Deck 18: B--Principles of Endocrinology: the Central Endocrine Glands

Question 1

Describe how the hypothalamus and pituitary gland function in the negative feedback control of cortisol secretion when a person is under stress. Mention all relevant hormones involved in the process.

Answer 1

Under stress, the hypothalamus secretes corticotropin-releasing hormone (CRH), which causes the pituitary gland to release adrenocorticotropic hormone (ACTH, also called corticotropin). The ACTH stimulates the adrenal cortex to secrete cortisol, which promotes metabolic changes that help resist stress. An increase in cortisol levels causes the hypothalamus to secrete less CRH, and this inhibition ultimately causes a decrease in the amount of cortisol secreted.

Question 2

Describe circadian rhythms and the roles played by the SCN, clock proteins, melanopsin, and melatonin to control them.

Answer 2

A circadian rhythm is repetitive oscillations in hormone levels that are very regular and cycle once every 24 hours. The SCN (suprachiasmatic nucleus) in the hypothalamus synthesizes clock proteins that accumulate during part of the day, but then decrease in concentration due to negative feedback. The fluctuating levels of clock proteins lead to cyclic changes in effector organs throughout the day. Melanopsin is a protein, found in certain ganglion cells of the eye, that enables these cells to cue to the SCN about the absence or presence of light. In turn, the SCN relays this information to the pineal gland, which secretes melatonin that helps keep the body's circadian rhythms synchronized with the light-dark cycle. More melatonin is secreted in the dark and plays an important role in promoting sleep.

Question 3

Use this figure to answer the corresponding questions.
Name all hormones shown in this figure that are classified as tropic hormones, and place the appropriate numbers by the hormone names.

Answer 3

TSH-1, ACTH-2, LH-6, FSH-7

Question 4

Describe the primary factors involved in growth.

Question 5

List the factors that could cause abnormal levels of secretion from endocrine glands, and explain why target cells may display abnormal responsiveness to a hormone.

Question 6

Compare and contrast the way in which lipophilic and hydrophilic hormones affect their target cells. Include in your answer the type of receptor used, the major events promoted inside the cell after these hormone attach to their specific receptors, and the relative amount of time required to see the effect of hormone binding.