Podcast
Questions and Answers
An excess of thyroid hormone results in increased metabolism in various tissues. What physiological response occurs?
An excess of thyroid hormone results in increased metabolism in various tissues. What physiological response occurs?
- Decreased cardiac output due to reduced blood volume
- Vasodilation in most body tissues, increasing blood flow (correct)
- Decreased oxygen utilization relative to metabolic rate
- Vasoconstriction in most body tissues, decreasing blood flow
A patient exhibits an increased metabolic rate, heat intolerance, and weight loss. Which hormone imbalance is most likely responsible for these symptoms?
A patient exhibits an increased metabolic rate, heat intolerance, and weight loss. Which hormone imbalance is most likely responsible for these symptoms?
- Hypersecretion of growth hormone
- Hyposecretion of thyroid hormone
- Hyposecretion of parathyroid hormone
- Hypersecretion of thyroid hormone (correct)
Administration of a high concentration of iodides reduces the rate of iodination of tyrosine. What is the INITIAL effect of this action?
Administration of a high concentration of iodides reduces the rate of iodination of tyrosine. What is the INITIAL effect of this action?
- Increased secretion of TSH
- Decreased endocytosis of colloid (correct)
- Increased size of the thyroid gland
- Increased activity of the iodide pump
What is the primary mechanism through which thyroid hormones exert their effects on target cells?
What is the primary mechanism through which thyroid hormones exert their effects on target cells?
A patient with hyperthyroidism is treated with propylthiouracil. What is the mechanism?
A patient with hyperthyroidism is treated with propylthiouracil. What is the mechanism?
A patient is diagnosed with congenital absence of deiodinase enzyme. What is the most likely consequence?
A patient is diagnosed with congenital absence of deiodinase enzyme. What is the most likely consequence?
TSH stimulates the thyroid gland by initially binding to receptors on the basal membrane surfaces of thyroid cells. What intracellular event is triggered by this?
TSH stimulates the thyroid gland by initially binding to receptors on the basal membrane surfaces of thyroid cells. What intracellular event is triggered by this?
After a thyroidectomy, a patient develops muscle weakness and increased excitability of the neuronal synapses. What thyroid hormone imbalance is responsible?
After a thyroidectomy, a patient develops muscle weakness and increased excitability of the neuronal synapses. What thyroid hormone imbalance is responsible?
Which cellular change is a direct result of thyroid hormone action?
Which cellular change is a direct result of thyroid hormone action?
A patient is diagnosed with Graves' disease. What would be expected in this patient?
A patient is diagnosed with Graves' disease. What would be expected in this patient?
One of the initial steps in the synthesis of thyroid hormones is the oxidation of iodide ions. What enzyme mediates this process?
One of the initial steps in the synthesis of thyroid hormones is the oxidation of iodide ions. What enzyme mediates this process?
Which condition would most likely result in increased TSH secretion?
Which condition would most likely result in increased TSH secretion?
A patient exposed to severe cold for a prolonged period exhibits elevated thyroid hormone levels. What is the mechanism?
A patient exposed to severe cold for a prolonged period exhibits elevated thyroid hormone levels. What is the mechanism?
A patient is experiencing oligomenorrhea. Excess thyroid hormone causes this due to?
A patient is experiencing oligomenorrhea. Excess thyroid hormone causes this due to?
What is the fate of monoiodotyrosine and diiodotyrosine after thyroglobulin digestion?
What is the fate of monoiodotyrosine and diiodotyrosine after thyroglobulin digestion?
What determines the rate of iodide trapping by the thyroid gland
What determines the rate of iodide trapping by the thyroid gland
Which of the following statements best describes the role of thyroglobulin in thyroid hormone synthesis?
Which of the following statements best describes the role of thyroglobulin in thyroid hormone synthesis?
What is the molecular mechanism by which thyroid hormone receptor (TR) activation leads to changes in gene expression?
What is the molecular mechanism by which thyroid hormone receptor (TR) activation leads to changes in gene expression?
Which of the following physiological conditions is most likely to result in a decrease in thyroid-stimulating hormone (TSH) secretion by the anterior pituitary?
Which of the following physiological conditions is most likely to result in a decrease in thyroid-stimulating hormone (TSH) secretion by the anterior pituitary?
A patient presents with symptoms suggesting hypothyroidism. Which laboratory finding would provide the strongest evidence for primary hypothyroidism (i.e., hypothyroidism due to a problem within the thyroid gland itself)?
A patient presents with symptoms suggesting hypothyroidism. Which laboratory finding would provide the strongest evidence for primary hypothyroidism (i.e., hypothyroidism due to a problem within the thyroid gland itself)?
Which non-genomic action(s) are effects of thyroid hormones?
Which non-genomic action(s) are effects of thyroid hormones?
A patient presents with muscle weakness, tremor, and an increased heart rate. Lab results indicate elevated T3 and T4. The patient likely has...
A patient presents with muscle weakness, tremor, and an increased heart rate. Lab results indicate elevated T3 and T4. The patient likely has...
Which factor directly leads to both increased heart rate and cardiac output during states of augmented thyroid hormone production?
Which factor directly leads to both increased heart rate and cardiac output during states of augmented thyroid hormone production?
Which treatment would be most effective in managing hyperthyroidism?
Which treatment would be most effective in managing hyperthyroidism?
Hypothyroidism's main characteristic is?
Hypothyroidism's main characteristic is?
How does thyroid hormone affect fat metabolism?
How does thyroid hormone affect fat metabolism?
Explain why congenital hypothyroidism results in abnormal growth and neurodevelopment?
Explain why congenital hypothyroidism results in abnormal growth and neurodevelopment?
How does thyroid hormone decrease the plasma cholesterol concentration?
How does thyroid hormone decrease the plasma cholesterol concentration?
What causes the enlargement of thyroid glands?
