Lab 24: Endocrine System Physiology I
How do you calculate oxygen consumption per hour?
(ml O2 consumed/1 min) * (60 minutes/hour) which equals (ml O2/hour)
A laboratory technician withdraws a blood sample from a vein in your upper arm knowing that the plasma glucose concentration will be _____ and the index finger
A laboratory technician withdraws a blood sample from a vein in your upper arm knowing that the plasma glucose concentration will be the same in both the arm vein and the index finger
What is a glucose standard curve?
A point of reference for converting optical density into glucose readings.
Your patients are pre-diabetic. What advice would you give them?
Advice can include a change in eating habits (i.e., opting for whole wheat and fiber-based carbohydrates instead of simple sugars) and exercise. In addition, some studies show that fecal implantation improves the microbiota that contributes to pancreatic and liver metabolisms.
An injection of TSH to an otherwise normal animal will cause which of the following? a. decreased levels of T4 secretion b. increased levels of TRH secretion c. hypothyroidism d. goiter development
An injection of TSH to an otherwise normal animal will cause goiter development
Propylthiouracil
Antithyroid drug, it inhibits the production of thyroxine
What is the effect of PTU injection on a hypophysectomized patient's BMR?
BMR decreased
What is the effect of PTU injection on a normal patient's BMR?
BMR decreased
What is the effect of PTU injection on a thyroidectomized patient's BMR?
BMR decreased
What is the effect of TSH injection on a hypophysectomized patient's BMR?
BMR increased
What is the effect of TSH injection on a normal patient's BMR?
BMR increased
What is the effect of TSH injection on a thyroidectomized patient's BMR?
BMR increased
What is the effect of thyroxine injection on a hypophysectomized patient's BMR?
BMR increased
What is the effect of thyroxine injection on a normal patient's BMR?
BMR increased
What is the effect of thyroxine injection on a thyroidectomized patient's BMR?
BMR increased
True or False: Insulin is a hormone secreted into the stomach to aid with starch digestion
False
If one has high thyroid levels (a BMR ____), they would be categorized as ____
If one has high thyroid levels (a BMR above 1800), they would be categorized as hyperthyroid
If one has low thyroid levels (a BMR ____), they would be categorized as ____
If one has low thyroid levels (a BMR below 1600), they would be categorized as hypothyroid
If one has normal thyroid levels (a BMR ____), they would be categorized as ____
If one has normal thyroid levels (a BMR from 1650 to 1750), they would be categorized as euthyroid
Why don't patients with normal, thyroidectomized, or hypophysectomized develop a goiter after injection with thyroxine
In all cases, TSH levels are not elevated by thyroxine injection
In the spectrophotometric assay, the optical density increases as ____
In the spectrophotometric assay, the optical density increases as the glucose concentration in the sample increases
Changes in blood glucose levels - When are insulin and glucagon secreted? - What cells produce and secrete insulin and glucagon?
Insulin - when blood glucose is too high Glucagon - when blood glucose is too low Beta cells produce insulin Alpha cells produce glucagon
What is the purpose of barium hydroxide?
It dissolves and clears both proteins and cell membranes of erythrocytes. This gets rid of everything that can interfere with the test and clear readings can be obtained.
Which of the following statements about metabolism is false? a. anabolism refers to the chemical reaction that build larger, more complex molecules b. catabolism refers to the chemical reaction that breaks down, large complex molecules into smaller molecules c. energy released in metabolism can be in the form of heat d. all of the energy from metabolism is ultimately stored in the chemical bonds of ATP
It is true that anabolism refers to the chemical reaction that build larger, more complex molecules, catabolism refers to the chemical reaction that breaks down, large complex molecules into smaller molecules, and that energy released in metabolism can be in the form of heat. It is not true that all of the energy from metabolism is ultimately stored in the chemical bonds of ATP
What is type 2 diabetes?
