The Thyroid Gland Flashcards
What are the two general functions of the thyroid?
Development and metabolism
What is the structure of the thyroid gland?
Follicular cells surround spheres of colloid
What do follicular cells synthesise and secrete?
Thyroid Hormone
What do C-cells secrete?
Calcitonin
What are the two forms of TH?
T4 and T3
What is the major form of TH?
T4
Which form of TH is more active?
T3
Where is T3 converted?
Target cells
What are the types of plasma protein that is bound to TH?
Thyroid binding globulin (mainly), transthyretin and albumin
What type of receptors are the TH receptors?
Nuclear
What does Thyroid hormone receptor activation require?
Dimerisation with another TR or retinoid X receptor
What are the two genes that encode thyroid hormone receptors?
TR alpha and beta
What are the subtypes of TRs?
1 and 2 of each
Which TR subtype is nonfunctional?
TRalpha2
What are the three main domains in a thyroid hormone receptor?
- where coregulatory factors bind
- DNA binding domain in the middle
- hormone recognition element
Why is selenium essential in the diet?
3-iodothyronine selenodeiodinases D1-3 control the amount of active T3 receptors there are
Which of the 3-iodothyronine selenodeiodinases increase T3 levels and which decrease?
D2 increases and D3 decreases
Do thyroid hormones need transporters to move across the cell membrane?
Yes
What is the cause and symptoms of Allen-Herndon-Dudley syndrome?
Mutations in MCT8 transporters of TH
Associated with psychomotor retardation
How does TH increase metabolic rate?
Increase number and size of mitochondria, positive ionotropic and chromotropic effects on heart and synergies with sympathetic nervous system
What energy metabolism functions does TH partake in?
Partially antagonises insulin signalling, gluconeogenesis and lipolysis
What type of feedback underlies TH production?
Negative
What do hypothalamic neurosecretory cells release?
Thyrotrophin releasing hormone into the portal capillaries
What does TRH stimulate?
Thyrotrophs or anterior pituitary to secrete thyroid stimulating hormone
What type of receptor is the receptor for TSH?
GPCR
What is the main effect of TSH?
Adenylate cyclase -> cAMP and PRA release, causing iodide uptake and the transcription of key enzymes
What does TSH cause?
- Growth in thyroid gland
- increased iodide uptake
- stimulates other reactions involved in TH synthesis
- stimulates uptake of colloid
What are the primary and secondary problems in hyperthyroidism?
Primary = thyroid gland Secondary = pituitary region
What is Graves’ disease?
Primary hyperthyroidism
How does Graves’ disease occur?
Autoimmune
What are the symptoms of Graves’ disease?
Weight loss, tachycardia, fatigue, diffuse goitre and opthamopathy
What are the pharmacological signs of Graves’ disease?
High circulating TH, low TSH
What is hashimotos?
Primary hyperthyroidism
What causes hashimotos?
Autoimmune
What are the pharmacological effects of hashimotos?
Low circulating TH, high TSH
What are the symptoms of hashimotos?
Lethargy, intolerance to cold, lack of growth and development and diffuse goitre
