AL-Mustansiriyah University College of science Biology Dept AL-Mustansiriyah University College of science Biology Dept. Zoology 4th class ENOCRINOLOGY LAB. (4) D NAME :

the highest rates of blood flow per gram of tissue. THE THYROID GLAND - The thyroid gland is the largest, butterfly-shaped endocrine glands & is located at the base of the neck immediately below the Larynx, on each side of & anterior to the trachea. The thyroid gland consists of two lobes of endocrine tissue (lying on either side of trachea) joined in the middle by a narrow portion of the gland called as the Isthmus. The thyroid has one of the highest rates of blood flow per gram of tissue. - In a normal adult male, it weighs 15-20 g but is capable of enormous growth, sometimes achieving a weight of several hundred grams. It looks like a bow tie & is even located in the appropriate place for a bow tie lying over the trachea just below the larynx! It develops from an evagination of the floor of the pharynx, and a thyroglossal duct marking the path of the thyroid from the tongue to the neck sometimes persists in the adult.

The Thyroid Thyroid Gland is UNIQUE among other endocrine glands in 3 ways 1. PHYSICAL Only gland which can be seen & palpated. 2. BIOCHEMICAL Only hormone that needs a trace element Iodine for its production 3. PHYSIOLOGY Hormone is stored in an extracellular site in the Thyroid Colloid. Trace elements are elements that occur in very small amounts in living organisms and are necessary for their health, growth and development. Whereas their shortage in the body may result in stunted growth and disease, their excess is also harmful. If deficient they need to be taken with diet.

Histology of Thyroid

Glycoprotein colloid, inside the follicle, called thyroglobulin The functional unit: follicle– epithelial cells (cuboidal )produces thyroid hormones Glycoprotein colloid, inside the follicle, called thyroglobulin A group of follicle forms a lobule surrounded by connective tissue (septum) A C B

THYROID HORMONES The Thyroid gland secretes 3 major hormones: Thyroxine or T4 : having 4 atoms of Iodine. (secreted in largest amount) Triiodothyronine or T3 : having 3 atoms of Iodine (secreted in lesser amount)

THYROID HORMONES About 93% of secreted hormone is T4, while 7% is T3. However, almost all T4 is ultimately converted into T3. The functions of the 2 hormones are the SAME but they differ in rapidity & intensity of action. T3 is about 4 times as potent as T4, and has a much greater biological activity but is present in blood in much smaller quantities & for a much shorter time!

Hyperthyroidism Hyperthyroidism is present when the thyroid gland is over secreting hormones. Hyperthyroidism occurs when the thyroid gland over secretes thyroid hormones. Thus, increasing the metabolic rate of the body and speeding up the body.

Causes of Hyperthyroidism Grave’s disease. A benign nodule on the thyroid. Thyroiditis. Taking too much of the synthetic thyroid hormone. 80% of cases are caused by an autoimmune disorder called Grave’s disease. A benign nodule on the thyroid can cause the thyroid to overproduce hormones. Older individuals are at high risk because of wear and tear to their bodies and thyroid. Thyroiditis is an inflammation of the thyroid gland and can cause the increase in thyroid hormones. Taking too much of the synthetic thyroid hormone can occur either because of a previous diagnosis of hypothyroidism or when the thyroid is surgically removed. Smoking and high stress situations can also increase a person’s risk for hyperthyroidism. Women are more likely to develop hyperthyroidism than men, because of their hormonal fluctuations.

Hypothyroidism Hypothyroidism is present when the thyroid gland is producing little or no thyroid hormones. Thus slowing things down.... Hyperthyroidism is present when the thyroid gland is producing little or no thyroid hormones. This slows the body down. People of any age can develop hypothyroidism. However, women age 60 and over are most prone to this disorder.

Causes of Hypothyroidism Hashimoto’s thyroiditis also known as chronic lymphocytic thyroiditis and Hashimoto's disease,( is an autoimmune disease in which the thyroid gland is gradually destroyed). Treatment for hyperthyroidism Congenital hypothyroidism Radiation therapy given to the head and/or neck Hashimoto’s thyroiditis is an autoimmune disease which causes the immune system make antibodies which attack and destroy the thyroid gland. This disease is more common in the elderly and women. It often goes unnoticed because it is painless. Treatment for hyperthyroidism can cause hypothyroidism if the thyroid is completely stopped and medication is not started soon enough. Congenital hypothyroidism happens when the infant is born with no thyroid gland. Radiation therapy can destroy the thyroid and cause hypothyroidism within 5 years. Side-effect hypothyroidism, also called secondary hypothyroidism, is very rare. It occurs when the pituitary develops a disorder and cannot produce TSH. Tumors or cysts on the pituitary gland can also cause hypothyroidism.