Age affects anus tightness primarily through changes in the internal anal sphincter (IAS) thickness, diameter, and muscle tone. As individuals age, studies have shown that there is a significant increase in the thickness and diameter of the IAS, which may initially suggest an increase in tightness. However, this increase in thickness does not correlate with an increase in anal pressure or muscle tone, leading to a paradoxical decrease in functional tightness.
Physiological Changes with Aging
- Increased Thickness and Diameter: Research indicates that older females exhibit a 33% thicker internal anal sphincter compared to younger females (4.5 ± 0.7 mm vs. 5.9 ± 1 mm), along with a larger inner diameter (20% increase) and outer diameter (27% increase) as they age. This suggests that the physical structure of the IAS changes significantly over time.
- Decreased Muscle Tone: Despite the increased thickness of the IAS, studies have demonstrated that aging is associated with a decrease in anal resting pressures and maximal squeeze pressures. Specifically, older women show lower maximum resting pressures compared to younger counterparts, indicating that while the sphincter may be thicker, its ability to generate pressure effectively diminishes.
- Impact of Collagen Deposition: Histological studies reveal that aging leads to increased collagen deposition within the IAS and decreased smooth muscle content. This change contributes to reduced elasticity and strength of the sphincter muscles, further compromising their ability to maintain tightness.
Functional Implications
- Anal Pressure Dynamics: According to Laplace’s law, which relates wall tension (or stress) to pressure within tubular structures like the anal canal, an increase in radius (diameter) without a corresponding increase in wall tension can lead to decreased internal pressure. In older adults, although there is an increase in IAS thickness, the decrease in muscle tone results in lower anal pressures.
- Risk of Fecal Incontinence: The combination of increased IAS size but decreased functional tightness correlates with a higher risk of fecal incontinence among older adults. As muscle tone decreases with age, individuals may find it more challenging to maintain continence during activities that increase abdominal pressure.
- Gradual Changes Over Time: The changes observed are gradual rather than abrupt; thus, individuals may not notice significant differences until later stages of life when combined factors such as hormonal changes post-menopause also play a role.
Conclusion
In summary, while anatomical measurements indicate that the internal anal sphincter becomes thicker and larger with age, these changes do not translate into greater tightness or effective closure due to concurrent decreases in muscle tone and anal pressures. This complex interplay highlights how aging can adversely affect anal function despite apparent structural increases.