How do the internal and external urethral sphincters differ structurally and functionally?

Verified step by step guidance

1. Identify the location of the internal and external urethral sphincters: The internal urethral sphincter is located at the junction of the bladder and urethra, while the external urethral sphincter is located further down the urethra, surrounding it.
2. Understand the structural differences: The internal urethral sphincter is composed of smooth muscle, which is involuntary, whereas the external urethral sphincter is composed of skeletal muscle, which is under voluntary control.
3. Explore the functional differences: The internal urethral sphincter helps maintain urinary continence by preventing the involuntary release of urine, while the external urethral sphincter allows for voluntary control over urination.
4. Consider the nervous system control: The internal urethral sphincter is controlled by the autonomic nervous system, specifically the sympathetic nervous system, which keeps it contracted. The external urethral sphincter is controlled by the somatic nervous system, allowing conscious control.
5. Summarize the roles in micturition: During urination, the internal sphincter relaxes as part of the involuntary reflex, while the external sphincter is consciously relaxed to allow urine to pass through the urethra.

Key Concepts

Internal Urethral Sphincter

The internal urethral sphincter is a smooth muscle structure located at the junction of the bladder and urethra. It is involuntary and controlled by the autonomic nervous system, allowing for the retention of urine. Its primary function is to maintain continence by preventing the flow of urine from the bladder until voluntary urination is initiated.

External Urethral Sphincter

The external urethral sphincter is composed of striated muscle and is located around the urethra, below the internal sphincter. It is under voluntary control, allowing individuals to consciously decide when to urinate. This sphincter plays a crucial role in urinary continence, enabling the fine-tuning of urination in response to social and environmental cues.

Structural Differences

Structurally, the internal urethral sphincter is made of smooth muscle, which is not under conscious control, while the external urethral sphincter consists of striated muscle, which is under voluntary control. This distinction is essential for understanding how these sphincters function in coordination to regulate urine flow and maintain bladder control.