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Questions and Answers

What is the primary mechanism by which group I hormones exert their effects?

  • By directly modifying existing enzymes in the cytoplasm
  • Through ion channels in the cell membrane
  • By forming a hormone receptor complex in the cytoplasm (correct)
  • By causing the release of other hormones from the endocrine glands

    • Which of the following is NOT a hormone classified as group I?

  • Insulin (correct)
  • Retinoic acids
  • Mineralocorticoids
  • Glucocorticoids

    • What role does the hormone receptor complex play once it is formed in group I hormones?

  • It initiates the process of cell division
  • It destroys unnecessary proteins in the cytoplasm
  • It binds to the DNA at the hormone response element (correct)
  • It transports nutrients into the cell

    • In group II hormones, what is the primary function of the second messenger?

    <p>To initiate the action of G proteins</p> Signup and view all the answers

    What kind of hormones utilize cAMP as a second messenger?

    <p>Hormones that bind to G protein-coupled receptors</p> Signup and view all the answers

    Which component is NOT part of the G protein structure?

    <p>Delta subunit</p> Signup and view all the answers

    How does the alpha subunit of G protein get activated?

    <p>When GDP is replaced by GTP</p> Signup and view all the answers

    What is the function of the GTPase activity of the alpha subunit?

    <p>To regenerate GDP from GTP</p> Signup and view all the answers

    What is the primary second messenger activated by the α-subunit of Gs protein?

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

    Which enzymatic action does protein kinase A (PKA) perform through phosphorylation?

    <p>It phosphorylates serine or threonine residues.</p> Signup and view all the answers

    What is the role of phosphodiesterases in relation to cAMP?

    <p>They hydrolyze cAMP to AMP.</p> Signup and view all the answers

    How does insulin affect the activity of phosphodiesterase?

    <p>It activates phosphodiesterase.</p> Signup and view all the answers

    What is a consequence of cholera toxins on the Gs protein signaling pathway?

    <p>Continuous activation of adenyl cyclase.</p> Signup and view all the answers

    Which protein do the catalytic subunits of protein kinase A phosphorylate to affect gene transcription?

    <p>CRE-binding proteins (CREB)</p> Signup and view all the answers

    What effect does Gi protein have on adenyl cyclase?

    <p>It inhibits adenyl cyclase activity.</p> Signup and view all the answers

    In the context of Gs protein signaling, what is primarily affected by the sustained phosphorylation of chloride channels?

    <p>Decreased sodium retention.</p> Signup and view all the answers

    What effect do thyroid hormones have on red blood cell formation?

    <p>They increase RBC formation.</p> Signup and view all the answers

    Which system is primarily affected by thyroid hormones to regulate heart rate?

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

    How do thyroid hormones influence muscle strength?

    <p>They lead to muscle weakness with high or low levels.</p> Signup and view all the answers

    Which of the following is a function of thyroid hormones related to the gastrointestinal tract?

    <p>Increase motility and appetite.</p> Signup and view all the answers

    What role do thyroid hormones play in the central nervous system?

    <p>They are essential for normal activity and development.</p> Signup and view all the answers

    What is the impact of thyroid hormones on kidney function?

    <p>They cause diuresis and increase excretion of K+, Ca++, and PO4.</p> Signup and view all the answers

    Which statement best describes the relationship between thyroid hormones and gonadal function?

    <p>They are essential for normal gonadal function.</p> Signup and view all the answers

    How do thyroid hormones influence blood pressure?

    <p>They increase systolic blood pressure and do not affect diastolic pressure.</p> Signup and view all the answers

    What anatomical structure is connected to the thyroid lobe by the suspensory ligament of Berry?

    <p>Cricoid cartilage</p> Signup and view all the answers

    Which nerve is related to the inferior surface of the thyroid gland?

    <p>Recurrent laryngeal nerve</p> Signup and view all the answers

    During a thyroidectomy, which structure is essential to include with the thyroid gland to prevent hemorrhage?

    <p>True capsule</p> Signup and view all the answers

    What is the orientation of the apex of each thyroid lobe?

