Endocrine System: Thyroid Gland and Hormones

Thyroid Gland and Its Hormones

• The thyroid gland is the largest endocrine gland in the body, located in the lower anterior region of the neck, weighing around 25-30 grams.
• It consists of two lobes connected by the isthmus part.
• The thyroid gland produces hormones that regulate growth, development, and metabolic activities in the body.

Thyroid Hormones

• TSH (Thyroid-Stimulating Hormone) regulates the production of thyroid hormones.
• T3 (Tri-iodothyronine) and T4 (Thyroxine) are the two main thyroid hormones.
• T3 is more active and has a shorter half-life than T4.
• T4 is less active but more abundant and converts to T3 in the plasma.
• Thyroid hormones stimulate tissue metabolism, increase sympathetic activity, and regulate body temperature and growth.

Functions of Thyroid Hormones

• Provide normal growth and development by stimulating protein synthesis.
• Regulate metabolic activities, increasing oxygen consumption and carbon dioxide production.
• Increase respiratory rate and heart rate.
• Stimulate the oxidation of fatty acids in adipose tissue.
• Convert glycogen into glucose in the liver and prevent glycogen formation.

Parathyroid Hormones

• The parathyroid gland is located around the thyroid gland and produces parathormone.
• Parathormone stimulates bone resorption, increases plasma calcium levels, and prevents osteoporosis.
• Deficiency in parathormone can lead to hypocalcemia, tetany, and cramps.

Pancreas Hormones

• Insulin is produced by the Langerhans islets and regulates blood sugar levels.
• Insulin stimulates glucose storage in the liver, enables glucose use in cells, and decreases blood sugar.
• Deficiency in insulin leads to diabetes mellitus, characterized by high blood sugar levels, and can cause hyperglycemia.
• Glucagon, on the other hand, increases glucose release from the liver, increasing blood sugar levels.

Adrenal Cortex Hormones

• The adrenal cortex produces steroid hormones, including glucocorticoids, mineralocorticoids, and androgens.
• Glucocorticoids (e.g., cortisol and corticosterone) affect protein, fat, and carbohydrate metabolism, and have anti-inflammatory effects.
• Mineralocorticoids (e.g., aldosterone) maintain fluid and electrolyte balance, reabsorbing sodium and excreting potassium and hydrogen ions.
• Androgens (e.g., androcorticoids) play a role in sexual development and gender instinct.

Adrenal Medulla Hormones

• The adrenal medulla produces adrenaline (epinephrine) and noradrenaline (norepinephrine).
• Adrenaline increases heart rate, blood pressure, and energy levels, while noradrenaline has more specific effects on the heart and blood vessels.

Endocrine Function of the Kidney

• The kidney produces renin, which helps regulate blood pressure, and erythropoietin, which stimulates erythropoiesis.
• The kidney also synthesizes prostaglandins, which have a role in mediating asthma and chronic inflammation in the lung.