The graph to the right shows how the excretion rate and filtered load of a freel
ID: 72147 • Letter: T
Question
The graph to the right shows how the excretion rate and
filtered load of a freely-filtered drug changes as the plasma
concentration of the drug increases. The drug is not
metabolized by the kidney. Use this information to answer
the following questions.
What is the GFR?
What is the Tm of the drug?
Which of the following terms best describes how the renal
tubules handle this drug (circle one answer)
Net Secretion Net Reabsorption No Net Transport
Excretion Rate & Filtered Load (ug/min)Explanation / Answer
1. Ans. Glomerular filtration rate (GFR) is a test used to check how well the kidneys are working. Specifically, it estimates how much blood passes through the glomeruli each minute. Glomeruli are the tiny filters in the kidneys that filter waste from the blood
GFR is dependent on renal blood flow, resistance to flow, and glomerular permeability. Normal GFR is about 100ml/min for women and 120 ml/min for men, but increases during pregnancy. It depends on body size, age diet, and physiologic state.Measuring GFR is a key indicator of kidney function.
2. Ans Crystalline material has a characteristic melting point. Tm (melting point) is a thermodynamic property characteristic for each material and may in some conditions changes in a slight manner (non significant) resulting from the purity state.
3. Ans. Factors that influence renal excretion include plasma drug concentration, plasma protein binding and renal function.
Drugs are transferred from the plasma into the urine by:
Glomerular filtration: Unbound drug molecules of less than 20'000 Da are filtered through the glomerulus with the primary urine.
Active tubular secretion: This mechanism is predominant in the proximal tubule. Several transportors are responsible for the tubular secretion of drugs: the P-glycoproteins (PGps), the multidrug resistance-associated proteins (MRPs), the organic anion transportors (OATs), the oragnic cation transportors (OCTs), etc. These transporters are not highly specific and may become saturated at high drug concentrations.
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