What causes the enlargement of thyroid glands?
A patient exhibits a greatly increased amount of thyroid hormone, what symptom is this most related to?
A patient exhibits a greatly increased amount of thyroid hormone, what symptom is this most related to?
What is the molecular weight of TSH?
What is the molecular weight of TSH?
An anterior pituitary secretory is controlled by a hypothalamic hormone. What hormone is this?
An anterior pituitary secretory is controlled by a hypothalamic hormone. What hormone is this?
What part of the thyroid gland sends out extensions that close around portions of the colloid?
What part of the thyroid gland sends out extensions that close around portions of the colloid?
What gland is known for storing large amounts of proteins?
What gland is known for storing large amounts of proteins?
What percentage of iodine is absorbed into the thyroid gland?
What percentage of iodine is absorbed into the thyroid gland?
Where is the thyroid gland located?
Where is the thyroid gland located?
The major constituent of colloid is?
The major constituent of colloid is?
What is the name of the term that concentrates the iodide in a cell?
What is the name of the term that concentrates the iodide in a cell?
What percentage of the hormones secreted by the thyroid gland is thyroxine?
What percentage of the hormones secreted by the thyroid gland is thyroxine?
Which characteristic of the thyroid gland contributes most significantly to its ability to rapidly adjust thyroid hormone output in response to fluctuating demands?
Which characteristic of the thyroid gland contributes most significantly to its ability to rapidly adjust thyroid hormone output in response to fluctuating demands?
Why is triiodothyronine (T3) considered more potent than thyroxine (T4) despite being present in smaller quantities in the blood?
Why is triiodothyronine (T3) considered more potent than thyroxine (T4) despite being present in smaller quantities in the blood?
What best describes the functional consequence of a mutation that impairs the activity of the sodium-potassium ATPase (Na+-K+ ATPase) pump in thyroid follicular cells?
What best describes the functional consequence of a mutation that impairs the activity of the sodium-potassium ATPase (Na+-K+ ATPase) pump in thyroid follicular cells?
Administration of an inhibitor of pendrin, a chloride-iodide counter-transporter, would have what direct effect on thyroid hormone synthesis?
Administration of an inhibitor of pendrin, a chloride-iodide counter-transporter, would have what direct effect on thyroid hormone synthesis?
What is the most likely outcome of a genetic defect that impairs the production of thyroglobulin?
What is the most likely outcome of a genetic defect that impairs the production of thyroglobulin?
Why does blocking the peroxidase enzyme system in thyroid cells lead to a decrease in thyroid hormone production?
Why does blocking the peroxidase enzyme system in thyroid cells lead to a decrease in thyroid hormone production?
What is the predicted effect of a mutation causing constitutive activation of the TSH receptor in thyroid follicular cells?
What is the predicted effect of a mutation causing constitutive activation of the TSH receptor in thyroid follicular cells?
What best describes the physiological mechanism underlying the extended duration of action observed after thyroxine (T4) administration?
What best describes the physiological mechanism underlying the extended duration of action observed after thyroxine (T4) administration?
What is a direct consequence of thyroid hormones increasing the activity of Na+-K+ ATPase in various tissues?
What is a direct consequence of thyroid hormones increasing the activity of Na+-K+ ATPase in various tissues?
A patient has elevated T3 and T4 levels but normal TSH levels. A possible explanation is?
A patient has elevated T3 and T4 levels but normal TSH levels. A possible explanation is?
How do thyroid hormones cause vasodilation in most body tissues?
How do thyroid hormones cause vasodilation in most body tissues?
Why is vitamin deficiency a concern in individuals with hyperthyroidism?
Why is vitamin deficiency a concern in individuals with hyperthyroidism?
Why does hyperthyroidism frequently lead to muscle weakness and fatigue?
Why does hyperthyroidism frequently lead to muscle weakness and fatigue?
How does thyroid hormone impact the inactivation rate of adrenal glucocorticoids by the liver, and what is the consequential feedback mechanism?
How does thyroid hormone impact the inactivation rate of adrenal glucocorticoids by the liver, and what is the consequential feedback mechanism?
What are the expected effects on TSH secretion upon exposure to cold temperatures for an extended period?
What are the expected effects on TSH secretion upon exposure to cold temperatures for an extended period?
Which ovarian condition can be caused by hypothyroidism?
Which ovarian condition can be caused by hypothyroidism?
Iodides are administered to patients who will undergo surgical removal of the thyroid gland in order to do what?
Iodides are administered to patients who will undergo surgical removal of the thyroid gland in order to do what?
Following thyroid hormones being inhibited and a goiter forming, what development would occur?
Following thyroid hormones being inhibited and a goiter forming, what development would occur?
Which of the following tests can be used when diagnosing hyperthyroidism?
Which of the following tests can be used when diagnosing hyperthyroidism?
Which of the following occurs for the concentrations of TSI in the plasma?
Which of the following occurs for the concentrations of TSI in the plasma?
Why are test doses of TRH usually increased during hypothyroidism?
Why are test doses of TRH usually increased during hypothyroidism?
Why is TBG useful to measure?
Why is TBG useful to measure?
TSH, also known as thyrotropin, is a what?
TSH, also known as thyrotropin, is a what?
What is a unique early effect after administering of TSH?
What is a unique early effect after administering of TSH?
TRH, a tripeptide amide, stimulates production of TSH and?
TRH, a tripeptide amide, stimulates production of TSH and?
What condition improves as hyperthyroidism treatments improve?
What condition improves as hyperthyroidism treatments improve?
Graves' disease is considered an...
Graves' disease is considered an...
Lack of iodine is most associated with
Lack of iodine is most associated with
Why does increasing blood flow increase thyroid hormones?
Why does increasing blood flow increase thyroid hormones?
How might someone sleeping 12 to 14 hours a day be described?
