The morphological principles of anorectal continence

Area of Science:

• Anatomy
• Physiology
• Gastroenterology

Background:

• Anal continence is a complex function involving multiple anatomical structures.
• The internal anal sphincter, composed of smooth muscle, plays a crucial role in maintaining continence.
• Understanding the unique properties of the internal anal sphincter is essential for comprehending anorectal function.

Purpose of the Study:

• To investigate the unique histological and pharmacological characteristics of the internal anal sphincter.
• To compare the internal anal sphincter with other gastrointestinal smooth muscles.
• To highlight the functional significance of the internal anal sphincter in maintaining anal continence.

Main Methods:

• Electron microscopy was used to examine the cellular structure of the internal anal sphincter.
• Pharmacological studies were conducted to assess the response of the internal sphincter to cholinergic and adrenergic stimuli.
• Comparative anatomical studies were performed to analyze the structure of the internal anal sphincter across different species.

Main Results:

• The internal anal sphincter lacks ganglion cells and the characteristic p-fibres found in other gastrointestinal smooth muscles.
• Both cholinergic and adrenergic nerve fibers induce contraction of the internal anal sphincter.
• Comparative anatomy reveals the internal anal sphincter's unique role, such as being the primary anal sphincter in kangaroos.

Conclusions:

• The internal anal sphincter possesses unique histological and pharmacological properties that differentiate it from the rest of the gastrointestinal tract.
• These unique features enable continuous, fatigue-resistant contraction essential for maintaining anal continence.
• The sphincter system's limited regenerative capacity underscores its robust design and the importance of preserving its function.