Pulm/Renal - Physiology - Body Fluids; Renal Hemodynamics, GFR, & Clearance; the Nephron Flashcards
A 20-year-old, unresponsive woman is brought to the ED with respiratory distress after ingesting ‘ecstasy’ and subsequently drinking large amounts of fluid.
Her lab results are shown below. Explain why she has these results.
Electrolytes:
- Na+ — 117 mmol/L*
- Cl- — 87 mmol/L*
- HCO3- — 15 mmol/L*
Serum osmolarity: 245 mOsm/kg
Urine specific gravity: 1.015
Her large intake of fluid has (due to dehydration and extreme thirst caused by ecstasy) has diluted out her electrolytes, so all are low, and her fluids are extremely dilute
In a healthy adult, what percentage of the body is typically made up by adipose?
What is the rest classified as?
20% (men: 10 - 20; women: 18 - 25);
lean body mass (80%)
How many liters of water are found in the average healthy 70 kg individual?
How much of this is intracellular? Extracellular? Plasma?
40 L;
25 L
15 L (11.5 L interstitial; 3.5 L plasma)
What is the 60-40-20 rule of thumb for fluids?
60% of body weight
40% intracellular
20% extracellular
What is the state of the water in the interstitium?
It is gel-like (combined with ground substance and other extracellular materials)
What term describes excess fluid in the interstitial space?
Edema
What proportion of lean body mass is water?
What percentage of a healthy individual is made up by lean body mass (non-adipose tissues, including water)?
73%;
80%
Body fat = Total weight - ____________________.
Lean body mass = total body water / _____.
Lean body mass;
0.73
Calculate the lean body mass and adipose fraction for the following patient.
5’4 woman
91 kg weight
40 L water
40 L / 0.73 = 54.8 L lean body mass
91 - 54.8 = 36.2 kg fat
36.2/91 = 40% adipose
Obesity can be defined by an individual’s adipose content (as a fraction of weight).
What percentage defines obesity in a man?
What percentage defines obesity in a woman?
≥ 25%
≥ 32%
What proportion of body water is intracellular?
What proportion is extracellular?
Of the extracellular, what proportion is plasma?
~2/3
~1/3
~1/4
The quantity of a substance in fluid is equal to the volume of fluid multiplied by:
The concentration of the substance
(Quantity = volume * concentration)
Evans blue dye is a substance that binds plasma proteins.
You administer 10 mg into an 80 kg patient’s bloodstream and remove a sample 10 min later. The evans blue dye concentration of the sample is 0.4 mg / 100 mL.
What is the plasma volume of the individual?
What is the blood volume of the individual?
Quantity administered = volume * concentration
10 mg = V * 0.4 mg / 100 mL
10 mg / 0.4 mg / 100 mL = V = 2500 mL
Plasma volume / fraction of plasma in the blood = blood volume
2500 mL / 0.55 = 4546 mL
What body fluid compartment volumes can be directly measured?
Which can only be indirectly measured?
Total body water,
ECF, plasma, blood volume;
ICF,
interstitial fluid
What substance can be used to measure total body water?
What substance can be used to measure ECF?
What substance can be used to measure blood volume?
What substance can be used to measure plasma volume?
D2O
Inulin
Radiolabeled iron
Radiolabeled albumin
How is the anion gap measured?
Cations - anions
(Na+ + K+) - (Cl- + HCO3-)
Calculate the anion gap for the following electrolytes.
Na+ — 117 mmol/L
Cl- — 87 mmol/L
HCO3- — 15 mmol/L
K+ — 4 mmol/L
(117 + 4) - (87 + 15) = 19
Besides electrolyte abnormalities, what might cause a change in the anion gap?
A change in organic anion concentrations (e.g. protein, ketones, etc.)
A 20-year-old, unresponsive woman is brought to the ED with respiratory distress after ingesting ‘ecstasy’ and subsequently drinking large amounts of fluid.
Her lab results are shown below. What is your diagnosis?
Electrolytes:
- Na+ — 117 mmol/L*
- Cl- — 87 mmol/L*
- HCO3- — 15 mmol/L*
Serum osmolarity: 245 mOsm/kg
Urine specific gravity: 1.015
Hyponatremia;
cerebral and pulmonary edema
(hypoosmolar syndrome)
What is the normal serum osmolality?
True/False. It is not a colligative property.
290 mOsm/kg;
false
What is a severe consequence of body hypoosmolality?
Cerebral edema (and eventual death)
Describe how each of the following will impact the ECF:
- An infusion of hypotonic fluid
- An infusion of isotonic fluid
- An infusion of hypertonic fluid
- Expands by less than the volume infused
- Expands by the volume infused
- Expands by more than the volume infused
How is the renal fraction calculated?
What is it normally?
Renal blood flow / cardiac output
20%
True/False.
The kidneys use up virtually 100% of the oxygen they receive.
False.
The kidneys actually use very little of the oxygen coming in and there is some shunting of oxygen through the arteriovenous system
True/False.
The renal arterial system is non-anastomotic, and it is easy for small segments to be infarcted.
True.
True/False.
Albumin’s size is the main reason it doesn’t leave the glomerulus through the filtration slits.
False.
Its charge is the main reason it doesn’t pass through
Protein loss in the urine will happen either because of loss of the _____________ or a widening of the ____________.
Charge barrier;
filtration slits
Renal resistance happens in which vessels?
