**Core Concept:** Secretomotor functions refer to the actions that stimulate the secretion of substances from الغدد. In this case, we are discussing the submandibular gland and the actions that regulate its secretion. The submandibular gland is a major salivary gland located in the floor of the mouth, with its ducts opening onto the ventral surface of the tongue.

**Why the Correct Answer is Right:** The correct answer, **Option C (Neurotransmitters)**, is right because neurotransmitters are chemical messengers that transmit signals across a synapse by binding to specific receptors on the postsynaptic neuron. They do not directly stimulate the secretion of substances from the submandibular gland, which is primarily regulated by hormones and local factors.

**Why Each Wrong Option is Incorrect:** Let's examine the other options and why they are incorrect:

A. **Hormones (Option D):** Hormones are chemical messengers that act over long distances to regulate physiological processes. They are responsible for stimulating the submandibular gland, particularly acetylcholine and vasoactive intestinal peptide (VIP). These hormones directly stimulate the gland to secrete saliva.

B. **Local Factors (Option B):** Local factors are elements that act in a specific area, such as the submandibular gland. Examples include acetylcholine and VIP, which stimulate the gland to secrete saliva.

C. **Neurotransmitters (Option C):** As explained above, neurotransmitters are chemical messengers that transmit signals across synapses, not stimulate the secretion of substances from the submandibular gland. They are involved in other physiological processes within the body.

**Clinical Pearl / High-Yield Fact:** The submandibular gland is regulated through a complex interplay between hormones (acetylcholine and VIP) and local factors (e.g., acetylcholine). These substances interact with the acinar cells of the gland, triggering the secretion of saliva, a crucial function in maintaining oral hydration and digestion.