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33 Cards in this Set
- Front
- Back
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name the two cell types found in the thyroid gland
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follicular cells and parafollicular cells
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what are parafollicular cells
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aka C cells
source of calcitonin |
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what type of transporters are found on the basolateral side of thyroid cell and what are their actions
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Sodium/Iodide symporter: brings I- into the cells
Na+/K+ antiporter - sodium is transported into the serum while the K is transported into the thyroid cell |
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where is thyroglobulin synthesized and what is it's role?
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in the epithelial cells surrounding the colloid
contains multiple tyrosine residues serves as a backbone for synthesis of T3 and T4 |
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who is iodide transported into the colloid?
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through a pendrin iodide transporter
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what is the action of TSH on the thyroid follicular cells?
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increases the activity of Na/I symporter on the basolateral membrane of the cell
brings iodide into the follicular cell |
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how does iodide leave the follicular cell and what happens to it?
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leaves via transporter called pendrin and enters lumen
follicular cell also secretes thyroglobulin thyroid peroxidase on the luminal surface of the secretory vesicle oxidizes I- to I(0) |
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what is the action of thyroid peroxidase?
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oxidized iodide to iodine
required H2O2 catalyzes the attachment of iodine to 3 or 5 position on tyrosine mediates conjugation of MIT, MIT and DIT to yield T3 or T4 |
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briefly describe the thyroglobulin molecule
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made up of multiple tyrosine residues
contains phenyl ring with hydroxyl group I can attach at either position 3 or 5 on the phenyl ring |
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what is the major form of coupled iodotyrosine
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T4
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briefly described what happens once iodoniated thyroglobulin is produced in the colloid?
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taken back up into the epithelial cells by pinocytosis
iodothyronines are hydrolyzed from thyroglobulin T4 and T3 secreted into the blood |
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what is T4
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thyroxine
contains 4 iodines on the 3 and 5 positions of two rings biologically inactive |
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what is T3
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triiodothyroxine
contains only 3 iodine residues on the basic backbone missing an iodine at the 3' position |
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describe how thyroid hormones are found in the plasma
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the majority of them are bound to thyroxine-binding protein (TBP)
- 70% of T4 -80% of T3 most of the remaining is bound to either albumin or transthyretin less than 1% of T3(0.3%) and T4 (0.03%) circulates in an unbound form |
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describe the duration of action of T4
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bound more stongly to binding proteins
longer latency - (2-3 days to effect) longer half life (7-15 days) peak effect at 10-12 days |
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describe the duration of action of T3
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latency of 6-12 hours
half life appx 1 day maximal effect at 2-3 days |
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what is the mechanism of TSH
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acts at a GPCR
stimulates adenylyl cyclase which activates cAMP at high concentration - TSH can also work through DAG and IP3 |
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describe the feedback regulation of the thyroid gland
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TRH affects the release of TSH
TSH works on the thyroid gland and produces T3 and T4 T3 has a negative feedback at the level of the hypothalamus and anterior pituitary |
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what are the cardiovascular effects of thyroid hormones
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increased cardiac contractility
increased heart rate |
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what are the effects on the liver by thyroid hormones
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increased gluconeogensis
increased glycogenolysis |
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what are the effects on skeletal muscle by thyroid hormones?
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increased protein catabolism
increased protein anabolism increased fast twitch muscle fibers |
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what are the effects on bone by thyroid hormones
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predominance of bone resoprtion vs bone formation
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how is BMR changed with excess thyroid hormones?
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increaed BMR
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how is BMR affected with hypothyroidism?
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decreased BMR
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how do the levels of TH effect growth and development
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normal thyroid function in utero and prepubertal requried for normal somatic growth and mental development
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what happens if there is a thyroid deficiency in uter?
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impaired CNS development
-thyroxine treatment must be instituted within a few days after birth -otherwise impairment of mental development results in cretinism impaired somatic growth -if administered soon after birht - there is a return to normal somatic growth |
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what is primary hypothyroidism
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defect in thyroid gland to produce T3 and T4
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what is secondary hypothyroidism
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pituitary dysfunction and inadequate secretion of TSH
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what is tertiary hypothyroidism?
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hypothalmic disfunction and inadequate production of TRH
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what is the treatment for hypothyroidism
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generally treated with exogenous thyroxine
T4 is converted to T3 in peripheral tissues |
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what is grave's disease?
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antibody that stimulates the TSH receptor on follicular cells
excessive production of T3 and T4 can develop a goiter or enlargement of thyroid tissue |
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what is the treatment for hyperthyroidism
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surgical removal of part of the thyroid gland
adminster drugs that block certain steps in T3 and T4 production administration of radioactive iodine |
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what is hashimoto's thyroiditis
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lymphocyte infiltration of thyroid tissue
autoimmune inhibition of Na/I symporter early phase:variable levels of T3 and T4 late phase:hypothyroidism |
