12 - unctional morphology of the thyroid gland. Iodine containing thyroid hormones. Physiological effects and control of secretion. Hyper –and hypothyroidism.

section

norphology of thyroid gland

iodine containing thyroid hromone

physiologic effects and control of secretion

hyper and hypothyroidism

norphology of thyroid gland

• comprised of two lobes found on each side of the trachea.

• Has rich blood supply for transporting hormones

• The two lobes are connected by an isthmus (a thin bridge of thyroid tissue).

• The gland contains two types of cells: follicular cells and parafollicular (C-cells)

• calcitonin helps to decrease level of ca2+ in blood.

• Follicular cells synthesize thyroid hormones: thyroxine (T4) and Triiodothyronine (T3)

iodine containing thyroid hromone

• Iodine, is needed by follicular cells in order for them to synthetize T3 and T4 hormones.

• Iodine is combined with amino acid tyrosine for synthesis of T3 and T4 hormones.

• These hormones regulate metabolism, body temperature and heart rate.

• The growth and development.

• The activity of the nervous system.

physiologic effects and control of secretion

• The amount of thyroid hormones released by the thyroid gland is controlled by TSH

• Low levels of T3 and T4 hormones leads to hypothalamus releasing- TRH- thyrotropin releasing hormone which causes the pituitary gland producing TSH which stimulates the thyroid gland to produce more hormones in a negative feedback mechanism. The thyroid gland produces:

  • 80% of T4 hormones and 20% of T3

  • T3 possesses -greater- 4 x hormone strength as T4.

hyper and hypothyroidism

1. Hyperthyroidism - a condition where thyroid gland is overactive therefore it produces excessive amounts of the thyroid hormones.

   • causes body processes to speed up.

   • The most common cause is Graves’ disease. And thyroid neoplasim- tumour

   • this causes the body to make an antibody called thyroid-stimulating immunoglobulin (TSI) which causes the thyroid gland to produce excess thyroid hormones.

   • Over consumption of iodine can also cause overproduction of thyroid hormones. Some symptoms of hyperthyroidism include: hand tremors, anxiety, rapid heartbeat, insomnia, increased frequency of bowel movements.

2. Hypothyroidism is caused when thyroid is underactive due to low production of thyroid hormones. Cause:

   • poor iodine intake

   • autoimmune thyroiditis, -an inflammation of the thyroid gland caused by the patient’s immune system. -hashimotos thyroiditis

   • Some symptoms of hypothyroidism include: goiter-- fatigue, low heart rate, weight gain, reduced appetite, poor memory, muscle stiffness.