(3D model by www.anatomylearning.com)
THYROID GLAND
The thyroid gland, which sits mid-line and anteriorly on the neck, is like the manager of a factory and maintains metabolic rate and serum calcium levels in the body (Cain, Campbell, Minorsky, Reece, Urry, 2017, Chapter 45). The thyroid gland secretes three different types of hormones, thyroxine (T4), triiodothyronine (T3), and calcitonin, all which act like supervisors of the factory.
Figure 1. Thyroid Gland (University of California Los Angeles Health, n.d.)
REGULATION OF T3 AND T4
When there is a decrease in the number of T3 and T4 hormones in the body, the metabolic rate decreases (Cain, Campbell, Minorsky, Reece, Urry, 2017, Chapter 45); similar to how the production of a factory declines from insufficient motivation by the supervisor on workers. The decrease in metabolic rate then causes a stimulus to be sent to the hypothalamus, which is located in the limbic system, from various sensory nerves; this would be like a report being sent from the factory to the chief operating officer (COO), the hypothalamus, that more supervisors are needed to increase worker motivation.
After receiving the stimulus from the various sensory neurons, the hypothalamus then releases a hormone called thyrotropin-releasing hormone (TRH) to the anterior pituitary gland (Cain, Campbell, Minorsky, Reece, Urry, 2017, Chapter 45); analogically, the COO is sending an internal company memo, TRH, to the division director, the anterior pituitary gland, regarding the issue.
The anterior pituitary gland would then release thyroid-stimulating hormone (TSH) via blood vessels to stimulate the thyroid gland (Cain, Campbell, Minorsky, Reece, Urry, 2017, Chapter 45); analogically, the division director is sending an intra-company email, TSH, to the manager informing that more supervisors are needed.
The thyroid gland would then release T3 and T4 hormones into the vessels, where then they would reach various organs of the body to stimulate them and cause them to increase their basal metabolic rates, such as increasing heat production and oxygen consumption, stimulation of the respiratory system and the cardiovascular system to increase blood flow and oxygen delivery to the body’s tissues, and to stimulate bone formation with the help of growth hormone (Cain, Campbell, Minorsky, Reece, Urry, 2017, Chapter 45); analogically, the manager puts more supervisors in the factory which then motivate the workers to increase their productivity, and for those supervisors to also work with an engineer, growth hormone, to create steel beams that maintain the skeletal structure of the factory.
As the levels of T3 and T4 hormones return to normal levels, a negative feedback mechanism occurs to decrease the levels of TRH and TSH being released by the hypothalamus and anterior pituitary gland, respectively, so that the body’s metabolic rate remains stable (Cain, Campbell, Minorsky, Reece, Urry, 2017, Chapter 45); analogically, as the number of supervisors goes up and productivity increases, reports are sent to the COO and division director to change company strategy and decrease the number of supervisors needed to motivate the workers, the company strategy will change once again that productivity is down. The cycle repeats itself when the levels of T3 and T4 are insufficient.
Figure 2. Control of Thyroid Hormones (Bowen, n.d.)
REGULATION OF CALCITONIN
Calcitonin is a hormone that helps regulate the level of serum calcium by lowering the amount of it in the bloodstream (Cain, Campbell, Minorsky, Reece, Urry, 2017, Chapter 45). Calcitonin prevents the breakdown of bone and stimulates the kidneys to excrete excess calcium from the bloodstream; analogically, the manager is sending a supervisor, calcitonin, to prevent any steel beams from being melted down and recycled inside the factory and to instruct the cleaning crew, the kidneys, to trash any excess steel.
The amount of calcitonin is reduced by a negative-feedback mechanism once the serum calcium reaches normal levels, and the cycle repeats itself once calcium increases again.
Resources:
Bowen, Richard. (n.d.). Control of thyroid hormone synthesis and secretion [digital image]. Retrieved from http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/thyroid/control.html
Cain, M. L., Campbell, N. A., Minorsky, P. V., Reece, J. B., Urry, L. A. (2017). Campbell biology. New York, NY: Pearson Education, Inc.
University of California Los Angeles Health. (n.d.). Thyroid gland [digital image]. Retrieved from https://www.uclahealth.org/endocrine-center/thyroid-faqs