Phospholipase C normally breaks down phosphatidylinositol (3,4,5)-trisphosphate (PIP3) into diacylglycerol (DAG) and inositol 1,4,5-triphosphate (IP3). This cascade eventually increases cytosolic calcium levels through its release from the endoplasmic reticulum and from the extracellular fluid. Malfunction in this enzyme results in PIP3 not being broken down.

Insulin is a peptide hormone that is released in the fed state. Thus, it promotes glucose storage and DNA replication, but decreases glycogen breakdown and the release of glucose.

Glucagon is a peptide hormone that is released in the fasted state. It stimulates macromolecule breakdown and the production and subsequent release of glucose into the blood stream. It is synthesized and released from the alpha-cells in the pancreatic islets.

Insulin release is induced by incretins in the blood (ex. GLP-1), and a high carbohydrate meal. Incretins are metabolic hormones that stimulate a decrease in blood glucose. Growth hormone does not cause an increase in blood insulin.

Beta-cells are found in the majority of the inner area of pancreatic islets. They are the most common cell in the pancreatic islet. Beta-cells produce both insulin and C-peptide, and are primarily active in the fed state. The gamma cells of the pancreatic islets secrete somatostatin.

C-peptide is produced in equal amounts as insulin, but has a longer half-life and thus is a better indicator of insulin release. Insulin is produced by beta-cells in the pancreas during a fed state. Insulin is involved in translocation of the GLUT-4 receptor.

Glucagon is released in a fasted or high-stress state (including increased concentration of blood cortisol or epinephrine). It is also induced when blood insulin levels are decreased. Recall that glucagon and insulin have antagonistic functions, and are thus secreted in opposite temporal patterns.

Tryptophan is a precursor for serotonin. Phenylalanine is a precursor for dopamine, norepinephrine, and epinephrine. Histamine acts both as a mediator of the inflammatory response and as a neurotransmitter in the central nervous system. Tyrosine is a precursor for dopamine. Serine is not a precursor for any neurotransmitter.

Glucagon receptors and beta-adrenoreceptors (for epinephrine) on cells trigger the release of cAMP, starting a phosphorylation cascade which ultimately activates glycogen phosphorylase and inhibits glycogen synthase. In liver cells, alpha-adrenoreceptors (also for epinephrine) releases calcium ions, which also begins a phosphorylation cascade ultimately leading to glycogen degradation. Glycogen is broken down into glucose which can undergo glycolysis for the production of ATP.

One must know the phosphorylation system in order to fully understand this conclusion, but logically, an increase of glucose in a cell (or insulin, which is released when blood glucose levels are high) shouldn't trigger a cell to make more glucose, as this implies there is an abundance of glucose in the cell.

Epinephrine, released by adrenal glands, is a neurotransmitter which is responsible for the "fight or flight" response, in which an organism needs energy fast. Therefore, an increase of glucose is needed for glycolysis.

Glucagon, released by the pancreas, is directly released when blood glucose levels are low, and therefore it is logical that it must signal for an increase of glucose production.

A hormone that has its receptor located on the surface of a cell will be a peptide hormone, not a steroid hormone. A steroid hormone can diffuse through the cell membrane and will find its receptor inside of the cell. The only peptide hormone listed as an answer choice is oxytocin.