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EXCI 360 > Thyroid hormones > Flashcards

Thyroid hormones Flashcards

1
Q

2 majors hormone secreted from thyroid gland

A

T4 -> 93% of secretion
T3-> 7% of secretion

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2
Q

what happen if there is chronic lack of TH

A

it can decrease the metabolic rate to 40 - 50% below normal. That will make someone feel cold and gain weight possibly.

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3
Q

what happen if there is chronic excess of TH

A

it can increase the metabolic rate to 60 - 100% above normal. That will make someone feel too hot and loose body weight possibly.

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4
Q

what is iodide trapping

A

The thyroid gland has an iodide pump to actively transport the iodides from the blood
into the thyroid gland

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5
Q

is iodide trapping effective

A

no only 20% of iodide in blood are taken by thyroid gland and the rest are excreted by kidney

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6
Q

concentration of iodide inside thyroid cell is _ time _ than that in blood

A

30 time higher

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7
Q

what is the only part of the body that require iodide

A

thyroid gland

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8
Q

thyroid gland is composed of many

A

follicles

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9
Q

follicle contain what

A

colloid

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10
Q

colloid is mainly composed of

A

glycoprotein called thyroglobulin

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11
Q

TH is contain in what

A

thyroglobulin

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12
Q

each thyroglobulin contain _ tyrosine amino acids

A

70

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13
Q

the thyroglobulin that contain TH will secrete where

A

into follicular colloid (follicle) to be stored

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14
Q

why the effect of TH defiency will not be observe for several month

A

The stored TH is normally sufficient to supply for the body for 2 to 3 months.

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15
Q

thyroglobulin can be synthesized by what

A

Golgi apparatus in the thyroid cell

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16
Q

what is needed to add iodide to the tyrosine

A

peroxidase

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17
Q

what happen if the peroxidase system is blocked or if there is not enough iodide

A

formation of TH will stop

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18
Q

digestive enzyme in thyroid gland are form from what

A

lysosome mixed with colloid

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19
Q

how does t4 and t3 are release from thyroglobulin

A

the proteinases (one of the enzymes) digest the thyroglobulin molecules and release thyroxine and triiodothyronine from thyroglobulin.

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20
Q

lack of what will cause iodine deficiency in gland cell

A

deiodinase enzyme because of failure of the recycling cycle

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21
Q

what is the hormone between t4 and t3 that is mainly used from tissue

A

T3 because T4 will be deiodinated to become T3 in few day

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22
Q

what happen when T4 and T3 enter in blood

A

combine immediately with plasma-binding protein

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23
Q

what are the main plasma-binding protein and which one is the main one

A

thyroxine-binding globulin (main)
thyroxine-binding prealbumin
albumin

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24
Q

half of (T3/T4) are release in cell in one day

A

T3

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25
Q

why does half of T4 is release in cell in 6 days

A

because of the plasma-binding protein higher affinity for T4

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26
Q

what happen when T4 and T3 enter tissue cell

A

they bind with intracellular proteins ( more strongly bind with T4 ) and will be used by the tissue cell slowly over days or weeks.

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27
Q

after injection of a large quantity of _ into a human being, there is a long/short latent period of _ days ( (with or no) affection on metabolic rate before the (T4/T3) activity is observed

A

thyroxine , long, 2-3, no, T4

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28
Q

T4 activity reach its maximum in _ days. Then it decrease with a _ life of about _ days even as long as _ month

A

10-12 days, half-life of about 15 days, 2 month

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29
Q

which action btw the one from t3 or T4 occurs faster and what is the latent period + reaches its max activity within how many days

A

T3, 6-12h latent period, within 2-3 days

30
Q

why does the release of T4 is slower than T3

A

bc of the high affinity of the plasma-binding protein for T4

31
Q

what is the general affection of TH

A

o cause nuclear transcription of genes for synthesizing large number of substances in the cells including:
* enzymes
* structural proteins
* transport proteins
* other substances

32
Q

what happen before the hormone acts on the gene

A

almost all the thyroxine is deiodinated to triiodothyronine, then T3 bind with intracellular thyroid hormone receptors in the nucleus.

