E

Part Two of Part 3 -- Endocrine System, A&P2.

Location of the Thyroid

  • The thyroid is located just below the Adam's apple, bridging across the thyroid cartilage.

  • It consists of two lobes: left and right, connected by a narrow strip called the isthmus.

Histology of the Thyroid

  • The thyroid is primarily made up of thyroid follicles, each surrounded by follicular cells.

  • Follicles are responsible for producing thyroid hormones, which are essential for metabolic regulation.

Thyroid Follicles and Hormone Production

  • Each follicular cell produces a precursor substance called thyroglobulin and pumps it into the follicle.

  • The follicular fluid, enriched with thyroglobulin, electrolytes, and most importantly, iodine, is called the colloid mixture.

  • Iodine is crucial as it binds with thyroglobulin to synthesize thyroid hormones.

Types of Thyroid Hormones

  • The primary thyroid hormones are T3 (triiodothyronine) and T4 (thyroxine).

  • T3 has three iodines, while T4 has four:

    • T3 (Triiodothyronine): More potent, binds to cells more effectively.

    • T4 (Thyroxine): More stable, predominant in circulation.

  • Both forms are critical for metabolic functions but have different characteristics and roles.

Functions of Thyroid Hormones

  • Metabolic Regulation: Increases metabolic activity across almost all cell types, effectively 'speeding up' cellular functions.

    • Hypothyroidism leads to fatigue and sluggishness due to lower metabolic rates.

    • Hyperthyroidism results in increased nervous energy, causing issues like insomnia and anxiety.

Growth and Development

  • Thyroid hormones are essential for normal growth and development, especially during childhood.

  • In children, inadequate thyroid hormone can lead to significant developmental issues.

Effects on the Gastrointestinal System

  • Thyroid hormone regulates GI secretions and motility:

    • Secretions: Involves digestive enzymes critical for food breakdown.

    • Mobility: Determines the speed of food transit through the intestines.

  • Hypothyroidism may cause constipation due to slower transit, while hyperthyroidism can lead to rapid movement resulting in weight loss.

Effects on the Integumentary System

  • Hypothyroidism: Results in dry skin, brittle hair, and hair loss.

  • Hyperthyroidism: Can lead to excessive sweating and overactive sweat glands, impacting skin health.

Diagnosing Thyroid Issues

  • Diagnosis and treatment require a comprehensive thyroid panel to assess both T3 and T4 levels:

    • Hashimoto’s Disease: An autoimmune disorder that can cause hypothyroidism.

    • Congenital defects: Birth-related anomalies affecting the thyroid.

    • Thyroiditis: Inflammation of the thyroid, potentially leading to hormone secretory issues.

Conditions Caused by Thyroid Dysfunction

  • Cretinism: Caused by hypothyroidism in children, leads to severe developmental delays and nervous system issues.

  • Myxedema: A term for symptoms caused by hypothyroidism in adults, including lethargy, dry skin, and fertility issues.

Treatment Options

  • Treatment for hypothyroidism typically involves hormone replacement therapy to restore normal levels.

  • For hypersecretion, symptoms will manifest in reverse, leading to weight management issues, excessive sweating, and sleep disturbances.