Question

In a laboratory experiment with three groups of students, one group drinks pure water, a second group drinks an equal amount of beer, and a third group drinks an equal amount of concentrated salt solution, all during the same time period. Their urine production is monitored for several hours. Order the groups of individuals from greatest to least urine production with an explanation for the volume changes. (hint: think of ADH)

Answer 1

Water has a tendency to move across a membrane from a lower osmolarity to a higher osmolarity. Then remember that water goes from low to high osmolarity, from weak to concentrated solutions. Thus if a person drinks salty water then water will move from the cells to the outside. Lowered osmolarity decreases ADH secretion, causing loss of water.

Increased salt consumption induces body water conservation.

“Alcohol is a diuretic. In fact for every 1g of alcohol drunk, urine excretion increases by 10ml. Alcohol also reduces the production of a hormone called vasopressin, which tells the kidneys to reabsorb water rather than flush it out through the bladder.

Thus greatest urine production will occur in a person who drinks wine, then a glass of water and finally in that person who drinks a glass of salty water.