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Phys Exam 3 > 20 - Thyroid Hormones > Flashcards

20 - Thyroid Hormones Flashcards

1
Q

_____ mg of iodine (iodides such as sodium iodide) are required each year. It is absorbed from the gut tract in the same manner as chlorides.

A

50

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2
Q

Sodium–Iodide symporter (2:1) is in the basal membrane of _______ cell. The energy for the pump comes from a sodium-potassium ATPase pump.

A

Thyroid

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3
Q

Iodide can be concentrated inside the cell 30-250x ______ concentration.

A

Plasma

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4
Q

Iodide is transported across the apical membrane of the cell into follicle via chloride-iodide counter-transporter called ________.

A

Pendrin

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5
Q

The membrane enzyme ________ catalyzes the conversion of iodide into iodine (I2).

A

Peroxidase

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6
Q

In the organification of iodine, it combined with ________ on thyroglobulin. Then it is catalyzed by peroxidase and results in __________ and __________.

A 
Tyrosine 
Monoiodotyrosine (MIT) 
Diiodotyrosine (DIT)
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7
Q

DIT + DIT makes…

A

Thyroxine (T4)

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8
Q

DIT + MIT makes…

A

Triiodothyronine (T3)

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9
Q

More (T4/T3) is formed than (T4/T3), but (T4/T3) is more active.

A

T4
T3
T3

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10
Q

________ molecule has MIT, DIT, T3, and T4 attached to it and is stored in the colloid until needed.

A

Thyroglobulin

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11
Q

Thyroid cells also secrete ________ into follicle. Each molecule of this has about 70 tyrosine amino acids which bind _______ to form thyroid hormones.

A

Thyroglobulin

Iodine

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12
Q

Iodide ions are converted to an oxidized form of iodine. Either nascent iodine (I2) or I3-. These can bind directly to ________.

A

Tyrosine

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13
Q

T/F. The major hormonal product is triiodothyronine (T3).

A

False. The major hormonal product is thyroxine (T4).

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14
Q

Each thyroglobulin contains about 30 molecules of ________. The thyroid can store several months supply of thyroid hormones.

A

Thyroxine

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15
Q

The apical surface of thyroid cells pinch off small portions of the follicular colloid to form _______ _______.

A

Pinocytic vesicles

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16
Q

Lysosomes fuse with the pinocytic vesicles and digest thyroglobulin molecules to release ________ and ________. These thyroid hormones then diffuse into blood.

A

Thyroxine (T4)

Triiodothyronine (T3)

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17
Q

Most of the iodinated tyrosine in the thyroglobulin does not become thyroid hormones but is recycled using a ________ enzyme. Deficiency of this mimics iodine deficiency.

A

Deiodinase

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18
Q

Most of released thyroid hormone is thyroxine which is then slowly deiodinated to from triiodothyronine. Conversion from T4 to T3 requires _________. T3 is more active than T4.

A

5’-iodinase

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19
Q

Most thyroid hormones (T4 and T3) entering blood are immediately bound to plasma proteins synthesized in the liver called…

A

Thyroxine-binding globulin (TBG)

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20
Q

A large does of injected thyroxine has no discernible effect on metabolic rate for several days, meaning it has a long latent period. T3 acts much (FASTER/SLOWER).

A

Faster

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21
Q

Before acting on the genes to increase gene transcriptions, one iodide is removed form almost all the thyroxine, thus forming _________. Intracellular thyroid hormone receptors have a high affinity for this.

A

Triiodothyronine (T3)

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22
Q

The thyroid hormone receptors are either attached to the DNA genetic strands or located in proximity to them. The thyroid hormone receptor usually forms a heterodimer with _______ at specific thyroid hormone response elements on the DNA. After binding with thyroid hormone, the receptors become activated and initiate the transcription process.

A

RXR (retinoid X receptor)

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23
Q

One of the principal functions of thyroxine might be simply to increase the number and activity of mitochondria, which in turn increases the rate of formation of _______ to energize the cellular function.

A

ATP

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24
Q

T/F. One of the enzymes that increases its activity in response to thyroid hormone is Na-K-ATPase. This increased activity in turn increases the rate of transport of both sodium and potassium ions through the cell membranes of some tissues. Because this process uses energy and increases the amount of heat produced in the body, it has been suggested that this might be one of the mechanisms by which thyroid hormone increases the body’s metabolic rate.

A

True

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25
Q

An important effect of thyroid hormone is to promote growth and development of the ______ during fetal life and for the first few years of postnatal life. If the fetus doesn’t secrete sufficient quantities then it can be greatly retarded and smaller than normal.

