The Endocrine System
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Questions and Answers

What is the difference in activity between T3 and T4 when binding to target receptors?

  • T4 is ten times more active than T3
  • T3 is five times more active than T4
  • T3 and T4 have the same activity
  • T3 is ten times more active than T4 (correct)

    • What stimulates the release of TSH from the anterior pituitary?

  • Release of TRH from the hypothalamus
  • Release of Calcitonin from the thyroid gland
  • High blood levels of TH
  • Low blood levels of TH (correct)

    • What is the effect of calcitonin on osteoclast activity?

  • It has no effect on osteoclast activity
  • It stimulates osteoclast activity
  • It stimulates osteoblast activity
  • It inhibits osteoclast activity (correct)

    • What is the function of parathyroid hormone (PTH)?

    <p>It regulates Ca2+ levels in the blood</p> Signup and view all the answers

    What happens when Ca2+ blood levels rise?

    <p>PTH release is inhibited</p> Signup and view all the answers

    What is the role of the parathyroid glands?

    <p>They regulate Ca2+ levels in the blood</p> Signup and view all the answers

    What stimulates the release of calcitonin?

    <p>High blood Ca2+ levels</p> Signup and view all the answers

    Where are the parathyroid glands located?

    <p>In the posterior aspect of the thyroid gland</p> Signup and view all the answers

    What is the primary function of mineralocorticoids?

    <p>Regulating electrolytes in extracellular fluid</p> Signup and view all the answers

    What is the significance of sodium ions in the body?

    <p>Affecting extracellular fluid volume and blood pressure</p> Signup and view all the answers

    What is the importance of potassium ions in the body?

    <p>Setting resting membrane potential</p> Signup and view all the answers

    What is the primary function of glucocorticoids?

    <p>Regulating glucose metabolism</p> Signup and view all the answers

    What is the effect of mineralocorticoids on blood pressure?

    <p>Increases blood pressure</p> Signup and view all the answers

    What is the location where mineralocorticoids regulate electrolytes?

    <p>Extracellular fluid</p> Signup and view all the answers

    What is the effect of potassium ions on cells?

    <p>Sets the resting membrane potential</p> Signup and view all the answers

    What is the reference source for the information about glucocorticoids and mineralocorticoids?

    <p>Marieb and Hoehn, 2019, table 16.5</p> Signup and view all the answers

    Which hormone is responsible for stimulating the production of milk?

    <p>Prolactin (PRL)</p> Signup and view all the answers

    Which two hormones regulate the release of Growth Hormone (GH)?

    <p>GHRH and GHIH</p> Signup and view all the answers

    What is the target tissue for Thyroid-stimulating Hormone (TSH)?

    <p>Thyroid gland</p> Signup and view all the answers

    What is the primary function of prolactin in relation to milk production?

    <p>To promote continued milk production in response to suckling</p> Signup and view all the answers

    Which hormone is responsible for stimulating the production of corticosteroids?

    <p>Adrenocorticotropic Hormone (ACTH)</p> Signup and view all the answers

    Where is the thyroid gland located in the body?

    <p>Anterior to the trachea in the neck</p> Signup and view all the answers

    What is the purpose of Growth Hormone (GH)?

    <p>To promote growth and development in children and adolescents</p> Signup and view all the answers

    What is the primary function of calcitonin?

    <p>To regulate calcium blood levels</p> Signup and view all the answers

    What is the role of Gonadotropin-releasing hormone (GnRH)?

    <p>To regulate the release of gonadotropins (FSH and LH)</p> Signup and view all the answers

    What is the effect of thyroid hormones on metabolic rate?

    <p>They increase metabolic rate</p> Signup and view all the answers

    What is the effect of rising blood levels of thyroid hormones on TSH release?

    <p>It inhibits the release of TSH</p> Signup and view all the answers

    What is necessary for the production of thyroid hormones T3 and T4?

    <p>A dietary supply of iodine</p> Signup and view all the answers

    Which hormone is responsible for inhibiting the release of Prolactin?

    <p>Prolactin-inhibiting hormone (PIH)</p> Signup and view all the answers

    What is the primary function of thyroglobulin in the thyroid gland?

    <p>To combine with iodine to form thyroid hormones</p> Signup and view all the answers

    What is the effect of thyroid hormones on tissue growth and development?

    <p>They stimulate tissue growth and development</p> Signup and view all the answers

    What is the relationship between prolactin and estrogen levels?

    <p>Prolactin levels are directly proportional to estrogen levels</p> Signup and view all the answers

    Which hormone is responsible for causing pelvic ligaments and pubic symphysis to relax and widen in preparation for childbirth?

