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BIOM3200 > 6. Hypothalamic – Pituitary - THYROID axis > Flashcards

6. Hypothalamic – Pituitary - THYROID axis Flashcards

1
Q

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

a) TRH - the thyroid-releasing hormone
b) TSH - thyroid-stimulating hormone
c) thyroid gland + thyroid hormones
d) many tissues

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2
Q

What are the two things that occur when you use TSH to stimulate the thyroid?

A
  1. thyroid growth
  2. production of thyroxine that regulates the secretion of TRH and TSH
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3
Q

match the colour to the following parts
a) thyroid gland
b) cricoid cartilage of the larynx
c) thyroid cartilage of larynx
d) trachea

A

a) blue
b) green
c) yellow
d) pink

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4
Q

Describe the structure of the thyroid gland - 2

A

contains 2 lobes that are connected via an isthmus

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5
Q

Match the following to one of the colours in the diagram; describe each
a) colloid - 3
b) follicular cells - 1
c) follicles - 2

A

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

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6
Q

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

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

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7
Q

How is iodide brought from the bloodstream into the follicular cells?

A

via a sodium-iodide transporter

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8
Q

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?

A

1 iodine = produces MIT (monoiodotyrosine)
2 iodines = produces DIT (diiodotyrosine

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9
Q

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?

A
  1. T3 - triiodothyronine = MIT (tyr ring interacting w/ 1 iodine) + DIT (tyr ring interaction w/ 2 iodines) = TRI
  2. 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.

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10
Q

Where in the cell are thyroid receptors found
a) blood vessels
b) cellular membrane
c) cytoplasm
d) nucleus

A

d

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11
Q

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

A

f) T3 works as well

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12
Q

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.

A
  1. iodide ion is taken up by the thyroid follicle
  2. iodide is converted to iodine
  3. 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
  4. when the anterior pit is stimulated TSH causes the T4/T3 to undergo endocytosis
  5. a plasma carrier protein transports the T3/T4 to the target cells
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13
Q

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

A
  1. T4 or T3 is carried down the blood stream to target cell via a carrier protein TBG
  2. All T4s that enter the cell are converted to T3 in the cytoplasm
  3. 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
  4. the hormone-receptor complex binds to the DNA
  5. this causes mRNA to be transcribed
  6. a protein is translated
  7. the response occurs
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14
Q

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

A
  1. TPO removes an electron from iodide to produce iodine
  2. iodine binds to the tyrosine residues that reside in the Tg to form MIT or DIT
  3. condensation (combining molecules while eliminating H2O) of MIT and DIT causes the residues to form T4 (DIT+DIT) or T3 (DIT+MIT)
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15
Q

What do the following terms stand for?
a) TPO
b) Tg
c) MIT
d) DIT
e) T4
f) T3

A

a) thyroid peroxidase
b) thyroglobulin
c) monoiodotyrosine
d) diiodotyrosine
e) tetraiodothyronine
f) triiodothyronine

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16
Q

What is this structure? How do you know?

A

T3 = a thyroglobulin with 3 iodine’s bound to 2 tyrosine residues (MIT + DIT)

17
Q

What is this structure? How do you know?

A

T4 = a thyroglobulin w/ 4 iodine’s bound to 3 tyrosine residues (DIT + DIT)

18
Q

Describe TBG

A

thyroxin-binding globulin = a plasma carrier protein that binds to T3 or T4 and transports it down the blood stream to its target cell

19
Q

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?

A

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

20
Q

what are the 3 hormones involved in the thyroid regulation?

A
  1. TRH - thyroid releasing hormone
  2. TSH - thyroid secretion hormone
  3. T3/T4 - tri/tetraiodothyronine
21
Q

Thyroid hormones are secreted the most b/w 10 and 14h why? How may this change for rodents?

A

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

22
Q

Describe the 3 physiological effects that thyroid hormones cause

A
  1. INC basal metabolic rate = rate in which the body uses NRG when it is at rest
  2. gonada development and fxn
  3. development of CNS of embryonic/fetal humans
23
Q

Describe the following thyroid hromonal dysfxns
a) hypothyroid - 4
b) hyperthyroid - 5

A

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

24
Q

Describe exophthalmos. What causes it?

A

protruding eyes that is caused by hyperthyroid thyroid hormonal dysfxn (too much TH)

25
Q

ANS the following wrt cretinism
a) what causes it? - 2
b) is it the same as dwarfism? If it differs explain how - 3
c) how is it treated?

A

a) maternal Hypothyroidism = mother who is pregnant has low levels of thyroid hormones
b) no ppl w/ cretinism is caused by reduced physical growth and severe mental deficiency, while dwarfism is just reduced physical growth
c) provide T4 soon after birth

26
Q

Why are thyroid hormones considered development dependent wrt the brain? - 3

A

a) formation of dendrites, axons, myelin and synapses
b) helps w/ neuronal migration
c) supplies the embryo/fetus w/ what it needs

27
Q

T or F - treatment of cretinism as long a it is provided soon after birth can alleviate some of the deficits caused by hypothyroidism however the best treatment is to provide it to mother in utero

A

F - if provided soon after birth symptoms will be completely restored

28
Q

What are the 2 external causes for Cretinism?

A

a) maternal hypothyroidism = low levels of TH in pregnant mother
b) iodine deficient diet

29
Q

what is the easiest way to ensure you will produce enough TH (assuming all the mech are working properly)?

A

consume salt it contains iodide which is used to produce TH

30
Q

Describe the pathway to causing goiters (hypothyroidsim) in 5 steps. What does the results tell you about the significance of TH?

A

a)
1. low iodide diet = Low TH produced
2. low TH in bloodstream
3. as a means of regulating TRH is over released
4. TSH is over released in the blood
5. excessive growth of the thyroid
b) TH no only stimulate thyroid growth but also regulates it so it you have low levels of TH the sys thinks it needs more TH causing an over growth of the thyroid

31
Q

Describe the pathway to causing graves disease (hyperthyroidism) in 4 steps. What does the results tell you about the significance of TH?

A

a)
1. antibodies over activate the thyroid gland
2. high levels of T3 and T4 in the blood
3. due to high levels of TH the sys regulates TRH and lowers it
4. TSH is DEC from the blood
b) this will result in exophthalmia = eyes protruding

32
Q

prescribing thyroid hormones’ is one way to test hypothyroidism distinguish the following types of TH given
a) synthetic
b) natural

A

a) artificial TH that is made to only have the hormone T4 itself
b) TH that is harvested from pigs and may contain other mechanisms other than the T4 itself such as the thyroid gland

33
Q

Match the following
a) common in cats
b) common in dogs
1. hyperthyroidism
2. hypothyroidism

A

a) 1
b) 2

34
Q

What are the 2 primary causes for hypothyroidism in dogs?

A
  1. lymphocytic thyroiditis = autoimmune
  2. idiopathic atrophy of thyroid = unknown source that destroys the thyroid
35
Q

What are the 2 secondary causes for hypothyroidism in dogs?

A
  1. neoplasia = cancer of thyroid
  2. cretinism
36
Q

What are the 6 ways to treat thyroid disorders

A
  1. surgery
  2. hormone supplementation of TH
  3. radiation therapy = if its cancer
  4. blockers that inhibit the production of T4 = hyper
  5. stimulants that activates the production of T4 = hypo
  6. diet = INC iodide

BIOM3200 (18 decks)

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