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12 Cards in this Set
- Front
- Back
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Substance T is present in the urine. Does this prove that it is filterable at the glomerulus?
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No. It is possible that it maybe be secreted by the tubules.
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Substance V is not normally present in the urine. Does this prove that it is neither filtered nor secreted?
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No. It may be filtered an/or secreted but the substance V entering the lumen via these routes may be completely reabsorbed.
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The oncentration of glucose in plasma is 100 mg/100 mL and the GFR is 125 ml/min. How much glucose is filtered per minute?
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125 mg/min.
125 x 100 = |
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A person is excreting abnormally large amounts of a particular amino acid. Just from the theoretical description of Tm-limited reabsorptive mechanisms in the text, list several possible causes.
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The plasma concentration might be so high that the Tm for the amino acid is exceeded, so all the filtered amino acid is not reabsorbed. A second possibility is that some other amino acid is present in the plasma in high concentration and is competing for reabsorption.
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The concentration of urea in urine is always much higher than the concentration in plasma. Does this mean that urea is secreted?
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No. urea is filtered and then partially reabsorbed. The reason its concentration in the tubule is higher than in the plasma is that relatively more water is reabsorbed than urea. Therefore, the urea in the tubule becomes concentrated. Despite the fact that urea concentration in the urine is greater than in the plasma, the amount excreted is less than the filtered load.
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If a person takes a drug that blocks the reabsoption of sodium, what will happen to the reabsorption of water, urea, chloride, glucose, and amino acids and to the secretion of hydrogen ions?
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They should all be decreased. The transport of all these substances is coupled, in one way or another, to that of sodium.
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Compare the changes in GFR and renin secretion occuring in response to a moderate hemorrhage in two individuals -- one taking a drug that block the sympathetic nerves to the kidneys and the other not taking such a drug.
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GFR would not go down as much and renin secretion would no go up as much as in a person not receiving the drug. The sympathetic nerves are a major pathway for both responses during hemorrhage.
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If a person is taking a drug that completely inhibits angiotensin-converting enzyme, what will happen to aldosterone secretion when the person goes on a low-sodium diet?
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There would be little if any increase in aldosterone secretion. The major stimulus for increased aldosterone secretion is angiotensin II, but this substance is formed from angiotensin I by the action of angiotensin-converting enzyme, and so blockade of this enzyme would block the pathway.
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In the steady state, what is the amount of sodium chloride excreted daily in the urine of a normal person ingesting 12g of sodium chloride per day? Explain.
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11 g/day. Urinary excretion in the steady state must be less than ingested sodium chloride by an amount equal to that lost in sweat and feces. This is normally quite small, less thatn 1 g/day, so that urine excretion in this case equals 11 g/day.
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A young woman who has suffered a head injury seems to have recovered but is thirsty all the time. What do you think might be the cause?
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If the hypothalamus had been damaged, there might be inadequate secretion of ADH. This would cause loss of a large volume of urine, which would tend to dehydrate the person and make her thirsty. Of course, the area of the brain involved in thirst might have suffered damage.
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A patient has a tumor in the adrenal cortex that coninuously secretes large amounts of aldosterone. What is this condition called and what effects does this have on the total amount of sodium and potassium in her body?
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Ths is primary aldosteronism or Conn's syndrome. Because aldosterone stimulates sodium reabsoption and potassium secretion, there will be total body retention of sodium and loss of potassium. Interestingly, the person in this siuation actually retains very little sodium because urinary sodium excretion returns to normal after a few days despite the coninued presence of the high aldosterone. One explanation for this is that GFR and atrial natriuretic factor both increase as a result of the initial sodium retntion.
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A person is taking a drug that inhibits the tubular secretion of hydrogen ions. What effect does this drug have on the body's balance of sodium, water, and hydrogen ions?
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Sodium and water balance would become negative because of increased excretion of these substances in the urine. The person would also develop a decreased plasma bicarbonate concentration and metabolic acidosis because of increased bicarbonate excretion. The effects on acid-base status are explained by the fact that hydrogen ion secretion-blocked by the drug-is needed both for bicarbonate reabsorption and for the excretion of hydrogen ion (contribution of new bicarbonate to the blood). The increased sodium excretion reflects the fact that much sodium reabsorption by the proximal tubule is achieved by Na/H countertransport. By blocking hydroen ion secretion, therefore, the drug also partially block sodium reabsorption. The increased water excretion occurs because the failure to reabsorb sodium and bicarbonate decreases water reabsroption resulting in an osmotic diuresis.
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