Flashcards in Thyroid Physiology Deck (19)
Describe the basic anatomy of the thyroid gland
2 lateral lobes and an isthmus
Near third tracheal ring
What are the three main arteries and veins of the thyroid?
Sup. & Inf. Arteries and Thyroid Ima artery (Inferior)
Sup. Mid & Inf thyroid veins
Where are thyroid hormones stored?
What three hormones does the thyroid make and secrete?
Basal metabolic rate
Describe the basic structure of T3 and T4
T4 = 2 Di-iodotyrosine
T3 = 1 DIT and 1 Mono-iodotyrosine
How does Iodine enter the colloid space? (Three transporters)
Basolateral membrane creates Na+ conc. gradient:
1) ATPase: Na+ out ,K+ in
2) Na-I Symporter: I- in Na+ in
3) Pendrin: I- in
What are some sources of iodine in the diet?
Milk and Dairy
Fruit and Veg grown in iodine-rich soil
After iodine enters the colloid space, how is T4 and T3 synthesised?
1) Oxidation of iodide (I-) to iodine (Io)
2) Iodination of thyroglobulin
3) Coupling: MIT + DIT = T3
DIT + DIT = T4
4) T3/T4 are bound to Thyroglobulin for storage or cleaved for secretion
Outline the Hypothalamus-Pituitary-Thyroid axis
1) Cold temperature/exercise/pregnancy - Hypothalamus releases thyrotropin releasing hormone (TRH)
2) TRH signals pituitary to release TSH
3) TSH signals thyroid to synthesise and secrete T3 and T4
4) T3 and T4 create -ve feedback to pituitary and hypothalamus.
What is TPO?
Thyroid Peroxidase: catalyses iodide oxidation and MIT and DIT coupling
How are T3 and T4 transported in the blood?
Lipophilic so need to be bound to Thyroxin Binding Globulin (70%) and Albumin (30%)
Describe the physiological effect of T3 and T4
Only free T3/T4 can enter cell and have an effect
Deiodinases interconvert T4 to T3 (only T3 can bind thyroid hormone receptor)
Name 4 physiological actions of T3 and T4
2) Maturation and Differentiation
3) Neurological functions (e.g. synapse formation)
What is Congenital hypothyroidism?
impaired physical (dwarfism, dystrophy bones, low BMR) and neurological development due to iodine deficiency during foetal development.
Screen: TSH heel prick test
What are symptoms of Hypothyroidism
(Hashimoto's Thyroiditis. Iodine Deficiency)
Fatigue and tiredness
Sensitivity to the cold
Dry skin and hair (alopecia)
Low mood and mental slowness
Heavy periods and fertility problems
What are symptoms of Hyperthyroidism
heat intolerance, sweating, warm, moist hands
weight loss despite increased appetite
palpitations / rapid pulse
tiredness and weak muscles
nervousness, irritability, mood swings
Thirst and polyuria
What lab investigations are used to test thyroid function?
Serum TSH - If abnormal then:
T4 - Free T4 (the fraction not bound to protein)
T3 - Free T3 (the fraction not bound to protein)
What are the treatments for Hyperthyroidism?
Anti-thyroid drug therapy