Week 9 Thyroid gland Flashcards
thyroid hormone examples:
T3 and T4
T4: Thyroxine
T3: tri-iodothyronine
how are T3 and T4 made?
Tyrosine is iodinated to become T3 and T4.
Thyroid hormone functions
- thermogenesis in brown adipose tissue (BAT)
- Basal metabolic rate
- growth development
- active mental processes
HPT system: hypothalamus-pituitary-thyroid system
Hypothalamus: Thyrotrophin releasing hormone (TRH)
Pituitary: Thyroid stimulating hormone (TSH)
Thyroid: releases T3 and T4
T3 and T4 has -ve feedback loop to Hypothalamus and pituitary.
T3 and T4 production ratio
Thyroid produces much more T4 than T3, T4:T3 is 14:1
The compartments of Thyroid Follicle and C cell
Thyroid follicle:
- Inner compartment: colloid (glue-like)
- outer layers: thyroid epithelial cells and basement membrane
C cell: parafollicular
What is the function of the colloid
The colloid makes T3 and T4!!
What is the function of the C cell? (hint: c)
C cell produces calcitonin. (Very close to parathyroid!!!)
Calcitonin is made to reduce osteoclast activity and bone resorption.
Thyroid hormone synthesis steps
- Iodine is pumped from plasma into the colloid.
- middle layer thyroid epithelial cells produces many thyroglobulin
- The enzyme TPO with H2O2 can iodinate the tyrosine residues bound on thyroglobulin.
- The colloid is reabsorbed into the epithelial cells.
- Colloid undergoes proteolysis and degraded.
- T3 and T4 are released from the colloid.
What stimulates the release of T3 and T4 from the thyroid follicles?
TSH, TSH can stimulate Ca2+ influx which leads to secretion of T3/T4.
What facilitates the process of iodinating tyrosine residues
the enzyme TPO and H2O2
In what forms do Thyroid Hormones exist in circulation?
They are 99.5% bound to proteins like thyroxine binding globulins and albumin…
They ARE INACTIVE.
What happens to T3/T4 when they get into cells?
- T4 gets converted to T3 through deiodinase 1/3
- T4 also gets converted to reverseT3 (rT3 - which is inactive) through deiodinase 1/2.
- T3 will bind to nuclear T3 receptors
-»» changes
Where does the majority of T3 production happen?
In liver, kidney cells, from the conversion of T4 to T3.
Common causes of hyperthyroidism:
- Graves Disease
- Multi-nodular goitre
- single toxic nodule
Graves Disease cause
Stimulated by antibodies to the TSH receptor
Graves Disease will lead to what symptoms?
Antibodies will stimulate T3 and T4 production.
Large smooth goitre
ophthalmopathy
What’s a common imaging technique used in observing the thyroid gland
Radio-isotope uptake, technitium