Final answer:
The main consequence of a non-functioning pituitary gland in a 2-year-old boy would likely be affected physical growth, as the gland is crucial for the production of growth hormone, which regulates development and size in children.
Step-by-step explanation:
If a 2-year-old boy's pituitary gland is not functioning correctly, the most likely consequence would be that his physical growth might be affected (option a). The pituitary gland plays a crucial role in growth because it produces growth hormone (GH), which is essential for normal development. In children, an underproduction of GH can lead to pituitary dwarfism, resulting in markedly reduced growth rates and symmetric body formation. Conversely, oversecretion of GH can result in gigantism, which is characterized by excessive growth.
The other consequences listed, such as neural networks slowing down, a decrease in neural transmission, and a drop in serotonin levels, are less directly related to pituitary gland dysfunction. The pituitary gland's primary role relates to the secretion of hormones that regulate various physiological processes including growth, puberty onset, and metabolic control. For instance, pituitary tumors can affect the timing of puberty due to the gland's influence on the production of sex hormones.
Moreover, the hypothalamus and pituitary are sensitive to negative feedback signals from sex hormones, which play a role during puberty but are not typically associated with serotonin levels or neural transmission as noted in options b, c, and d.