Renal Toxicology
The kidney is responsible for maintaining fluid balance. It does this by filtering water and salts from the blood, then reabsorbing about 99% of them. While this seems inefficient, it allows very fine control of the body's fluid. There are about 2.5 million nephrons in the human kidneys. They are all basically the same, so it is customary to just look at one. The main physiology is diagrammed below.
The kidneys receive an enormous blood flow, about 25% of cardiac output. From that renal blood flow, about 1/2.5 millionth arrives via small arteries at the glomerulus at the beginning of each nephron. There 20% to 40% of the blood is "filtered," meaning it leaves the blood vessel (capillary) and enters the nephron. The larger molecules remain in the blood, for example, only 0.005% of albumin-sized molecules will enter the nephron. Molecules with a molecular weight of less than 5000 Dalton will be 100% filtered. In the part of the nephron closest to the glomerulus, ingeniously called the proximal tubule, sodium is actively pumped back into the blood and water follows, so the 70% of the salts and water go back to the blood in the proximal tubules. Near the start of the nephron, also in the proximal tubule, are cells that pump organic anions, cations, acids and bases from the blood directly into the tubule. The beginning and end of the nephron is in the outer layer of the kidney, called the cortex. The middle portion, called the loop of Henle descends into the middle of the kidney, called the medulla. The kidney get saltier towards medulla, so the loop of Henle travels through a very salty environment, but even here, as the loop descends into the medulla, it pumps salt out of the tubular fluid. Finally as the loop rises out of the medulla back to the cortex, the loop of Henle gets thick and impermeable to water. Water would flow out of the loop by osmotic pressure, since the medulla is much saltier than the tubular fluid. This impermeable region of the loop, however, has cells that can permit water to flow, they are controlled by a hormone, ADH (anti diuretic hormone), which is secreted by nerves from the hypothalamus that terminate in the pituitary. So the final adjustment of water balance happens in the loop of Henle and is controlled by ADH. The nephron then terminates in large vessels that handle more fluid. At this point the tubular fluid is called urine.
So with that general introducing to the physiology of the kidney, some mechanism of toxicity are apparent. Since most xenobiotics of interest are less than 5000 daltons, they will all be filtered at the glomerulus. As they proceed down the tubule and water is pumped out, the xenobiotics are concentrated. Hence a substance that may be at a relatively low concentration in the blood will reach a higher concentration in the kidneys. If the xenobioitic is one that will be actively secreted into the tubule, it will first be concentrated in the cells of the nephron from which they will be pumped. These cells will be exposed to a higher concentration than other cells in the body. Finally, when the xenobiotic is a high concentration in the tubular fluid, there is a concentration gradient that may lead to their being reabsorbed in tubules. This will permit those cells to experience a higher concentration than other tissues. Not obvious is that the kidney cells have many xenobiotic metabolizing enzymes, especially P450's, second only to the liver. If a chemical is activated by the P450, it will happen in the kidney as well as the liver.
Your text mentions several tests of kidney function that are used to determine if the kidneys are damaged. Here I only want to mention one, creatinine. Urine concentrations of chemicals are often used as surrogate for the blood concentrations (which are in turn used as a surrogate for concentrations at the receptors of interest). But urine volume and ionic contents vary considerably. Creatinine is used to normalize urine concentration of chemicals. Creatinine is made in the muscles at a more or less constant rate, and is present in the blood at a stable concentrations. Creatinine is freely filtered, not reabsorbed, and minimally secreted by the kidneys. As a good approximation, creatinine is made in the muscles at about the rate it is excreted via the kidneys, hence its stable concentration in the blood. So, it is common for drug testing and many medical tests of kidney function to express the concentration of chemicals in the urine as chemical / creatinine which automatically compensates for urine volume. From here the creatinine story can get complex. While creatinine concentrations are fairly stable and predictable, they do vary a little. The results of these tests are used for some very heavy determinations, such as who will loose their pilot's license, and such, so there is lots written about the fine points. A comparison of the concentration of creatinine in the blood with that of the urine can be used to determine the glomerular filtration rate.
Besides your book, Tox Tudor has some nice diagrams. old Tox Tudor Kidney or new Tox Tudor