thyroid metabolic hormones

Question 1

all thyroid hormones

Answer 1

thyroxine and triidothyronine (T4 AND T3 ) and calcitonin

Question 2

function

Answer 2

increase metabolism

Question 3

metabolically active hormone secreted by thyroid is

Answer 3

thyroxine which is coverter to triidothyronine later and its the most potent hormone

Question 4

anatomy of thyroid gland

Answer 4

has follicles
that has secretory substance called colloid and cuboidal epithelial cells which scerete the hormone into the follicles and also the follicles have glycoprotein which is thyroglobulin which contains the hormone and secretes it back into the follicles and they need to cross the follicular epithelium into the blood to go to the target organ

Question 5

what is required to form thyroxine

Answer 5

iodine
50 milligram per year as iodide which is present in table salt
1/mg per week

Question 6

iodine fate when ingested

Answer 6

secreted by kidney

1/5th is taken by thyroid cells in the circulatory system for synthesis of thyroid hormone

Question 7

sodium idodide symporter

Answer 7

The
basal membrane of the thyroid cell has the specific ability
to pump the iodide actively to the interior of the cell. This
pumping is achieved by the action of a sodium-iodide
symporter, which co-transports one iodide ion along with
two sodium ions across the basolateral (plasma) membrane into the cell.

Question 8

energy for sumporter comes from

Answer 8

na-k atpase pump which pumps na ions out making the inside deficient in na and makes a concentration gradient for symporter to function

Question 9

iodide trapping

Answer 9

This process of concentrating the iodide in the cell is

called iodide trapping

Question 10

how iodiide is transported from the thyroid cells into the follicles

Answer 10

pendrin

chloride iodine co transportation ( combines with amino acid tyrosine inside the follicles)

Question 11

how thyroid hormone is formed

Answer 11

Each molecule of thyroglobulin contains about 70 tyrosine amino acids, and they are the major substrates
that combine with iodine to form the thyroid hormones.
Thus, the thyroid hormones form within the thyroglobulin molecule. That is, the thyroxine and triiodothyronine
hormones formed from the tyrosine amino acids remain

Question 12

Oxidation of the Iodide Ion

Answer 12

iodide
ions to an oxidized form of iodine, either nascent iodine
(I0
) or I3
which is then capable of combining directly
with the amino acid tyrosine. This oxidation of iodine is
promoted by the enzyme peroxidase and its accompanying hydrogen peroxide, which provide a potent system
capable of oxidizing iodides.

Question 13

The
binding of iodine with the thyroglobulin molecule is
called

Answer 13

organification of the thyroglobulin.

Question 14

iodination
of tyrosine and final formation of the two important
thyroid hormones, thyroxine and triiodothyronine

Answer 14

Tyrosine is first iodized to monoiodotyrosine and then to diiodotyrosine. Then, during the next few minutes, hours, and
even days, more and more of the iodotyrosine residues
become coupled with one another.
he molecule thyroxine (T4), which is formed when two
molecules of diiodotyrosine are joined together; the thyroxine then remains part of the thyroglobulin molecule.
Or one molecule of monoiodotyrosine couples with
one molecule of diiodotyrosine to form triiodothyronine
(T3), which represents about one fifteenth of the final
hormones. Small amounts of reverse T3 (RT3) are formed
by coupling of diiodotyrosine with monoiodotyrosine,
but RT3 does not appear to be of functional significance
in humans.

