Thyroid and Parathyroid
4. Thyroid Gland
- Largest endocrine gland.
- It includes 2 lobes on either side of the trachea.
- The lobes are interconnected with isthmus (a connective tissue).
- Thyroid gland is made of follicles & stromal tissues.
- Follicular cells secrete the following hormones:
1. Thyroxin (tetraiodothyronine, T4) & Triiodothyronine (T3)
- Their functions are:
- Regulation of basal metabolic rate (BMR).
- Physical, mental and sexual development.
- Support RBC formation.
- Control metabolism of carbohydrates, proteins & fats.
- Maintain water and electrolyte balance.
2. Thyrocalcitonin (TCT)
- A protein hormone. It regulates (lowers) blood calcium levels (Hypocalcaemic hormone).
- Iodine is essential for normal hormone synthesis in thyroid.
Hypothyroidism (Goiter)
- Enlargement of thyroid gland due to deficiency of iodine.
- In adult women, it causes irregular menstrual cycle.
- Hypothyroidism during pregnancy affects the baby causing stunted growth (cretinism), mental retardation, low intelligence quotient, abnormal skin, deaf-mutism etc.
Hyperthyroidism
- Abnormal increase of thyroid hormones resulting in adverse effects on the physiological activities.
- It is caused due to development of the nodules or the cancer of thyroid gland.
Exophthalmic goiter (Grave’s disease)
- It is a form of Hyperthyroidism. Symptoms are enlargement of thyroid gland, protruded eyeballs, increased BMR & weight loss.
5. Parathyroid Gland
- 4 parathyroid glands are present on back side of the thyroid gland, one pair each in the two lobes of thyroid gland.
- They secrete Parathyroid hormone (PTH) – a peptide hormone.
Functions of parathyroid hormone
- Increases Ca2+ level in blood (hypercalcaemic hormone).
- Stimulates the bone resorption (demineralization).
- Stimulates the reabsorption of Ca2+ by the renal tubules and increases Ca2+ absorption from the digested food.
- Along with TCT, it helps in calcium balance in the body.
