09-07-2007, 02:10 PM
29. The correct answer is B. Antidiuretic hormone (ADH)
secretion from the posterior pituitary can be disrupted
after head injuries, causing a condition called œcentral
diabetes insipidus. Because the distal tubular segments
cannot absorb water in the absence of ADH, large
amounts of water are excreted (choice D). This loss of
water from the body causes dehydration and increased
osmolarity (choice A) of the body fluids. The thirst
mechanisms are activated and large amounts of water
are consumed (choice E), which helps to prevent large
decreases in total body water that would otherwise lead
to death. The amount of sodium that is excreted will
match exactly the amount of sodium that is consumed;
thus sodium excretion (choice C) is unchanged.
secretion from the posterior pituitary can be disrupted
after head injuries, causing a condition called œcentral
diabetes insipidus. Because the distal tubular segments
cannot absorb water in the absence of ADH, large
amounts of water are excreted (choice D). This loss of
water from the body causes dehydration and increased
osmolarity (choice A) of the body fluids. The thirst
mechanisms are activated and large amounts of water
are consumed (choice E), which helps to prevent large
decreases in total body water that would otherwise lead
to death. The amount of sodium that is excreted will
match exactly the amount of sodium that is consumed;
thus sodium excretion (choice C) is unchanged.