Question 15

release of thyroxine and triiodothyronine

Answer 15

The apical surface of thyroid cells sends out pseudopod extensions that close around small portions of the colloid to form pinocytic vesicles that enter the apex of the thyroid cell. Then lysosomes in the cell cytoplasm immediately fuse with these vesicles to form digestive vesicles containing digestive enzymes from the lysosomes mixed with the colloid. Multiple proteases among the enzymes digest the thyroglobulin molecules and release thyroxine and triiodothyronine in free form, which then diffuse through the
base of the thyroid cell into the surrounding capillaries.
Thus, the thyroid hormones are released into the blood

Question 16

why iodine deficiency happens

Answer 16

About three quarters of the iodinated tyrosine in the thyroglobulin never become thyroid hormones but remain monoiodotyrosine and diiodotyrosine. During the digestion of the thyroglobulin molecule to cause release of thyroxine and triiodothyronine, these iodinated tyrosines also are freed from the thyroglobulin molecules. However, they are not secreted into the blood. Instead, their iodine is cleaved from them by a deiodinase enzyme that makes virtually all this iodine available again for recycling within the gland for forming additional thyroid hormones. In the congenital absence of this deiodinase enzyme, many persons become iodine deficient because of failure of this recycling process.

Question 17

Thyroxine and Triiodothyronine Are Bound to

Plasma Proteins

Answer 17

They combine
mainly with thyroxine-binding globulin and much less so
with thyroxine-binding prealbumin and albumin.

Question 18

latency of these hormones are caused by

Answer 18

the prolonged period of action
of these hormones are probably caused by their binding
with proteins both in the plasma and in the tissue cells,
followed by their slow release.

Question 19

general affect of thyroid hormone

Answer 19

activate nuclear transcription of many genes

Question 20

THYROID HORMONES INCREASE

CELLULAR METABOLIC ACTIVITY

Answer 20

then thyroxine or triiodothyronine
is given to an animal, the mitochondria in most cells of the animal’s body increase in size and number. Furthermore, the total membrane surface area of the mitochondria increases almost directly in proportion to the increased metabolic rate of the whole animal.
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.

Question 21

an important effect of thyroid hormones on body

Answer 21

growth of skeletal features and growth of brain in fetus and post natal life

Question 22

Stimulation of Carbohydrate Metabolism

Answer 22

increase carbo metabolism
increase insulin secretions
increase glucose uptake, absorption from git, glycolysis, gluconeogenesis

Question 23

Stimulation of Fat Metabolism

Answer 23

increase fat mobilization from adipose tissue and increase fatty acid oxidation for energy

Question 24

Effect on Plasma and Liver Fats

Answer 24

increased thyroid
hormone decreases the concentrations of cholesterol,
phospholipids, and triglycerides in the plasma
increases secretions of above mention in feces and bile secretions by liver
and also by activating low density lipo protein receptors on liver which remove low density lipo proteins from the liver

Question 25

Increased Requirement for Vitamins

Answer 25

high thyroid secretions decreases the vitamin quantities as it increases the need for vitamins by increasing the quantities of enzymes

Question 26

Decreased Body Weight

Answer 26

increase thyroid decreases the weight and vice versa

Question 27

Increased Blood Flow and Cardiac Output

Answer 27

increase thyroid hormone increases metabolism which increases 02 utilization causes vasodilation specially in skin. also increases blood flow everywhere for heat elimination and increases cardiac output

Question 28

Increased Heart Rate

Answer 28

Therefore, thyroid hormone seems to have a direct effect on the excitability of the heart, which in turn increases the heart rate. . This effect is especially important because the heart rate is one of the sensitive physical signs that the clinician uses in determining whether a patient has excessive or diminished thyroid hormone production

Question 29

Increased Heart Strength

Answer 29

increase thryoid glang increase enzymatic activity which in turn increases the heart strrngth also increase throyd hormone depresses the heart and can causes cardiac decompensation secndarily to myocardial failure and increase work load due to increase cardiac output

Question 30

Normal Arterial Pressure.

