Question

1. Primary hypothyroidism is caused by a dysfunctional or nonfunctional thyroid gland. Describe the endocrine axis that regulates the secretion of thyroid hormone, including all organs and hormones that are a part of it. What effect does thyroid hormone have on its target tissues and organs? Which of the afore-mentioned hormones would you expect to find above normal levels in an individual with primary hypothyroidism?

2. Vaccination provides immunity to specific pathogens and is an important means of reducing infectious diseases within the population. If an individual is exposed to a pathogen that they were previously vaccinated against, which immune cells would you expect to be activated to provide immunity? What type of immune reaction was generated immediately following the vaccination? And how do these two immune reactions differ? Be specific.

3. Cholecystectomy is surgical removal of the gallbladder. Describe at least one reason (other than abdominal pain) that this surgery might be performed. How would removal of the gallbladder affect the physiology of digestion? And what specific dietary modifications would be necessary for a patient who has had a cholecystectomy?

Answer 1

1. The thyroid gland is under the control of the thyroid-stimulating hormone which is produced by the anterior pituitary. The release of TSH is governed by the release of Thyrotropin-releasing hormone (TRH) from the hypothalamus. TRH stimulates the release of TSH from the pituitary, which stimulates thyroid hormone release from the thyroid gland. As blood concentrations of thyroid hormones increase, they inhibit both TSH and TRH, leading to a reduction in the formation of thyroxine. The thyroid hormone is necessary for the regulation of metabolism. It affects virtually every organ system in the body. For instance, in the cardiovascular system, it increases the heart rate and blood pressure. It increases the rate of glycolysis and other catabolic processes. Thyroid hormone also increases thermiogenesis, causes sweating, increases the rate of breathing, increased expression of respiratory enzymes, etc.

In primary hypothyroidism, TSH is usually elevated. The release of TRH is regulated by feedback inhibition from thyroxine levels. In primary hypothyroidism, thyroxine levels are low. Thus even TRH levels will be high. In milder cases of hypothyroidism, the TSH and TRH may be in normal limits.

2. If an individual is exposed to a pathogen that they were previously vaccinated against, the memory cells are activated. Reactivated memory cells differentiate to plasma cells and begin antibody production. A memory cells a long-lived lymphocyte capable of responding to a particular antigen on its reintroduction, long after the exposure that prompted its production.

The initial response to a vaccine is similar to that of the primary response upon first exposure to a pathogen. It is slow and limited. The antigen is presented by an antigen-presenting cell to a helper T-cell. The T-cell releases cytokines that lead to the proliferation of B-cells.  But the reactivation of memory cells is a fast process. The antibody generation is very swift.

3. Carcinoma of the gall bladder is another indication for surgical removal of the gall bladder. When the gallbladder is removed, bile made by the liver can no longer be stored between meals. Instead, the bile flows directly into the intestine anytime the liver produces it. This impairs the digestion of fats. After a cholecystectomy, patients are advised to avoid eating high-fat foods, fried and greasy foods. They are encouraged to eat a low-fat diet with plenty of dietary fibers and proteins.