Thyroid Hormone Synthesis and Regulation

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38 Questions

What is the role of peroxidase enzymes in the synthesis of thyroid hormones?

To form T1 and T2

What is the result of lack of iodine in the diet?

Enlargement of the thyroid gland

What is the function of thyroxine-binding globulins (TBGs) produced by the liver?

To bind and transport T3 and T4

What is the outcome of untreated myxedema?

Gland atrophy

What is the cause of cretinism?

Thyroid hormone insufficiency in infancy

What is the characteristic symptom of exophthalmos?

Edema and fibrosis of the tissue behind the eyes

What is the treatment for hyperthyroidism?

Surgical removal of the thyroid gland or radioactive iodine

What is the role of TRH in regulating thyroid hormones?

To overcome negative feedback

What is the primary factor controlling cortisol secretion?

ACTH stimulation from the pituitary gland

What is a primary characteristic of Cushing's syndrome?

Elevated blood glucose levels

What is a consequence of low glucocorticoid levels?

Severe dehydration and hypotension

What is the primary function of androgens?

Initiation of puberty and secondary sex characteristics

What is the primary product of chromaffin cells in the adrenal medulla?

Epinephrine and norepinephrine

What is the effect of epinephrine on the heart?

Increased heart rate

What is the primary consequence of a deficiency in adrenal medulla hormones?

No significant consequences

What is the role of norepinephrine in the body?

Influence on peripheral vasoconstriction and blood pressure

What is the primary function of testosterone in the male reproductive system?

Initiates maturation of male reproductive organs

Which hormone is responsible for stimulating the release of HCl in the stomach?

Gastrin

Which of the following organs is responsible for producing erythropoietin, a hormone that stimulates the production of red blood cells?

Kidneys

What is the primary function of human chorionic gonadotropin (hCG) produced by the placenta?

Influences the course of pregnancy

Which of the following hormones is involved in the sensation of satiety and stimulates increased energy expenditure?

Leptin

Which of the following structures is derived from the mesoderm germ layer?

Endocrine glands that produce steroid hormones

What is the primary function of atrial natriuretic peptide (ANP) produced by the heart?

Inhibits aldosterone production, reducing blood pressure and blood volume

What is the primary function of cholecalciferol produced by the skin?

Is the precursor of vitamin D

Which hormone is most affected by pollutants, leading to high cancer rates in certain areas?

Glucocorticoids

What is the consequence of ovaries becoming unresponsive to gonadotropins?

The inability to bear children

What is the effect of declining GH levels with age?

Increased muscle atrophy

Which hormone is responsible for the bone-demineralizing effects in women?

Parathyroid hormone (PTH)

What is the consequence of declining thyroid hormone with age?

Lower basal metabolic rate

What is a potential benefit of supplemental GH?

Spurring muscle growth and reducing body fat

What is the primary function of mineralocorticoids in regulating electrolyte concentrations of extracellular fluids?

Maintaining sodium ion balance by reducing excretion of sodium from the body

What is the effect of a lack of mineralocorticoids on the body?

A decrease in blood volume and an increase in potassium ion concentration

What is the primary function of aldosterone in regulating sodium ion balance?

Stimulating the reabsorption of sodium by the kidneys

What is the effect of aldosterone on potassium ion concentration?

It sets the resting membrane potential of cells

What is the effect of aldosteronism on the body?

It leads to hypertension and edema due to excessive sodium retention

What is the role of the renin-angiotensin system in regulating aldosterone release?

It stimulates the release of aldosterone

What is the effect of cortisol on blood sugar levels?

It increases blood sugar levels by stimulating gluconeogenesis

What is the effect of cortisol on blood volume?

It maintains blood volume by preventing water shift into tissues

Study Notes

Thyroid Hormone Synthesis

  • Iodine attaches to tyrosine, mediated by peroxidase enzymes, forming T1 (monoiodotyrosine, or MIT) and T2 (diiodotyrosine, or DIT)
  • Iodinated tyrosines link together to form T3 and T4

Thyroid Hormone Regulation

  • Regulation of thyroid hormones is by negative feedback
  • Hypothalamic thyrotropin-releasing hormone (TRH) can overcome the negative feedback, especially in pregnancy or exposure of infants to cold

Thyroid Hormone Disorders

  • Myxedema: a full-blown hypothyroid syndrome, symptoms include low metabolic rate, feeling chilled, constipation, thick dry skin, puffy eyes, edema, lethargy, and mental sluggishness
  • Cretinism, or congenital hypothyroidism, results from thyroid hormone insufficiency in infancy, characterized by mental retardation, short disproportionate body, thick tongue and neck
  • Hyperthyroidism, or thyrotoxicosis, occurs when thyroid hormones are produced in excessive quantities, characterized by elevated metabolic rate, sweating, rapid irregular heartbeat, nervousness, and weight loss

Calcitonin

  • Regulates electrolyte concentrations of extracellular fluids
  • Without mineralocorticoids, potassium ion concentration of the extracellular fluid rises markedly, sodium and chloride are rapidly lost from the body, and the total extracellular fluid volume and blood volume become greatly reduced

Mineralocorticoids - Aldosterone

  • Maintains Na+ balance by reducing excretion of sodium from the body
  • Stimulates reabsorption of Na+ by the kidneys, and enhances Na+ reabsorption from perspiration, saliva, and gastric juice
  • Regulated by four different factors: [K+] and [Na+] of the ECF, renin-angiotensin system, ACTH, and atrial natriuretic peptide (ANP)

Glucocorticoids - Cortisol

  • Helps the body resist stress by keeping blood sugar levels relatively constant, maintaining blood volume and preventing water shift into tissue
  • Provokes gluconeogenesis, rises in blood glucose, fatty acids, and amino acids
  • Regulated by ACTH, with negative feedback of cortisol on the hypothalamus and pituitary gland
  • Excessive levels of glucocorticoids can lead to Cushing's syndrome, characterized by elevated blood glucose levels, loss of muscle and bone protein, water and salt retention, and redistribution of fat
  • Low levels of glucocorticoids can lead to Addison's disease, characterized by decreased glucose and Na+ levels, weight loss, severe dehydration, and hypotension

Gonadocorticoids - Sex Hormones

  • Androgens contribute to the onset of puberty, appearance of secondary sex characteristics, and sex drive in females
  • Androgens can be converted into estrogens after menopause

Adrenal Medulla

  • Made up of chromaffin cells that secrete epinephrine and norepinephrine
  • Secretion of these hormones causes blood glucose levels to rise, blood vessels to constrict, the heart to beat faster, and blood to be diverted to the brain, heart, and skeletal muscle

Other Hormone-Producing Structures

  • Heart: produces atrial natriuretic peptide (ANP), which inhibits aldosterone, reducing blood pressure, blood volume, and blood sodium concentration
  • Placenta: a temporary endocrine organ that releases hormones that influence the course of pregnancy
  • Gastrointestinal tract: enteroendocrine cells release local-acting digestive hormones, such as gastrin, secretin, and cholecystokinin
  • Kidneys: secrete erythropoietin, which signals the production of red blood cells
  • Skin: produces cholecalciferol, the precursor of vitamin D
  • Adipose tissue: releases leptin, which is involved in the sensation of satiety and stimulates increased energy expenditure

Learn about the process of thyroid hormone synthesis, including the formation of T1, T2, T3, and T4, and how they are regulated by negative feedback. This quiz covers the details of thyroid hormone production and regulation.

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