Answers to Review Questions - Chapter 46

1.  What is an advantage of excreting nitrogenous wastes in the form of urea? What is a disadvantage?

Urea is less toxic than ammonia and thus can accumulate in tissues in higher concentrations without causing damage. However, because it is water-soluble, more water is needed to excrete urea than to excrete uric acid.

2.  Which structure(s) in the mammalian body is/are associated with each of the following: a) urea formation, b) urine formation, c) temporary storage of urine, d) conduction of urine out of the body?

a) Urea formation is associated with the liver, (b) the kidney produces urine, (c) the urinary bladder stores urine, and (d) the urethra conducts urine out of the body.

3.  Which part(s) of the nephron is/are associated with the following? a) filtration, b) reabsorption, c) secretion

(a) Filtration is associated with Bowman’s capsule and the glomerulus.

(b) Reabsorption occurs in the proximal convoluted tubule, the loop of Henle, the distal convoluted tubule, and the collecting duct.

(c) Secretion occurs mainly in the distal convoluted tubule.

4.  Through what sequence of structures does a drop of filtrate pass as it moves from Bowman’s capsule to the urinary bladder?

From Bowman’s capsule, the filtrates pass sequentially through the proximal convoluted tubule, the loop of Henle, the distal convoluted tubule, the collecting duct, the ureter, and finally to the urinary bladder.

5.  How is urine volume regulated? Explain.

Urine volume is regulated primarily by ADH. When blood volume decreases, the concentration of salts increases; this change is sensed by the hypothalamus, which in turn stimulates the posterior lobe of the pituitary to release ADH. ADH travels to the collecting ducts where the ADH makes the walls permeable to water. Consequently, more water is reabsorbed into the bloodstream instead of being excreted, and urine volume decreases.

6.  What are the actions of the renin-angiotensin-aldosterone pathway?

In the renin-angiotensin-aldosterone pathway, the juxtaglomerular apparatus secretes renin, which in turns converts angiotensinogen to angiotensin I, which is then converted to angiotensin II. Angiotensin II stimulates aldosterone secretion, raises blood pressure, and stimulates sodium reabsorption and the secretion of ADH.