A

Brain

26
Q

Thyroid hormone stimulates almost all aspects of ________ metabolism, including rapid glucose uptake by cells, enhanced glycolysis, enhanced gluconeogenesis, increased rate of absorption form the GI tract, and even increased insulin secretion.

A

Carbohydrate

27
Q

Thyroid hormone also stimulates fat metabolism because lipids are mobilized rapidly from fat tissue, which decreases the fat stores of the body to a greater extent than almost any other tissue element. Mobilization of lipids from fat tissue also increases the free fatty acid concentration in the plasma and greatly accelerates the ________ of free fatty acids by the cells.

A

Oxidation

28
Q

(INCREASED/DECREASED) thyroid hormone decreases the concentrations of cholesterol, phospholipids, and triglycerides in the plasma, even though it increases the free fatty acids. Conversely, (INCREASED/DECREASED) thyroid secretion greatly increases the plasma concentrations these and almost always causes excessive deposition of fat in the liver.

A

Increased

Decreased

29
Q

T/F. Because thyroid hormone increases the quantities of many bodily enzymes and because vitamins are essential parts of some of the enzymes or coenzymes, thyroid hormone increases the need for vitamins. Therefore, a relative vitamin deficiency can occur when excess thyroid hormone is secreted, unless at the same time increased quantities of vitamins are available.

A

True

30
Q

Because thyroid hormone increases metabolism in almost all cells of the body, excessive quantities of the hormone can occasionally increase the BMR rate _____ to _____ precent above normal. Conversely, when no thyroid hormone is produced, the BMR rate falls to almost one-half normal.

A

60

100

31
Q

A greatly (INCREASED/DECREASED) amount of thyroid hormone almost always decreases body weight, and a greatly (INCREASED/DECREASED) amount of thyroid hormone almost always increases body weight; however, these effects do not always occur because thyroid hormone also increases the appetite, which may counterbalance the change in metabolic rate.

A

Increased

Decreased

32
Q

Increased metabolism in the tissues causes more rapid utilization of oxygen than normal and the release of greater than normal quantities of metabolic end products from the tissues. These effects cause ________ in most body tissues, thus increasing blood flow. As a consequence of increased blood flow, cardiac output also increases.

A

Vasodilation

33
Q

The heart rate (INCREASES/DECREASES) considerably more under the influence of thyroid hormone than would be expected from the increase in cardiac output. Therefore, thyroid hormone seems to have a direct effect on the excitability of the heart. This is one of the sensitive physical signs clinicians use to assess for excess or diminished thyroid hormone production.

A

Increases

34
Q

The mean arterial pressure usually remains about normal after administration of thyroid hormone. Because of (INCREASED/DECREASED) blood flow through the tissues between heartbeats, the pulse pressure is often increased, which the systolic pressure elevated 10 to 15 mmHg in hyperthyroidism and the diastolic pressure reduced a corresponding amount.

A

Increased

35
Q

The increased rate of metabolism increases the utilization of oxygen and the formation of _______ _______; these effects activate all the mechanisms that increase the rate and depth of respiration.

A

Carbon dioxide

36
Q

Thyroid hormone increases both the rates of secretions of the digestive juices and the motility of the GI tract. Hyperthyroidism therefore often results in _______, whereas lack of thyroid hormone can cause ________.

A

Diarrhea

Constipation

37
Q

In general, thyroid hormone (INCREASES/DECREASES) the rapidity of cerebration. Conversely, lack of thyroid hormone (INCREASES/DECREASES) rapidity of cerebration. A person with hyperthyroidism is likely to be extremely nervous and have many psychoneurotic tendencies.

A

Increases

Decreases

38
Q

A slight (INCREASE/DECREASE) in thyroid hormone usually makes the muscles react with vigor, but when the quantity of hormone becomes excessive, the muscles become weakened because of excess protein catabolism. Conversely, (INCREASE/DECREASE) in thyroid hormone causes the muscles to become sluggish, and they relax slowly after a contraction.

A

Increase

Decrease

39
Q

One of the most characteristic signs of _________ is a fine muscle tremor. It is believed to be caused by increased reactivity of the neuronal synapses in the areas of the spinal cord that control muscle tone. The tremor is an important means for assessing the degree of thyroid hormone effect on the CNS.

A

Hyperthyroidism

40
Q

Because of the exhausting effect of thyroid hormone on the musculature and on the CNS, persons with hyperthyroidism often have a feeling of constant tiredness, but because of the excitable effects of thyroid hormone on the synapses, it is difficult to sleep. Conversely, extreme somnolence is characteristic of _________, with sleep sometimes lasting 12 to 14 hours a day.

