fluid colloid osmotic pressure: 8 mmHg

Plasma Colloid osmotic pressure: - 28 mmHg

NET: 13 mmHg

36
Q

Which of the following would you expect from the IV infusion of 1 L 0.45% NaCl (145 mOsm/kg H2O) into a patient? [disregard urine output]

A. ECF volume increases ~ 500 mL and ICF
volume increases ~ 500 mL.
B. ECF volume increases ~ 333 mL and ICF
volume increases ~ 666 mL.
C. ECF volume increases ~ 666 mL and ICF
volume increases ~ 333 mL.
D. ECF volume increases ~ 1000 mL and ICF
0% volume increases ~ 0 mL.
E. ECF osmolality increased
A

C. ECF volume increases ~ 666 mL and ICF

volume increases ~ 333 mL.

37
Q

Which of the following would you expect from the IV infusion of 1 L 5% dextrose in water into a patient? [disregard urine output]

A. ECF volume increases ~ 500 mL and ICF
volume increases ~ 500 mL. 
B. ECF volume increases ~ 333 mL and ICF
volume increases ~ 666 mL. 
C. ECF volume increases ~ 1000 mL and ICF
volume increases ~ 0 mL.
D. ECF volume increases ~ 666 mL and ICF
volume increases ~ 333 mL. 
E. ECF osmolality has increased
A

B. ECF volume increases ~ 333 mL and ICF

volume increases ~ 666 mL.

38
Q

What is specific gravity? When can it be high?

A
  • Specific gravity is defined as the weight of a
    volume of solution divided by the weight of an
    equal volume of distilled water
  • Urine specific gravity can be high (1.040 to
    1.050) in patients who have received an injection
    of radiocontrast dye even though the urine
    osmolality is similar to that of plasma
  • Normal human plasma has a specific gravity in
    the range of 1.008 to 1.010

Medical Physiology (43 decks)

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