A 26-year-old gymnastics instructor presents with complaints ofmuscle weakness in her face that comes and goes, but has beengetting worse over the past two months. Most notably, she complainsthat her \"jaw gets tired\" as she chews and that swallowing hasbecome difficult. She also notes diplopia (\"double vision\") whichseems to come on late in the evening, particularly after readingfor a few minutes. At work, it has become increasingly difficult to\"spot\" her gymnasts during acrobatic moves because of upper armweakness.

On physical examination, she has notable ptosis (\"drooping\") ofboth eyelids after repeated blinking exercises. When smiling, sheappears to be snarling. Electromyographic testing revealedprogressive weakness and decreased amplitude of contraction of thedistal arm muscles upon repeated mild shocks (5 shocks per second)of the ulnar and median nerves. Both her symptoms andelectromyographic findings were reversed within 40 seconds ofintravenous administration of edrophonium (Tensilon), anacetylcholinesterase inhibitor (i.e. an \"anticholinesterase\").Blood testing revealed high levels of an anti-acetylcholinereceptor antibody in her plasma, and a diagnosis of myastheniagravis was made.

Jill was treated with pyridostigmine bromide, which is along-acting anticholinesterase drug, and was also started onprednisone, which is a corticosteroid drug. She also underwentoccasional plasmapheresis when her symptoms became especiallysevere. She was given a prescription of atropine as needed toreduce the nausea, abdominal cramps, diarrhea, and excessivesalivation she experienced as side effects of theanticholinesterase drug.

Questions (1pt each)

1. Why are nausea, abdominal cramps, diarrhea, and excessivesalivation all side effects of the anticholinesterase drug she istaking?

2. Why is atropine beneficial in treating the gastrointestinalside effects mentioned in question #2?

3. Why does repetitive nerve stimulation result in decreasedamplitude of the muscle contractions?

4. What is plasmapheresis and why must Jill undergoplasmapheresis when her symptoms become especially severe?

5. Jill's doctor advises her that she is at increased risk forrespiratory failure. Why?