Thyroid Gland and Hormones Overview

Thyroid Gland

• The thyroid gland produces thyroid hormones, which include thyroxin (T4), triiodothyronine (T3), and thyrocalcitonin.
• Thyroxin (T4) and triiodothyronine (T3) are produced by follicular cells, while thyrocalcitonin is produced by parafollicular cells.
• T4 and T3 both contain iodine.
• Both hormones are comprised of two tyrosine amino acids and either four or three atoms of iodine respectively.

Functions of Thyroid Hormones

• Thyroid hormones have metabolic, growth, and effect on body systems functions

• Metabolic Functions

  • Calorigenic action: Increases mitochondrial size and number in cells, which increases ATP production, basal metabolic rate, and energy consumption.
  • Metabolic processes:
    • Carbohydrate: Increases glucose levels and utilization by increasing glycolysis, glycogenolysis, and gluconeogenesis.
    • Lipids: Has a powerful lipolytic action on fat stores, causing depletion of fat stores and decreasing weight.
    • Protein: At normal levels, thyroid hormones stimulate protein synthesis (anabolic) but high levels cause protein catabolism.

• Growth Functions: Thyroid hormones affect growth and development, particularly in children.

• Effect on Body Systems:

  • Cardiovascular system: Increases heart rate and strength of contractility, resulting in an increased systolic blood pressure.
  • Respiratory system: Increases the rate and depth of respiration.
  • Gastrointestinal tract: Increases appetite and food intake. Also increases secretion and motility.

Thyroid Gland

• The thyroid gland produces thyroid hormones
  • Thyroxine (T4) - produced by follicular cells
  • Triiodothyronine (T3) - produced by follicular cells
  • Thyrocalcitonin - produced by parafollicular cells, decreases calcium levels in the body

Thyroid Hormones

• Contain Iodine
• T4 and T3 have a similar structure, both contain two tyrosine amino acids linked, with 4 or 3 iodine atoms respectively

Functions of Thyroid Hormones

• Metabolic Functions:
  • Calorigenic action: Increases the size and number of mitochondria in cells, resulting in increased ATP production, increased basal metabolic rate (BMR), and energy consumption
  • Metabolic processes:
    • Carbohydrate: Increases glucose levels in the blood.
    • Lipids: Has a strong lipolytic effect on fat stores, causing depletion of fat stores and weight loss.
    • Protein: Stimulates protein synthesis at normal levels, but high levels of thyroid hormones cause protein catabolism
• Growth: Essential for normal growth and development
• Effect on Body Systems:
  • Cardiovascular system: Increased heart rate and contractility, increased systolic blood pressure
  • Respiratory system: Increased rate and depth of breathing
  • Gastrointestinal tract: Increased appetite, food intake, secretion, and motility

Thyroid Gland

• The thyroid gland secretes thyroid hormones.
• The thyroid gland is composed of follicular and parafollicular cells.
• Follicular cells secrete thyroxin (T4) and Triiodothyronine (T3), which are iodine-containing hormones.
• Parafollicular cells secrete thyrocalcitonin, which lowers calcium levels in the blood.

Thyroid Hormones

• T4 and T3 have a highly similar structure comprised of two tyrosine amino acids connected with either 4 or 3 iodine atoms respectively.
• Thyroid hormones regulate metabolism, growth, and development.

Functions of Thyroid Hormones

• Metabolic Functions

  • Calorigenic Action: Increases the size and number of mitochondria, leading to increased ATP production and thus, basal metabolic rate and energy consumption.
  • Metabolic Processes:
    • Carbohydrate: Increases glucose levels in blood through increased glycolysis, glycogenolysis, and gluconeogenesis.
    • Lipids: Promotes fat breakdown through lipolysis and reduces fat stores causing weight loss.
    • Protein: At normal levels, thyroid hormones stimulate protein synthesis (anabolic). However, high levels cause protein breakdown (catabolic).

• Growth: Contribute to growth and development, especially during childhood and adolescence.

• Effect on Body Systems:

  • Cardiovascular System: Increases heart rate, contractility, and systolic blood pressure.
  • Respiratory System: Increases respiratory rate and depth.
  • Gastrointestinal Tract: Increases appetite, food intake, and secretion and motility.

This quiz covers the structure and functions of the thyroid gland, focusing on the hormones it produces, including thyroxin (T4) and triiodothyronine (T3). It delves into the metabolic roles of these hormones and their impact on growth and body systems. Test your knowledge on the crucial aspects of thyroid function.