    <p>Relaxin</p> Signup and view all the answers

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

    <p>Initiates maturation of male reproductive organs</p> Signup and view all the answers

    Which organ produces atrial natriuretic peptide in response to high blood pressure and blood volume?

    <p>Heart</p> Signup and view all the answers

    What is the function of erythropoietin produced by the kidneys?

    <p>Stimulates the production of red blood cells</p> Signup and view all the answers

    What is the inactive form of vitamin D produced by the skin?

    <p>Cholecalciferol</p> Signup and view all the answers

    What is the active form of vitamin D produced by the liver and kidneys?

    <p>Calcitriol</p> Signup and view all the answers

    What is the primary function of vitamin D in the body?

    <p>Required for absorption of calcium into the blood stream</p> Signup and view all the answers

    Which of the following is a consequence of atrial natriuretic peptide's action on the kidneys?

    <p>Increased urine output</p> Signup and view all the answers

    Which hormone stimulates the anterior pituitary gland to secrete adrenocorticotropic hormone (ACTH)?

    <p>Corticotropin Releasing Hormone (CRH)</p> Signup and view all the answers

    Which two hormones regulate the release of Growth Hormone (GH) from the anterior pituitary gland?

    <p>Growth Hormone Releasing Hormone (GHRH) and Growth Hormone Inhibiting Hormone (GHIH)</p> Signup and view all the answers

    What is the function of Prolactin Inhibiting Hormone (PIH) in the hypothalamic-pituitary axis?

    <p>Inhibits the release of Prolactin from the anterior pituitary gland</p> Signup and view all the answers

    Which hormone stimulates the anterior pituitary gland to secrete Thyroid Stimulating Hormone (TSH)?

    <p>Thyrotropin Releasing Hormone (TRH)</p> Signup and view all the answers

    What is the function of Growth Hormone Inhibiting Hormone (GHIH) in the hypothalamic-pituitary axis?

    <p>Inhibits the release of Growth Hormone from the anterior pituitary gland</p> Signup and view all the answers

    Which hormone stimulates the anterior pituitary gland to secrete Follicle Stimulating Hormone (FSH) and Luteinising Hormone (LH)?

    <p>Gonadotropin Releasing Hormone (GnRH)</p> Signup and view all the answers

    What is the effect of prolactin on milk production in response to suckling?

    <p>It promotes continued milk production</p> Signup and view all the answers

    What is the composition of the follicles in the thyroid gland?

    <p>Colloid and thyroglobulin</p> Signup and view all the answers

    What is the role of parafollicular cells in the thyroid gland?

    <p>They produce calcitonin</p> Signup and view all the answers

    What is the effect of thyroid hormones on the body's metabolic rate?

    <p>They increase metabolic rate</p> Signup and view all the answers

    What is necessary for the production of thyroid hormones T3 and T4?

    <p>Dietary supply of iodine</p> Signup and view all the answers

    What is the relationship between prolactin and estrogen levels?

    <p>Prolactin levels increase with estrogen levels</p> Signup and view all the answers

    What is a consequence of exposure to pollutants on the endocrine system?

    <p>Disruption of hormone function, including sex hormones, thyroid hormone, and glucocorticoids</p> Signup and view all the answers

    What happens to ovarian function with age?

    <p>Ovaries undergo significant changes and become unresponsive to gonadotropins</p> Signup and view all the answers

    What is the effect of aging on testosterone levels?

    <p>Testosterone levels diminish with age, but the effect is not usually seen until very old age</p> Signup and view all the answers

    What is the effect of aging on Growth Hormone (GH) levels?

    <p>GH levels decline with age, contributing to muscle atrophy</p> Signup and view all the answers

    What is the effect of aging on thyroid hormone (TH) levels?

    <p>TH levels decline with age, contributing to lower basal metabolic rates</p> Signup and view all the answers

    What is the effect of lack of estrogen in older women?

    <p>They become more vulnerable to the bone-demineralising effects of PTH</p> Signup and view all the answers

    Which hormone is responsible for stimulating gamete production?

    <p>Follicle-stimulating hormone (FSH)</p> Signup and view all the answers

    Which hormone inhibits the release of Growth Hormone (GH)?

    <p>Growth hormone–inhibiting hormone (GHIH)</p> Signup and view all the answers

    Which hypothalamic hormone regulates the release of Adrenocorticotropic Hormone (ACTH)?

    <p>Corticotropin-releasing hormone (CRH)</p> Signup and view all the answers

    What is the primary function of Thyroid-stimulating Hormone (TSH)?