33
Q

more than _ % of the TH that binds to receptor is _, less than _ % of TH that bind to receptor is _

A

90 %, T3, 10 %, T4

34
Q

Effect of Thyroid Hormones on Mitochondria

A
  • Increase the number mitochondria.
  • Increase the total membrane surface area (size) of mitochondria ➔ increase the
    formation rate of ATP to energize cellular function.
35
Q

Effect of TH on Carbohydrate Metabolism

A
  • Increase absorption rate of glucose from gastrointestinal tract.
  • Increase uptake rate of glucose by cells (independent of insulin)
  • Enhance glycolysis (use of glucose for energy through anaerobic conversion of glucose to
    lactic acid).
  • Enhance gluconeogenesis ( formation of glycogen from protein or fat ).
  • Increase insulin secretion, which also promotes glucose uptake.
  • TH decreases glycogen stores in the liver and skeletal muscle, this is called
    glycogenolysis, it allows more glucose to enter the circulation.
36
Q

Effect of TH on fat metabolism

A
  • In adipose tissue, TH will increase fat catabolism, this is called lipolysis, defined as a breakdown of triglycerides into free fatty acids.
  • When this happens, TH mobilizes fatty acids from fat tissues, which increases free fatty acids concentration in the plasma.
  • Accelerate oxidation of free fatty acids by cells.
  • TH decrease the quantity of cholesterol, phospholipids and triglyceride in plasma even
    though it increases the free fatty acids. (because TH increases the secretion rate of
    cholesterol in the bile and consequent loss of cholesterol in the faeces).
  • In the hepatic cells (in the liver), TH can promote fat anabolism, this is called de novo lipogenesis, defined as the creation of new triglycerides from glucose, glycerol and free fatty acids.
    o “Thyroid hormones are a well-known inducer of hepatic de novo
    lipogenesis
  • “Although thyroid hormones stimulate lipogenesis, there is a net reduction in total hepatic
    triglycerides during hyperthyroidism due to fatty acid metabolism occurring at a higher
    rate than fatty acid synthesis.” Sinha 2018
37
Q

T/F:”Thyroid hormones are a well-known inducer of hepatic de novo
lipogenesis

A

t

38
Q

what happen if there is lack of TH

A

it causes excessive deposition of fat in liver. This is due to the lower amount of catabolism in the liver.

39
Q

what happen if there is prolonged hypothyroidism

A

severe arteriosclerosis (hardening of arteries) due to accumulation of cholesterol.

40
Q

novo lipogenesis is defined as

A

as the creation of new triglyceride from glucose, glycerol and FFA

41
Q

Effect of TH on protein metabolism.

A
  • TH will increase protein synthesis in many tissues to help them maintain or increase
    their chemical reactions. That is an anabolic effect TH has at normal levels.
  • If TH is in excess, it will also increase proteolysis, since the tissues are active they need protein turnover to increase. This is a catabolic effect, but it helps with growth to occur properly. Over time though, it can weaken the muscle in a hyperthyroid
    patient.
42
Q

increase proteolysis is which type of effect

A

catabolic

43
Q

The Effect of TH in Increasing Active Transport of Ions Through Cell Membrane

A
  • TH can activate enzymes: Na-ATPase and K-ATPase, ➔ increase the transport rate of Na and K ions through cell membrane of tissues.
  • Increase heat production in the body because
  • active transport uses energy from ATP.
  • TH also causes most cell membrane to become leaky to Na ions, which activates the Na pump.
44
Q

The Effect of TH on Growth

A
  • Lack of TH ( hypothyroid ) causes growth rate retarded for growing children.
  • Excessive TH ( hyperthyroid ) causes rapid skeletal growth, early bone mature for
    children.
45
Q

The effect of TH on the Cardiovascular System

A
  • Increase blood flow and cardiac output because of the rapid utilization of oxygen for increased metabolism.
  • Increase heart rate because of the increase of cardiac output.
  • Increase the strength of the heart beat ( because of increased enzymatic activity ).
  • Increase slightly blood volume because of vasodilation which allows increased quantities
    of blood to collect in the circulatory system.
  • Increase arterial pressure because of the increased blood flow.
46
Q

The Effect of TH on Respiration

A
  • Increase rate and depth of respiration because of increased rate of metabolism ➔
    increased use of oxygen.
47
Q

The effect of TH on Gastrointestine Tract

A
  • Increase secretion rate of digestive juice and motility of gastrointestinal tract.
  • Excessive TH causes diarrhea and lack of TH causes constipation.
48
Q

The effect of TH On Central Nervous System

A
  • Increase brain activity ( cerebration ).
  • Excessive TH ( hyperthyroid ) cause anxiety, extreme worry and paranoia.
49
Q

what happen on muscle with excessive TH

A
  • Muscle becomes weakened with excessive TH, because of excessive protein catabolism.
50
Q

what happen to muscle with lack of TH

A
  • Lack of TH causes muscle to become sluggish and slow relaxation after a contraction.
51
Q

which metabolism is the only that increase with a decrease of T3, T4

A

serum (cholesterol)

