Question

For each of the following conditions, provide a possible effect in the body (be sure to include your rationale for each for full credit):

    Hyposecretion of PIH

    Hypersecretion of GnRH

    Tumor within the adrenal cortex

    Hyperthyroidism

Chief Complaint: 37 year old female complaining of acute pain over her right flank and persistent abdominal pain.

History: A 37 year old female presents to her physician’s office with acute pain over her right flank and persistent abdominal pain. Additionally, she reports a 2 year history of generalized fatigue and depression associated with difficulty concentrating and significant mood swings. She has no history of drug or alcohol use and no significant family history. Following ultrasound examination she is diagnosed with a kidney stone. Laboratory tests of serum parathyroid levels reveal an abnormally high parathyroid hormone concentration of 125 pg/mL. The patient is further diagnosed with hyperparathyroidism and it is determined that exploratory surgery is needed. Once the parathyroid glands have been exposed they are visually and physically examined. On palpation a small mass is found on the right inferior parathyroid gland and removed. Parathryoid hormone levels were monitored until returning to normal limits.

Guiding Questions

1. Given what you know about the function of the parathyroid gland what is another substance in the blood serum that you would expect to be outside of normal limits? Why?

2. What are the upstream regulators of parathyroid function? In other words, what is the normal flow of information to either stimulate or suppress parathyroid function?

3. What are the downstream effectors that the parathyroid hormone acts on? How does this explain the symptoms our patient presented with?

4. Propose a possible treatment for the patient in this case study. How does this treatment improve conditions for the patient? Are these improvements seen at the cellular, tissue, organ or systemic level?  

5. Relate this case to the general homeostatic mechanism pathway - identify the setpoint, variables, receptor(s), effector(s), and integrating center in this specific case.

Answer 1

1. I would expect serum calcium levels to also be abnormally high. PTH stimulates osteoclasts and increases resorption of bone. This will elevate the levels of calcium in the blood.

2. The primary trigger for secretion of parathyroid hormone is low serum calcium levels.

Low serum calcium > secretion of PTH > efflux of calcium from bone, reduced urinary loss of calcium, enhanced absorption of calcium from intestine

3. The downstream effectors that PTH acts on are:

Bones - stimulates osteoclasts leading to increased resorption of calcium from bone

Kidney - increases reuptake of calcium from proximal convoluted tubule of nephron

Gastrointestinal tract - PTH stimulates the activation of Vitamin D. This leads to increased absorption of Calcium from the intestines.

Flank pain - due to kidney stones. Excess serum calcium is filtered by nephrons leading to formation of calculi in the kidney

Difficulty in concentrating and significant mood swings are known symptoms of primary hyperparathyroidism. But the exact mechanism of how hypercalcemia leads to these psychiatric manifestations is still being evaluated by scientists.

4. The possible treatment options that are available for this patient include:

Surgical excision of the tumour - this is the best possible treatment option. Although this may cause hypocalcemia in the patient, it can be prevented with dietary calcium supplementation. Surgery offers a permanent cure to this condition.

Pharmacotherapy

a. Cinacalcet - a calcimimetic drug that inhibits the production of PTH by the parathyroid gland

b. Bisphosphonates - these improve levels of calcium in the bones. Alendronate is widely used

c. Raloxifen - This is a selective estrogen receptor modulator. It significantly reduces the level of calcium in the blood.

5. Calcium homeostasis:
The setpoint is serum calcium level (normal range 9-11 mg/dL)
Variables - serum calcium level, PTH levels
Receptors - PTH receptors in the kidney tubules, on the osteoclasts
Effectors - Kidney tubules, GIT, Osteoclasts in bone
Integrating centre - The parathyroid gland