It occurs when the body does not properly use insulin. Unreactive to insulin
Using oxygen consumption per hour, how do you calculate the metabolic rate per kilogram of body weight?
Metabolic rate = (ml O2/hour)/(weight in kg) which equals (ml O2/kg/hour)
In the hypophysectomized rat was there any change in metabolic rate when you injected propylthiouracil? Explain.
No, there was no change in metabolic rate from PTU injection. The hypophysectomized rat already cannot produce thyroxine (from lack of the ability to produce TSH to then stimulate thyroxine synthesis) so an inhibitor of thyroxine synthesis does not have an effect.
In the thryoidectomized rat was there any change in metabolic rate when you injected TSH? Explain.
No. Since the thyriodectomized rats do not have a thyroid gland (and therefore cannot produce thyroxine endogenously), addition of TSH does not increase thyroxine levels or, correspondingly, metabolic rate.
Which of the rats developed a goiter after injection with thyroxine? Explain.
None of the rats developed a goiter after injection with thyroxine. A goiter is formed from excessive stimulation of the thyroid by TSH. The injected thyroxine exerts negative feedback on both TRH and TSH release, so that the TSH would be lower than normal and a goiter would not be formed.
Would a patient with normal, thyroidectomized, or hypophysectomized develop a goiter after injection with thyroxine?
None of these patients would develop a goiter with a thyroxine injection
Would a patient with normal, thyroidectomized, or hypophysectomized develop a goiter after injection with PTU?
Only the normal patient would develop a goiter
Would a patient with normal, thyroidectomized, or hypophysectomized develop a goiter after injection with TSH?
Only the thyroidectomized patient would develop a goiter
How would you treat a thyroidectomized animal so that it functions like a "normal" animal?
Provide them with T4 supplements
A patient with FPG (fasting plasma glucose levels) values greater than or equal to 126 mg/dl in two FPG test is diagnosed with diabetes. FPG values bn 110 and 126 mg/dl indicate impairment or borderline impairment of insulin-mediated glucose uptake by cells. FPG values less than 110 mg/dl are considered normal.
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Blood glucose level is maintained by two important hormones: insulin and glucagon. Insulin is secreted by the beta (β) cells of the Islets of Langerhans of the pancreas in response to an increased blood glucose level. Its target tissues are all cells in the body, except red blood cells and neurons. It tells its target cells to insert a GLUT-4 glucose carrier into their cell membrane so that they may take glucose out of the blood for metabolism. Glucagon, on the other hand, is secreted by the alpha (α) cells of the Islets of Langerhans in response to a decreased blood glucose level. Its target tissues are the liver and adipose tissue. It tells the adipocytes to release fat from their cells as an alternate energy source for our body's cells. It also tells the liver to break down glycogen into glucose and release that glucose into the bloodstream and to convert non-carbohydrate chemicals such as fat into glucose. These two hormones are antagonistic: insulin acts to lower blood glucose level after a meal and glucagon acts to raise it during starvation. Type I Diabetes Mellitus is a condition wherein the body does not produce insulin. It is usually caused by an autoimmune disorder that destroys the β cells of the pancreas. The result is that blood sugar increases to a dangerously high level as there is no way of getting glucose into the body's cells. Patients diagnosed with Type I DM are put on insulin therapy, where they have daily injections of recombinant insulin to replace the insulin that would otherwise naturally control their glucose level. Type II Diabetes Mellitus is a condition wherein the body's cells begin to develop insulin insensitivity and ignore the insulin being secreted naturally by the body. This is usually due to chronic over-section of insulin in people who are obese or inactive. Patients diagnosed with Type II DM are advised to lose weight, eat a low carbohydrate diet and exercise. They can also be put on medication to increase insulin sensitivity, and some even go on insulin injections. You will be testing the blood of five patients to see if any are diabetic or pre-diabetic. A fasting blood glucose level below 110 mg/dl is considered normal; a fasting glucose level between 110-126 mg/dl is considered pre-diabetic; and a fasting blood glucose level over 126 is considered diabetes. Your first step in determining the glucose concentration in the blood of your patients is to create a standard curve. You may remember doing this in the spectrophotometry lab that we completed in the beginning of the semester. Recall that a standard curve is a plot of known values, used to determine an unknown value. Your next step is to measure the optical density and glucose concentration from your five patients. Use the standard curve above to determine glucose concentration based on the optical density value that you obtain through the experiment.