    <p>Regulating the release of thyroid hormones</p> Signup and view all the answers

    What is the effect of rising blood levels of thyroid hormones on TSH release?

    <p>Inhibition of TSH release</p> Signup and view all the answers

    Which hormone is responsible for stimulating the adrenal cortex to release corticosteroids?

    <p>Adrenocorticotropic Hormone (ACTH)</p> Signup and view all the answers

    What is the primary function of gonadocorticoids?

    <p>To contribute to the onset of puberty and sex drive</p> Signup and view all the answers

    What is the effect of glucocorticoid drugs on blood pressure?

    <p>They decrease blood pressure by blocking the release of renin and aldosterone</p> Signup and view all the answers

    What is the primary function of the adrenal medulla?

    <p>To secrete epinephrine and norepinephrine in response to short-term stress</p> Signup and view all the answers

    What is the effect of melatonin on the body?

    <p>It affects the timing of sexual maturation and puberty, and influences sleeping patterns</p> Signup and view all the answers

    What is the primary function of the adrenal cortex?

    <p>To secrete cortisol and aldosterone in response to prolonged stress</p> Signup and view all the answers

    What is the effect of stress on the adrenal gland?

    <p>It stimulates the release of epinephrine and norepinephrine in response to short-term stress, and cortisol and aldosterone in response to prolonged stress</p> Signup and view all the answers

    Study Notes

    Growth Hormone (GH)

    • GH levels peak during adolescence, typically around puberty, as the body undergoes significant growth and development. This surge in GH levels is essential for the completion of physical growth and development.

    • Infants and children have the highest levels of GH due to promotion of growth. In fact, GH is responsible for the rapid growth and development that occurs during childhood and adolescence. GH plays a crucial role in the growth of bones, muscles, and other tissues.

    • GH release is regulated by two hypothalamic hormones: Growth Hormone-Releasing Hormone (GHRH) and Growth Hormone-Inhibiting Hormone (GHIH). GHRH stimulates the release of GH from the pituitary gland, while GHIH suppresses GH release, preventing excessive production.

    Thyroid-Stimulating Hormone (TSH)

    • Target tissue is the thyroid gland
    • Stimulates normal development and secretory activity of the thyroid gland
    • Release is triggered by Thyrotropin-Releasing Hormone (TRH) from the hypothalamus
    • Rising blood levels of thyroid hormones inhibit TSH release

    Adrenocorticotropic Hormone (ACTH)

    • Stimulates the adrenal cortex to release corticosteroids
    • Regulation of ACTH release is triggered by Corticotropin-Releasing Hormone (CRH) from the hypothalamus
    • Internal and external factors such as fever, hypoglycemia, and stressors can alter CRH release

    Gonadotropins (FSH and LH)

    • FSH stimulates gamete production
    • LH promotes production of gonadal hormones
    • Regulation of gonadotropin release is triggered by Gonadotropin-Releasing Hormone (GnRH) from the hypothalamus during and after puberty
    • Absent from the blood in prepubertal boys and girls

    Prolactin (PRL)

    • Stimulates milk production
    • Regulation of release is primarily controlled by Prolactin-Inhibiting Hormone (PIH) (dopamine)
    • Decrease in PIH leads to increased PRL release
    • PRL levels rise and fall in rhythm with estrogen levels

    Thyroid Gland

    • Located anterior to the trachea in the neck
    • Releases thyroid hormones T3 and T4
    • Gland composed of repeated follicles filled with thyroglobulin
    • Thyroglobulin + iodine combines to form thyroid hormones which are then released into the bloodstream

    Thyroid Hormone (TH)

    • Major metabolic hormone that affects nearly every cell in the body
    • Increases metabolic rate and heat production
    • Regulates development and maintenance of tissues
    • Dietary supply of iodine is needed for TH production

    Calcitonin

    • Released in response to high blood calcium ion levels
    • Produced by parafollicular cells located in the thyroid gland
    • Inhibits osteoclast activity and stimulates osteoblast activity
    • Antagonist to Parathyroid Hormone (PTH)

    Parathyroid Glands

    • Four to eight tiny glands embedded in the posterior aspect of the thyroid gland
    • Cells secrete Parathyroid Hormone (PTH)
    • PTH - most important hormone in calcium homeostasis
    • Secretes PTH at low calcium blood levels

    Parathyroid Hormone (PTH)

    • Stimulates osteoclasts to digest bone matrix and release calcium into the bloodstream
    • Enhances reabsorption of calcium and secretion of phosphate by kidneys
    • Promotes activation of vitamin D

