Pituitary gland is directly under the influence of neurohormones of hypothalamus while thyroid is indirectly influenced.
I. Neurohormonal regulation of pituitary:
1. Hypothalamus secretes releasing factors and inhibiting factors and hence regulate the secretions of pituitary (hypophysis).
2. Hypothalamus forms the hypothalamohypophysial axis through which transportation of neuro-hormones take place.
3. Pituitary secretes a variety of hormones which influence other endocrine glands of the body. E.g. GH, PRL, TSH, ACTH, Gonadotropins
II. Neurohormonal regulation of thyroid :
1. Hypothalamus secretes TRF [Thyrotropin releasing factor] which influences the anterior pituitary to release TSH.
2. TSH in turn stimulates thyroid follicles to produce and release two thyroid hormones – T3 and T4 . (Thyroxin)
3. Increase in T3 and T4 triggers negative feedback mechanism that stops the secretion of TRF.
(4) As the pituitary does not get the signal in the form of TRF TSH secretion is stopped.