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Insulin is a hormone produced by the beta cells of the endocrine portion of the pancreas. This hormone is vital to the regulation of plasma glucose levels, or "blood sugar," because the hormone enables our cells to absorb glucose from the bloodstream. Glucose absorbed form the blood is either used as fuel for metabolism or stored as glycogen (aka animal starch), which is most notable in liver and muscle cells. About 75% of glucose consumed during a meal is stored as glycogen. As humans do not feed continuously (we are considered "discontinuous feeders"), the production of glycogen from a meal ensures that a supply of glucose will be available for several hours after a meal. Furthermore, the body has to maintain a certain level of plasma glucose to continuously serve nerve cells bc these cell types use only glucose for metabolic fuel. When glucose levels in the plasma fall below a certain value, the alpha cells of the pancreas are stimulated to release the hormone glucagon. Glucagon stimulates the breakdown of stored glycogen into glucose, which is then released back into the blood. When the pancreas does not produce enough insulin, type 1 diabetes mellitus results. When the pancreas produces enough insulin but the body fails to respond to it, type 2 diabetes mellitus results. In either case, glucose remains in the bloodstream, and the body's cells are unable to take it up to serve as the primary fuel for metabolism. The kidneys then filter the excess glucose out of the plasma. Bc the reabsorption of filtered glucose involves a finite number of transporters in kidney tubule cells, some of the excess glucose is not reabsorbed into the circulation. Instead, it passes out of the body in urine (hence sweet urine as the name diabetes mellitus suggests).
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Metabolic rate (MR) is the amount of energy required for necessary body functions. There are several factors that control MR, including gender (males have a higher MR) and age (MR decreases with age). There is also a hormone made by our thyroid gland that increases MR; this hormone is called Thyroxine (TH). Thyroxine's release is a multi-step process. The hypothalamus first secretes a hormone called Thyrotropin Releasing Hormone (TRH). This in turn stimulates the anterior pituitary (adenohypophysis) to secrete a hormone called Thyroid Stimulating Hormone (TSH). TSH then heads down to the thyroid gland where it stimulates the follicular cells to secrete Thyroxine. Therefore, several organs are necessary for the proper release of Thyroxine: the hypothalamus, the pituitary gland and the thyroid gland. In this lab, you will be calculating the metabolic rate of different rats. One rat is normal. The other has undergone a thyroidectomy, which is the surgical removal of the thyroid gland. And the last rat has undergone a hypophysectomy, which is the surgical removal of the pituitary gland. The metabolic rate of these rats will be measured at baseline, after they are given thyroxine, after they are given thyroid stimulating hormone, and finally after they are given propylthiouracil, which is a drug that blocks the formation of thyroxine by preventing the binding of iodine to tyrosine. Small fluctuations in metabolic rate are normal throughout the day. For the purpose of this lab, we will only be analyzing significant changes in metabolic rate (>100). We will also be noting if a goiter forms in any of the rats. A goiter is an overgrowth of the thyroid gland, which can result from excess TSH secretion or reduced TH secretion.
