Endocrine system: Thyroid hormones and function– computer simulation
Introduction
Two main controlling systems of the body are nervous system and endocrine system. Though
both the system primarily rely on negative feedback mechanism, the nervous system manage its
rapid control by nerve impulses, where as the endocrine system influences the metabolic activity
by hormones. Endocrine gland or tissue produces and secrets hormones which act as a chemical
messenger once released into the blood and transported throughout the body. Hormonal effect on
the body is diverse and widespread which include reproduction, growth and development,
mobilization of body’s defenses; maintain sodium, water and nutrient balance and regulating
cellular metabolism. Metabolism involves catabolism and anabolism. Catabolism is a process by
which complex molecules are broken into simple substances and anabolism is the process when
simple substances are made into complex molecules by enzymes. During the catabolism process,
the energy is released and used to make ATP. The most important hormone in maintaining
metabolism is thyroxine secreted by thyroid gland. The production of Thyroxine is really
controlled by pituitary gland which secretes Thyroid Stimulating Hormone (TSH). When TSH is
released into the blood to thyroid gland, it causes the thyroid gland to make more Thyroxine.
Rising Thyroid hormone level sends a negative feedback to hypothalamus which results into
releasing of Thyrotropin releasing hormone (TRH) which regulates the release of TSH.. Thus,
the hypothalamus and pituitary gland control the release of Thyroxine and ultimately animal’s
metabolic rate. In this computer stimulated experiment, we can see how different gland and their
secretion are interdependent to each other to maintain the metabolism.
Objective:
Activity 1- Determining the Baseline Metabolic rate.
Activity 2- Determining the Effects of Thyroxine on Metabolic Rate.
Activity 3- Determinig the Effects of TSH on metabolic rate.
Materials:
* Human Anatomy and Physiology Laboratory Manual by Elaine N. Marieb and Susan J.
Mitchell. Ninth Edition. Cat version. Exercise number 28B. Activity 1, 2, & 3 (page PEx-5154).
* Physio-Ex Version 8 Laboratory experiment in physiology. Pearson/Benjamin Cumings
ARGOSY.
Method:
Formula used to determine the oxygen consumption per hour for the rateml Oxygen used
1 minute
X 60 minutes
1 hour
Formula used to determine the metabolic rate per kilogram of body weight
Metabolic rate ml oxygen /kg/hr = ml oxygen/hr
Wt. in Kg
Results:
Baseline
Weight (gr)
Normal rat
249.7
Thyriodectomized
245.7
rat
Hypophysectomized 245.3
rat
Oxygen (ml/min)
Oxygen (ml/h)
7.1
6.7
426
402
Metabolic rate
Oxygen
(ml/kg/hr)
1704
1634.15
6.3
378
1542.86
Chart 1 - determining the baseline metabolic rate of each rate.
With Thyroxine
Weight (gr)
Oxygen (ml/min)
Oxygen (ml/h)
Normal rat
249.4
7.9
474
Metabolic rate
Oxygen
(ml/kg/hr)
1903.61
Thyroidectomized
245.9
7.6
456
1853.66
7.1
426
1745.90
Hypophysectomized 244
rat
Chart 2 - Determining the effect of Thyroxine on Metabolic Rate.
With TSH
Weight (gr)
Oxygen (ml/min)
Oxygen (ml/h)
Normal rat
250.6
7.8
468
Metabolic rate
Oxygen
(ml/kg/hr)
1864.54
Thyroidectomized
244.8
6.5
390
1591.84
Hypophysectomized 245.9
7.5
450
1844.26
Chart 3 determining the effect of TSH on metabolic Rate.
Discussion:
During the activity 1, the normal rat showed the fastest baseline metabolic rate compared to
Thyroidectomized rat (thyroid gland removed) and Hypophysectomized rat(pituitary gland
removed). Since thyroid gland has been removed from the thyoidectomized rat, it could not
produce Thyroxine to maintain the original metabolic rate, and hypodectomized rat could not
release the Thyrotropin releasing hormone to stimulate the release of TSH. Hence its metabolism
was the slowest.
After thyroxine was injected to the rats in activity 2, all three rats showed not much change in
their baseline weight, but they showed higher metabolism rate than thier baseline metabolic rate
because releasing of more thyroxine into the body enhanced the capacity of making more ATP
which resulted in higher metabolic rate.
During the activity 3, when the normal rat was injected with TSH, it showed growth in
their metabolic rate compared to its baseline metabolic rate because the hormone TSH stimulate
its thyroid gland into making more thyroid hormone which finally resulted into increasing
metabolic rate. When the Thyroidectomized rat was injected with TSH, its metabolic rate
declined because there was no thyroid gland to stimulate.
When Hypophysectomized rat was injected with TSH, it showed the rapid growth in its
metabolism rate compared to its baseline metabolic rate. Since the hypothalamus was removed, it
could not send the releasing hormone (TRH) to pituitary gland to secrete TSH. Therefore, its
baseline metabolic rate was low. When it is injected by TSH, it shows growth in its metabolism
because the thyroid gland gets the stimulation to secrete more Thyroid hormone. As thyroid
gland secretes and releases more thyroid hormone, the body’s metabolism is improved.
References
* Human Anatomy and Physiology Laboratory Manual by marib Elaine and Susan Mitchell.
Ninth Edition Cat Version. Exercise number 28B, page number PEx 51-54.
* Physio Ex Version 8 laboratory Experiment in physiology. Pearson/Benjamin Cumings
ARGOSY.
* Marib,Elaine Nicpon. Human Anatomy & physiology. San Francisco: Person Benjamin
Cumings,2007. Pages 605-624.