Final answer:
Cellular dehydration causes osmotic thirst while dehydration of the blood stream leads to hypovolemic thirst. Osmotic thirst occurs due to the concentration of solutes in the blood, and hypovolemic thirst is triggered by a reduction in blood volume. Conditions like diabetes insipidus can lead to increased thirst and urination due to inadequate ADH production affecting water retention.
Step-by-step explanation:
Cellular dehydration causes osmotic thirst, whereas dehydration of the blood stream leads to hypovolemic thirst. The terms 'osmotic' and 'hypovolemic' are used to describe the physiological responses to dehydration in different compartments of the body. When cells lose water to the extracellular space due to excessive water loss, it causes an increase in the concentration of extracellular fluid, leading to osmotic thirst. Water from the cells is drawn out, causing the cells to shrink. On the other hand, when there is a loss of blood volume, for instance, from vomiting, diarrhea, or blood loss, this leads to hypovolemic thirst, which triggers a thirst response for water replenishment to restore blood volume.
Osmotic thirst is triggered by osmoreceptors in the hypothalamus that sense the increased solute concentration in the blood. These receptors then signal the brain to create a sensation of thirst. Hypovolemic thirst, however, is related to the overall blood volume rather than solute concentration, and it prompts the body to intake fluid to replenish the lost volume.
In conditions like diabetes insipidus, where ADH (antidiuretic hormone) production is insufficient, there is an inability to retain water, leading to increased thirst and urination. ADH is crucial as it helps the kidneys retain water and thus maintains hydration status. If the secretion of ADH is insufficient, this causes the kidneys to excrete excessive amounts of water, leading to dehydration and triggering the thirst response.