Which of the following is (are) NOT important as a stimulus in the gastric phase of gastric secretion?

A. Calcium ion levels: The parathyroid glands secrete parathyroid hormone (PTH), which regulates blood calcium levels. Removal without hormone replacement would lead to hypocalcemia.
B. Anion levels: Anion balance is not directly controlled by the thyroid or parathyroid glands.
C. Potassium ion levels: Potassium is mainly regulated by aldosterone and kidneys, not the thyroid or parathyroid.
D. Sodium ion levels: Sodium balance is also regulated by aldosterone, not parathyroid hormone.

A. Posterior pituitary releases ADH: Dehydration increases blood osmolarity. This is sensed by hypothalamic osmoreceptors. In response, the hypothalamus signals the posterior pituitary to release antidiuretic hormone (ADH). ADH then acts on the distal convoluted tubules and collecting ducts of the kidney to promote water reabsorption, thereby concentrating the urine and reducing blood osmolarity.

B. Adrenal medulla releases aldosterone: Aldosterone is released from the adrenal cortex, not medulla, and is more responsive to low sodium or high potassium, not directly to osmolarity.

C. Kidneys release erythropoietin: Erythropoietin is released in response to hypoxia, not dehydration or osmolarity.

D. Anterior pituitary releases oxytocin: Oxytocin is released by the posterior pituitary, and it is not involved in osmolarity or water balance.

E. Adrenal cortex releases norepinephrine: Norepinephrine is released by the adrenal medulla, and is involved in fight-or-flight, not osmolarity regulation.