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22 spring: Physiology > Test 3: lecture 7 > Flashcards

Test 3: lecture 7 Flashcards

1
Q

___ fills a thyroid follicle

A

colloid

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2
Q

two types of thyroid hormone

A

Thyroxine (T4)

Triiodothyronine (T3)

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3
Q

Thyroxine (T4)

A

Thyroxine (T4)

formed and secreted solely by the thyroid (93%)

longer half-life than T3

less potent than T3

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4
Q

Triiodothyronine (T3)

A

formed and secreted by the thyroid (7%)

mainly formed by deiodination of T4 in peripheral tissues

more active on a cellular level than T4

shorter half-life than T4

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5
Q

T3 or T4 have a longer half life

A

T4

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6
Q

___ is the precursor for thyroid hormones

A

thyroglobulin

a protein hormone (a glycoproteins made by two subunits)

made by the ER and the Golgi → stored in colloid

>100 tyrosyl residues; 25-30 get iodinated; 4-8 end up in T3 and T4

T3 and T4 are synthesized by iodination of tyrosyl residues that are part of thyroglobulin

T3 and T4 remain part of thyroglobulin until secreted into blood

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7
Q

how are T3 and T4 made

A

some of the tyrosyl residues in thyroglobulin are iodinated

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8
Q

what happens to injected iodine

A

thyroid gland takes most of it

some is recycled

rest of it is excreted in urines or in stool

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9
Q
A

synthesis, storage and secretion of T3 and T4 by the thyroid gland

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10
Q

iodide pump

A

moves iodine into follicular cells (Na/I co transporter)

moves Iodide against its chemical and electric gradient

TSH stimulates iodide trapping

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11
Q

why is thiocyanate not used for HTN medication any more

A

blocks iodide pump leading to decrease of iodide in follicular cell of the thyroid → hypothyroidism

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12
Q

how does iodide turn into I2

A

I(thyroid peroxidase + hydrogen peroxide) → nascent iodine/ I2

I is oxidized into I2

occurs at the apical membrane of thyroid cell (near colloid)

this reaction is inhibited by anti-thyroid drugs and too much iodide

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13
Q

___ will inhibit the oxidation of iodide into I2

A

some anti-thyroid drugs and by too much iodide

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14
Q

how do MIT and DIT form

A

iodination of tyrosyl residue

(add iodide by adding I2 and iodinase)

MIT has 1 iodide

DIT has 2 iodide

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15
Q

what does the coupling reaction due in the thyroid

A

converts DIT + DIT→ T4 and alanine

converts MIT + DIT → T3 and alanine

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16
Q

how are T3 and T4 released from the thyroglobulin

A

T3 and T4 are stuck of thyroglobulin in colloid

this is eaten by follicular cell and broken down by lysosomal and enzymes

T3 and T4 is then released

MIT and DIT have their I recycled to be used to make more thyroglobulins

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17
Q

what happens to the I on the thyroglobulin after the T3 and T4 have been cleaved?

A

MIT and DIT have their I recycled to be used to make more thyroglobulins

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18
Q

how is T3 and T4 made and released

A

I taking into cell by Na/I co-transporter

I is oxidized into I2

I2 is used to turn Tyrosyl into MIT and DIT (iodination- MIT has one I, DIT has 2 I)

coupling results in T3 and T4 and alanine (DIT + DIT→ T4 and alanine. MIT + DIT → T3 and alanine)

DIT, MIT, T3 and T4 all stuck together on thyroglobulin in the colloid

this is taken up and broken down by lysosomal enzymes

T3 and T4 transported out of cell

DIT and MIT have their I cleaved to be reused

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19
Q

how long does colloid last

A

3 months of thyroid T3 and T4

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20
Q

99% of T3 and T4 in blood is ___

A

bound to proteins made by the liver

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21
Q

free or bound thyroid hormones effect cellular activity

A

free hormones less than 0.3% of all thyroid hormones

will also inhibit pituitary secretion of TSH

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22
Q

___ will inhibit pituitary secretion of TSH

A

free T3 and T4

less then 0.3% of all thyroid hormone in the blood

23
Q

____ binds to T3 and T4 in the blood and lasts for 5 days

A

thyroxine-binding globulin (TBG)

(a type of thyroid hormone binding protein made by the liver)

highest affinity for T3 and T4

most T3 and T4 bound to TBG

half-life – 5 days

24
Q

___ is specific for T4 in the blood

A

thyroxine-binding prealbumin

(a type of thyroid hormone binding protein made by the liver)

specific for T4

intermediate affinity and capacity

half-life – 2 days

25
Q

___ binds to T3 and T4 and lasts 13 days

A

albumin (a type of thyroid hormone binding protein made by the liver)

lowest affinity for T3 and T4

high capacity due to its abundance in blood

half-life – 13 days

26
Q

what turns T4 into T3

A

5’ deiodinase

overfeeding stimulates this

illness and fasting inhibits this

27
Q

where is the receptor for T3

A

in the nucleus → will result in transcription of genes

28
Q

if you have a high Basal metabolic rate, you have ___ thyroid hormones

A

high

29
Q

effects of thyroid hormone

A
  1. catabolic hormone: increases basal metabolic rate
  2. increases the metabolism of almost all active tissues
  3. increases the number and activity of mitochondria → increases amount of ATP
  4. increases membrane-bound Na+-K+ ATPase activity (because there is more ATP available