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Metabolism is the broad range of biochemical reactions occuring in the body. Metabolism includes anabolism and catabolism. Anabolism is the building up of small molecules into larger, more complex molecules via enzymatic reactions. Energy is stored in the chemical bonds formed when larger more complex molecules are formed. Catabolism is the breakdown of large, complex molecules into smaller molecules via enzymatic reactions. The breaking of chemical bonds in catabolism releases energy that the cell can use to perform various activities, such as forming ATP. The cell does not use all the energy released by bond breaking. Much of the energy is released as heat to maintain a fixed body temperature, especially in humans. Humans are homeothermic organisms that need to maintain a fixed body temperature to maintain the activity of various metabolic pathways in the body. The most important hormone for maintaining metabolism and body heat is thyroxine (thyroid hormone), also known as tetraiodothyronine, or T4. Thyroxine is secreted by the thyroid gland, located in the neck. The production of thyroxine is controlled by the pituitary gland, or hypophysis, which secretes thyroid stimulating hormone (TSH). The blood carries TSH to its target tissue, the thyroid gland. TSH causes the thyroid gland to increase in size and secrete thyroxine into the general circulation. If TSH levels are too high, the thyroid gland enlarges. The resulting glandular swelling in the neck is called a goiter.
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The endocrine system is composed of glands that secrete hormones into the bloodstream, thereby influencing distant tissues or organs.
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The hypothalamus in the brain is also a vital participant in thyroxine and TSH production. It is a primary endocrine gland that secretes several hormones that affect the pituitary gland. The Thyrotropin-releasing hormone (TRH) is directly linked to thyroxine and TSH secretion. TRH from the hypothalamus stimulates the anterior pituitary to produce TSH, which then stimulates the thyroid to produce thyroxine. These events are part of a classic negative feedback mechanism. When circulation levels of thyroxine are low, the hypothalamus secretes more TRH to stimulate the pituitary gland to secrete more TSH. The increase in TSH further stimulates the secretion of thyroxine from the thyroid gland. The increased levels of thyroxine will then influence the hypothalamus to reduce its production of TRH. TRH travels from the hypothalamus to the pituitary gland via the hypothalamic-pituitary portal system. This specialized arrangement of blood vessels consists of a single portal vein that connects two capillary beds. The hypothalamic-pituitary portal system transports many other hormones from the hypothalamus to the pituitary gland. The hypothalamus primarily secretes tropic hormones, which stimulate the secretion of other hormones. TRH is an example of a tropic hormone because it stimulates production of thyroxine
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The hypothalamus stimulates the anterior pituitary by TRH. The anterior pituitary stimulates the thyroid gland by TSH. The thyroid gland stimulates target cells and inhibits the hypothalamus and the anterior pituitary by thyroid hormones.
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The inability of body cells to take up glucose from the blood also results in skeletal muscle cells undergoing protein catabolism to free up amino acids to be used in forming glucose in the liver. This action puts the body into a negative nitrogen balance from the resulting protein depletion and tissue wasting. Other associated problems include poor wound healing and poor resistance to infections.
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Why does a normal patient develop a palpable goiter with a TSH injection?
TSH receptors on the thyroid gland are excessively stimulated
How do the baseline metabolic rates of the thyroidectomized and hypophysectomized rats compare with the normal rat? Explain any differences.
The baseline metabolic rates are lower in both the thyroidectomized and hypophysectomized rats compared with the normal rat.
To measure the amount of plasma glucose in a patient sample
The glucose concentration of the sample will be measured and the optical density will be extrapolated from the glucose standard curve
Which of the following statements is true? a. TRH travels from the hypothalamus to the thyroid gland via the hypothalamic-thyroid portal system b. The hypothalamus primarily secretes tropic hormones that stimulate the secretion of other hormones c. Both TRH and TSH are tropical fruit drinks d. When plasma levels of thyroxine are low, the hypothalamus will secrete TSH and stimulate the pituitary gland to secrete more TRH
The hypothalamus primarily secretes tropic hormones that stimulate the secretion of other hormones
Why does a normal patient develop a palpable goiter with a propylthiouracil injection?
The injection decreases the negative feedback mechanism on TSH
Which of the rats developed a goiter after injection with TSH? Explain.
