The Thyroid gland Flashcards
Thyroid function
Developmental - essential for normal development, especially CNS and bone
Metabolic - essential for normal metabolism of many-body tissues
Anatomy of the thyroid gland
Rich blood supply
Right and left Lobe
Pyramidal lobe
The blood supply for the thyroid
Inferior thyroid artery from subclavian
Superior thyroid artery from carotid
Histology
Follicular cells
Colloid (mainly thyroblobulin)
C- cell (parafollicular cell)
Follicular cells
Synthesize and secrete TH
C cells
Calcitonin
What are thyroid hormones derived from?
Tyrosine molecules
Thyroid hormones
T4: Major form released to blood, less active (prohormone)
T3: active form, converted in target cells
How much of the thyroid hormone is bound to plasma protein?
99%
What are the thyroid hormones bound to?
Mainly thyroid-binding globulin (~ 70%), also transthyretin (10-20%), albumin (10-20%)
Thyroid hormone receptors
Belong to nuclear receptor superfamily, Ligand-activating transcription factors
TH and receptors
High affinity for T3
Activation requires dimerization with another TR or retinoid X receptor (RXR)
TRs encoded by two genes: TR alpha and TR beta
Functions of TH
Increase Metabolic rate
- Number and size of mitochondria, enzymes in metabolic chain, Na/K ATPase activity
- Positive inotropic and chronotropic effects
- Synergizes with sympathetic nervous system
Energy metabolism
- Partially antagonizes insulin signalling
- Gluconeogenesis, lipolysis
Action TSH
Increases Iodine uptake
Stimulates other reactions involved in TH synthesis
Stimulates uptake of colloid
Induces growth of thyroid gland
Euthyroid
Normal thyroid function
Hyperthyroidism
TH excess
Primary: problem is thyroid gland itself
Secondary: problem is pituitary regulation
Hypothyroidism
TH defiency
Grave’s disease
Primary hyperthyroidism Autoimmune High circulating TH, low TSH Weight loss, tachycardia, fatigue Diffuse goiter (TSH receptor stimulation) Opathalmopathy
Hashimoto’s
Primary hypothyroidism Autoimmune Low circulating Lethargy, intolerance to cold Lack of growth and development Diffuse goitre