A

Hypothyroidism

41
Q

(INCREASED/DECREASED) thyroid hormone increases the rates of secretion of several other endocrine glands, but it also increases the need of the tissues for the hormones.

A

Increased

42
Q

For normal sexual function, thyroid secretion need to be approximately _______. In men, lack of thyroid hormone is likely to cause loss of libido; a great excess of the hormone, however, sometimes causes impotence.

A

Normal

43
Q

In women, lack of thyroid hormone often causes menorrhagia and polymenorrhea – that is, excessive and frequent menstrual bleeding. In other women, a lack or increase of thyroid hormone may cause irregular periods and occasionally even amenorrhea, absence of menstrual bleeding. It is also likely to result in a greatly decreased _______, like men.

A

Libido

44
Q

This is an anterior pituitary hormone that increases secretion of T3 and T4 by the thyroid gland. It also increases all the known secretory activities of the thyroid glandular cells. The most important early effect it causes is the proteolysis of thyroglobulin.

A

TSH

45
Q

Most of the varied effects of TSH on the thyroid cell result from activation of the “second messenger” ______ system of the cell.

A

cAMP

46
Q

The first event in this activation is binding of TSH with specific TSH receptors on the basal membrane surfaces of the thyroid cell. This binding then activates adenylyl cyclase in the membrane, which increases the formation of cAMP inside the cell. Finally, the cAMP acts as a second messenger to activate a ______ ______, which causes multiple phosphorylations throughout the cell. Causes immediate increase in thyroid hormone secretion.

A

Protein kinase

47
Q

Anterior pituitary secretion of TSH is controlled by a hypothalamic hormone called ______, which is secreted by nerve endings in the median eminence of the hypothalamus.

A

TRH

48
Q

One of the best-known stimuli for increasing TRH secretion by the hypothalamus, and therefore TSH secretion by the anterior pituitary gland, is exposure of an animal to ______.

A

Cold

49
Q

Various emotional reactions can also effect the output of TRH and TSH and therefore indirectly affect the secretion of thyroid hormones. Excitement and anxiety – conditions that greatly stimulate the sympathetic nervous system – cause an acute (INCREASE/DECREASE) in secretion of TSH, perhaps because these states increase the metabolic rate and body heat and therefore exert an inverse effect on the heat control center.

A

Decrease

50
Q

Increased thyroid hormone in the body fluids (INCREASES/DECREASES) secretion of TSH by the anterior pituitary. This is inhibitory feedback.

A

Decreases

51
Q

Fill in the missing steps below:

Hypothalamus — ______ — Anterior pituitary — TSH — Thyroid gland — _______ — Increased cellular metabolism

A

TRH

Thyroxine

52
Q

Thyroxine provides inhibitory feedback to the…

A

Anterior pituitary

53
Q

Increased cellular metabolism provides inhibitory feedback to…

A

Hypothalamus

Anterior pituitary

54
Q

Hyperthyroidism can cause this disease, which has high concentrations of circulating thyroid-stimulating immunoglobulins – these are IgG components that mimic TSH and bind to TSH receptors and result in high concentrations of circulating thyroxine and low levels of TSH.

A

Graves’ disease

55
Q

(HYPERTHYROIDISM/HYPOTHYROIDISM) can cause Graves’ disease and Adenoma. Its symptoms include high state of excitability, intolerance to heat, increased sweating, mild to extremes weight loss, varying degrees of diarrhea, and muscle weakness.

A

Hyperthyroidism

56
Q

(HYPERTHYROIDISM/HYPOTHYROIDISM) has symptoms including nervousness or other psychic disorders, extreme fatigue, inability to sleep, tremor in hands, and exophthalmos (bulging of eye).

A

Hyperthyroidism

57
Q

What are the treatments for hyperthyroidism?

A

Surgical removal of most of thyroid gland

Treatment with radioactive iodine

58
Q

This can cause Hashimoto disease (autoimmunity), endemic goiter, and Cretinism. Some symptoms include myxedema and atherosclerosis.

A

Hypothyroidism

59
Q

What is the treatment for hypothyroidism?

A

Oral medication

60
Q

These antithyroid druge inhibit idione uptake (inhibit I- Na+ cotransport).

A

Thiocyanate

Perchlorate anions

61
Q

This antithyroid drug inhibits peroxidase and can be used to treat for hyperthyroidism.

A

Propylthiouracil

62
Q

This antithyroid drug decreases thyroid activity when present in very high concentrations.

A

Iodides

Phys Exam 3 (10 decks)

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