How might someone sleeping 12 to 14 hours a day be described?
One of the most characteristic signs of hyperthyroidism is?
One of the most characteristic signs of hyperthyroidism is?
Why do people with hyperthyroidism have a hard time sleeping?
Why do people with hyperthyroidism have a hard time sleeping?
If TRH signals don't make it to the pituitary...?
If TRH signals don't make it to the pituitary...?
Decreasing secretion of TSH would result in?
Decreasing secretion of TSH would result in?
In which system is endocytosis first used?
In which system is endocytosis first used?
What hormone helps the storage of cells in colloid?
What hormone helps the storage of cells in colloid?
In a scenario where the thyroid gland is exposed to an autoimmune attack that mimics TSH, leading to hyperstimulation, which of the following intracellular events would be most directly upregulated?
In a scenario where the thyroid gland is exposed to an autoimmune attack that mimics TSH, leading to hyperstimulation, which of the following intracellular events would be most directly upregulated?
A researcher is investigating potential therapeutic targets for hypothyroidism. Which of the following interventions would most effectively address the underlying cause of iodine deficiency-induced goiter?
A researcher is investigating potential therapeutic targets for hypothyroidism. Which of the following interventions would most effectively address the underlying cause of iodine deficiency-induced goiter?
A novel drug is designed to enhance the coupling of monoiodotyrosine (MIT) and diiodotyrosine (DIT) within thyroglobulin. What effect would this drug have on thyroid hormone synthesis?
A novel drug is designed to enhance the coupling of monoiodotyrosine (MIT) and diiodotyrosine (DIT) within thyroglobulin. What effect would this drug have on thyroid hormone synthesis?
A patient presents with a mutation affecting the megalin receptor in thyroid follicular cells. How would this mutation affect thyroid hormone homeostasis?
A patient presents with a mutation affecting the megalin receptor in thyroid follicular cells. How would this mutation affect thyroid hormone homeostasis?
If a patient is given a drug that inhibits the action of the Na+-K+ ATPase pump in thyroid follicular cells, which step in thyroid hormone synthesis would be directly impaired?
If a patient is given a drug that inhibits the action of the Na+-K+ ATPase pump in thyroid follicular cells, which step in thyroid hormone synthesis would be directly impaired?
A patient presents with elevated levels of thyroid hormones due to a tumor secreting large quantities of T3 and T4, what effect would this have on the thyroid gland?
A patient presents with elevated levels of thyroid hormones due to a tumor secreting large quantities of T3 and T4, what effect would this have on the thyroid gland?
Why does the administration of iodides help with patients undergoing the surgical removal of a thyroid gland?
Why does the administration of iodides help with patients undergoing the surgical removal of a thyroid gland?
A researcher discovers a compound that selectively blocks the action of thyroid hormone receptors in the liver, but not in other tissues. What metabolic effect would be most directly observed following administration of this compound?
A researcher discovers a compound that selectively blocks the action of thyroid hormone receptors in the liver, but not in other tissues. What metabolic effect would be most directly observed following administration of this compound?
A patient presents with a goiter and elevated TSH levels, with tests revealing a defect in iodothyrosine deiodinase. What compensatory mechanism is likely to occur in the thyroid gland?
A patient presents with a goiter and elevated TSH levels, with tests revealing a defect in iodothyrosine deiodinase. What compensatory mechanism is likely to occur in the thyroid gland?
A patient who has had their anterior pituitary separated from the Hypothalamus, would still experience what?
A patient who has had their anterior pituitary separated from the Hypothalamus, would still experience what?
A woman with hyperthyroidism experiences oligomenorrhea. What is the most likely underlying mechanism for this reproductive issue?
A woman with hyperthyroidism experiences oligomenorrhea. What is the most likely underlying mechanism for this reproductive issue?
In cases of hyperthyroidism where excess thyroid hormone leads to increased protein catabolism and muscle weakness, what compensatory mechanism in skeletal muscle might temporarily offset this catabolic effect?
In cases of hyperthyroidism where excess thyroid hormone leads to increased protein catabolism and muscle weakness, what compensatory mechanism in skeletal muscle might temporarily offset this catabolic effect?
A patient with iodine deficiency develops a goiter. However, after several years, the goiter becomes nodular and starts autonomously producing excess thyroid hormones, leading to hyperthyroidism. What is the most likely sequence of events?
A patient with iodine deficiency develops a goiter. However, after several years, the goiter becomes nodular and starts autonomously producing excess thyroid hormones, leading to hyperthyroidism. What is the most likely sequence of events?
A researcher is studying the non-genomic effects of thyroid hormones in cardiomyocytes. Which of the following mechanisms is most likely involved in the rapid increase in heart rate observed after T3 administration?
A researcher is studying the non-genomic effects of thyroid hormones in cardiomyocytes. Which of the following mechanisms is most likely involved in the rapid increase in heart rate observed after T3 administration?
A new drug is being developed that selectively enhances the deiodination of T4 to T3 in peripheral tissues. What potential side effect should be monitored in patients taking this drug?
A new drug is being developed that selectively enhances the deiodination of T4 to T3 in peripheral tissues. What potential side effect should be monitored in patients taking this drug?
A thyroid tumor is found to be producing excessive amounts of thyroglobulin, but T3 and T4 levels remain low. What enzymatic deficiency would best explain this presentation?
A thyroid tumor is found to be producing excessive amounts of thyroglobulin, but T3 and T4 levels remain low. What enzymatic deficiency would best explain this presentation?
Why does the text mention hypothyroidism possibly resulting in menorrhagia and polymenorrhea?
Why does the text mention hypothyroidism possibly resulting in menorrhagia and polymenorrhea?
Which diagnostic method is the MOST accurate to use for severe hyperthyroidism?
Which diagnostic method is the MOST accurate to use for severe hyperthyroidism?
