Final answer:
The parasympathetic ANS increases urinary output by transmitting nerve impulses that cause the detrusor muscle to contract and the internal urethral sphincter to relax, coupled with inhibition of somatic motor neurons, resulting in the relaxation of the external sphincter. Reduced sympathetic stimulation also increases renal blood flow and urine production.
Step-by-step explanation:
The mechanisms by which the parasympathetic autonomic nervous system (ANS) increases urinary output involve a series of neural and physiological responses. When the bladder becomes stretched by accumulating urine, stretch receptors get activated, sending nerve impulses to the sacral region of the spinal cord. This generates a spinal reflex that results in a parasympathetic outflow, which causes the contraction of the detrusor muscle and relaxation of the involuntary internal urethral sphincter. Additionally, somatic motor neurons are inhibited by the spinal cord, leading to the relaxation of the skeletal muscle of the external urethral sphincter, allowing urination to occur. In essence, the autonomic system is responsible for the initial steps leading to bladder emptying, while voluntary control over the external sphincter muscle allows the timing of the final act of urination.
Furthermore, the reduction of sympathetic stimulation contributes to increased blood flow through the kidneys, facilitating a greater volume of urine production. The autonomic system, particularly the parasympathetic branch, plays a significant role in not only the act of urination but also in the regulation of the internal conditions that lead to increased urine volume.