    Mineralocorticoids

    • Regulates electrolytes (primarily sodium and potassium ions) in extracellular fluid
    • Importance of sodium ions: affects extracellular fluid volume, blood volume, and blood pressure
    • Importance of potassium ions: sets resting membrane potential of cells

    Glucocorticoids

    • Necessary for normal sperm production
    • Maintains reproductive organs in a functional state

    Glucocorticoid Drugs

    • Used to control chronic inflammatory disorders due to their anti-inflammatory properties
    • Decrease blood pressure by blocking renin and aldosterone secretion

    Gonadocorticoids (Sex Hormones)

    • Most weak androgens are converted to testosterone in tissue cells, while some are converted to oestrogen
    • Contribute to:
      • Onset of puberty
      • Appearance of secondary sex characteristics
      • Sex drive in women
      • Oestrogen in postmenopausal women

    Adrenal Gland

    • Adrenal medulla secretes epinephrine and norepinephrine in response to short-term stress (fight or flight response)
    • Adrenal cortex secretes cortisol and aldosterone in response to prolonged term stress

    Pineal Gland

    • Small gland located in the brain
    • Secretes melatonin
    • Melatonin affects:
      • Timing of sexual maturation and puberty
      • Sleeping patterns
      • Melatonin levels vary during the daily cycle

    Hypothalamic Hormones

    • Regulate growth, development, metabolism, and homeostasis
    • All act on the anterior pituitary gland
    • 4 releasing hormones and 2 inhibiting hormones

    Hypothalamic-Pituitary Relationships

    • Axons extend from the hypothalamus through the infundibulum (stalk of the pituitary gland) into the posterior pituitary lobe/gland
    • GH levels peak during adolescence and decline with age
    • Infants and children have the highest levels of GH due to promotion of growth needed in the individual

    Growth Hormone (GH)

    • Release is chiefly regulated by 2 hypothalamic hormones:
      • Growth hormone-releasing hormone (GHRH) stimulates the anterior pituitary to secrete GH
      • Growth hormone-inhibiting hormone (GHIH) inhibits the release of GH from the anterior pituitary

    Thyroid-Stimulating Hormone (TSH)

    • Target tissue is the thyroid gland
    • Stimulates normal development and secretory activity of the thyroid gland (release of thyroid hormones)
    • Release triggered by thyrotropin-releasing hormone (TRH) from the hypothalamus
    • Rising blood levels of thyroid hormones inhibit TSH release

    Adrenocorticotropic Hormone (ACTH)

    • Stimulates the adrenal cortex to release corticosteroids
    • Regulation of ACTH release:
      • Triggered by hypothalamic corticotropin-releasing hormone (CRH) in daily rhythm
      • Internal and external factors such as fever, hypoglycemia, and stressors can alter release of CRH

    Gonadotropins

    • Follicle-stimulating hormone (FSH) stimulates gamete (egg or sperm) production
    • Luteinising hormone (LH) promotes production of gonadal hormones
    • Regulation of gonadotropin release:
      • Triggered by gonadotropin-releasing hormone (GnRH) from the hypothalamus during and after puberty
      • Suppressed by gonadal hormones (feedback)

    Prolactin (PRL)

    • Stimulates milk production
    • Regulation of release:
      • Primarily controlled by prolactin-inhibiting hormone (PIH) (dopamine)
      • Decrease in PIH leads to increased Prolactin release

    Thyroid Gland

    • Located anterior to the trachea in the neck
    • Releases thyroid hormones T3 (triiodothyronine) and T4 (thyroxine)
    • Gland composed of repeated follicles filled with the glycoprotein thyroglobulin
    • Thyroglobulin + iodine combines to form the thyroid hormones which are then released into the bloodstream

    Thyroid Hormone (TH)

    • Major metabolic hormone which affects nearly every cell in the body
    • Increases metabolic rate and heat production (calorigenic effect)
    • Regulation of growth and development
    • Maintenance of dietary iodine is required for production of T3 and T4

    Endocrine System Across the Life Span

    • Most endocrine organs operate well until old age
    • Exposure to pollutants disrupts hormone function
    • Sex hormones, thyroid hormone, and glucocorticoids are vulnerable to the effects of pollutants
    • Interference with glucocorticoids may help explain high cancer rates in certain areas
    • Ovaries undergo significant changes with age and become unresponsive to gonadotropins
    • Testosterone also diminishes with age, but effect is not usually seen until very old age
    • GH levels decline with age - accounts for muscle atrophy with age
    • TH declines with age, contributing to lower basal metabolic rates
    • PTH levels remain fairly constant with age, but lack of estrogen in older women makes them more vulnerable to bone-demineralising effects of PTH

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