The arteries, afferent arteriole, and efferent arteriole
The glomerular filtration rate is maintained at a high pressure to overcome what pressure that would keep fluid in the glomerulus?
The colloid osmotic pressure
(hydrostatic pressure - osmotic pressure)
What is the average GFR?
What is the average renal blood flow?
125 mL / min (180 L / day);
1200 mL / min
What are the three intrinsic mechanisms of renal blood flow control?
Autoregulation (myogenic)
Tubuloglomerular feedback (tubular pressures increase –> glomerular pressure increases in response)
Paracrine factors
What are the main extrinsic mechanisms of renal blood flow control?
Sympathetic nerves
Hormones (including ANP)
Which are the vasoconstricting hormones affecting renal blood flow?
Epinephrine
Angiotensin II
Endothelin
Which are the vasodilating hormones affecting renal blood flow?
Prostaglandins
Bradykinin
Atrial natriuretic peptide
Nitric oxide
Does angiotensin II affect glomerular filtration or systemic arteriolar constriction?
Both
In what electrolyte circumstance is an NSAID more likely to decrease GFR?
Sodium-depleted circumstances
(increased vasoconstriction effect)
Atrial natriuretic peptide causes a decrease in the release of what two other hormones?
What effect does ANP have on the vasculature?
Renin,
aldosterone;
renal vasodilation
What effect do tubuloglomerular feedback and autoregulation have on renal blood flow?
What effect do they have on GFR?
Both maintained during fluctuations in arterial pressure
What effect does the renin-angiotensin system have on renal blood flow?
What effect do they have on GFR?
Reduces both
What substance partially counteracts the effects of angiotensin II?
Prostaglandins
Via what clearance equation is GFR calculated?
Clearancex = Urine flow * Urinex / Plasmax
True/False.
In order for a substance to be useful in calculating GFR via the clearance equation, it must be:
freely filtered at the glomerulus,
not reabsorbed or secreted,
not metabolized or degraded,
easily measured.
True.
What are some endogenous substances that can be used for measuring GFR?
Inulin;
mannitol;
radiolabeled compounds
Calculate the GFR for the following patient using the results of this 24-hour urine collection:
1.6 L urine
Urine creatinine 105 mg / dL
Plasma creatinine 0.9 mg / dL
130 ml/min
((1600 mL / 24 hours / 60 min) * 105 mg / dL) / 0.9 mg / dL
The plasma concentration of what substance is a good indicator of their GFR?
What is a normal value for this substance?
Creatinine;
1 mg/dL
If the plasma creatinine level is 1, what does this indicate about the glomerular filtration rate?
If it increases to 2, what does this indicate?
If it increases to 3, what does this indicate?
If it increases to 4, what does this indicate?
Normal GFR (~120 mL/min) (i.e. 100%/1)
GFR down to 50% (~60 mL/min) (i.e. 100%/2)
GFR down to 33% (~40 mL/min) (i.e. 100%/3)
GFR down to 25% (~30 mL/min) (i.e. 100%/4)
What would a plasma creatinine concentration of 5 roughly indicate about GFR?
A GFR of 24 mL/min (normal: 120 mL/min)
(100% function / 5)
Calculate the GFR for the following patient using the results of this 24-hour urine collection:
Urine flow: 3 mL/min
Urine inulin 9.5 mg / mL
Plasma inulin 0.26 mg / mL
110 mL/min
(UF * Ux)/Px
If calculating GFR via renal plasma flow, what equation would be used?
Renal plasma flow = (Urine flow * Urinex) / (Pa(x) - Pv(x))
What is a useful substance for calculating GFR via renal plasma flow?
Why?
Para-aminohippurate;
it is fully secreted
True/False.
Measuring GFR via clearance necessitates a substance that is fully filtered.
AND
Measuring GFR via renal plasma flow necessitates a substance that is neither secreted nor reabsorbed.
False.
- Measuring GFR via renal plasma flow necessitates a substance that is fully filtered (e.g. para-aminohippurate).*
- AND*
- Measuring GFR via clearance necessitates a substance that is neither secreted nor reabsorbed (e.g. inulin).*
If a substance’s clearance is less than the GFR, what does this indicate?
There is net reabsorption
If a substance’s clearance is greater than the GFR, what does this indicate?
There is net secretion of the substance
If a substance’s clearance is less than the GFR, what does this indicate?
If a substance’s clearance is greater than the GFR, what does this indicate?
Net reabsorption;
net secretion
Where does the majority (67%) of filtered sodium and water get reabsorbed in the nephron?
Where does the next 25% get reabsorbed?
And the final 7 - 8%?
The proximal convoluted tubule;
the loop of Henle;
the DCT/collecting duct
True/False.
< 1% of filtered water and sodium actually gets excreted in the urine.
True.
Describe the relative amounts of sodium and water reabsorbed in each part of the nephron.
Which portion of the nephron is known as the ‘bulk reasborber?’
The proximal convoluted tubule
Basolateral Na+/K+ ATPases maintain a low sodium concentration in the proximal tubular cells.
What process does this facilitate and of what substances?
Apical reabsorption via sodium-linked cotransport;
glucose, amino acids, lactate, citrate, succinate, etc.
Via what mechanism is sodium maintained at a very low concentration in proximal tubule cells so that a gradient exists for sodium-linked cotransport of a variety of organic anions and other substances?
Basolateral Na+/K+ ATPases
What type of inhibition exists between solutes vying for position with the sodium-solute cotransporters in the PCT lumen?
Competitive inhibition