Answer 30

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

Question 31

increased respiration

Answer 31

increase o2 utilization and co2 production icnreases the rate of respiration

Question 32

Increased Gastrointestinal Motility

Answer 32

increases secretions of gastric juices (enzymes) hyperthyroidism - diarrehao hypothyroidism- constipation

Question 33

Excitatory Effects on the Central Nervous System

Answer 33

In general, thyroid hormone increases the rapidity of cerebration, although thought processes may be dissociated; conversely, lack of thyroid hormone decreases rapidity of cerebration. A person with hyperthyroidism is likely to be extremely nervous and have many psychoneurotic tendencies, such as anxiety complexes, extreme worry, and paranoia

Question 34

Effect on the Function of the Muscles

Answer 34

slight increase- muscles become vigor excessive - become weakened because of excessive protein catabolism less- become sluggish

Question 35

Muscle Tremor

Answer 35

One of the most characteristic signs of hyperthyroidism is a fine muscle tremor it is not as it happens in parkinsons but by placing a piece of paper on the finger and seeing the degree of vibration which is causes by increase activity of neuronal synapses in the area of spinal cord which is responsible for muscle tone The tremor is an important means for assessing the degree of thyroid hormone effect on the central nervous system

Question 36

Effect on Sleep

Answer 36

hyperthyroidism because of increase activity of muscles and cns person is always tired by increase activity of synapses the person will have difficulty sleeping people with somnolence can sleeo for 12-14 hours a day

Question 37

Effect on Other Endocrine Glands

Answer 37

increasing glucose metabolism increase s insulin production increasing bone formation increases parathyroid hormone secretions also increases the rate of inhibition of glucocorticoid hormones by adrenal through liver which increases the secretions of adrenocorticotropic from anterior pituatry which increases the secreyions of glucocorticoid from adrenal glands

Question 38

effect of sexual function

Answer 38

In men, lack of thyroid hormone is likely to cause loss of libido; a great excess of the hormone, however, sometimes causes impotence. In women, lack of thyroid hormone often causes menorrhagia and polymenorrhea—that is, excessive and frequent menstrual bleeding, respectively. Yet, strangely enough, in other women a lack of thyroid hormone may cause irregular periods and occasionally even amenorrhea (absence of menstrual bleeding). Hypothyroidism in women, as in men, is likely to result in a greatly decreased libido. To make the picture still more confusing, in women with hyperthyroidism, oligomenorrhea (greatly reduced bleeding) is common, and occasionally amenorrhea occurs

Question 39

effect of tsh released by anterior pituitary

Answer 39

1. increase iodine trapping by increasing the activity of iodine pump 3. increase iodinization of tyrosine 4. increasing the site and number of thyroid cells 5. increase proteolysis of thyroglobulin 6. increase secretory activity of thyroid cells

Question 40

secretion of tsh is controlled by

Answer 40

Anterior pituitary secretion of TSH is controlled by a hypothalamic hormone, thyrotropin-releasing hormone (TRH), which is secreted by nerve endings in the median eminence of the hypothalamus. From the median eminence, TRH is then transported to the anterior pituitary by way of the hypothalamic-hypophysial portal blood,

Question 41

Antithyroid Substances Suppress | Thyroid Secretion

Answer 41

thiocyanate, propylthiouracil, and high concentrations of inorganic iodides.

Question 42

Thiocyanate Ions Decrease Iodide Trapping

Answer 42

The same active pump that transports iodide ions into the thyroid cells can also pump thiocyanate ions, perchlorate ions, and nitrate ions. Therefore, the administration of thiocyanate (or one of the other ions as well) in a high enough concentration can cause competitive inhibition of iodide transport into the cell—that is, inhibition of the iodide-trapping mechanism. The decreased availability of iodide in the glandular cells does not stop the formation of thyroglobulin; it merely prevents the thyroglobulin that is formed from becoming iodinated and therefore from forming thyroid hormones. This deficiency of thyroid hormones in turn leads to increased secretion of TSH by the anterior pituitary gland, which causes overgrowth of the thyroid gland even though the gland still does not form adequate quantities of thyroid hormones. Therefore, the use of this cyanates and some other ions to block thyroid secretion can lead to the development of a greatly enlarged thyroid gland, which is called a goiter.

Question 43

goiter. | Propylthiouracil Decreases Thyroid Hormone Formation

Answer 43

it blocks the affect of peroxidase which is important in the iodinization of tyrosine and it stops the coupling of 2 iodized tyrosine to form thyroxine and trridothyronine causes goiter

Question 44

Iodides in High Concentrations Decrease Thyroid | Activity and Thyroid Gland Size.

