Answers to Study Questions

CHAPTER 1

• 1–1. (b) Renal corpuscles are distributed throughout the cortex, which includes the region just above the cortico-medullary border (i.e., the juxtamedullary region). None are in the medulla.

• 1–2. (c) Each glomerulus is associated with a nephron, which includes a loop of Henle. Each collecting duct is formed from the coalescence of several nephrons.

• 1–3. (d) Balance implies that input equals output, which can occur at normal or abnormal levels of amounts in the body, or normal or abnormal input, so long as the inputs are matched by equal outputs.

• 1–4. (c) The macula densa cells are located in the tubule where it passes between the afferent and efferent arterioles. This location is at the end of the thick ascending limb of the loop of Henle just before it becomes the distal tubule.

• 1–5. (d) A healthy young 70-kg person contains about 42 L of water (∼60% of body weight), and filters up to 180 L of plasma each day.

• 1–6. (a) Secretion implies transport from tubular cell to the lumen. Most often the substance entered the cell from the blood, but it could also be synthesized and then transported.

CHAPTER 2

• 2–1. (d) Most efferent arterioles feed peritubular capillaries, but those associated with juxtamedullary glomeruli feed vascular bundles that descend into the medulla.

• 2–2. (d) While various factors affect how much plasma is filtered, the glycocalyx, basement membrane, and particularly the slit diaphragms bridging the foot processes of podocytes, all of which are extracellular, are the key determinants of what is filtered.

• 2–3. (a) Rapid control is exerted over the contractile properties of vascular smooth muscle that in turn affects hydrostatic pressure in glomerular capillaries.

• 2–4. (d) Other than larger molecules that are only partially or slightly filtered, the plasma concentrations of a small freely filtered substance are not altered by filtration because water and the substance in question are filtered in the same proportions.

• 2–5. (c) The lowering of pressure upstream from the glomerulus is offset by contraction of the efferent arteriole, an action that by itself raises glomerular capillary pressure. The net effect leaves glomerular capillary pressure almost unchanged.

• 2–6. (a) Glomerular capillary pressure starts at about 60 mm Hg and falls very little along the length of the capillaries. This value is far higher than in most peripheral capillaries.

CHAPTER 3

• 3–1. (d) The excretion rate of a substance divided by its plasma concentration yields the clearance.

• 3–2. (a) The metabolic clearance rate represents the sum of all clearance routes. Since there are two major routes of clearance (kidneys and feces) the metabolic clearance must be higher than either one alone. The fact that the drug has a higher urinary concentration than plasma concentration mainly reflects the reabsorption of water.

• 3–3. (c) In the second test both the plasma concentration and filtered load (and hence rate of excretion) are increased, yielding offsetting effects on ...