Drinking can be induced by:
B i.e. Osmotic stimulation of supraoptic nucleusBody respond to increased plasma osmolality in two ways.(i) By increasing ADH secretion which decrease water excretion by kidney(ii) By stimulating thirst centre which increase water intakeIn both these mechanism osmoreceptors are involved.(iii) Supraoptic nucleus near anterior hypothalamus causes ADH secretion.(iv) Preoptic nucleus is centre for thirst stimulationThe osmotic threshold for thirst is same or slightly (-5%) greater than the threshold for increased ADH secretion.It is still unceain whether the same osmoreceptors mediate both effects That means centre for ADH secretion and thirst stimulation might be same or stimulation of one can lead to both the mechanism. Thus with increase in osmolality 1st thing to occur is ADH secretion followed by thirst stimulation.Aquaporins: are water channelsAq 1, 2, 3 - Present in kidneyAq, 2 - Vasopressine responsive in collecting ductAq 4 - In BrainAq 5 - In salivary gland, lacrimal gland, Respiratory tract.Vasopressin secretion is regulated by osmoreceptors, that are situated outside blood- brain barrier & located in circumventricular organs primarily in OVLT/ supraoptic crestQ
Electrical stimulation of the posterior hypothalamus
Osmotic stimulation of supraoptic nucleus
Lesions in the paraventicular nucleus
Neuronal lesion of the preoptic nucleus