Thyroid and parathyroid glands Dr.Isabel Hwang Department of Physiology Faculty of Medicine University of Hong Kong May 2007
Thyroid and parathyroid glands Dr. Isabel Hwang Department of Physiology Faculty of Medicine University of Hong Kong May 2007
The thyroid gland straddles the esophagus,just below the larynx,in the neck. Superior thyroid artery Larynx Thyroid gland Common carotid artery Trachea (a) Inferior thyroid artery
The thyroid gland straddles the esophagus, just below the larynx, in the neck
Thyroid gland becomes functional early in fetal life as it plays a role in the development of brain cells(forming nerve terminals/synapse/ dendrites/myelin) The follicular cells take part in almost all stages of TH synthesis and secretion Colloid Thyroid follicle (contains thyroglobulin) Follicular cells
Thyroid gland becomes functional early in fetal life as it plays a role in the development of brain cells (forming nerve terminals/ synapse/ dendrites/ myelin) The follicular cells take part in almost all stages of TH synthesis and secretion Colloid
THYROID Biosynthesis. lodine/iodide trapping Oxidation of iodide Incorporation (iodination) Coupling TSH affects all these steps plus release of thyroid hormones Bound to plasma proteins
THYROID Biosynthesis. Iodine/iodide trapping Oxidation of iodide Incorporation (iodination) Coupling TSH affects all these steps plus release of thyroid hormones Bound to plasma proteins
Thyroid Hormone: ·Amino acid hormones containing 2 tyrosine molecules each bound to iodine molecules; Regulates metabolic activities of all cell types,especially glucose oxidation (energy heat production) Formed by joining 2 tyrosine- iodine complexes (MIT/DIT) MIT-monoiodotyrosine DIT-diiodotyrosine
Thyroid Hormone: • Amino acid hormones containing 2 tyrosine molecules each bound to iodine molecules; • Regulates metabolic activities of all cell types, especially glucose oxidation (energy & heat production) • Formed by joining 2 tyrosineiodine complexes (MIT/DIT) MIT-monoiodotyrosine DIT-diiodotyrosine
2 Types of Thyroid Hormones 1.Thyroxine(T) Major hormone released from thyroid follicles Contains 4 iodine atoms -More abundant than T3 Synthesis occurs in follicular cell colloid via the combination of DIT DIT OH NH2 T4 (thyroxine)
2 Types of Thyroid Hormones 1. Thyroxine (T 4) - Major hormone released from thyroid follicles - Contains 4 iodine atoms - More abundant than T 3 - Synthesis occurs in follicular cell colloid via the combination of DIT + DIT
2.Triiodothyronine(T3) Generally formed from T by cleaving an iodine molecule(deiodinase in target cells) More potent than T4 Contains 3 iodine atoms Synthesis occurs in the follicular cell colloid via the combination of DIT MIT OH NH T3 3,5,3'-tr iodothyronine)
2. Triiodothyronine (T 3) - Generally formed from T 4 by cleaving an iodine molecule (deiodinase in target cells) - More potent than T 4 - Contains 3 iodine atoms - Synthesis occurs in the follicular cell colloid via the combination of DIT + MIT
Thyroid follicles are sacs lined with follicular cells and containing a substance called colloid Colloid contains thyroglobulin folicular cells Inactive Active Colloid Reabsorption Parafollicular lacunae cells
• Thyroid follicles are sacs lined with follicular cells and containing a substance called colloid • Colloid contains thyroglobulin
Thyroid Hormone Synthesis and Secretion
Thyroid Hormone Synthesis and Secretion
Capillary Interstitial fluid Follicle cell Lumen of follicle (colloid) lodide is lodide is oxidized and Ditfusion Down conc/electrical gradient ○》 OH (DIT) Luminal borde ○-OH (MIT) ein (TG Thyroid peroxidase cell and secreted to colloid) Lysosomes- Free imino DIT at another spot Lysosoma enzymes T release Ta Ta OH 1. T3 T4 -doT3 Endocytosis of thyroglobulir contains la and I4 molecule
Luminal border Down conc/electrical gradient Thyroid peroxidase