Answer 44

reduce the rate of iodide trapping so that the rate of iodination of tyrosine to form thyroid hormones is also decreased. Even more important, the normal endocytosis of colloid from the follicles by the thyroid glandular cells is paralyzed by the high iodide concentrations. Because this is the first step in release of thyroid hormones from the storage colloid, there is almost immediate shutdown of thyroid hormone secretion into the blood decreases thyroid activity, the size of thyroid gland and blood supply thats why its administered into patients before thyroid removal surgery to decrease the blood flow through the gland

Question 45

grave disease

Answer 45

Graves’ disease, the most common form of hyperthyroidism, is an autoimmune disease in which antibodies called thyroid-stimulating immunoglobulins (TSIs) formagainst the TSH receptor in the thyroid gland. These antibodies bind with the same membrane receptors that bind TSH and induce continual activation of the cAMP system of the cells, with resultant development of hyperthyroidism. The TSI antibodies have a prolonged stimulating effect on the thyroid gland, lasting for as long as 12 hours, in contrast to a little over 1 hour for TSH. The high level of thyroid hormone secretion caused by TSI in turn suppresses anterior pituitary formation of TSH. Therefore, TSH concentrations are less than normal (often essentially zero) rather than enhanced in almost all patients with Graves’ disease. The antibodies that cause hyperthyroidism almost certainly occur as the result of autoimmunity that has developed against thyroid tissue

Question 46

Thyroid Adenoma.

Answer 46

Hyperthyroidism occasionally results from a localized adenoma (a tumor) that develops in the thyroid tissue and secretes large quantities of thyroid hormone As long as the adenoma continues to secrete large quantities of thyroid hormone, secretory function in the remainder of the thyroid gland is almost totally inhibited because the thyroid hormone from the adenoma depresses the production of TSH by the pituitary gland

Question 47

synptoms of hyperthyroidism

Answer 47

(1) a high state of excitability, (2) intolerance to heat, (3) increased sweating, (4) mild to extreme weight loss (sometimes as much as 100 pounds), (5) varying degrees of diarrhea, (6) muscle weakness, (7) nervousness or other psychic disorders, (8) extreme fatigue but inability to sleep, and (9) tremor of the hands.

Question 48

what is exophthalmos

Answer 48

Most people with hyperthyroidism exhibit some degree of protrusion of the eyeballs, as in Figure 77-8. This condition is called exophthalmos

Question 49

what effects does exophthalmos has on eyes

Answer 49

ulcers of cornea, irritation and dryness of cells of eye epithelium and damage to optic nerve affecting eye vision

Question 50

cause of protruding eyes

Answer 50

edematous swelling of the retro-orbital tissues and degenerative changes in the extraocular muscles. I

Question 51

Diagnostic Tests for Hyperthyroidism.

Answer 51

1. The basal metabolic rate is usually increased to +30 to +60 in severe hyperthyroidism. 2. The concentration of TSH in the plasma is measured by radioimmunoassay. In the usual type of thyrotoxicosis, anterior pituitary secretion of TSH is so completely suppressed by the large amounts of circulating thyroxine and triiodothyronine that there is almost no plasma TSH. 3. The concentration of TSI is measured by radioimmunoassay. This concentration is usually high in thyrotoxicosis but low in thyroid adenoma.

Question 52

Treatment in Hyperthyroidism.

Answer 52

removal of thyroid gland by first administrating propylthiouracil and then iodide to decrease the size of thyroid gland and diminish the blood supply

Question 53

Hypothyroidism

Answer 53

Hypothyroidism, like hyperthyroidism, is often initiated by autoimmunity against the thyroid gland (Hashimoto’s disease), but in this case the autoimmunity destroys the gland rather than stimulates it. The thyroid glands of most of these patients first demonstrate autoimmune “thyroiditis,” which means thyroid inflammation. Thyroiditis causes progressive deterioration and finally fibrosis of the gland, with resultant diminished or absent secretion of thyroid hormone.