    <p>Directed upwards towards the oblique line of thyroid cartilage</p> Signup and view all the answers

    The posterior border of the thyroid lobe is related to which of the following?

    <p>Parathyroid glands</p> Signup and view all the answers

    Which surfaces are present in the isthmus of the thyroid gland?

    <p>Anterior and posterior</p> Signup and view all the answers

    Which structure is NOT related to the medial surface of the thyroid lobe?

    <p>Common carotid artery</p> Signup and view all the answers

    What anatomical structure lies deep to the true capsule of the thyroid gland?

    <p>Dense venous plexus</p> Signup and view all the answers

    What is the primary function of thyrotropin-releasing hormone (TRH)?

    <p>Stimulates release of TSH from anterior pituitary</p> Signup and view all the answers

    Which feedback mechanism involves T3 and T4 levels directly suppressing TSH release?

    <p>Direct Feedback</p> Signup and view all the answers

    What role does Long Acting Thyroid Stimulator (LATS) serve in the body?

    <p>Acts as a long-term thyroid hormone stimulator</p> Signup and view all the answers

    What happens to a normal person when excess iodine is ingested?

    <p>Is stored in the thyroid gland without raising thyroxine levels</p> Signup and view all the answers

    What is the effect of excess iodine on a hyperthyroid person?

    <p>Inhibits biosynthesis of T4 due to inactivation of TSH</p> Signup and view all the answers

    What hormone is secreted by parafollicular C-cells in the thyroid gland?

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

    Which system predominantly stimulates thyroid secretion?

    <p>Sympathetic nervous system</p> Signup and view all the answers

    What is the Wolff-Chaikoff effect?

    <p>Inhibition of organification of iodide by excess iodine</p> Signup and view all the answers

    What is indicated by a fasting blood glucose level that is normal, but rises above 180 mg/dl after a glucose load and falls back to fasting level in less than 2 hours?

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

    Which condition is characterized by a flat glucose tolerance test where blood glucose levels fail to rise normally after glucose load?

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

    What does an HbA1c value of greater than or equal to 6.5% indicate?

    <p>Diabetes mellitus</p> Signup and view all the answers

    What is the normal range for fructosamine levels?

    <p>2.4 - 3.4 mmol/L</p> Signup and view all the answers

    What is the significance of serum C-peptide levels in diabetic patients?

    <p>Assess β-cell function</p> Signup and view all the answers

    Which of the following is NOT a method for monitoring diabetes in patients?

    <p>Fasting serum insulin</p> Signup and view all the answers

    In which of the following conditions does fructosamine level increase?

    <p>Uncontrolled diabetes</p> Signup and view all the answers

    What is the principle behind the formation of glycosylated hemoglobin (HbA1c)?

    <p>Non-enzymatic glycosylation of hemoglobin</p> Signup and view all the answers

    Study Notes

    Feedback Mechanisms in Endocrine System Control

    • A typical feedback loop involves gland A releasing hormone A, which stimulates gland B to release hormone B. Hormone B then regulates the release of hormone A.
    • Positive feedback: Hormone A stimulates hormone B, leading to more of hormone A.
    • Negative feedback: Hormone A inhibits hormone B, which decreases the release of both hormones. This maintains a stable plasma level of hormone B.

    Types of Feedback Mechanisms

    • Extrinsic feedback:
      • Negative feedback:
        • Long-loop feedback:
          • Direct: hormonal/chemical communication between the target gland and the anterior pituitary.
          • Example: Thyroxine (from thyroid gland) decreases TSH (from anterior pituitary), while decreased thyroxine increases TSH.
          • Indirect: hormonal/chemical communication between the target gland (thyroid gland) and the hypothalamus.
          • Example: Increased thyroxine --> decreased TRF (from hypothalamus) --> decreased TSH (from anterior pituitary) --> decreased thyroxine.
        • Short-loop feedback: Hormonal/chemical communication between anterior pituitary and hypothalamus.
        • Ultrashort (auto-feedback): Hormonal communication within the same gland.
    • Intrinsic feedback (Intracellular): Negative feedback at the cellular level, such as the Wolff-Chaikoff effect where large quantities of iodide inhibit thyroid hormone synthesis.

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