A 34-year-old woman comes to the clinic due to dizziness and mild confusion over the last week. The patient has a history of seizures beginning in childhood and was recently started on carbamazepine by her neurologist. Her temperature is 36.7 C (98 F), blood pressure is 121/72 mm Hg, pulse is 68/min, and respirations are 13/min. Physical examination is within normal limits. Laboratory studies show a low serum sodium concentration. It is determined that the patient's condition is caused by increased release of a hormone that is co-secreted with neurophysins. This hormone is most likely secreted into the circulation at which of the following sites?

Question

A 34-year-old woman comes to the clinic due to dizziness and mild confusion over the last week.  The patient has a history of seizures beginning in childhood and was recently started on carbamazepine by her neurologist.  Her temperature is 36.7 C (98 F), blood pressure is 121/72 mm Hg, pulse is 68/min, and respirations are 13/min.  Physical examination is within normal limits.  Laboratory studies show a low serum sodium concentration.  It is determined that the patient's condition is caused by increased release of a hormone that is co-secreted with neurophysins.  This hormone is most likely secreted into the circulation at which of the following sites?

Quizplus · Accepted Answer

11ec160b_3aca_98e0_9249_172cdb3771c5_MD0001_00 This patient most likely has the syndrome of inappropriate antidiuretic hormone secretion (SIADH), which can be caused by a multitude of drugs, including carbamazepine, cyclophosphamide, and selective serotonin reuptake inhibitors. Antidiuretic hormone (vasopressin) and oxytocin are synthesized within magnocellular neurons found in the supraoptic and paraventricular nuclei of the hypothalamus. Most magnocellular neurons produce either vasopressin or oxytocin. Once translated, these hormones are packaged into vesicles and travel via anterograde axonal transport to the posterior pituitary (neurohypophysis). There, the hypothalamic axons terminate into Herring bodies, which are specialized nerve terminals that act as storage sites for the secretory vesicles. These vesicles also contain proteins known as neurophysins that are involved in posttranslational hormone processing and stabilization during axonal transport. Vasopressin and oxytocin and their associated neurophysins are then secreted from the posterior pituitary into the hypophysial vein to enter the systemic circulation. (Choice A) The anterior pituitary (adenohypophysis) is the glandular portion of the pituitary that lies closest to the optic chiasm. It is composed of various hormone-secreting cells, including somatotropes (growth hormone), lactotropes (prolactin), gonadotropes (FSH and LH), thyrotropes (TSH), and corticotropes (ACTH). (Choice B) This is the vestigial intermediate lobe of the pituitary gland, which is derived from the posterior wall of Rathke's pouch during embryonic development. It is not a significant source of secretory products in humans, but can secrete a small amount of melanocyte-stimulating hormone. (Choices D and E) The posterior hypothalamus is involved in the control of sympathetic responses, including temperature regulation; the mammillary bodies are important for memory recall. These regions do not directly secrete hormones. Educational objective: Vasopressin and oxytocin are synthesized within neurons found in the paraventricular and supraoptic nuclei and are released into the circulation from axon terminals in the posterior pituitary. Neurophysins are involved in the posttranslational processing and stabilization of oxytocin and vasopressin within neurosecretory vesicles during transport to the posterior pituitary. __________ References: Progressive decline of vasopressin secretion in familial autosomal dominant neurohypophyseal diabetes insipidus presenting a novel mutation in the vasopressin-neurophysin II gene. (http://www.ncbi.nlm.nih.gov/pubmed/14510916)

A 34-Year-Old Woman Comes to the Clinic Due to Dizziness