Question

A 21-year-old male visits with his family doctor at the urging of his parents when home for Spring Break. The parents are concerned because their son has lost a significant amount of weight. The young man is concerned because he is experiencing a heart rate of 120bpm while at rest and much higher when exercising. Additionally, his blood pressure averages 137/82 based upon four recordings. He has a recurring headache, tremors in his hands and suffers dyspnea.

This individual has been generally health for his entire life, eats a reasonably good diet and is very active, thus the above symptoms are concerning. Standard blood tests show normal levels of blood cells, however there is an elevated amount of metadrenalines (metabolite by-product of adrenaline) and the urinalysis also shows an elevated amount of metabolites of catecholamines. The physician then orders a 24-hour urine test where the patient collects urine at regular intervals for a 24-hour period. The patient is warned to avoid stimulants such as cocoa and caffeine during this time period. The results of this test confirm elevated metabolites of catecholamines. The physician suspects a condition called pheochromocytoma, which is a (usually) non-cancerous tumor of the adrenal gland. This tumor causes the excess secretion of catecholamines. To confirm this suspicion, the physician orders a specialized type of CT scan, called MBIG. This type of scan utilizes radioactive iodine as a contrast agent for visualization of masses as described above. A sample of MIBG results is shown below:

The MIBG confirms the presence of a tumor on the adrenal gland and the young man is scheduled for surgery to remove the mass. It is non-cancerous and he resumes his life. As a side note, current estimates are that only about 10% of adrenal tumors are cancerous.

4. Based upon your answers in #1, do you think that catecholamines would bind to extracellular or intracellular receptors in their target cells? Why? Describe how catecholamines would effect a cellular change inside their target cells based on where their receptors are located. Do you think that many of the body’s cells would be targets for these hormones? Why or why not? (3 pts)

Answer 1

4.Catecholamines bind to receptors on the surface of cells (extracellular) that comprises target organs. Catecholamines unlike the steroid hormones (which use receptors inside the target cells) cannot cross the cell membrane because of which they cannot use receptors inside the target cells as an example, epinephrine which is a catecholamine and water soluble, therfore can bind to extracellular receptors.

Hormones cause cellular changes by binding to a receptor on target cells, catecholamines bind to receptors on plasma membrane surface and trigers a signalling pathway to change the cells activity, the hormone which binds at surface remains at the surface of cell, while the intracellular product remains inside the cell, the hormone which initiates the signalling pathway is called first messanger, which activates second messanger in the cytoplasm, one important second messanger is the cyclic AMP (cAMP), when protien binds to its membrane receptor, G-protien is activated, when hormone is not bound to the receptor, G-protien is not active, when a hormones binds to a receptor G-protien is activated, the activated G-protien activates a membrane bound enzyme called adenylyl cyclase, which trigers cellular response. Cellular response to hormones include the production of protien, enzymes and altered membrane permeablity.

Many of the cells in our body would not be target for these hormones, the body's response to diffrent catecholamines depend on two major types of adrenergic receptors, alpha adrenergic receptors and beeta adrenergic receptors, in general activation of alpha adrenergic receptors results in vasoconstriction, contraction of uterine muscles, dilation of pupils etc and activation of beeta adrenergic receptors resultsa in vasodilation, increase in heart rate, dilation of bronchi, stimulation of cardiac contraction etc.