Mod 5 Thyroid and parathyroid glands Flashcards
What is the metabolic hormone?
a hormone that affects every cell
What are the two metabolic hormones?
Thyroxine (T4) and triiodothyronine (T3)
What are the differences between T4 and T3?
they are structurally similar but have different numbers of iodine atoms bound
What is T4?
T4 is the major hormone secreted by the thyroid gland
What is T3?
T3 is formed by the target tissues by the conversion from T4 and more biologically active
Difference between amino-acid based hormones and steroid hormones?
both are amino acid-based hormones, but also a lipid-soluble hormone enters the target cells binding to the intracellular receptors in nucleus, initiates mRNA transcription for protein synthesis
What are the main effects of the thyroid hormones T4 and T3 in the body?
1) regulating metabolic rate and body temperature
2) tissue growth and development
3) maintain blood pressure
What is thyroid hormone synthesis?
- Thyroid hormone synthesis include large quantities of TH stored extracellularly - enough for 2-3 months
What happens to the TSH?
TSH from the anterior pituitary binds to receptors on follicular cells
1) stored TH secreted
2) synthesis more colloid to refill follicle lumen
What are the steps in synthesising TSH?
1) Thyroglobulin is synthesised and discharged into the follicle lumen
2) Iodide is trapped (active transported in)
3) iodide is oxidized to iodine
4) iodine attached to tyrosine in colloid and forming DIT and MIT
5) iondated tyrosines are linked together to form T4 and T3
6) thyroglobulin colloid is endocytosed and combined with a lysosome
7) lysosomes enzymes cleave T4 and T3 from thyroglobulin and hormones diffuse into the bloodstream
Where does hormone synthesis occur?
Thyroid hormone synthesis occurs in thyroid gland follicles, extracellular and intracellular steps, thyroid hormones are formed from tyrosine amino acids and (lipid-soluble) and dietary iodine.
How do thyroid hormones get transported and regulated?
Most T4 and T3 immediately bind to transport proteins, binds to target receptors but T3 - 10 times more active
More tissues have enzymes to convert T4 to T3
How is hormone synthesis under control of the anterior pituitary?
stimulated by a decrease in TH blood levels, hypothalamic TRH (e.g. upon exposure to cold in infants), inhibited by the increase in TH blood levels, GHIH, dopamine, and glucocorticoids - excessively high in iodine
ORDER?
stress/cold –> hypothalamus –> TRH–> anterior pituitary –> TSH –> thyroid gland –> thyroid hormone T4 and T3
What is the hyperthyroid disorders? - interactivity cause
causes- primary thyroid gland defect, low dietary iodine, secondary to adequate TRH or TSH
What are some hyperthyroid symptoms? (underactivity)
myxedema (mucous swelling), low metabolic rate, chilled, constipation, thick dry skin, puffy eyes, lethargy.
Hyperthyroid? Goiter?
due to the primary thyroid gland defect/lack of iodine, a goiter may form ( an increase in TSH), treatment T4 thyroxine supplements
Why is the thyroid gland & hormone important
it is critical for normal growth and brain development, that is why iodine supplements are recommended in pregnancy and breast feeding.
Hyperthyroid: overactivity?
Grave’s disease, causes autoimmune conditions, abnormal antibodies (TSI) mimic TSH
What are symptoms of grave’s disease?
increase in metabolic rate, sweating, high and irregular heartbeat, nervousness, weight loss, eyeball protude, goiter due to an increase in TSI
What is the treatment for Grave’s disease?
surgery and radioactive iodine
Thyroid gland: calcitonin hormone?
- calcitonin is released by parafollicular cells in response to an increase in Ca 2+ levels
What are the causes of the calcitonin hormone?
basically unknown, is made into pharmacological doses- bone, used to treat paget’s disease and osteoporosis (because it inhibits bone reabsorption and release calcium) Ca2+ uptake
Label the parathyroid gland
0pp
Why are the parathyroid glands important?
they are important for Ca 2+ balance, Ca controls nerve impulses, muscle contractions, blood clotting and intracellular signaling. (NOTE DIAGRAM)
Parathyroid imbalance? Excess
Hyperparathyroidism occurs when there is an excess of parathyroid hormone, it causes a parathyroid tumor. Ca+ leaches from bones, hypercalcemia –> depressed nervous system, abnormal reflex, weak muscle Ca salts deposit in kidneys and store (moth-eaten appearance and spontaneous fractures)
Parathyroid deficiency?
Hypoparathyroidism - a deficiency in PTH, it causes parathyroid trauma or surgical removal
sym: hypocalcemia - excitable neurons and tingling, twitching muscles, can result in respiratory paralysis and death
treatments: Vitamin D –> Ca carbonate supplement and high calcium
