NATIONAL CENTER FOR CASE STUDY TEACHING IN SCIENCE Part IIl-Sandy Thompson A 25-
ID: 3512623 • Letter: N
Question
NATIONAL CENTER FOR CASE STUDY TEACHING IN SCIENCE Part IIl-Sandy Thompson A 25-year-old preschool teacher, Sandy Thompson, has not been feeling like herself lately. She has been feeling quite tired and her co-workers have commented on her droopy eyelids. Additionally, she is experiencing weakness in her arms and legs, has difficulty talking clearly and even her students parents have been concerned that Sandy hasn't been ocing er appy at work. One day at lunch, Sandy started to choke on her food, causing one of her coworkers pertorm the Heimlich maneuver on her. While the scare didn't cause any permanent damage, Sandy is convinced that it is time to go see a doctor. When she finally arrives at her appointment with Dr. Wayne, she explains to Dr. Wayne what has been going on, and the doctor decides to run a few blood tests. Sandy's blood work results are presented below. S.Thompson-Test Results Resut 115/73 36.5 94 144 4.3 100 11.3 154 Present Normal Range 90-120/60-80 36-38 70-110 135-145 3.5-5.0 100 4.6-12 80-180 Not Present Test Blood Pressure Hematocrit (6) Glucose (mg/d) Sodium (mmoll) Potassium (mmolL) AChE Activity Test(%) Tetraiodothyronine or thyraxine (T (ngldl) Serum Triodothyronine (T.) ngld) Antibodies for ACh Receptors Questions 1. What symptoms is she experiencing 2. What levels from her blood work are abnormal? 3. How would antibodies against ACh receptors affect the neuromuscular junction? 4. How would andbodies against the ACh receptors affect the influx of Na' into the cell?Explanation / Answer
1. She is experiencing the symptoms of Myasthenia gravis.
2. The antibodies for Acetylcholine (ACh) receptors are present in her blood, which is absent in a normal person.
3. Antibodies against ACh receptors are autoantibodies generated by the immune system that target the self-proteins i.e. acetylcholine receptors present on skeletal muscle fibers. ACh receptors bind to acetylcholine which is a neurotransmitter that transmits impulses between nerve cells. Acetylcholine is released at the end of a nerve ending and travels across the gap between the nerve ending and a muscle fiber at the neuromuscular junction to cause muscle contraction. AChR antibodies bind to these receptors and prevent acetylcholine from binding to it or may start an inflammatory reaction that can degrade these receptors at the neuromuscular junction.
4. When ACh is bound to its receptor, the ligand gated ion channels in the skeletal muscle cell membrane opens to allow the entry of sodium. The influx of sodium depolarizes the membrane which in turn opens the voltage gated ion channels. This results in initiation of an action potential along the plasma membrane of the skeletal muscle. Thus, antibodies against ACh receptors would inhibit this depolarization.
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