A patient has a mutation that causes an increase in TSH production, what effect would this have on the follicular cells?
A patient has a mutation that causes an increase in TSH production, what effect would this have on the follicular cells?
Thyroid hormone increases the rate at which adrenal glucocorticoids are inactivated by the liver. What is most likely secondary to this action?
Thyroid hormone increases the rate at which adrenal glucocorticoids are inactivated by the liver. What is most likely secondary to this action?
Iodine deficiency can cause issues if this enzyme does not release the iodide:
Iodine deficiency can cause issues if this enzyme does not release the iodide:
What would happen if the TSH receptor in the thyroid gland experiences an autoimmune attack?
What would happen if the TSH receptor in the thyroid gland experiences an autoimmune attack?
A patient is diagnosed with a rare genetic defect resulting in non-functional pendrin transporters in thyroid follicular cells. Which of the following immediate effects would be expected?
A patient is diagnosed with a rare genetic defect resulting in non-functional pendrin transporters in thyroid follicular cells. Which of the following immediate effects would be expected?
If a patient has their blood flow restricted, what would be expected to happen to thyroid levels?
If a patient has their blood flow restricted, what would be expected to happen to thyroid levels?
Which hormone is considered unusual among the endocrine glands due to storing large amounts of hormones?
Which hormone is considered unusual among the endocrine glands due to storing large amounts of hormones?
A patient who is diagnosed with hyperthyroidism is having an increased appetite, what factor may be counterbalancing the change in metabolic rate?
A patient who is diagnosed with hyperthyroidism is having an increased appetite, what factor may be counterbalancing the change in metabolic rate?
Mutations that modify the structure of thyroglobulin, impairing its ability to be proteolytically cleaved by lysosomal enzymes, would likely result in:
Mutations that modify the structure of thyroglobulin, impairing its ability to be proteolytically cleaved by lysosomal enzymes, would likely result in:
Administering a novel drug that blocks the binding of thyroid hormones to plasma proteins (e.g., thyroxine-binding globulin) would be expected to:
Administering a novel drug that blocks the binding of thyroid hormones to plasma proteins (e.g., thyroxine-binding globulin) would be expected to:
A patient with hypothyroidism is prescribed levothyroxine. After several weeks, the patient's TSH levels remain elevated, but free T4 levels are within the normal range. What is the most likely cause of this discrepancy?
A patient with hypothyroidism is prescribed levothyroxine. After several weeks, the patient's TSH levels remain elevated, but free T4 levels are within the normal range. What is the most likely cause of this discrepancy?
Calcitonin, which is secreted by the thyroid gland, plays a crucial role in the metabolism of glucose.
Calcitonin, which is secreted by the thyroid gland, plays a crucial role in the metabolism of glucose.
Thyroxine (T4) is converted into triiodothyronine (T3) exclusively within the thyroid gland, ensuring that only T3 is released into circulation.
Thyroxine (T4) is converted into triiodothyronine (T3) exclusively within the thyroid gland, ensuring that only T3 is released into circulation.
Thyroid hormone synthesis relies on the presence of thyroglobulin, a unique glycoprotein containing tyrosine amino acids, but thyroglobulin is not stored within the thyroid follicles.
Thyroid hormone synthesis relies on the presence of thyroglobulin, a unique glycoprotein containing tyrosine amino acids, but thyroglobulin is not stored within the thyroid follicles.
The iodide pump, or sodium-iodide symporter, works by transporting one iodide ion along with two potassium ions using energy derived from the sodium-potassium ATPase pump.
The iodide pump, or sodium-iodide symporter, works by transporting one iodide ion along with two potassium ions using energy derived from the sodium-potassium ATPase pump.
Iodide trapping is most efficient when TSH levels are low, as TSH inhibits the activity of the iodide pump in thyroid cells.
Iodide trapping is most efficient when TSH levels are low, as TSH inhibits the activity of the iodide pump in thyroid cells.
The process of organification involves the slow and indirect binding of unoxidized iodine with the thyroglobulin molecule within thyroid cells.
The process of organification involves the slow and indirect binding of unoxidized iodine with the thyroglobulin molecule within thyroid cells.
During the coupling reaction in thyroid hormone synthesis, reverse T3 (RT3) is the predominant hormone formed and exhibits significant functional importance in humans.
During the coupling reaction in thyroid hormone synthesis, reverse T3 (RT3) is the predominant hormone formed and exhibits significant functional importance in humans.
The thyroid gland is unique in its ability to store only small quantities of hormones, typically enough for a few days, ensuring rapid response to hormonal demands.
The thyroid gland is unique in its ability to store only small quantities of hormones, typically enough for a few days, ensuring rapid response to hormonal demands.
Thyroxine and triiodothyronine are transported in the blood primarily as free hormones, allowing them to easily diffuse into tissue cells.
Thyroxine and triiodothyronine are transported in the blood primarily as free hormones, allowing them to easily diffuse into tissue cells.
Triiodothyronine has a longer latent period and duration of action compared to thyroxine due to its stronger binding with plasma and intracellular proteins.
Triiodothyronine has a longer latent period and duration of action compared to thyroxine due to its stronger binding with plasma and intracellular proteins.
Thyroid hormones primarily act by directly influencing cellular activities in the cytoplasm, without significantly altering gene transcription in the nucleus.
Thyroid hormones primarily act by directly influencing cellular activities in the cytoplasm, without significantly altering gene transcription in the nucleus.
Thyroid hormones decrease the number and activity of mitochondria in cells, thereby reducing the overall metabolic rate.
Thyroid hormones decrease the number and activity of mitochondria in cells, thereby reducing the overall metabolic rate.
Increased levels of thyroid hormones lead to decreased glycolysis, reduced gluconeogenesis, and diminished absorption of glucose in the gastrointestinal tract.
