Which of the following organs is NOT a parasympathetic effector organ?

The kidney is considered primarily a sympathetic effector organ rather than a parasympathetic one. While the parasympathetic nervous system does influence various functions of other organs, such as the heart, smooth muscles, and exocrine glands, the kidney's regulation is chiefly under sympathetic control. This is because the sympathetic nervous system primarily governs renal blood flow and the filtration rate through the activation of receptors that respond to stress or low blood volume.

In contrast, the heart is modulated by the parasympathetic nervous system primarily through the vagus nerve, leading to a decrease in heart rate. Smooth muscle, found in various organs such as the digestive tract, is also influenced by the parasympathetic system to promote contraction and movement. Additionally, exocrine glands, which secrete substances like saliva and digestive enzymes, are activated by the parasympathetic system to enhance secretion. Therefore, the kidney stands out as an organ whose primary regulatory pathway is sympathetic, highlighting its distinction from the other options listed.