Endocrine System: Thyroid and Parathyroid Glands

Overview

• Presentation covers thyroid and parathyroid glands.
• Images provided in the module illustrate these glands.

Image Descriptions

1. Trachea and Larynx
   • Upper portion is the larynx.
   • Thyroid gland appears as a globular structure below.
2. Dorsal Surface View
   • Parathyroid glands visible on the model.
3. Rat Dissection
   • Probe points to a lobe of the thyroid gland near the trachea.
4. Microscope Image
   • Thyroid gland on the left, parathyroid gland on the right.
   • Features: follicles (follicular cells + colloid), parafollicular cells.

Thyroid Gland

Hormones

• Thyroid Hormone (TH)

  • Includes T3 and T4.
  • Produced by follicles (follicular cells + colloid).
  • Requires iodine; deficiency leads to goiter.
  • Functions: increases metabolic rate, heart rate, respiratory rate, stimulates growth with growth hormone.
  • Disorders: Iodine deficiency, Graves’ disease (autoimmune causing hyperthyroidism).
  • Hypothyroidism (low function) and hyperthyroidism (high function) relate to TH levels.

• Calcitonin

  • Produced by parafollicular cells.
  • Decreases blood calcium levels.
  • Inhibits osteoclasts, leading to increased bone density.
  • Slightly inhibits renal calcium reabsorption.

Parathyroid Gland

Parathyroid Hormone (PTH)

• Produced by parathyroid glands.
• Increases blood calcium levels.
• Stimulates osteoclast activity, releasing calcium from bones.
• Aids in vitamin D synthesis.

Antagonistic Relationship

• Calcitonin vs. Parathyroid Hormone
  • They are antagonists, performing opposite functions.
  • Work together for bone health and calcium balance.