The Thyroid Gland Flashcards
What does TH produce?
Thyroid Hormones (T3 and T4)
What cells do the thyroid gland contain?
C cells - secretes calcitonin
Follicular Cells - Support thyroid hormone synthesis and surround hollow follicles
What is thyroglobulin?
A large protein rich in tyrosine residues
Describe the link between iodide and follicular cells?
Follicular cells concentrate iodide cells from plasma and transport it to colloid where is combines with tyrosine to form thyroid hormones
How does iodide enter follicular cells?
Na+/I- transporter
How does iodide enter the colloid?
Via the pendrin transporter
How is iodide added on to tyrosine?
Enzymes are exocytosed into the colloid, alongside thyroglobulin. This catalises the reaction of the addition of iodide to tyrosine
What occurs when one iodine molecule to tyrosine?
Monoiodotyrosine is made
What occurs when two molecules of iodide are added to tyrosine?
Diiodotyrosine
What happens when MIT is added to DIT?
T3 is formed
What happens when two molecules of DIT are added together?
T4 is formed
How do cells respond to TSH?
Portions of the colloid are taken back up into the follicular cell by endocytosis. Within the cells, vesicles which contain proteolytic enzymes that cut the thyroglobulin to release thyroid hormones
Where do T3 and T4 circulate?
The plasma
To what does T3 and T4 bind to?
Thyroxine-binding Globulin
When is Thyroid Hormone release stimulated?
During exercise, pregnancy and when you’re cold
What inhibits TSH?
Somatostatin
What inhibits TSH and conversion of T4 to T3?
Glucocorticoids
What is T3?
The active form of thyroid hormone
What is T4?
The plasma form of thyroid hormone
What is the function of Thyroid Hormone?
They bind to nuclear receptors in the target cells and change transcription and translation to alter protein synthesis
What affect does TH have on metabolic rate?
It increases it and promotes thermogenesis
What affect does TH have on hepatic gluconeogenesis?
It increases it
What affect does TH have proteolysis and lipolysis?
There is an net increase
What does lack of TH result in?
Retarded growth
What is congenital hypothyroidism caused by?
Dietary iodine deficiency in the mother
What is graves disease?
An autoimmmune disease where antibodies produced bind and micmic TSH which continuously activates the thyroid gland. Increased release of TH switches off TSH release from ant. pituitary, Plasma [TSH] is very low.
What is a thyroid adenoma?
Hormone secreting thyroid tumour
Why are those with hyperthyroidism intolerant to heat and experience weight loss?
There is an increased metabolic rate and heat production
Increased protein catabolism in hyperthyroidism causes what symptoms?
Muscle weakness/weight loss
Why do hyperthyroidism patients have an altered nervous system function?
Hyperexcitable reflexes and physiological disturbances occur in hyperthyroidism
What is the result of the elevated cardiovascular function seen in hyperthyroidism?
Increased HR/ Contractile Force, High output, cardiac failure
What are some cause of Hypothyroidism?
Hashimoto’s Disease (Autoimmune attack on thyroid gland), Dietary iodine deficiency, Idiopathic
What are the symptoms of hypothyroidism?
Weight gain/cold intolerance (Decreased metabolic rate and heat production), Brittle nails/Thin skin (disrupted protein synthesis), Slow speech/reflexes and fatigue (altered nervous system function), Slow heart rate and weaker pulse (reduced CVS function)
