6. Hypothalamic – Pituitary - THYROID axis Flashcards
Name the hormones/targets in each section wrt the thyroid axis pathway
a) hypothalamic hormones - 1
b) anterior pit hormones - 1
c) endocrine targets, hormones they secrete - 2
d) non-endocrine targets - 1
a) TRH - the thyroid-releasing hormone
b) TSH - thyroid-stimulating hormone
c) thyroid gland + thyroid hormones
d) many tissues
What are the two things that occur when you use TSH to stimulate the thyroid?
- thyroid growth
- production of thyroxine that regulates the secretion of TRH and TSH
match the colour to the following parts
a) thyroid gland
b) cricoid cartilage of the larynx
c) thyroid cartilage of larynx
d) trachea
a) blue
b) green
c) yellow
d) pink
Describe the structure of the thyroid gland - 2
contains 2 lobes that are connected via an isthmus
Match the following to one of the colours in the diagram; describe each
a) colloid - 3
b) follicular cells - 1
c) follicles - 2
a) yellow - use TPO to attach Iodine to tyrosine residues in thyroglobulin
b) blue
c) green - the part of the cell that takes up iodine from the blood
ANS the following wrt thyroglobulin
a) what produces it? - 2
b) describe its strucutre - 2
c) where is it found? - 1
d) What does the iodine interact w/? - 2
e) is the iodide directly added to the thyroglobulin right after it enters the cell? - 3
a) follicle cells w/in the thyroid gland
b) a polypeptide chain that contains many tyrosines
c) in the colloid of the follicle cells
d) the Tyr rings
e) no, its converted from iodide to iodine by TPO
How is iodide brought from the bloodstream into the follicular cells?
via a sodium-iodide transporter
the converted iodine appears to attach to the tyrosine rings of the thyroglobulin. how many iodines can interact w/ a single rings? What does it produce?
1 iodine = produces MIT (monoiodotyrosine)
2 iodines = produces DIT (diiodotyrosine
There are multiple types of thyroid hormones that are produced by the follicle cells. What are the 2 types and how do they come to be?
- T3 - triiodothyronine = MIT (tyr ring interacting w/ 1 iodine) + DIT (tyr ring interaction w/ 2 iodines) = TRI
- T4 - tetraiodothyronine = DIT + DIT = TETRA
Basically its dep on the number of iodines interacting w/ each tyr ring on the polypeptide as well as how it folds.
Where in the cell are thyroid receptors found
a) blood vessels
b) cellular membrane
c) cytoplasm
d) nucleus
d
Using this chart describes the mode of secretion wrt thyroid hormones
a) how is it synthesized (in advance or on demand)
b) how is it stored?
c) how is it released from the thyroid gland
d) How is it transported in the blood (dissolved in the plasma or bound to a carrier protein)
e) does it have a long or short half-life?
f) provide an example of this type of hormone
f) T3 works as well
Describe the 6 steps involved in producing thyroid hormones; include the following terms; thyroid follicle, iodide, iodine, MIT, DIT, T3, T4, thyroglobulin, TSH, tyr ring, anterior pit, endocytosis, plasma carrier protein.
- iodide ion is taken up by the thyroid follicle
- iodide is converted to iodine
- iodine interacts w/ the tyr ring on the thyroglobulin to produce MIT and/or DIT
4a. T3 is produced by combining MIT + DIT
4b. T4 is produced by combining DIT + DIT - when the anterior pit is stimulated TSH causes the T4/T3 to undergo endocytosis
- a plasma carrier protein transports the T3/T4 to the target cells
Describe the 7 steps to thyroid hormones binding to thyroid receptors and include the following terms; T4, T3, Carrier protein, TBG, binding protein, blood, cytoplasm, nucleus, Hormone-receptor complex, DNA, mRNA, protein
- T4 or T3 is carried down the blood stream to target cell via a carrier protein TBG
- All T4s that enter the cell are converted to T3 in the cytoplasm
- T4s bind to binding proteins w/in the cytoplasm as is translocated into the nucleus where it binds to its receptor w/in the nucleus
- the hormone-receptor complex binds to the DNA
- this causes mRNA to be transcribed
- a protein is translated
- the response occurs
Describe the 3 steps involved in producing the thyroid hormones including the following terms; TPO, iodide, iodine, tyrosine residue, Tg, MIT, DIT, condensation, T3, T4
- TPO removes an electron from iodide to produce iodine
- iodine binds to the tyrosine residues that reside in the Tg to form MIT or DIT
- condensation (combining molecules while eliminating H2O) of MIT and DIT causes the residues to form T4 (DIT+DIT) or T3 (DIT+MIT)
What do the following terms stand for?
a) TPO
b) Tg
c) MIT
d) DIT
e) T4
f) T3
a) thyroid peroxidase
b) thyroglobulin
c) monoiodotyrosine
d) diiodotyrosine
e) tetraiodothyronine
f) triiodothyronine
What is this structure? How do you know?
T3 = a thyroglobulin with 3 iodine’s bound to 2 tyrosine residues (MIT + DIT)
What is this structure? How do you know?
T4 = a thyroglobulin w/ 4 iodine’s bound to 3 tyrosine residues (DIT + DIT)
Describe TBG
thyroxin-binding globulin = a plasma carrier protein that binds to T3 or T4 and transports it down the blood stream to its target cell
We know that T3/T4 needs to be transported through the BVs via a carrier protein does this same protein carry this hormone into its target cell? Why/why not?
No, the T3/T4 needs to be unbound by the carrier protein in order to diffuse into the mem of the target cell as the transporter is too bulky
what are the 3 hormones involved in the thyroid regulation?
- TRH - thyroid releasing hormone
- TSH - thyroid secretion hormone
- T3/T4 - tri/tetraiodothyronine
Thyroid hormones are secreted the most b/w 10 and 14h why? How may this change for rodents?
a) this is because thyroid hormones kick start the metabolism and this time of day is when the most action is taken place
b) rodents are nocturnal therefore their thyroid hormones would be secreted at night due to that being when the metabolism needs to be highest
Describe the 3 physiological effects that thyroid hormones cause
- INC basal metabolic rate = rate in which the body uses NRG when it is at rest
- gonada development and fxn
- development of CNS of embryonic/fetal humans
Describe the following thyroid hromonal dysfxns
a) hypothyroid - 4
b) hyperthyroid - 5
a) low levels of thyroid hormone
- low basal metabolic rate = weight gain
- lethargic/tiredness
- sensitive to cold temps
b) high levels of thyroid hormone
- INC basal metabolic rate = weight loss
- muscular weakness
- nervousness
- exophthalmos
Describe exophthalmos. What causes it?
protruding eyes that is caused by hyperthyroid thyroid hormonal dysfxn (too much TH)
