Thyroid, Parathyroid and Adrenal Gland Flashcards
Where is the thyroid gland located?
Below the larynx, on the anterior and lateral surfaces of the trachea
What hormones are made and secreted in the thyroid gland?
Thyroid hormone : essential for optimal metabolic activities
Calcitonin : involved in calcium homeostasis
What is the structure of the thyroid gland?
Composed of small spherical sacs called follicles
Each follicle surrounded by follicular cells - site of thyroid hormone synthesis
Clear cells lie in clusters between follicles and make calcitonin
Storage of a lipid soluble hormone (thyroid hormone)
Thyroglobulin (TGB) protein is made in thyroid follicles and contains tyrosine (Y)
Iodine enters follicle cell from blood and reacts with tyrosine in TGB
Thyroid hormones detach from iodised TGB as needed (T3 more active, t4 more plentiful)
T3 and T4 travel bound to a carrier protein (thyroid binding globulin, TBG) to target cells
Why is iodine a necessary part of our diet?
It is required for the production of the thyroid hormone (TGB)
Target cell activation process by thyroid hormone
Made in advance and stored until required
Travels bound to carrier protein then detaches and enters target cell
T3 binds to T3 receptor in nucleus and specific genes are activated to transcribe mRNA
mRNA translation occurs in cytoplasm and specific proteins are synthesised
Control of thyroid hormone secretion process
External stimuli that come together cause the hypothalamus to realise TRH
TRH stimulates anterior pituitary to release TSH,
TSH stimulates thyroid gland to secrete T3 and T4
T3 and T4 stimulate increase in basal metabolism rate, growth, alertness and reflexes
T3 and T4 inhibit TSH and TRH production
What is basal metabolic rate?
Amount of energy used when doing literally nothing. Changes throughout lifetime, children very high, adults low
More muscle = increased metabolic rate
What are the three actions of the thyroid hormone?
Growth
Alertness
Metabolism
What is the thyroid hormones effect on metabolism?
Increases body heat production
Stimulates fatty acid oxidisation
Increases proteolysis
Stimulates carbohydrates metabolism
How is calcium homeostasis controlled?
The concentration of extra cellular calcium is tightly controlled, immediate adjustments can be made by rapid exchanges of calcium between bone and blood
What is reabsorption and resorption?
Reabsorption : brought back into body
Resorption : break down mineral portion of bone to bring Ca back to blood
What are the three hormones involved in calcium regulation?
Parathyroid hormone (PTH)
Calcitroil
Calcitonin
What do the parathyroid glands do?
Secrete parathyroid hormone (PTH)
PTH is essential for life
What happens when you have low blood calcium levels?
Decreased blood calcium concentration stimulates parathyroid gland to secrete PTH which stimulates calcium reabsorption in kidneys and increase in bone breakdown resulting in increase release of calcium into blood and decreased urinary excretion of calcium
Increase in blood calcium inhibits decrease in blood calcium
What happens when there is a decrease in plasma?
Leads to an increase in PTH release which stimulates bone breakdown, kidney Ca2+ reabsorption and conversion of Vit D to calcitriol
Adrenaline secretion pathway
Stimulus is stress which stimulates hypothalamus
Hypothalamus stimulates sympathetic preganglionic fibres which stimulate adrenal medulla to secret adrenaline
Adrenaline secretion stimulates metabolic effects in skeletal muscle, liver and fat
