Hypothalamic–pituitary–thyroid axis Hypothalamic–pituitary–thyroid axis The hypothalamic–pituitary–thyroid axis (HPT axis for short, a.k.a. thyroid homeostasis or thyrotropic feedback control) is part of the neuroendocrine system responsible for the regulation of metabolism. As its name suggests, it depends upon the hypothalamus, the pituitary gland, and the thyroid gland. The hypothalamus senses low circulating levels of thyroid hormone (Triiodothyronine (T3) and Thyroxine (T4)) and responds by releasing thyrotropin-releasing hormone (TRH). The TRH stimulates the anterior pituitary to produce thyroid-stimulating hormone (TSH). The TSH, in turn, stimulates the thyroid to produce thyroid hormone until levels in the blood return to normal. Thyroid hormone exerts negative feedback
Pituitary adenoma superior quadrantanopia. Lateral expansion of a pituitary adenoma can also compress the abducens nerve, causing a lateral rectus palsy. Also, a pituitary adenoma can cause symptoms of increased intracranial pressure. Prolactinomas often start to give symptoms especially during pregnancy, when the hormone progesterone increases the tumor's growth rate. Various types of headaches are common in patients with pituitary adenomas. The adenoma may be the prime causative factor behind the headache or may serve to exacerbate a headache caused by other factors. Amongst the types of headaches experienced are both chronic and episodic migraine, and more uncommonly various unilateral headaches; primary