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FOE > Endo Physio Chap 3 > Flashcards

Endo Physio Chap 3 Flashcards

1
Q

Location of thyroid gland?

A

Below larynx, anterior and lateral to trachea

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2
Q

Hormones of thyroid gland?

A

Thyroxine
Triiodothyronine
Calcitonin

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3
Q

In what percentage are T3 and T4 secreted by thyroid gland?

A

T3 → 7%
T4 → 93%

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4
Q

What is the difference in potency, quantities and intensity of action b/w T-3 and T4?

A

T3 is 4 times more potent but present in smaller amounts in blood and persists for shorter time compared to T4

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5
Q

Physiological anatomy of thyroid gland?

A

, Have follicles → filled with colloid (thyroglobulin) and lined by cuboidal epithelial cells called follicular cells
. Thyroid gland also have C cells → secrete calcitonin.
Blood supply is 5 times greater than its weight

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6
Q

Amount of iodine required for synthesis of normal value of thyroxine?

A

50 milligrams / year
1 mg / week.

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7
Q

Is all the iodine ingested used by thyroid gland?

A

No, only about one fifth of ingested incline is used by thyroid gland.

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8
Q

Is all the iodine ingested used by thyroid gland?

A

No, only about one fifth of ingested incline is used by thyroid gland.

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9
Q

What are the steps of synthesis of? Thyroid hormones?

A
  1. Iodide trapping
  2. Oxidation of iodide to iodine
  3. Synthesis of thyroglobulin
  4. Organification / iodination of thyroglobulin
  5. Formation of T3, T4 s MIT DIT
  6. Exocytosis through cell to blood.
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10
Q

How does iodide trapping occurs?

A

The iodide is transported actively to the cell through iodide-sodium symporter which cotransport two sodium and one include into cell

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11
Q

Where does the energy for transporting iodine comes from?

A

Sodium-pottassium atpase → which establishes the low intracellular concentration of sodium.

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12
Q

In normal gland, how much the iodine pump concentrates the iodide in cell?

A

30 times its concentration in blood.

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13
Q

What is the most important factor that influences the iodide trapping ?

A

TSH

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14
Q

How is the trapped iodide transported from thyroid cells into the follicle or colloid?

A

By chloride- iodide counter transporter molecule called pendrin

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15
Q

Where is thyroglobulin formed in the cells?

A

Endoplasmic reticulum and Golgi apparatus

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16
Q

How marry tyrosine are present in one molecule of thyroglobulin?

A

70 residues of tyrosine.

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17
Q

What is the substrate that combine with iodine to form thyroxine and where is it present?

A

Iodine attaches to tyrosine present in thyroglobulin and it is stored in thyroglobulin until required

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18
Q

What reagent and enzyme is required for oxidation of iodine?

A

Hydrogen peroxide and peroxides enzyme.

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19
Q

Where is the peroxides enzyme found in the cell?

A

Within the apical membrane of follicular cell or attached to its membrane.

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20
Q

What oxidised form of iodide is used to form thyroid hormones?

A

Nascent iodine or I3-

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21
Q

What is organification and where does it occurs?

A

The ordination of thyroglobulin ( the binding of iodine with the tyrosine of thyroglobulin )
It occurs in the colloid of follicles.

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22
Q

What is the enzyme required to speed up organification?

A

Peroxidase

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23
Q

What are the products of organification?

A

MIT, DIT , thyroxine, triiodothyronine and reverse T3

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24
Q

After the completion of formation of thyroid hormones how many thyroxine molecules are attached to each thyroglobulin molecule?

A

30 thyroxine Molecules and a few T3 molecules

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25
Q

Thyroid hormones are stored in follicles, for how long can these hormones supply the body?

A

2 - 3 months

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26
Q

What is the process through which T4 and T3 are released to blood?

A

It is released through the follicular cells by pinocytosis

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27
Q

What enzymes are used to separate T3 and T4 from thyroglobulins?

A

Proteases → present in lysosomes → when they fuses with pinocytotic vesicles.

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28
Q

How does the thyroglobulin molecules goes to blood?

A

, It attaches with a protein located on luminal membrane of follicular cells called megalin

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29
Q

How does the thyroglobulin molecules goes to blood?

A

, It attaches with a protein located on luminal membrane of follicular cells called megalin

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30
Q

What amount of iodinated tyrosine remains as MIT and DIT and never becomes thyroid hormones?

A

Three quarters

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31
Q

What amount of iodinated tyrosine remains as MIT and DIT and never becomes thyroid hormones?

A

Three quarters

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32
Q

What is the fate of MIT and DIT ?

A

Their iodine is cleaved from them by deiodinase enzyme → this iodine becomes available for recycling

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33
Q

What happens in congenital absence of deiodinase?

A

The person becomes iodine deficient because of failure of recycling

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34
Q

How much and What form of thyroid hormone is used by tissues?