The normal rat and hypophysectomized rat each developed a goiter from TSH injection. The TSH injection resulted in excessive TSH stimulation of the thyroid in both of these rats, leading to a goiter. The thyroidectomized rat did not develop a goiter because it does not have a thyroid.
Which of the rats developed a goiter after injection with propylthiouracil? Explain.
The normal rat was the only rat that developed a goiter from PTU. PTU prevents the synthesis of thyroxine. The lack of synthesis of thyroxine prevents thyroxine from exerting negative feedback on TSH, so that TSH levels increase. The elevated TSH then excessively stimulates the thyroid gland, producing a goiter. The goiter did not form in the hypophysectomized rat because, even though thyroid hormone levels were low, the hypophysectomized rat does not have an anterior pituitary gland to produce TSH. In the case of the thyroidectomized rat, a goiter was not formed because, although thyroid hormone levels were low and TSH levels were high (from lack of negative feedback from thyroid hormone), the thyroidectomized rat lacks a thyroid gland that would form the goiter
In the thryoidectomized rat was there any change in metabolic rate when you injected propylthiouracil? Explain.
There was no change in metabolic rate when the thyroidectomized rat was injected with PTU. Since the thyroidectomized rat does not have a thyroid, and thyroxine already could not be produced, the addition of PTU (an inhibitor of thyroxine synthesis) would have no effect.
When a normal patient is injected with thyroxine, what would happen?
They will become hyperthyroidic and develop a goiter
When a thyroidectomized patient is injected with TSH, what would happen?
They will become hyperthyroidic and develop a goiter
Thyroxine is
Thyroxine is the most important hormone for maintaining metabolic rate and body temperature
To obtain an accurate spectrophotometric measurement of glucose concentration in a sample one might add ____ to prevent blood clots
To obtain an accurate spectrophotometric measurement of glucose concentration in a sample one might add heparin to prevent blood clots
What is the purpose of heparin?
To prevent clotting which would interfere with clear glucose readings
Your patients are diabetic. What advice would you give them? What course of treatment should they follow?
Treatment would depend on the type: Type 1: Insulin therapy Type 2: Lose weight, eat low-carbohydrate diet, exercise, and possibly medication to increase insulin sensitivity.
True or False: Insulin decreases plasma glucose levels
True
True or False: Insulin is a hormone secreted by the beta cells of the endocrine portion of the pancreas
True
True or False: Insulin promotes the storage of glucose in the form of glycogen
True
What is type I diabetes?
When the pancreas produces little or no insulin.
In the hypophysectomized rat was there any change in metabolic rate when you injected thyroxine? Explain.
Yes, injection of the hypophysectomized rat with thyroxine did increase metabolic rate. The hypophysectomized rat lacks the ability to produce TSH to stimulate thyroxine synthesis. However, injecting thyroxine exogenously provides another source of thyroxine and increases metabolic rate.
In the normal rat was there any change in metabolic rate when you injected propylthiouracil? Explain.
Yes, there was a decrease in metabolic rate after injection of PTU. PTU prevented the synthesis of thyroxine, so there was less thyroxine in the blood to increase metabolic rate.
In the normal rat was there any change in metabolic rate when you injected thyroxine? Explain.
Yes, there was a significant increase in metabolic rate of the normal rat after thyroxine injection. Thyroxine drives metabolic rate, and by adding additional thyroxine from the injection, metabolic rate further increased. The normal rat thus exhibited hyperthyroidism.
In the normal rat was there any change in metabolic rate when you injected TSH? Explain.
Yes, there was an increase in metabolic rate in the normal rat after injection of TSH. TSH stimulates the synthesis of thyroxine from the thyroid gland, so the injection of TSH increased blood levels of thyroxine, resulting in increased metabolic rate.
In the thryoidectomized rat was there any change in metabolic rate when you injected thyroxine? Explain.