– increased heat production

5.stimulation of carbohydrate metabolism

increases Glucose uptake, glycolysis, and gluconeogenesis

6.stimulation of fat metabolism

increases free fatty acids concentration in the blood. decreases cholesterol & phospholipid concentrations in the blood

30
Q

why does blood cholesterol decrease with thyroid hormone

A

thyroid stimulates LDL

will cause cholesterol to be taken up into the cell

31
Q

why will thyroid increase heat production

A

causes more mitochondria→ more ATP

= more activity of Na/K ATPase pump → more heat

32
Q

what are some other effects of thyroid hormone

A
  1. increased cardiac output, heart rate & strength
  2. increased respiration, gastrointestinal motility and secretion
  3. excitation of central nervous system
  4. essential for growth
  5. essential for development of brain
33
Q

how will thyroid effect HR

A

hypo- decreased HR

hyper- increased HR

34
Q

hypo or hyper thyroidism causes constipation

A

hypo

hyper thyroid leads to increase in GI motility → diarrhea

35
Q

thyroid is essential for development of the ___

A

brain

36
Q

hyperthyroidism

A

increased metabolism → weight loss

intolerant of heat

very anxious → increased sympathetic innervation

diarrhea → increased GI mobility

always hungry but never gaining weight

37
Q

hypothyroidism

A

lethargic

weight gain- slow metabolism

cold intolerance

constipation

38
Q

if you inject thyroxine what happens

A

slow onset and long duration

39
Q

TSH

A

Thyroid-stimulating hormone (TSH or thyrotropin)

  1. TSH is a glycoprotein (protein hormone)
  2. increased activity of the iodide pump
  3. increased iodination of tyrosine
  4. increased secretory activity of thyroid cells
  5. increased proteolysis of thyroglobulin
  6. increased number and size of thyroid cells
40
Q

how does TSH work on thyroid

A

TSH is a protein hormone made by the anterior pituitary

binds to surface of follicular cell and causes release of cAMP to act as second messenger

41
Q

TRH

A

Thyrotropin-releasing hormone (TRH) from the hypothalamus

  1. TRH is a tripeptide amide – pyroglutamyl-histidyl-proline amide (peptide hormone)
  2. binds to TRH receptors in the pituitary cell membrane
  3. activates the phospholipase second messenger system
  4. stimulates pituitary secretion of TSH
42
Q

TRH uses ___ second messenger system

A

phospholipase

(Thyrotropin-releasing hormone (TRH) from the hypothalamus)

43
Q

negative feedback regulation of hypothalamopituitary- thyroid axis

A
44
Q

what happens to TSH if there is no iodide?

A

increases

I is needed to make T3 and T4 to turn off TSH, no I means no T3 and no T4

results in free hormones, endemic goiter (hypothyroidism), TSI (thyroid-stimulating immunoglobulin) (hyperthyroidism

45
Q

goiter is caused by

A

lack of iodide in the diet

hypothyroidism

I is needed to make T3 and T4 to turn off TSH, no I means no T3 and no T4

46
Q

TSI

A

TSI (thyroid-stimulating immunoglobulin)

binds to TSH receptors on thyroid glands and stimulates thyroid to make T3 and T4 → hyperthyroidism

no feed back control

treated by removing thyroid gland

47
Q

what happens to thyroid hormone synthesis with stress

A

decreases

stress inhibits hypothalamus

48
Q

____ decrease iodide trapping and causes a goiter

A

Thiocyanate ions (an anti-thyroid substance)

49
Q

___ inhibits the peroxidase enzyme and causes a goiter

A

1.Propylthiouracil (an anti-thyroid substance)

50
Q

___ decrease all phases of thyroid activity and decrease thyroid gland size.

A

1.Iodide in high concentration (100x)

51
Q

Hyperthyroidism is a common disease of middle-older aged cats.

What would the major clinical signs be?

A

increased metabolism → weight loss

intolerant of heat

very anxious → increased sympathetic innervation

diarrhea → increased GI mobility

always hungry but never gaining weight

exhausted easily

52
Q

. Hypothyroidism is a common disease of adult dogs. What would the major clinical signs be?

A

lethargic

weight gain- slow metabolism

cold intolerance

constipation

53
Q

What is the best way to diagnose hyperthyroidism in cats?

A

T4 and TSH blood tests: High T4, low TSH.

54
Q

What is the best way to diagnose hypothyroidism in dogs?

A

T4 and TSH blood tests: Low T4, high TSH.

22 spring: Physiology (34 decks)

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