Increased levels of thyroid hormones lead to decreased glycolysis, reduced gluconeogenesis, and diminished absorption of glucose in the gastrointestinal tract.
Thyroid hormone causes the body to store fat to a greater extent than almost any other tissue element.
Thyroid hormone causes the body to store fat to a greater extent than almost any other tissue element.
Excessive thyroid hormone always leads to significant weight gain due to increased appetite and enhanced metabolic processes.
Excessive thyroid hormone always leads to significant weight gain due to increased appetite and enhanced metabolic processes.
Increased thyroid hormone levels typically decrease blood flow and cardiac output due to reduced tissue metabolism.
Increased thyroid hormone levels typically decrease blood flow and cardiac output due to reduced tissue metabolism.
Increased thyroid hormone enhances the absorption of vitamins in the intestines, preventing vitamin deficiencies.
Increased thyroid hormone enhances the absorption of vitamins in the intestines, preventing vitamin deficiencies.
The primary feedback mechanism to regulate thyroid hormone secretion involves the direct stimulation of TSH release from the anterior pituitary by elevated T3 and T4 levels.
The primary feedback mechanism to regulate thyroid hormone secretion involves the direct stimulation of TSH release from the anterior pituitary by elevated T3 and T4 levels.
Propylthiouracil increases thyroid hormone formation by enhancing the activity of peroxidase enzyme, which is required for iodination of tyrosine
Propylthiouracil increases thyroid hormone formation by enhancing the activity of peroxidase enzyme, which is required for iodination of tyrosine
Radioactive iodine treatment for hyperthyroidism works because the thyroid gland absorbs a high percentage of the injected dose, allowing the radiation to destroy hyperactive thyroid cells.
Radioactive iodine treatment for hyperthyroidism works because the thyroid gland absorbs a high percentage of the injected dose, allowing the radiation to destroy hyperactive thyroid cells.
Match each iodinated tyrosine derivative with its correct description:
Match each iodinated tyrosine derivative with its correct description:
Match the following antithyroid substances with their primary mechanism of action:
Match the following antithyroid substances with their primary mechanism of action:
Match the following clinical manifestations with their associated thyroid condition:
Match the following clinical manifestations with their associated thyroid condition:
Match the following effects with the hormone primarily responsible for mediating them:
Match the following effects with the hormone primarily responsible for mediating them:
Match each component of the hypothalamic-pituitary-thyroid axis with its function:
Match each component of the hypothalamic-pituitary-thyroid axis with its function:
Match the effects of thyroid hormones with their underlying mechanisms:
Match the effects of thyroid hormones with their underlying mechanisms:
Match each of the following metabolic effects to the action of thyroid hormones:
Match each of the following metabolic effects to the action of thyroid hormones:
Match the causes to the types of hypothyroidism:
Match the causes to the types of hypothyroidism:
Match each condition with the appropriate intervention:
Match each condition with the appropriate intervention:
Match the laboratory parameters to the condition:
Match the laboratory parameters to the condition:
Flashcards
Thyroid metabolic hormones
Thyroid metabolic hormones
Increases metabolic rate; secreted by thyroid gland.
Thyroxine (T4) and Triiodothyronine (T3)
Thyroxine (T4) and Triiodothyronine (T3)
Thyroid hormones that increase metabolic rate.
Thyroid Gland
Thyroid Gland
Located below the larynx; secretes T3, T4 and calcitonin.
Calcitonin
Calcitonin
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Thyroid-Stimulating Hormone (TSH)
Thyroid-Stimulating Hormone (TSH)
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Thyroid follicles
Thyroid follicles
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Thyroglobulin
Thyroglobulin
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Iodide trapping
Iodide trapping
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Sodium-Iodide Symporter (NIS)
Sodium-Iodide Symporter (NIS)
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Pendrin
Pendrin
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Oxidation of Iodide
Oxidation of Iodide
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Organification of Thyroglobulin
Organification of Thyroglobulin
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Deiodinase
Deiodinase
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Bound thyroid hormones
Bound thyroid hormones
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Thyroid hormone action
Thyroid hormone action
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Triiodothyronine (T3)
Triiodothyronine (T3)
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Cellular effects of thyroid hormone
Cellular effects of thyroid hormone
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Effect on mitochondria
Effect on mitochondria
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Effect on ion transport
Effect on ion transport
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Effect on growth
Effect on growth
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Carbohydrate Metabolism
Carbohydrate Metabolism
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Fat Metabolism
Fat Metabolism
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Effect on Plasma and Liver Fats
Effect on Plasma and Liver Fats
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Increased Blood Flow and Cardiac Output
Increased Blood Flow and Cardiac Output
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Effect on the Function of the Muscles
Effect on the Function of the Muscles
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TSH function
TSH function
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TRH function
TRH function
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Feedback Effect of Thyroid
Feedback Effect of Thyroid
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Antithyroid Substances
Antithyroid Substances
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Hyperthyroidism
Hyperthyroidism
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Thyroid Adenoma
Thyroid Adenoma
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Diagnostic Tests for Hypothyroidism
Diagnostic Tests for Hypothyroidism
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Thearpy of Hypothyrodism
Thearpy of Hypothyrodism
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Cretinism
Cretinism
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T4 and T3 Hormones
T4 and T3 Hormones
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Iodine Requirement
Iodine Requirement
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Role of Pendrin
Role of Pendrin
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What is Thyroglobulin?
What is Thyroglobulin?
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Release of thyroglobulin
Release of thyroglobulin
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Iodine deficiency
Iodine deficiency
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Transportation to tissues
Transportation to tissues
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Thyroid general effects
Thyroid general effects
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Increased metabolism
Increased metabolism
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Increased Heart Rate
Increased Heart Rate
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Muscles and thyroid
Muscles and thyroid
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TSH levels
TSH levels
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What is a result of Hypothyroidism?
