Thyroid Gland Flashcards Preview

Phase 1 - S2 Metabolism, Endocrinology, Haematology > Thyroid Gland > Flashcards

Flashcards in Thyroid Gland Deck (32)
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where is the thyroid gland located

below the thyroid cartilage


what joins the 2 lobes of the gland together

the isthmus


true or false: the thyroid gland is the first endocrine gland to develop



describe the embryological development of the thyroid gland

at the base of the tongue there is epithelia proliferation
this descends down the thyroglossal duct and passes infront of the hyoid bone
the duct then degenerates
the detached thyroid then continues to migrate


what are thyroid follicles

spherical shapes lined by simple cuboidal epithelium of follicular cells filled with colloid


what type of cells are parathyroid glands made up of

principal cells and chief cells


what types of cells are thyroid glands made up of

follicular cells and parafollicular cells (bigger)


what do parafollicular cells produce



what do follicular cells produce

thyroglobulin and the thyroid hormones T3 and T4


what does colloid do

store the thyroglobulin


what residues are the thyroid hormones made up of

T3 - MIT + DIT
T4 - DIT + DIT


describe the process of making the thyroid hormones from the tyrosine residues

the tyrosine residues on the thyroglobulin undergo iodination
coupling then occurs were the residues couple to become the hormone


what enzyme is required to regulate the production of the thyroid hormones

thyroid peroxidase


what does thyroid peroxidase do

- oxidises iodide to iodine
- adds the iodine to the tyrosine residues
- couple the MIT and DIT residues within the thyroglobulin protein


how much of the bodys iodine is in the thyroid glands



how is iodide taken up from the blood

through a sodium iodide symporter


what happens to the thyroid hormones attached to the thyroglobulin in order to be releases

the thyroglobulin is taken into the follicular cells from the colloid by pinocytosis
a lysosome fuses and the enzymes break down the protein to release the hormones


which thyroid hormone is mostly made

90% is T4 but most of this is converted into T3 in the kidneys and liver


how are T3 and T4 transported in the blood

by being bound to the protein thyroxine-binding globulin


how is the hormonal output of the hormones regulated

thyrotropin releasing hormone is produced from the hypothalamus and goes to the anterior pituitary where it causes the release of thyroid stimulating hormone which goes to the thyroid gland to cause the production of the thyroid hormones


what effect do the thyroid hormones have

- increase metabolic rate
- stimulate metabolic pathways
- increase sympathetic effect


describe the structure of the thyroid stimulating hormone

glycoprotein hormone composed of 2 non-covalently bound subunits (alpha and beta)


describe how TSH stimulates the thyroid gland to release the hormones

The TSH binds to a GPCR on the surface of the follicular cell which activates alpha s and q g proteins
this stimulates the iodide uptake and the thyroglobulin production by the cell eventually leading to the production of the hormones


how do the thyroid hormones increase metabolic rate

- increasing number and size of mitochondria
- stimulating synthesis of enzymes in the respiratory chain


what do the thyroid hormones stimulate metabolic pathways

- stimulates lipolysis and beta oxidation of fatty acids
- stimulates entry of glucose into cells increasing gluconeogenesis and glycogenolysis


how do thyroid hormones increase sympathetic effect

increase andrengeric receptor number on cells so they increase their uptake of catecholamines


how do the thyroid hormones affect the cardiovascular system

increases the hearts responsiveness to catecholamines causing positive inotropy and positive chronotropy


how do the thyroid hormones affect the nervous system

increase myelination of nerves and development of neurones


where are thyroid hormone receptors found

in the nucleus bound to a specific sequence of DNA


what happens when the hormones bind to the thyroid receptor

there is a conformational change causing the receptor to activate transcription allowing gene expression