When a nervous stem cell differentiates into a neuron versus a neuroglial cell.

When the high level of a substance decreases the production and secretion of a hormone.

When an injury activates a few platelets that lead to the activation of thousands of plasma fibrinogen until a blood clot is formed.

When the cardiovascular, respiratory, urinary, nervous and endocrine systems coordinate to maintain blood pH between 7.35 and 7.45.