Yes. In the thyroidectomized rat, thyroxine cannot be endogenously produced because the thyroid gland was removed. By injecting exogenous thyroxine, thyroxine would be present in the blood and metabolic rate would be increased.
In the hypophysectomized rat was there any change in metabolic rate when you injected TSH? Explain.
Yes. Since the hypophysectomized rat lacks an anterior pituitary, it cannot produce endogenous TSH to stimulate thyroxine synthesis. Exogenous injection, however, provides another source of TSH, which then stimulates the thyroid gland to produce thyroxine.
Which of the following statements is true? a. plasma glucose levels are controlled by the opposing actions of insulin and glucagon b. plasma glucose can be converted into glycogen stores in liver and muscle cells c. glucose is the primary fuel for nerve cell metabolism d. all of the above
all of the above
Barium Hydroxide
clears both proteins and cell membranes for clear glucose readings
As a result of the missing hormone(s) in the hypophysectimized rat, what would be some expected symptoms?
decreased basal metabolic rate
If an animal has been hypophysectomized, what effect would you expect to see in the hormone levels in its body?
decreased basal metabolic rate because no thyroxine production.
What are some lifestyle choices you might suggest to patients with borderline impaired plasma glucose readings
exercise, low fat and low carb diet, higher percent of total diet being veggies
What are the treatments for pre-diabetics?
exercise, weight loss, low carb diet, low fat diet, anti-diabetic medication
what is the primary fuel for nerve cell metabolism
glucose
glucose is stored as
glycogen in the liver
An injection of propylthiouracil to an otherwise normal animal will cause what?
goiter development
A male patient has had successive fasting plasma glucose readings of 115, 110, and 122 mg/dl. The healthcare provider will inform him that
he appears to have impairment or borderline impairment of insulin-mediated glucose uptake by his cells
After a TSH injection, a hypophysectomized patient would be euthyroid, hypothyroid, or hyperthyroid?
hyperthyroid
An injection of thyroxine to an otherwise normal rat will cause what?
hyperthyroidism
"pathway" for hormone release
hypothalamus --> pituitary --> another endocrine organ(s) --> target cells
After a PTU injection, a hypophysectomized patient would be euthyroid, hypothyroid, or hyperthyroid?
hypothyroid
After a PTU injection, a normal patient would be euthyroid, hypothyroid, or hyperthyroid?
hypothyroid
After a PTU injection, a thyroidectomized patient would be euthyroid, hypothyroid, or hyperthyroid?
hypothyroid
To maintain plasma glucose homeostasis
insulin-mediated transport of glucose into cells acts as negative feedback when plasma glucose levels rise.
What causes a goiter?
iodine deficiency
what does it mean if something is hypophysectomized?
it means they had their pituitary gland surgically removed.
what does it mean if something is thyroidectomized?
it means they had their thyroid gland surgically removed.
Thyroid Stimulating Hormone (TSH) is
produced in the pituitary gland
inability of body cells to take up glucose from blood results in skeletal muscle cells undergoing
protein catabolism
Thyrotropin-releasing hormone (TRH) is
secreted by the hypothalamus
a female patient has had successive fasting plasma glucose readings of 130, 140, and 128 mg/dl. The healthcare provider will inform her that
she has developed diabetes
glucagon is a hormone
that opposes the action of insulin.
A diagnosis of type 2 diabetes mellitus implies that
the body's cells are unresponsive to circulating insulin
A diagnosis of type 1 diabetes mellitus implies that
the pancreas is not producing sufficient insulin
Describe the relationship between optical density and glucose concentration
they are directly proportional, as glucose concentration increases, optical density will increase
If an animal has been thyroidectomized, what hormone(s) would be missing in its blood?
triiodothyronine and thyroxine .
What causes a goiter and why?
usually caused by a lack of iodine in the diet. unresponsive vein response, expanding in size and in need of T3 and T4 chemicals.