Final answer:
Dehydration increases blood osmolality, and ADH secreted in response to this condition helps conserve water by increasing renal reabsorption. This homeostatic mechanism is critical in maintaining fluid balance within the body.
Step-by-step explanation:
Dehydration leads to an increase in blood osmolality as a result of decreased water content in the bloodstream. When dehydration occurs, for instance, due to the injection of a hypertonic solution, the osmotic pressure of the blood increases. This causes fluid to move from the tissues into the blood, temporarily increasing blood volume. However, the excess volume is typically corrected by the kidneys excreting excess solutes and water, resulting in a net loss of body water. The antidiuretic hormone (ADH) plays a crucial role in this process. It is released in response to high blood osmolarity and acts on the kidneys to increase water reabsorption, decreasing urine volume and helping to lower blood osmolarity back to normal. While conditions like diabetes can lead to severe dehydration due to an osmotic diuresis, ADH aids in regulating blood pressure and volume by controlling water retention in conjunction with sodium levels in the body.