Researchers interested in the physiology of the kidney made the measurements shown in table 27.1. On the basis of your understanding of how the kidney works, explain why some substances are found at the same concentration in the plasma and glomerular filtrate and why albumin, a plasma protein, is not. Also explain why concentrations of urea, uric acid, potassium, and chloride are higher in the urine than in the glomerular filtrate, but concentrations of glucose and sodium are lower in the urine than in the glomerular filtrate. Create a flowchart that traces a drop of water from the time it enters the mouth until it is voided in the urine of a mammal. You will have to list structures from the digestive, circulatory, and excretory systems.
Table 27.1 Concentrations of Selected Substances (mg/100 ml fluid)
Substance Plasma Glomerular Filtrate Urine
Albumin 4,500 0 0
Glucose 100 100 0
Urea 26 26 1,820
Uric acid 4 4 53
Na 330 330 297
K 16 16 192
Cl 350 350 455