Copy of Lab 9 Mini Lesson Learning Guides

Mini-Lesson 4: The Thyroid Gland

Key Terms

• Colloid: A protein-rich fluid found within the follicles of the thyroid gland, where thyroid hormone synthesis occurs.

• Follicles: Spherical structures in the thyroid gland that contain colloid and are lined by follicular cells responsible for thyroid hormone production.

• Iodide trapping: The active transport of iodide ions from the bloodstream into thyroid follicular cells.

• Pendrin: A protein that transports iodide from follicular cells into the colloid for hormone synthesis.

• Thyroglobulin: A glycoprotein produced by follicular cells that serves as a precursor for thyroid hormone synthesis.

• Thyroid hormone: A collective term for the hormones T3 (triiodothyronine) and T4 (thyroxine), which regulate metabolism.

• Thyroxine (T4): The predominant thyroid hormone in circulation; contains four iodine atoms.

• Triiodothyronine (T3): The more biologically active thyroid hormone; contains three iodine atoms.

Study Questions and Answers

1. Where is the thyroid gland located and what is its composition?
   The thyroid gland is located in the anterior neck, just below the larynx. It is composed of numerous follicles filled with colloid and lined by follicular cells, which synthesize thyroid hormones.

2. What is the difference between the structure of thyroxine and triiodothyronine (in relation to the number of iodines)? Which is more likely to be found in the blood plasma, and which is more likely to be bound to target cell receptors?

   • T4 (thyroxine) has four iodine atoms, whereas T3 (triiodothyronine) has three.

   • T4 is more abundant in blood plasma, but T3 is more biologically active and more likely to bind to target cell receptors.

3. What are the seven steps involved in thyroid hormone synthesis and secretion that are stimulated by TSH binding to its receptors on follicle cells?

   • Iodide trapping

   • Transport of iodide into colloid via pendrin

   • Iodination of thyroglobulin

   • Coupling of iodotyrosines to form T3 and T4

   • Endocytosis of iodinated thyroglobulin

   • Proteolysis to release T3 and T4

   • Secretion of T3 and T4 into the bloodstream

4. How is thyroid hormone secretion regulated by the HPT (hypothalamus-pituitary-thyroid) axis?
   Flowchart:

   • Hypothalamus releases thyrotropin-releasing hormone (TRH) → stimulates

   • Anterior pituitary to release thyroid-stimulating hormone (TSH) → stimulates

   • Thyroid gland to produce and release T3 and T4, which inhibit TRH and TSH release via negative feedback.

5. What are the main actions of thyroid hormone?

   • Increases basal metabolic rate

   • Enhances protein synthesis and growth

   • Stimulates nervous system activity

   • Regulates body temperature

   • Increases heart rate and cardiac output

Mini-Lesson 5: Thyroid Dysfunction & Endocrine Response to Stress

Key Terms

• Autoimmune thyroiditis: Inflammation of the thyroid due to an autoimmune attack.

• Catecholamines: Hormones released by the adrenal medulla (e.g., epinephrine, norepinephrine) that activate the sympathetic nervous system.

• Congenital hypothyroidism: A thyroid deficiency present at birth, often caused by iodine deficiency.

• Goiter: Thyroid gland enlargement due to overstimulation.

• Graves' disease: An autoimmune disorder causing hyperthyroidism.

• Hashimoto's disease: An autoimmune disorder leading to hypothyroidism.

Study Questions and Answers

1. Causes and symptoms of hypothyroidism?

   • Causes: Iodine deficiency, Hashimoto's disease, congenital defects

   • Symptoms: Fatigue, weight gain, cold intolerance, dry skin, slow metabolism

2. Common cause of goiter?

   • Excessive stimulation of the thyroid by TSH due to iodine deficiency or autoimmune disorders.

3. What is congenital hypothyroidism and the most common cause?

   • A thyroid deficiency at birth; iodine deficiency is the most common cause.

4. Causes and symptoms of hyperthyroidism?

   • Causes: Graves' disease, thyroid tumors

   • Symptoms: Weight loss, heat intolerance, increased heart rate, nervousness

5. Graves' disease vs. Hashimoto's disease?

   • Graves’ disease: Hyperthyroidism due to autoimmune stimulation.

   • Hashimoto’s disease: Hypothyroidism due to autoimmune destruction.

6. Main adrenal catecholamine and what stimulates its secretion?

   • Epinephrine, released in response to sympathetic nervous system activation.

7. How do adrenal catecholamines reinforce the sympathetic nervous system?

   • Increase heart rate, blood pressure, glucose availability, and alertness.

Mini-Lesson 6: The Endocrine Response to Stress – The Adrenal Glands

Key Terms

• Addison’s disease: Primary adrenal insufficiency causing cortisol deficiency.

• Cushing’s syndrome: Excess cortisol due to prolonged glucocorticoid exposure.

• Glucocorticoids: Hormones (e.g., cortisol) that regulate metabolism and immune responses.

Study Questions and Answers

1. Hormones secreted by adrenal cortex zonas?

   • Zona glomerulosa: Aldosterone (mineralocorticoid)

   • Zona fasciculata: Cortisol (glucocorticoid)

   • Zona reticularis: Androgens

2. How is cortisol secretion regulated by the HPA axis?

   • Hypothalamus releases CRH → stimulates anterior pituitary to release ACTH → stimulates adrenal cortex to release cortisol (negative feedback regulation).

3. Why do cortisol, norepinephrine, and catecholamines increase during stress?

   • They help mobilize energy, increase alertness, and maintain homeostasis.

4. Physiological functions of cortisol?

   • Basal levels: Maintain metabolism, blood pressure, and immune function.

   • During stress: Increase glucose availability, suppress inflammation, and aid in survival.

5. Primary vs. secondary adrenal insufficiency?

   • Primary (Addison’s disease): Adrenal gland failure, low cortisol, high ACTH.

   • Secondary: Pituitary failure, low ACTH and cortisol.

6. Cushing’s syndrome vs. Cushing’s disease?

   • Cushing’s syndrome: Excess cortisol from any cause.

   • Cushing’s disease: Caused by an ACTH-secreting pituitary tumor.

7. Other hormones affected by stress?

   • Increased: Epinephrine, norepinephrine, glucagon.

   • Decreased: Insulin, reproductive hormones.