#10.4 Thirst

water content

WATER PROPERTIES THAT THE BODY MONITORS:

osmolality or solute concentration

water content

WATER PROPERTIES THAT THE BODY MONITORS:

monitored by the brain to prevent cellular dehydration

blood volume

WATER PROPERTIES THAT THE BODY MONITORS:

pressure or volume

blood volume

WATER PROPERTIES THAT THE BODY MONITORS:

monitored by the heart and kidneys to ensure sufficient blood pressure

hypothalamus

integrates hydration signals

diuresis

means "urination"

osmotic thirst

TYPES OF THIRST:

triggered by high solute (salt) concentration

hypervolemic thirst

TYPES OF THIRST:

triggered by low blood volume

molarity

measure of number of particles per unit of solution, regardless of size of each particle

semipermeable membrane

membrane where water can pass but solutes cannot

osmotic thirst

TYPES OF THIRST:

occurs when concentration of solutes (Na+, ions) in the EXTRACELLULAR fluid becomes too high

osmotic thirst

TYPES OF THIRST:

occurs when eating salty foods, dehydration, or diarrhea causing loss of more water than salt

osmotic thirst

TYPES OF THIRST:

solution - increase water intake

hypervolemic thirst

TYPES OF THIRST:

occurs when there is a decrease in blood volume or there is blood loss

hypervolemic thirst

TYPES OF THIRST:

occurs when hemorrhage, severe vomiting or diarrhea, excessive sweating, major injury/trauma

hypervolemic thirst

TYPES OF THIRST:

solution - water and solute (salt) intake

osmotic thirst

MECHANISM OF WHICH TYPE OF THIRST?

solute concentration increase -> water leaves cells -> cells shrink -> osmoreceptors in brain detect shrinkage -> triggers thirst and water-seeking behavior

hypervolemic thirst

MECHANISM OF WHICH TYPE OF THIRST?

baroreceptors detect low blood pressure -> baroreceptor signal brain via vagus nerve -> kidney detects decrease in blood flow -> kidney release enzyme renin -> Renin initiates angiotensin cascade

Water conservation

THIRST REGULATION <

Excreting concentrated urine. Decreasing sweat or other autonomic responses

Anticipatory thirst regulation

THIRST REGULATION <

humans drink while eating to facilitate digestion

Overnight Regulation

THIRST REGULATION <

body's circadian rhythm triggers increased secretion of Vasopressin (ADH) shortly before sleep

Vasopressin (ADH)

THIRST REGULATION:

hormone conserves water (inhibiting urination) and also stimulates thirst, prompting us to drink before we sleep and enter a period where drinking is impossible

Stopping Drinking

THIRST REGULATION <

stop drinking long before the ingested water reaches the blood and cells

Subfornical Organ (SFO)

THIRST REGULATION:

area where its neuron's activities are suppressed after one minute of drinking/cooling the tongue

Subfornical Organ (SFO)

THIRST REGULATION:

stops water-seeking behavior when its neurons' activity is suppressed, indicating that the need is fulfilled