A

T3 and 35 micrograms / day

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35
Q

What are the plasma proteins to which thyroid hormones bind and where are they synthesised?

A

1 thyroxine binding globulin
2 thyroxine binding pre albumin
3 thyroxine binding albumin
They are synthesised in liver

36
Q

Which thyroid hormone have the more affinity for plasma proteins and intracellular proteins?

A

Thyroxin have more affinity than triiodothyronine

37
Q

How much time does it take for the half of the thyroxin and T3 to be released to the cell?

A

6 days for T4
1 day for T3
Because of its affinity difference

38
Q

How much time does it takes for T3 and T4 to reach its maximum activity?

A

10 to 12 days for T4
2 to 3 days for T3

39
Q

Why does the thyroid hormones have a slow onset and long period of action ?

A

Because of their affinity to bind with plasma proteins and intracellular proteins

40
Q

Why is thyroxin changed to T3 in the cell?

A

Because intranuclear thyroid receptors have more affinity for T3 thanT4

41
Q

Mechanism of action of thyroid hormone?

A

It attaches to its intranuclear receptor which forms a heterodimer with retinoid X receptor at specific thyroid hormone response element on DNA ====== which activates the receptor and thus transcription and translation occurs

42
Q

What is the non genomic effects of thyroid hormone?

A

Regulation of ion channels
Oxidative phosphorylation
Activation of intracellular second messenger system

43
Q

Where does the non genomic effect of thyroid hormones occurs in the cell?

A

In the plasma membrane , cytoplasm and mitochondria

44
Q

What is the effect of thyroid hormones of mitochondria and what happens in turn to these effects?

A

Mitochondria increases in number and size → mitochondrial surface area also increases in response to increased metabolic rate.
Increase in mitochondrial number and size causes increased production of ATP

45
Q

What is the effect of thyroid hormone on Na-K ATPase ?

A

Thyroid hormone increases the activity of sodium pump and it also makes the membrane leaky to sodium which also increases sodium pump activity.

It is considered to be one of the mechanism by which thyroid hormones increases metabolic rate as sodium pump uses a lot of ATP

46
Q

What is the most important effect of thyroid gland in growth?

A

It promotes growth and development of brain during fatal life and first few years of postnatal life.
It also helps in growth of bones.

47
Q

What is the effect of thyroid hormones on carbohydrate?

A

It enhances all aspects of carbohydrate metabolism → glycolysis, gluconeogenesis and absorption through git
It also increases insulin.

48
Q

Effect of thyroid hormone on fats?

A

All aspects of fat metabolism enhances → rapid mobilization of fats from its stores and increase in plasma free fatty acids→ increased oxidation of fatty acids

49
Q

Effect of thyroid hormones on cholesterol, phospholipids and triglycerides?

A

Increase thyroid hormones → decreases all these fats in plasma
Decrease thyroid hormones → increases all these fats in plasma and causes fatty liver

50
Q

What is the mechanism through which thyroid hormone decreases Plasma cholesterol?

A

It increases LDL receptors on liver cells and thus LDL ( cholesterol) is rapidly excreted through bile in feces

51
Q

Why does thyroid hormone increases vitamins requeiments?

A

Because it increases enzyme quantities in body and vitamins are essential parts of many enzymes

52
Q

Effect of thyroid hormone on body weight?

A

Increased thyroid hormone → decreased body weight
Decreased thyroid hormone → increased body weight

But these effects not always occurs because thyroid hormone also increases appetite → which may counter balance

53
Q

Effect on blood flow and Co of thyroid hormones?

A

It increases blood flow to the tissues because of
Increased metabolic rate more oxygen is utilized and more metabolic waste is produced.

Due to this increased blood flow, cardiac output also increases

54
Q

Effect of thyroid hormone on heart rate?

A

It has a direct effect on the excitability of heart and thus increases heart rate more than would be increased by co

55
Q

What sensitive physical sign does clinician uses in determining excess or diminished thyroid hormone secretion?

A

Heart rate

56
Q

What happens to heart strength when thyroid hormone secretion is slightly increased and when it is markedly increased?

A

Slightly increased → increases heart strength due to increase in enzymatic activity

Markedly increased → decreases heart strength due to long term protein catabolism

57
Q

What happens to arterial pressure after administration of thyroid hormone?

A

Mean arterial pressure remains same but pulse pressure is increased due to increase in systolic pressure and decrease in diastolic pressure.

58
Q

Effect of thyroid hormone on respiration?

A

Increased rate and depth of respiration → due to increased oxygen utilization and carbon dioxide production.

59
Q

Effect of thyroid hormone on git?

A

It increases both gut secretions and motility.
That’s why
Hyper → diarrhea
Hypo → constipation.

60
Q

Effect on central nervous system?

A

Thyroid hormone increases rapidity- of celebration
Hyper → extremely nervous, have anxiety, extreme worry and paranoia

61
Q

What happens to muscles when thyroid hormone is slightly increased, when it is excessively released and when it is not released?