52
Q

which metabolism is the only one to decrease with a increase of T4,T3

A

serum (cholesterol)

53
Q

which hypothalamic hormone is secreted by nerve ending in the median eminence

A

thyrotropin-releasing hormone

54
Q

where thyrotropin-releasing hormone is secrete

A

median eminence of hypothalamus

55
Q

how TRH is transported to ant. pituitary

A

through hypothalamic-hypophyseal portal vessel

56
Q

what happen when TRH bind with TRH receptor on the pituitary membrane

A

activate phospholipase second messenger system to produce phospholipase C

57
Q

how does TSH cause increase release of T3 and
T4

A

by increasing
* Proteolysis of thyroglobulin
* Activity of iodide pump
* Iodination of tyrosine for forming TH
* Size and number of thyroid cells

58
Q

how does TSH is controlled by direct feedback

A

Increased TH will directly affect anterior pituitary to cause decrease of secretion of TSH
➔ decrease the release of TH ➔ eventually to maintain a constant concentration of free TH in the circulatory body fluids.

59
Q

how does TSH controlled by indirectly feedback

A

Increased TH ➔ increased metabolic function ➔ increased heat production ➔ increased body temperature ➔ affect on hypothalamus, which is the body temperature controlling centre ➔ cause decreased release of TRH from hypothalamus ➔ decreased release of TSH from anterior pituitary ➔ decreased release of TH from thyroid cells.

60
Q

how can we increase body temperature

A

increase TH

61
Q

t4 promote (increase/decrease) metabolism, this (increase/decrease) metabolism make _, which (indirectly/directly) negatively regulate the hypothalamus and pituitary.

A

increased, heat, indirectly

62
Q

TSH (indirectly/directly) negativity (promote/inhibit) the anterior pituitary.

A

directly, inhibit

63
Q

TSH (promote/inhibit) the thyroid gland but when (positive/negative) feedback occurs, TSH can go down to almost 0

A

promote, negatively

64
Q

what happen with the thyroid with hyperthyroidis

A

increase 2-3 time in size.
The number of thyroid cell increase several time more than the size increase,
the secretion rate increase 5-15 time normal

65
Q

what are the principal cause of hyperthyroidism

A

autoimmunity ,history of the person an excessive amount of thyroid cell antigens has been released from the thyroid cells. This causes the formation of antibodies against thyroid gland itself.

thyroid stimulating immunoglobulin is the antibody and have much prolonged stimulating effect on the thyroid gland (12h vs 1h) so the high level of TH secretion caused by this antibody will suppress the production of TSH by anterior pituitary

66
Q

what can also cause over secretion of TH

A

thyroid adenoma (tumor)

67
Q

what are the symptom of hyperthyroidism

A
  • High state of excitability
  • Intolerance to heat
  • Increased sweating
  • Mild to extreme weight loss
  • Different degrees of diarrhea
  • Muscle weakness
  • Nervousness
  • Exophthalmos ( protrusion of eyeballs )
  • Extreme fatigue
  • Inability to sleep
  • Tremor of hands
  • Other psychiatric disorders
68
Q

what cause hypothyroidism

A

autoimmunity against the thyroid gland but instead of stimulate it, it destroyed it

Insufficient intake of iodine cause development of extremely large thyroid gland ( called endemic goiters ). Size is increased to 10 - 20 times normal.

. Enlarged thyroid gland can occur in patients who have inflammation of the thyroid. They do not have iodine deficiency ( called “ idiopathic nontoxic colloid goiter “ ). The exact cause is unknown yet. The possible explanations are as follows.

69
Q

what are some genetic abnormality that can lead to hypothyroidism

A

Deficient iodide-trapping mechanism ( not enough iodines pumped in ),
* Deficient peroxidase system ➔ iodides are not oxidized to iodine,
* Deficient coupling of iodinated tyrosine in thyroglobulin ➔ TH cannot be formed,
* Deficiency of deiodinase enzyme ➔ iodine cannot be recovered from iodinated
tyrosines ➔ deficiency of iodine.

70
Q

symptom of hypothyroidism

A
  • Fatigue
  • Extreme somnolence (feeling sleepy)
  • Extreme muscular sluggishness (slow to respond)
  • Slow heart rate
  • Decreased blood volume and cardiac output
  • Increased weight
  • Constipation
  • Mental sluggishness
  • Depressed growth of hair
  • Scaling of skin
  • Edematous appearance ( myxedema )
  • Increase of blood cholesterol ➔ arteriosclerosis
71
Q

what can symptom can only occurs with hypothyroidism

A
72
Q

what are the common sign and symptom of hypo and hyperthyroidism

A

EXCI 360 (14 decks)

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