60

60 CASE 60


A 56-year-old man comes to his family physician complaining of fecal incontinence.


The patient had surgery 6 months earlier to treat rectal hemorrhoids. The surgery was successful, but over the past 2 months the patient indicates difficulty in determining when he needs to have a bowel movement.



PHYSICAL EXAMINATION



VS: T 37°C, P 76/min, R 15/min, BP 130/90 mm Hg, BMI 27

PE: No apparent abnormalities. Digital examination of the rectum does not show any signs of rectal prolapse.


LABORATORY STUDIES



Anal manometry: Decreased tone in the internal anal sphincter but normal tone in the external anal sphincter

Proctosigmoidoscopy: Muscle damage to the internal anal sphincter

Anal electromyography: Nerve damage


DIAGNOSIS


Fecal incontinence



PATHOPHYSIOLOGY OF KEY SYMPTOMS


Feces are normally prevented from exiting the body due to contraction of the internal anal sphincter and the external anal sphincter. The internal anal sphincter is a band of circular smooth muscle located at the distal portion of the rectum. As with all gastrointestinal sphincters, the internal anal sphincter is normally contracted. The external anal sphincter is a ring of voluntary skeletal muscle that both surrounds the internal anal sphincter and extends to the anus. The external anal sphincter is innervated by the alpha-motor neurons of the pudendal nerve and is under voluntary control. The external anal sphincter is also usually contracted.


The rectum is usually empty. When feces enter the rectum from the sigmoid colon, the rectum is distended and afferent sensory nerves initiate an increase in peristalsis that forces the feces toward the anus. The approaching wave of peristalsis relaxes the internal anal sphincter and causes the external anal sphincter to contract. Rectal distention initiates an urge to defecate, and if the external anal sphincter is allowed to relax, defecation will commence. The defecation reflex can be augmented by contraction of the abdominal muscles to force fecal contents from the sigmoid colon into the rectum.


The defecation reflex requires intact enteric nerves, afferent sensory signals transmitted to the spinal cord, efferent parasympathetic nerves from the spinal cord, and a functional pudendal nerve (Fig. 60-1). These nerves can be disrupted by surgery, such as the surgery to repair hemorrhoids.


image

FIGURE 60–1 Afferent and efferent pathways of the parasympathetic mechanism for enhancing the defecation reflex.

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Jul 4, 2016 | Posted by in PHYSIOLOGY | Comments Off on 60

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