What is a result of Hypothyroidism?
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Endemic Goiters
Endemic Goiters
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Protrusion of the eyeballs
Protrusion of the eyeballs
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Thyroid Hormone Receptors
Thyroid Hormone Receptors
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Graves' Disease
Graves' Disease
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Thyroid effects
Thyroid effects
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Muscle Tremor
Muscle Tremor
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Propylthiouracil
Propylthiouracil
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Iodides
Iodides
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Free Thyroxine
Free Thyroxine
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Exophthalmos
Exophthalmos
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Autoimmune Thyroiditis
Autoimmune Thyroiditis
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Vitamin Requirements
Vitamin Requirements
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Pinocytosis in Thyroid Cells
Pinocytosis in Thyroid Cells
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Increased Respiration Rate
Increased Respiration Rate
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Thyroid-Stimulating Immunoglobulins (TSIs)
Thyroid-Stimulating Immunoglobulins (TSIs)
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Thyrotropin-Releasing Hormone (TRH)
Thyrotropin-Releasing Hormone (TRH)
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Normal Arterial Pressure
Normal Arterial Pressure
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Effect on Sleep
Effect on Sleep
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Hashimoto's Disease
Hashimoto's Disease
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Myxedema
Myxedema
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Endemic Colloid Goiter
Endemic Colloid Goiter
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Thiocyanate's thyroid effect
Thiocyanate's thyroid effect
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Iodide trapping Rate
Iodide trapping Rate
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Hypothyroidism effect
Hypothyroidism effect
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Study Notes
- The thyroid is an endocrine gland found below the larynx, anterior to the trachea
- It weighs roughly 15-20 grams in adults
- It secretes thyroxine (T4) and triiodothyronine (T3)
- T3 and T4 elevates the body's metabolic rate
- Complete lack of thyroid secretion can cause the basal metabolic rate to fall 40-50% below normal
- Extreme excesses of thyroid secretion can increase the basal metabolic rate to 60-100% above normal
- Thyroid hormone secretion is controlled by thyroid-stimulating hormone (TSH) from the anterior pituitary gland
- Calcitonin, involved in calcium metabolism, is also secreted by the thyroid gland
- The chapter will discuss thyroid hormone formation, secretion, metabolic functions, and regulation
Thyroid Metabolic Hormones Synthesis and Secretion
- 93% of the metabolically active hormones secreted by the thyroid is thyroxine
- The remaining 7% is triiodothyronine
- The body converts almost all thyroxine to triiodothyronine in tissues
- Both triiodothyronine, and thyroxine are functionally important
- Though qualitatively similar, their rapidity and intensity differs
- Triiodothyronine is four times more potent than thyroxine
- Triiodothyronine is present in smaller quantities, and lasts for a shorter time than thyroxine
Physiological Anatomy of the Thyroid Gland
- The thyroid is made up of closed follicles, 100-300 micrometers in diameter
- Follicles are filled with a secretory substance called colloid
- Colloid is made up of cuboidal epithelial cells, that secrete into the interior of the vessels, and thyroglobulin, a glycoprotein
- Before entering the blood to function, follicle secretions must be absorbed back through the follicular epithelium
- At five times the gland's weight each minute, the thyroid gland has a high rate of blood flow
- It has a blood supply as great as that of any other area of the body, with the possible exception of the adrenal cortex
- C cells secrete calcitonin, which contributes to plasma calcium ion concentration regulation
Iodine and Thyroxine Formation
- Around 50 milligrams of ingested iodine, approximately 1 mg per week, as iodides are needed annually to form normal quantities of thyroxine
- Common table salt is iodized with 1 part sodium iodide to every 100,000 parts sodium chloride to prevent iodine deficiency
- Chloride and ingested iodides are absorbed alike
- The cells of the thyroid gland only use 1/5th of circulating blood iodides for thyroid hormone synthesis
- Most iodides are rapidly excreted by the kidneys
Iodide Pump
- The pump is also called the sodium-iodide symporter for for iodide trapping
- Iodide transport from the blood into thyroid glandular cells and follicles is the first stage in thyroid hormone creation
- The thyroid cell's basal membrane pumps iodide into the cell using the sodium-iodide symporter
- The symporter co-transports one iodide ion along with two sodium ions across the basolateral membrane into the cell
- The (Na+-K+ ATPase) pump transports sodium out of the cell, providing the energy for transporting iodide against a concentration gradient
- Iodide concentration in a normal gland is around 30 times its concentration in the blood
- Fully active thyroid glands can have a concentration ratio as high as 250 times
- TSH concentration is most important factor influencing the rate of iodide trapping
- TSH stimulates the iodide trapping process
- Hypophysectomy greatly diminishes iodide trapping activity
- Iodide is transported across the apical membrane into the follicle by pendrin, a chloride-iodide ion counter-transporter molecule
- Thyroid epithelial cells also secrete thyroglobulin into the follicle
- Thyroglobulin contains tyrosine amino acids to which the iodine binds
Thyroglobulin
- The thyroid cells produce thyroglobulin
- They synthesize and secrete a large glycoprotein molecule into the follicles, with a molecular weight of 335,000
- About 70 tyrosine amino acids are in each molecule of thyroglobulin
- They are the major substrates to combine with iodine to form the thyroid hormones