Question 54

enlarged thyroid gland in hypothyroidism

Answer 54

goiter

Question 55

Endemic Colloid Goiter Caused by Dietary Iodide Deficiency

Answer 55

Swiss Alps, the Andes, and the Great Lakes region of the United States, insufficient iodine is present in the soil for the foodstuffs to contain even this minute quantity. Therefore, in the days before iodized table salt, many people who lived in these areas developed extremely large thyroid glands, called endemic goiters. The following mechanism results in the development of large endemic goiters: Lack of iodine prevents production of both thyroxine and triiodothyronine. As a result, no hormone is available to inhibit production of TSH by the anterior pituitary, which causes the pituitary to secrete excessively large quantities of TSH. The TSH then stimulates the thyroid cells to secrete tremendous amounts of thyroglobulin colloid into the follicles, and the gland grows larger and larger. However, because of lack of iodine, thyroxine and triiodothyronine production does not occur in the thyroglobulin molecule and therefore does not cause the normal suppression of TSH production by the anterior pituitary. The follicles become tremendous in size, and the thyroid gland may increase to 10 to 20 times its normal size.

Question 56

Idiopathic Nontoxic Colloid Goiter

Answer 56

but most of these patients show signs of mild thyroiditis; therefore, it has been suggested that the thyroiditis causes slight hypothyroidism, which then leads to increased TSH secretion and progressive growth of the noninflamed portions of the gland.

Question 57

abnormalities in nontoxic idiophatic colloid goiter

Answer 57

1. A deficient iodide-trapping mechanism, in which iodine is not pumped adequately into the thyroid cells 2. A deficient peroxidase system, in which the iodides are not oxidized to the iodine state 3. Deficient coupling of iodinated tyrosines in the thyroglobulin molecule so that the final thyroid hormones cannot be formed 4. Deficiency of the deiodinase enzyme, which prevents recovery of iodine from the iodinated tyrosines that are not coupled to form the thyroid hormones (this

Question 58

Physiological Characteristics of Hypothyroidism

Answer 58

They include fatigue and extreme somnolence, with persons sleeping up to 12 to 14 hours a day, extreme muscular sluggishness, a slowed heart rate, decreased cardiac output, decreased blood volume, sometimes increased body weight, constipation, mental sluggishness, failure of many trophic functions in the body as evidenced by depressed growth of hair and scaliness of the skin, development of a froglike, husky voice, and, in severe cases, development of an edematous appearance throughout the body called myxedema

Question 59

myxedema

Answer 59

shows such a patient, demonstrating bagginess under the eyes and swelling of the face. In this condition, for reasons that are not explained, greatly increased quantities of hyaluronic acid and chondroitin sulfate bound with protein form excessive tissue gel in the interstitial spaces, which causes the total quantity of interstitial fluid to increase

Question 60

atherosclerosis

Answer 60

decrease level of thyroid gland increases blood cholesterol level which increases the chances of atherosclerosis and other vascular diseases specially people who have myxedema and are prone to more peripheral vascular diseases like deafness and coronary artery diseases

Question 61

Diagnostic Tests for Hypothyroidism

Answer 61

The basal metabolic rate in myxedema ranges between −30 and −50. In addition, the secretion of TSH by the anterior pituitary when a test dose of TRH is administered is usually greatly increased (except in the rare instances of hypothyroidism caused by depressed response of the pituitary gland to TRH).

Question 62

treatment of hypothyroidism

Answer 62

daily ingestion of thyroid hormones

Question 63

what is cretinism

Answer 63

This condition is characterized especially by failure of body growth and by mental retardation. It results from congenital lack of a thyroid gland (congenital cretinism), from failure of the thyroid gland to produce thyroid hormone because of a genetic defect of the gland, or from a lack of iodine in the diet (endemic cretinism).