THYROID glands Flashcards
(44 cards)
What is the middle lobe of the thyroid in which not everyone has?
Pyramid- connected to the isthmus
What are the types of cells and molecules in thyroid gland?
Follicular cells and colloid (makes follicles) Parafollicular cells
What is the function of parafollicular cell?
Makes calcitonin
What is the function of follicles
Makes thyroxine
How many parathyroid glands do we have ; name them
4 Superior and inferior on BOTH LOBES
What is the function of the parathyroid gland?
Calcium metabolism; to control calcium levels
What nerve lies very close to the thyroid? What does it supply?
Recurrent laryngeal nerve Supplies vocal cords
Describe the embryology of thyroid gland: how it forms in embryo
Midline outpouching from floor of pharynx; originates from base of tongue
Thryoglossal ducts develops
Divides into 2 lobes
Thyroglossal duct disappear leaving FORAMEN CAECUM
Final position by week 7 Thyroid gland develops
In the steps of synthesis of thyroxine, describe what happens in the FOLLICULAR CELLS
Iodide ions diffuse into follicular cell from capillary TSH bind to TSH-R;
This stimulates production of TG (thyroglobulin)
Also TPO is made(Thyroperoxidase)
In the steps of synthesis of thyroxine, describe what happens in the COLLOID
Iodide ions diffuse into colloid and becomes OXIDISED
TG goes into colloid and bind with Iodine (iodination).
MIT and DIT are formed
They undergo coupling reactions with DIT to form T3 and T4
Describe the roles of TPO, in synthesis of thyroxine
Binds to H2O2 and Catalyses TG reactions
What properties of thyroglobulin allows it to undergo iodination
It has tyrosine residue that can be iodinated
What happens to T3 and T4 after they have been synthesised
Secreted out of thyroid into the blood to target organ
What’s the acronym of the following MIT,DIT, T3 and T4
MIT- Monoiodotyrosine DIT- diiodotyrosine T3- 3,5,3 TRI-iodothyronine T4- thyroxine
Of the following which is active and inert T3, T4
T3- active T4- inert
What compounds can T4 be deiodinated to? Which is active
T3 ( 2 iodine in primary bottom chain )
Reverse T3- 2 iodine in top secondary chain; this is INACTIVE
What enzymes convert T4 to T3; where are they found?
Deiodinase enzymes; found in all target cells.
Outline the origins of the main T3 in target cells
80% from T4
20% from direct thyroidal secretion
What proteins does T3/T4 bind to in order to be transported in the blood.
TBG(Thyroid binding globulin)- 70-80%
Albumin- 10-15%
Prealbumin-
What percentage of T3 and T4 are unbounded to proteins in the blood; what are their properties?
- 05% of T4
- 5% of T3
They are bio active
What does T3 and T4 do in target cells in order to bring about a physiological effect
Alter gene expression in nucleus
What is the function of thyroid in foetus
Growth and development; especially the CNS
How does the baby gets its thyroid?
From mother; it crosses placenta
What is untreated congenital hypothyroidism called?
Cretinism
