3. Drinking behavior
• Water deprivation produces an on signal that is
detected by receptors in the nervous system.
• The neural reactions to this signal initiate
behavior gear to the reinstate then normal water
level.
• When the normal level is reached once again, and
of signal is converted to the brain to stop drinking
thus to understand water intake at physiological
level it is not enough to understand the signals
that turn it on and off the receptors that monitor
the signals
8. • Thirst Mechanism
• Thirst center is in the lateral nucleus of
hypothalamus. There are some osmoreceptors
in the areas adjacent to thirst center
• When the ECF volume decreases, the
osmolality of ECF is increased.
• If the osmolality increases by 1% to 2%, the
osmoreceptors are stimulated
9.
10. • ADH Mechanism
• Simultaneously, when the volume of ECF
decreases with increased osmolality, the
supraoptic nucleus is stimulated and ADH is
released.
• ADH causes retention of water by facultative
reabsorption in the renal tubules.
It increases the ECF volume and brings the
osmolality back to the normal level.
11. •On the contrary, when ECF volume is increased,
the supraoptic nucleus is not stimulated and
ADH is not secreted.
• In the absence of ADH, more amount of water is
excreted through urine and the volume of ECF is
brought back to normal.
12. Detection
There are many different receptors for
sensing the crystal volume or an
increase to osmolite concentration.
Decreased volume
1. Renin Angiotensin system RAS
13. Hypovolemia leads to activation of the renin
angiotensin system (RAS) and a decrease in
atrial natriuretic peptide. These mechanisms,
along their other functions, contribute to elicit
thirst, by affecting the sub fornical organ.
For instance, angiotensin II, activated in RAS,
is a powerful dipsogen (ie it stimulates thirst)
which acts via the subfornical organ.
14. • Arterial baroreceptors sense a decreased
arterial pressure, and signals to the central
nervous system in the area postrema and
nucleus tractussolitarius.
Cardiopulmonary receptors sense a
decreased blood volume, and signal to
bareapostrema and nucleus
tractussolitarius[2] as well.
15. Increased osmolite
volume
• An increase in osmotic pressure, e.g. after eating a
salty meal activate osmo receptors.
• There are osmo receptors already in the central
nervous system, more specifically in the
hypothalamus, notably in two circumventricular
organs that lack an effective blood brain barrier, the
organum vasculosum of the
laminaterminalisorganumvasculosum of the lamina
terminalis (OVLT) and the subfornicalorgan (SFO).
