TH Mechanism of Action Flashcards
What are thyroid hormones modified by?
Enzymes in target tissues
How do thyroid hormones interact with thyroid hormone receptors?
To modulate transcription of target genes
What are the major functions of thyroid hormones?
Metabolism, growth, and development
What major roles do thyroid hormones play in neurological development?
Neurological development and neurogenesis
Which thyroid hormone is produced more, T4 or T3?
T4
What is the principle carrier of thyroid hormones in the blood?
Thyroxine-binding globulin (TBG)
What is the function of deiodinases?
Convert circulating T4 to bioactive T3
What type of effects do thyroid hormones have at the nuclear thyroid hormone receptor?
Genomic and non-genomic effects
What are the two main categories of biological responses to thyroid hormones?
- Effects on metabolic pathways
- Effects on cellular differentiation and development
How do thyroid hormones affect metabolic activity?
They stimulate diverse metabolic activities leading to an increase in basal metabolic rate
What is the relationship between thyroid hormones and lipid metabolism?
Stimulate fat mobilization and enhance oxidation of fatty acids
What is a diagnostic indication of hypothyroidism?
Increased blood cholesterol concentration
How do thyroid hormones affect carbohydrate metabolism?
Enhance insulin-dependent entry of glucose into cells and increase gluconeogenesis and glycogenolysis
What is the role of thyroid hormones in growth?
Necessary for normal growth in children and promotes growth synergistically with GH and IGF-1
At what gestational week does the fetal Hyp-Pit-Thyroid axis function in mammals?
Week 11
What essential function do thyroid hormones serve in brain development?
Stimulate axonal growth and development
What cardiovascular effects do thyroid hormones have?
Increase heart rate, cardiac contractility, and promote vasodilation
How do thyroid hormone levels affect the central nervous system?
↓ leads to mental sluggishness; ↑ induces anxiety and nervousness
What is the relationship between thyroid hormones and reproductive behavior?
Dependent on having essentially normal levels of thyroid hormones
True or False: Hypothyroidism is commonly associated with infertility.
True
Fill in the blank: Thyroid hormone receptors are encoded by two genes, designated _____ and _____.
[alpha] and [beta]
What are the four different thyroid hormone receptors recognized?
- alpha-1
- alpha-2
- beta-1
- beta-2
What is the effect of TR binding to DNA without T3?
Leads to repression of transcription
What is the effect of the thyroid hormone-receptor complex binding to DNA?
Activates transcription
How do TRs interact with DNA?
Bind to thyroid/T3 response elements (TREs)
What is the composition of TREs?
Two AGGTCA ‘half sites’ separated by four nucleotides
What is the highest affinity binding form of TR?
Heterodimer with the retinoid X receptor (RXR)
