Download Laboratory Exercise 18: Experiments in Hormonal Action

Laboratory Exercise 18: Experiments in Hormonal Action
Hormones circulate via the blood and exert their effects on specific organs, called target
tissue.
A. The Effect of Epinephrine on the Frog Heart
Epinephrine increases the frequency and strength of the heart’s contractions. This same
effect is observed when the SNS stimulates the heart. Acetylcholine, from the
parasympathetic nervous system, slows heart rate and decreases strength of the heart’s
contractions. This same effect is observed when the vagus nerve (PNS) stimulates the
heart.
B. The Effect of Insulin on an Organism’s Behavior
Insulin is secreted by the pancreas into the blood. It circulates to the muscles, adipose
and other connective tissues where it increases the rate of glucose uptake across the cell
membranes of these cells. Insulin in excess causes too rapid drop in the blood glucose
level, resulting in hypoglycemia. However, the nervous system depends exclusively on
glucose as an energy source. When glucose is removed from the blood at a higher rate
than normal due to the excess insulin, organism is placed under stress as it can not obtain
sufficient glucose from the blood. The organism will demonstrate hyperirritability,
followed by convulsions, coma and death if the normal blood glucose concentration is not
quickly restored.
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Physio-Ex Exercise - Endocrine System Physiology
Thyroid Gland Physiology
Objectives
1. Define the terms: metabolism, hormone replacement therapy.
2. Explain the function of thyroxine (T3 and T4) in maintaining an animal’s metabolic rate.
3. Explain the function of thyroid-stimulating hormone (TSH) on an animal’s metabolic rate.
4. Explain how hormone replacement therapy works.
The endocrine system exerts its effects on the entire body and on specific tissues and organs.
Computer simulations allow the study of the effects of hormones on body by use of “virtual”
animals.
Hormones and Metabolism
Metabolism – all biochemical reaction occurring in the body. Metabolism involves:
a. Catabolism – a process by which complex large molecules broken down into simple small
molecules by the use of enzymes.
b. Anabolism – a process by which simple small molecules are built up into complex large
molecules by the use of enzymes.
During anabolism energy is stored in the chemical bonds of the complex molecules.
During catabolism energy is released from the chemical bonds of the complex molecules used
for several cellular functions.
a. The physiological and biochemical activities of the cell,
b. The production of ATP and
c. Given off as body heat to maintain a constant body temperature for metabolic reactions to
occur in the cells of the body.
The thyroid gland secretes the hormone thyroxine (T3 and T4) to maintain metabolism and body
heat. The production of thyroxine is controlled by TSH secretion from the anterior pituitary
gland. TSH is carried by the blood to the thyroid gland (the target tissue) to cause the thyroid to
produce thyroxine. Indirectly then the animal’s metabolic rate is the result of pituitary TSH
secretion.
In this experiment three rats will be used. One rat is normal; the second rat has its thyroid gland
removed, thyroidectomized (Tx); the third rat has its pituitary gland removed, hypophysectomized
(Hypox).
You will perform 3 experiments on each animal:
1. Determine the basal metabolic rate.
2. Determine the metabolic rate after it has been injected with T4.
3. Determine the metabolic rate after it has been injected with TSH.
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Questions and Answers to Activities 1-3.
Activity 1: Determining Baseline Metabolic Rates (BMR)
1. How did the metabolic rates of the three rats differ?
Normal – Rat with intact thyroid gland and pituitary gland had a relatively high BMR.
Tx – Rat with removed thyroid gland and intact pituitary gland had a relatively low BMR.
Hypo – Rat with removed pituitary gland and intact thyroid gland had a relatively low BMR.
2. Why did the metabolic rates differ?
Normal rat produces sufficient thyroid hormones (T3, T4) and thyroid-stimulation hormone (TSH) to
maintain a relatively high cell metabolism as demonstrated by a relatively high O2 consumption.
Tx rat has a low concentration of T3 and T4, so cell metabolism is slow as indicated by lower O2
consumption compared to the normal rat.
Hypo rat has low concentration of TSH, so cannot stimulate the thyroid gland cells to produce T3
and T4, thus cell metabolism is slow as indicated by a lower O2 consumption compared to the
normal rat.
Activity 2: Determining the Effect of Thyroxine on Metabolic Rate
1. What was the effect of thyroxine on the normal rat’s metabolic rate? How does it
compare to the normal rat’s BMR?
The effect of exogenous T3 and T4 on normal rat’s metabolism was to increase the BMR as
demonstrated by the increased O2 consumption above the normal BMR.
Why was this effect seen?
The T3 and T4 stimulates use of oxygen by the cells to produce ATP by increasing the cell
metabolism of carbohydrates, lipids and proteins.
2. What was the effect of thyroxine on the Tx rat’s metabolic rate? How does it compare to the Tx rat’s
BMR?
The effect of exogenous T3 and T4 on Tx rat’s metabolism was to increase the metabolic rate
compared to the BMR of a Tx rat.
Why was this effect seen?
The T3 and T4 stimulated the body cells directly to increase cell metabolism as indicated by increased
O2 consumption compared to the Tx rat.
3. What was the effect of thyroxine on Hypo rat’s metabolic rate? How does it compare to the Hypo rat’s
BMR?
The effect of exogenous T3 and T4 on the Hypo rat was to increase cell metabolic rate
compared to the BMR of a Hypo rat.
Why was this effect seen?
The T3 and T4 stimulated the body cells directly to increase cell metabolism as indicated by
increased O2 consumption compared to the Hypo rat.
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Activity 3: Determining the Effect of TSH on Metabolic Rate
1. What was the effect of TSH on the normal rat’s metabolic rate? How does it compare to the normal
rat’s BMR?
The effect of exogenous TSH injection on the normal rat’s metabolism was to increase the BMR
as demonstrated by increase of O2 consumption above the normal rat’s BMR.
Why was this effect seen?
The TSH increased the production of T3 and T4 of the intact thyroid gland.
2. What was the effect of TSH on the Tx rat’s metabolic rate? How does it compare to the Tx rat’s
BMR?
The effect of exogenous TSH on a Tx rat’s metabolism does not change the BMR compared to the
Tx rat’s BMR.
Why was this effect seen?
The TSH has no thyroid gland to stimulate T3 and T4 production.
3. What was the effect of TSH on the Hypo rat’s metabolic rate? How does it compare to the Hypo
rat’s BMR?
The effect of exogenous TSH on a Hypo rat’s metabolism was to increase the BMR compared to
Hypo rat’s BMR.
Why was this effect seen?
The TSH replaces the lost TSH due to pituitary gland removal and increased T3 and T4
production, since there is an intact thyroid gland as indicated by increased O2 consumption
compared to the Hypo rat.
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