First consider the products of the cells in the anterior pituitary. Acidophils include somatotropes (produce growth hormone) and mammotropes (produce prolactin). Basophils are either thyrotropes (produce TSH), gonadotropes (produce LH and FSH) or corticotropes (produce ACTH). Basophilic cells are all regulated by feedback inhibition, where the products of the target organs they stimulate can act directly on the anterior pituitary to downregulate the production of the initial hormone (LH, FSH, TSH, and ACTH). In castration, the cells in the testis that are normally stimulated by LH and FSH are gone and can't produce hormones to downregulate their production. Instead, the absence of negative feedback causes an increase in LH and FSH produced by the basophilic gonadotropes of the anterior pituitary. These cells subsequently hypertrophy in a vain attempt to induce some type of response in the testis (which are no longer there). Histologically, this is seen as hypertrophy and increased numbers of basophils in the anterior pituitary. Now see if you can figure out what would happen to the pituitary if other glands were removed (for example the thyroid).