Clinical cases and Situational tasks

109. The deficiency of the thiamine in the human organism results in many neurologic symptoms: the lost of reflexes, increased excitability, dizziness. Explain, why the thiamine deficiency has such negative influence on the function of brain?

Answer: Glucose is the main source of energy for the brain.The main reaction in glucose breakdown is oxidative decarboxylation of the pyruvate with the participation of thiamine diphosphate. The lack of the latter inhibits the degradation of pyruvate to СО₂, Н₂О and ATP synthesis.

110. It is known, that glycogen, being the energetic store of the organism, is accumulated in liver and muscles, but never in brain, although the nervous tissue consumes a lot of glucose. Why glycogen is not accumulated in brain?

Answer: Glycogen is accumulated in brain tissue in the amount up to 0.1%. Its increased content would induce the increase of the brain weight and intracranial pressure, brain atrophy and death.

111. Glutamate, transported with blood to the brain tissue, is converted there to glutamine. Concentration of glutamine in blood going from brain is increased, Name the source of the supplementary amount of glutamine and biochemical significance and mechanism of these transformations.

Answer: Nervous system is the most sensitive to the toxic effect of ammonia. In brain tissue free ammonia is produced mainly as a course of hydrolytical deamination of AMP. Glutamate plays a crucial role in ammonia excretion, partially entering from blood and partially it is produced in the brain tissue from -ketoglutarate as a result of transamination and reductive amination. The latter is the most important mechanism of the ammonia detoxification in the brain. Glutamate under the influence of highactive glutamine synthetase bonds one more molecule of ammonia and is converted to glutamine, excreted from brain to blood.

112. The mother of a 16-year-old female calls the clinic because of concerns about her daughter’s eating habits. The mother states the she will not eat anything and is obsessed with exercise and losing weight. She also states that her daughter has been more withdrawn from friends and family. After discussion with the mother, the patient comes in for a physical examination. The patient is 5 ft 1 in tall and weighs 85 lb. She is in no acute distress but appears to have a depressed affect. The patient states she is worried that her friends will think she is fat if she eats more. She denies any binge eating. Her physical examination is normal, other than dry skin and thin fine hair on extremities. Laboratory tests reveal that she is anemic and has a low albumin and magnesium level. She has normal liver and thyroid tests. What is the most likely diagnosis? What potential medical problems may develop in a patient with this disorder? How can this disorder affect her menstrual cycles?

Answer: Diagnosis is anorexia nervosa. This is differentiated from bulimia because she denies binge eating with associated guilty feelings. Medical complications: Dry skin, lanugo, bradycardia, hypotension, dependent edema, hypothermia, anemia, osteoporosis, infertility, cardiac failure, and even death. Menstrual complications: Amenorrhea secondary to depression of the hypothalamic-pituitary axis. Infertility will result secondary to anovulation. Anorexia nervosa is a disease affecting primarily young women who have distorted body images. Although their weight is less than 30 percent under ideal body weight, they see themselves as overweight. Anorectics often use diuretic and laxative agents to accomplish their weight loss. Patients with bulimia, who usually induce emesis, may be at normal weight or even above ideal body weight; in contrast, anorectics are almost always under ideal body weight. Often, affected individuals become amenorrheic, have fine lanugo hair, and become hypothermic. Therapy must be multifaceted and include family and individual counseling, behavioral modification, and possibly medication. Severe cases may be fatal.