- The thyroxine and triiodothyronine hormones form within the thyroglobulin molecule, and remain part of it while stored in the follicular colloid
Oxidation of the Iodide Ion
- The essential step in thyroid hormone formation is conversion of iodide ions to either nascent iodine (Iº) or I3−
- This nascent iodine (Iº) or I3− is capable of combining directly with the amino acid tyrosine
- Peroxidase is responsible and is accompanied by hydrogen peroxide, which creates a system capable of oxidizing iodides
- Peroxidase is found on the apical or attached to it
- Peroxidase creates the exact point in the cell where the thyroglobulin exits from the Golgi apparatus and through the cell membrane, into the stored thyroid gland colloid
- Thyroid hormone cease to form in a hereditarily absent or blocked peroxidase system
Iodination of Tyrosine
- Iodination is the biding of iodine with the thyroglobulin molecule
- Molecular iodine binds directly but slowly with the amino acid tyrosine
- Thyroid peroxidase enzyme causes the process to occur within seconds or minutes
- Iodine binds with about one sixth of the tyrosine amino acids within the thyroglobulin molecule
- Iodination's enzymatic function is called “Organification” of thyroglobulin
Hormonal Product of Coupling Reaction
- Tyrosine is first iodized to monoiodotyrosine, then to diiodotyrosine
- The molecular form of the major hormone product is thyroxine (T4)
- Thyroxine (T4) is formed when two molecules of diiodotyrosine are joined
- Thyroxine (T4) remains part of the thyroglobulin molecule
- Triiodothyronine (T3) forms when one molecule of monoiodotyrosine couples with one molecule of diiodotyrosine
- Triiodothyronine (T3) is about one-fifteenth of the final hormones
- Very small amounts of reverse T3 (RT3) are created by coupling of diiodotyrosine with monoiodotyrosine
- RT3 appears to be functionally insignificant in humans
Storage
- Large amounts of thyroid hormone can be stored
- Up to 30 thyroxine molecules and a few triiodothyronine molecules store in each thyroglobulin molecule
- Thyroid hormones in follicles ensures normal supply to the body for 2-3 months
- Ceasing thyroid hormone synthesis does not create immediate physiological effects of deficiency
Thyroxine and Triiodothyronine Release
- Thyroxine and triiodothyronine get cleaved instead of releasing most of the thyroglobulin into the circulating blood
- Thyroid cells release free hormones through a process
- Apical cell surfaces release pseudopod extensions
- The pseudopod extensions close around portions of colloid, forming pinocytic vesicles that enter the thyroid cell apex
- Lysosomes form digestive vesicles
- Digestive vesicles contain digestive enzymes from the lysosomes mixed with the colloid
- Multiple proteases digest the thyroglobulin molecules
- Free thyroxine and triiodothyronine releases
- Those hormones then diffuse through the base of the thyroid cell to surrounding capillaries
- Hormones are then released into blood
- Some colloid thyroglobulin binds to megalin
- It then enters the thyroid cell via endocytosis
- The megalin-thyroglobulin-carried across the cell via transcytosis to the basolateral membrane, and part of the megalin remains bound
- The bound megalin is then released into the capillary blood
- Three-fourths of iodinated tyrosine in thyroglobulin is monoiodotyrosine and diiodotyrosine, and does not convert into thyroid hormone
- However, a deiodinase enzyme cleaves iodine and recycles it for additional thyroid hormone production
- Congenital absence of the deiodinase enzyme results in iodine deficiency because of failure of recycling
Daily Secretion Rates
- About 93% of released thyroid hormone is thyroxine; the remaining 7% is triiodothyronine
- Over a few days, about half the thyroxine gets deiodinated to form additional triiodothyronine
- Roughly 35 micrograms of triiodothyronine is used daily with the tissues
Transport to Tissues
- Over 99% of the bound thyroxine and triiodothyronine combine with plasma proteins
- Mainly the liver-synthesized thyroxine-binding globulin does this process
- But thyroxine-binding prealbumin and albumin too
Release Rates
- Both thyroxine and triiodothyronine again bind with intracellular proteins in the tissue cells
- Thyroxine is released slower than triiodothyronine
- Tissue cells store the hormones to be used over days and weeks rather than all at once
- Half the thyroxine is released from the blood to tissue cells about every 6 days
- Half the triiodothyronine is released to the cells in roughly 1 day
Time Duration of Effectiveness
- There is a roughly 2-3 day long latent period after thyroxine is injected into a human
- After the latency, rate increase and reaches maximum in roughly 10-12 days
- The half life is roughly 15 days
- Some activity lasts as long as 6 weeks to 2 months
- Triiodothyronine acts roughly 4x more rapidly than does thyroxine
- Latency is roughly only 6-12 hours, and cellular maximums are 2-3 days
Thyroid Hormones and Gene Transcription
- Thyroid hormone generally activates nuclear transcription
- Protein enzymes, structural proteins, transport proteins and more get made in the body's cells
- The entire body exhibits a generalized function
Hormone Conversion
- One iodide comes off almost all thyroxine thus creating triiodothyronine
- To increase genetic transcription, intracellular thyroid hormone receptors have a high affinity for triiodothyronine
- Greater than 90% of hormone that binds with the receptors is triiodothyronine
- Receptors with heterodimer with retinoid X receptor (RXR) at DNA sequences on the thyroid hormone response elements
- Receptors activate after binding, and start transcription
- Messengers then create on cytoplasmic ribosomes to creates hundreds of new intracellular proteins
- However, the proteins each receive different percentages
- Some increase slightly, and others increase by as much as sixfold
- Most of the process results from functions of the created new proteins
- Thyroid hormones also appear to have non-genomic cellular effects
- Rapid effects of thyroid hormones cannot be explained by protein synthesis changes
- Actions have been found in the heart, the pituitary, and in the adipose tissue
- Actions can occur on the plasma membrane, cytoplasm, and in the organelles
- Actions include regulation of oxidative phosphorylation and ion channels
- Involvement of activation intracellular secondary messengers including cyclic adenosine monophosphate (cAMP) or protein kinase signaling cascades
