Thyroid Gland Flashcards
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
true
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
calcitonin
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
90-95%
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
what is the section of DNA to which the thyroid receptor is pre bound to called
a hormone response element
why does the thyroid gland move up when swallowing
because it is encased in the pre-tracheal fascia which attaches it to the trachea and larynx
