Thyroid Gland Flash Cards - Anatomy & Physiology

Question	Answer		Article
Describe embryological origin of the Thyroid Gland.	The thyroid gland is a downgrowth from the pharyngeal endoderm of the developing tongue.		Link to Article
Describe the location of the thyroid gland, it's closely associated structures and anatomical landmarks.	The thyroid gland is adjacent to the cranial part of the trachea, closely associated with the Parathyroid Glands which may be within or close to the thyroid gland itself. Close to the thyroid gland are the Sternohyoid and Sternothyroid muscles, the recurrent laryngeal nerve and the carotid sheath.		Link to Article
Describe the blood supply and venous drainage of the Thyroid Gland.	Supply: Cranial Thyroid Artery and Caudal Thyroid Artery Venous Drainage: Thyroid Vein (leading to Internal Jugular Vein).		Link to Article
The Thyroid gland consists of various sized follicles. What is the name of the cells which line the lumen of the follicles, and what is their function?	Follicular Cells - these synthesize thyroglobulin in their golgi apparatus. Thyroglobulin is a glycoprotein consisting of 70 linked tyrosine molecules and is the source of thyroid hormones.		Link to Article
Label the following histological section: (Image 1 below)	A - Connective Tissue Capsule B - Thyroid Follicles C - Connective Tissue Septum D - Blood Vessels in Capsule.		Link to Article
Which Letter represents the location of the C-Cells of the Thyroid Gland, and what is their function in 'Image 1' below?	A represents the C Cells. The C-Cells (aka Parafollicular Cells) produce Calcitonin, a hormone which acts to lower the plasma calcium level.		Link to Article
Define and describe the process of Iodide Trapping.	Iodide trapping is the process by which Iodide molecules (I-) are concentrated in the colloid at a level up to 250x greater than the plasma level. The Na+/I- symport in the basal membrane of the follicular cells moves the iodine from the plasma, into the cell. From here it is transported into the colloid. The follicular cells and the pumps function in response to Thyroid Stimulating Hormone from the Pituitary Gland.		Link to Article
Name the three hormones produced in the thyroid gland and describe how they are transported around the body?	Hormones: Triiodothyronine (T3), Thyroxine (T4) and Reverse T3. Thyroid hormones are lipid soluble, thus require a binding protein in order to travel in the bloodstream. Thyroid Binding Globulin caries 70-80% of the circulating hormone, with Thyroxine Binding Pre-Albumin, and Albumin carrying the remainder.		Link to Article
What are Hormone A and Hormone B in this schematic diagram ('Image 2' below) of the Hypothalamic - Pituitary - Thyroid Axis:	Hormone A: TRH - Thyrotropin Releasing Hormone Hormone B: TSH - Thyroid Stimulating Hormone (Thyrotropin)		Link to Article
Decribe the effects that T3 and T4 have on the following systems/physiological mechanisms:	Musculoskeletal System Carbohydrate metabolism Fat metabolism Basal Metabolic Rate Cardiovascular System Nervous System Alimentary System Musculoskeletal system - Thyroid hormone promotes bone growth Carbohydrate metabolism - Thyroid hormone stimulates glucose uptake, glycolysis, gluconeogenesis Fat metabolism - Thyroid hormone mobilises lipids from adipose stores. Accelerates oxidation of lipids to produce energy (occurs within mitochondria). Increases size and number of mitochondria. Basal Metabolic Rate (BMR) - Thyroid hormone causes and increase in BMR in all tissues except brain, spleen, gonads. Results in increased heat production, increased oxygen consumption. Cardiovascular actions - Thyroid hormone increases Cardiac output, heart rate and contractility. Nervous system - thyroid hormones are required for development of this system. They also enhance the sympathetic nervous system (by increasing epinephrine receptors). Alimentary System - Thyroid hormone increases appetite and feed intake, increases secretion of pancreatic enzymes and increases motility.		Link to Article

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