Metabolic Activity
- Increase metabolic activities
- The basal metabolic activity/rate is at roughly 60-100% above normal when large quantities of thyroid hormones are secreted
- Utilize the food for energy greatly
- Protein and protein synthesis greatly increase
- Mental processes excited
- Stimuli on the other endocrine glands increase
Number and Activity
- Giving thyroxine or triiodothyronine to an animal increases the amount of mitochondria in cell bodies
- Size increases as well
- More membrane surface of the mitochondria increase
- Function of thyroxine said to increase the activity too
- Increase number and activity increases function
Transport of Ions
- The activity goes up in reaction to the thyroid hormone sodium and potassium ions
- Through the cell membranes of certain tissues increases the activity
Growth
- Thyroid hormone does this on both growth and specific effects
- Essential to metamorphic change
- Increases the growth in humans
- The rate grows in children
- Skeletal growth goes up greatly
- Causes the child to get taller
- Bones also mature and may shorten
- Promotes growth and development of the brain during fetal life and the first few years of postnatal life
- Lack of thyroid hormone can greatly retard the brain and stunt the growth of the brain before and after birth
- A child can remain mentally deficient throughout its life without specific thyroid therapy
Specific Body Functions
- All carbohydrate metabolism gets stimulated
- In the fat metabolism
- lipids mobilized rapidly
- lipid increase
- Mobilization of lipids from fat tissue increases free fatty acid concentration in the plasma and accelerates oxidation of free fatty acids
- plasma alteration
- liver fat increase
- Decreased thyroid secretion usually increases the plasma concentrations of cholesterol, phospholipids, and triglycerides
- This also causes excessive fat deposition in the liver
- Increased level of thyroid hormone decreases plasma cholesterol concentration
- The thyroid decreases concentrations of cholesterol, phospholipids, and triglycerides in the plasma, even though it increases the free fatty acids
Vitamins
- All the enzyme quantities need vitamins
- Deficiencies in vitamins may occur
Basal Metabolic Rate
- Metabolism in many cells require hormones
- Higher quantities may produce hormones faster and higher
- Inversely, half as reduced as well
Bodily Metrics
- Weight can vary
- Metabolism changes
- Blood flow increases and faster oxygen
- Tissue metabolism is greater
- Heat elimination becomes greater
- Cardiac output rises
Heart Rate
- Can be more due to hormones
- Clinicians usually use rate to see the diminished or heightened
Strength
- More increase of heat
- Muscle increases
- Protein declines
Pressure
- Mean arterial usually constant
- Pressure greater
Respiration
- Rate in metabolism goes up
- Activated by certain functions
Motility
- Can be more, so digestion increased
- Can be diarrhea
Central Nervous System
- Processing increases
- Thought can go away
- Lack is inversely related
- Can have anxieties and worries
Muscles
- Makes them react better to stimulus
- Strength decline to over usage
Tremor
- Usually caused by excess
- Occurs at rapid frequency
Sleep
- Exhaustion is due to this hormone
- Hard to sleep
- Lack of it can cause being slowed down and slower
Endocrine
- Can increase and decrease
- Insulin is dependent
- Thyroid hormone increases the secretion rates of several other endocrine glands
- It also increases the need of the tissues for the hormones
- For example, increased thyroxine secretion increases the rate of glucose metabolism in the body
- It causes a need for increased insulin secretion by the pancreas
- Thyroid gland also affects many metabolic activities of bone formation
Sexual Function
- Proper function needs level about constant
- Lack is not good
- Periods and menstruation can fluctuate and vary
- Hypothyroidism in women/men decreases libido
- Hyperthyroidism in women can cause oligomenorrhea and occasionally amenorrhea
- Thyroid hormone on gonads probably yields from reactions on the direct metabolic effects and control function of the anterior pituitary
Thyroid Hormone Mechanism
- Precisely correct secretion
- Controls anterior pituitary
- Controls hypothalamus
- Feedback dependent
TSH
- TSH is thyrotropin and TSH also comes from the anterior pituitary
- TSH is needed for thyroxine
- Hormone increase and has affect on glands
- Has these functions on the thyroid gland: increases proteolysis of stored thyroglobulin, increasing circulating thyroid hormones, increases activity of iodide pump, increases binding, increases size and secretory activity of cells, increases number of cells
TRH
- Anterior hormones dependent on this
- From hypothalamic and neurons
- TRH is tripeptide amide
- TRH stimulates the cells of the anterior pituitary to output TSH
Release effects
- In cold
- Animals to the core need this function
- Reactions depend
- Can make output for TRH to have reactions affect body heat
- Sympathetic to affect secretions
- Excitement and anxiety increase the metabolic rate and body heat. That will decrease TSH hormone release
Feedback effects
- Hormones decrease
- Secretions increase if higher
- Increased thyroid hormones in body fluids decreases TSH secretion
Anti-thyroid Sub Effects
- Suppress secretion
- Drugs that help in function
- Thiocyanate Ions impact reduction
- Includes thiocyanate, propylthiouracil, and high concentrations of iodides
Thyroids
- Lower amount
- Has impacts on function due to surgery, for example
Hyperthyroidism
- Too much. Obvious reasons
- Causes: Toxic goiter
Thyroid Adenoma and Graves
- Autoimmune in nature
- TSH formation issues
- Graves' disease is one example TSI antibodies are formed against TSH receptor against the thyroid gland
Hyperthyroid and symptoms
- High excitability
- Intolerant to heat
- Sweat more
- Loose weight
- Vary due to the symptoms
- Can be exophthalmos(protrusion of eyeballs)
Hypothyroidism
- General effects
- Auto-immunity issues
- Hashimoto's disease is an example
Goiter
- Lack of Iodide - Deficiency
- Has characteristics
Functions
- Is to increase all aspects
- To decrease certain function
- Body characteristics can decrease
Crentinism
- Has skeletal issues
- Soft issues too
Aftermath and treatment
- Steady level
- Maintained
- Can survive many years by undergoing process for 50 plus years
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