A

Slight increase → muscles react with vigor
Extensive increase → muscle becomes weakened due to protein catabolism
Lack → muscles becomes singgish and relax slowly after contraction

62
Q

Why does muscle tremors occurs in hyperthyroidism?

A

Increased activity of neuronal synapses in area of spinal cord that controls muscle tone.
It is an important means for assessing degree of thyroid hormone effect on. Central nervous system.

63
Q

What is the effect of hypo and hyperthyroidism on sleep?

A

Hyper→ constant feeling of tiredness( because of exhausting effect on muscles and brain) and difficulty to sleep ( excitable effect onsynapses)
Hypo → extreme drowsiness with sleep lasting 12 to 14 hours a day.

64
Q

Effect of thyroid hormone on endocrine glands?

A

It increases glucose metabolism → insulin is secreted.
It increases metabolic activity related to bone formation → parathyroid hormone is secreted.
It increases inactivation of glucocorticoids in liver → glucocorticoids are secreted.

65
Q

Effect of thyroid hormone on the sexual function in men?

A

Hypo → loss of libido
Hyper → impotence

66
Q

Effect of thyroid hormone on sexual function in females?

A

Hypo → menorrhagia ( excessive bleeding), polymenorrhea ( frequent menstrual bleeding) and occasionally amenorrhe ( absence of menstration)

Hyper → oligomenorrhea ( greatly reduced bleeding, ) and occasionally amenorrhea

67
Q

What are the 5 main effects of TSH on thyroid gland?

A

1.it increases the proteolysis of thyroglobulin to release T3 and T4
2.it increases iodine pump activity → increasing iodine trapping
3. Increases iodination of tyrosine
4. Increase in size of thyroid cells
5. Increase in number of thyroid cells → from cuboidal to columnar and more in folding of epithelium into follicles.

68
Q

What is the most early effect of TSH on thyroid gland?

A

Proteolysis of thyroglobulin to release T3 and T4 → occurs within 30 minutes

69
Q

What is the most early effect of TSH on thyroid gland?

A

Proteolysis of thyroglobulin to release T3 and T4 → occurs within 30 minutes

70
Q

Which second messenger pathway is used by TSH ?

A

Adenylyl cyclase- cAMP system.

71
Q

What is the chemical structure of TRH ?

A

Tripeptide amide → pyroglutamyl-histidyl-proline-amide

72
Q

Which second messenger system is used by TRH for release of TSH?

A

Phospholipase C system

73
Q

Does the TSH secretion reduces t0 zero when hypothalamic hypophysicl portal blood is blocked?

A

It is greatly reduced but it doesn’t reduces to zero.

74
Q

Does the TSH secretion reduces t0 zero when hypothalamic hypophysicl portal blood is blocked?

A

It is greatly reduced but it doesn’t reduces to zero.

75
Q

Effect of cold on TRH secretion?

A

It is one of the best known stimuli for increasing TRH and TSH production

76
Q

Effect of neurogenic stimuli on TRH secretion?

A

Neurogenic stimuli like excitement and anxiety causes decrease in TRH and TSH production because these stimuli increases metabolic rate and body heat.

77
Q

Would the effects of emotions and cold be observed if the hypophysial stalk is cut?

A

No. Because these effects are mediated through hypothalamus

78
Q

Best known anti-thyroid drugs?

A
  1. Thiocynate
  2. Propylthiouracil
  3. High concentrations of inorganic iodide
79
Q

How does thiocynate decreases thyroid hormones and does it effects the formation of thyroglobulin?

A

It acts as competitive inhibitor of iodide for iodine pump. → causes inhibition of iodine trapping.
It doesn’t effect thyroglobulin formation.

80
Q

Does triocynate causes goiter ?

A

Yes because TSH keeps stimulating the thyroid gland but there is no iodine for formation of T3 and T4 → so the gland becomes enlarged.

81
Q

How does propylthiouracil blocks thyroid hormone formation and does it effects thyroglobulin formation?

A

By blocking the peroxidase enzyme that courses inclination and fusion of MIT and DITs
It doesn’t block formation of thyroglobulin

82
Q

Does propylthiouracil causes goiter ?

A

Yes.

83
Q

Effect of inorganic iodide on thyroid hormone formation?

A

Decreases iodine trapping thus decreasing iodination.
Most important → it paralyse the endocytosis of colloid (thyroglobulin) into follicle.

84
Q

Does high inorganic iodine concentration causes goiter ?

A

’ No → it actually decreases the size of thyroid gland and its blood supply. → and for this reason the inorganic iodine is given 2 to 3 days before surgical removal of thyroid gland.

85
Q

Does high inorganic iodine concentration causes goiter ?

A

’ No → it actually decreases the size of thyroid gland and its blood supply. → and for this reason the inorganic iodine is given 2 to 3 days before surgical removal of thyroid gland.

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