Physiology of Micturition

Summary

This video explains the physiology of micturition, detailing the organs and structures involved in urine production and release. It highlights key components such as the kidneys, bladder, urethra, and muscles like the detrusor and sphincters. The video explores the role of different nerve systems—parasympathetic, sympathetic, and somatic—in controlling the bladder and sphincters, both involuntarily and voluntarily. It distinguishes between male and female urinary tracts, focusing on receptors, nerve signals, and the nervous system's involvement in holding and releasing urine. Lastly, it outlines the reflexes triggered during the voiding process.

Takeaways

• 🔬 The micturition process involves several key organs: kidneys, ureters, bladder, and urethra.
• 🧠 The central nervous system, particularly the pons, controls the micturition process.
• 🟡 The bladder stores urine and is composed of the detrusor muscle, which can contract and relax.
• 🚻 Males have an internal sphincter, prostate gland, and a longer urethra, while females lack an internal sphincter and have a shorter urethra.
• 🔗 The pelvic, pudendal, and hypogastric nerves play crucial roles in controlling the contraction and relaxation of bladder muscles and sphincters.
• 🧪 The receptors involved in micturition include muscarinic M3, beta-adrenergic B3, alpha-1, and nicotinic receptors, each affecting different parts of the urinary tract.
• 💡 The sympathetic nervous system facilitates urine retention by relaxing the detrusor muscle and contracting the internal sphincter.
• 🔄 The parasympathetic nervous system is responsible for voiding by contracting the detrusor muscle.
• 📶 Sensory (afferent) pelvic nerves respond to bladder stretching and help signal the need to urinate.
• 🔄 When the bladder is full, the pontine micturition center inhibits sympathetic activity and stimulates parasympathetic activity, allowing for urination.

Q & A

What is the primary function of the bladder in the process of micturition?

The primary function of the bladder in micturition is to store urine until it is ready to be expelled from the body. When the bladder contracts, it releases urine, which then travels through the urethra and exits the body.

What role does the detrusor muscle play in micturition?

The detrusor muscle is a muscle in the bladder that contracts to expel urine during micturition. It relaxes to allow the bladder to fill with urine and contracts to facilitate urination.

What are the key differences between the male and female urinary tracts?

The key differences are that males have a longer urethra, an internal sphincter, and a prostate gland, while females have a shorter urethra and no internal sphincter or prostate. This shorter urethra in females increases the likelihood of urinary tract infections (UTIs).

How does the parasympathetic nervous system influence micturition?

The parasympathetic nervous system controls voiding (urination). Specifically, the pelvic nerve, which releases acetylcholine (ACh), stimulates the M3 receptors on the detrusor muscle, causing the bladder to contract and expel urine.

What is the role of the hypogastric nerve in micturition?

The hypogastric nerve, part of the sympathetic nervous system, is responsible for urinary retention. It releases noradrenaline (norepinephrine) that binds to beta-3 receptors on the detrusor muscle to relax it and to alpha-1 receptors on the internal sphincter to contract it, preventing urination.

How does the pudendal nerve function in the control of urination?

The pudendal nerve is a somatic nerve that is under voluntary control. It releases acetylcholine (ACh) to stimulate nicotinic receptors on the external sphincter, causing the sphincter to contract, which helps in holding urine and preventing urination when necessary.

What triggers the voiding reflex during urination?

The voiding reflex is triggered when the bladder becomes full and stretches, activating the pelvic afferent (sensory) nerves. These nerves send signals to the sacral region of the spinal cord, which leads to the stimulation of parasympathetic efferent nerves, causing the detrusor muscle to contract and the sphincters to relax, allowing urination.

What role does the pons play in the micturition process?

The pons, specifically the pontine micturition center, is crucial in controlling the micturition process. It coordinates signals from the central nervous system, including the inhibition of the sympathetic nervous system (to allow urination) and the stimulation of the parasympathetic system (to trigger detrusor muscle contraction and sphincter relaxation).

How do sensory pelvic nerves contribute to the process of micturition?

Sensory pelvic nerves detect the stretching of the bladder as it fills with urine. When the bladder is full, these nerves send fast signals to the sacral region of the spinal cord, which triggers the micturition reflex, resulting in the bladder contracting and the sphincters relaxing.

What happens during micturition when the bladder is empty?

When the bladder is empty, the sensory pelvic nerves send slow impulses to the sacral region of the spinal cord, which stimulates the hypogastric nerve to contract the internal sphincter and relax the detrusor muscle. This process, along with the voluntary contraction of the external sphincter via the pudendal nerve, helps retain urine in the bladder.