Which of the following(s) is/are true concerning the control of the volume of body water?

c. The kidney is the primary effector organ in controlling water balance

d. The conversion of angiotensin I to angiotensin II is dependent on the amount of the enzyme, renin, available

e. Nitric oxide plays a number of important roles in regulation of renal hemodynamics

Changes in volume are detected both by osmoreceptors, which detect changes in plasma osmolality and baroreceptors, which are sensitive to changes in pressure. The osmoreceptors are responsible for day-to-day fine-tuning of volume whereas the baroreceptors contribute relatively little to the control of fluid balance under normal conditions. Changes in effective circulating volume are sensed by the volume receptors of the intrathoracic capacitance vessels and atria, the pressure receptors of the aortic arch and carotid arteries, the intrarenal baroreceptors, and, to a lesser extent, by the hepatic and cerebrospinal volume receptors. These baroreceptors control volume by means of sympathetic and parasympathetic connections. The atria also appear to serve as endocrine organs capable of directing responses to volume changes with the elaboration of the hormone, atrial natriuretic peptide. The major hormonal mediator of baroreceptor modulation of volume control is the renin-angiotensin system. The end result of this complex system of receptors or messengers is a change in sodium and water balance mediated by the kidneys. It is through changes in sodium and water reabsorption that volume and pressure ultimately normalize. Renin is a proteolytic enzyme that is released in response to changes in arterial pressure, changes in delivery of sodium to the macula densa of the distal convoluted renal tubule, increases in beta adrenergic activity and increases in cellular cAMP. Renin cleaves angiotensin I from circulating angiotensinogen. Angiotensinogen is  abundant, so this reaction is enzyme dependent rather than substrate dependent. Angiotensin I is further cleaved to angiotensin II which acts with locally and systemically to increase vascular tone. Angiotensin II affects sodium reabsorption by decreasing renal plasma flow and the glomerular filtration coefficient. Finally, angiotensin II increases sodium reabsorption by direct tubular action as well as by stimulation of aldosterone release from the adrenal cortex. The importance of nitric oxide and its many biologic functions has recently been recognized. Nitric oxide participates in the regulation of renal hemodynamics and renal handling of water and electrolytes.