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ENDOCRINE SYSTEM > Thyroid Gland > Flashcards

Thyroid Gland Flashcards

1
Q

Develops as an endodermal outgrowth or an evagination from the midline of the floor of the pharynx, between tuberculum impar and copula

A

Thyroid gland

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2
Q

The thickening becomes what duct

A

Thyroglossal duct

- wc elongates and later be bilobed

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3
Q

The duct becomes a solid cord and migrates down the neck passing thru the developing

A

Hyoid bone

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4
Q

Site of origin of the thyroglossal duct on the tongue remajns as a pit called the

A

Foramen cecum

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5
Q

Thyroid gland location

A

Below larynx on either side of and the anterior to trachea

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6
Q

Thyroid gland and relation to larynx, trachea, esophagus

A

Below larynx on either side
Anterior to trachea

Trachea lies inferior to larynx, esophagus is posterior to it

Surgical removal of thyroid may lead to injury of these organs

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7
Q

Thyroid gland and relation to parathyroid glands

A

Parathyroid glands - embedded posterior to thyroid gland, superior & inferior pole

Inadvertent removal during thyroidectomy causes hypoparathyroidism

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8
Q

Thyroid gland and relation to recurrent laryngeal nerve

A

These bilateral branches of the vagus nerve pass posteromedially along the groove between the esophagus and the trachea

Tumor invasion or injury results to hoarseness

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9
Q

Thyroid gland and relation to neck muscles & great vessels

A

Common carotid artery lies immediately lateral to the thyroid

Tumor invasion or injury may cause injury to any or all adjacent structures

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10
Q

Relation to lobes: ANTEROLATERALLY

A

The sternothyroid, superior belly of omohyoid, and anterior border of the sternocleidomastoid

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11
Q

Relation to lobes: POSTEROLATERALLY

A

Carotid sheath w the common carotid artery, the internal jugular vein, and vagus nerve

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12
Q

Relation to lobes: MEDIALLY

A

Larynx, trachea, pharynx and esophagus

Associated w these are cricothyroid muscle and its nerve supply, external laryngeal nerve

Between esophagus & trachea = recurrent laryngeal nerve

Rounded posterior border of each lobe is posterior to the superior and inferior parathyroid glands and the anastomosis between the superior and inferior thyroid arteries

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13
Q

Relations of the Isthmus

A

Anteriorly: the sternothyroids, sternohyoids, anterior jugular veins, fascia, and skin

Posteriorly: the second, third, and fourth rings of the trachea

The terminal branches of the superior thyroid arteries anastomose along its upper border

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14
Q

Thyroid gland is firmly attached to the laryngotracheal skeleton via the

A

Visceral or pretracheal fascia

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15
Q

When swallowing, what moves? Thyroid masses or brachial cysts and dermoid cyst

A

Thyroid masses

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16
Q

What lvl of the thyroid does the base lie?

A

4th and 5th tracheal ring

Others sources: attached to travhea from the midlvl of thyroid cartilage to the 5th and 6th travheal cartilage

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17
Q

Thyroid wt

A

Approx 15-20g

Some source: 16 +/- 6 g (10-22)

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18
Q

Each lobe is approx what thickness and length

A

2 to 2.5cm in thickness and width at its largest diameter and 4cm length

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19
Q

Thyroid lobes are connected by a narrow bridge of tissue called

A

Isthmus

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20
Q

A vascular organ surrounded by a sheath derived from the

A

pretracheal layer of deep fascia

  • sheath attaches the gland to the larynx and trachea
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21
Q

Isthmus extends across the midline in front of the

A

2nd, 3rd or 4th tracheal rings

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22
Q

A pyrimidal lobe projects upward from the isthmus, usually to

A

the left of the midline

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23
Q

A fibrous or muscular band frequently connects the pyramidal lobe to the hyood bone; if it’s musculare it is referred to as

A

Levator glandulae thyroideae

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24
Q

Abnormalities in the pattern of thyroid dev, s/a persistence of this tract leads to a

A

thyroglossal duct cyst

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25
Q

Protrusion of tongue causes movement of thyroglossal duct cyst as opposed to

A

True thyroid masses (e.g goiter) wc move on deglutition

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26
Q

Fxnal unit of thyroid gland

A

Follicle (acinus) surrounded by a rich capillary plexus

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27
Q

The ht of the follicular epithelium varies w the degree of stimulation of

A

TSH

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28
Q

The ht of the follicular epithelium varies w the degree of stimulation of

A

TSH

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29
Q

Glandular epi veries w the degree of stimulation

A

Columnar: active
Flat: inactive

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30
Q

Lumen of the follicle filled w a clear, amber proteinaceous fluid called

Also a major constituent of thyroid mass

A

Colloid

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31
Q

Extend to colloid from the apical (adluminal) border, wc is the site od iodination rxn

A

Microvilli

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32
Q

Also occurs in the apical border

A

Initial phase of thyroid hormone secretion (i.e resorption of the colloid by endocytosis)

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33
Q

Parafollicular (C) cells secrete

Do not border on the follicular lumen

A

Calcitonin

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34
Q

Major constituent of colloid is the large glycoprotein that contains thyroid hormones within its molecule

A

Thyroglobulin

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35
Q

When the gland is inactive

A

The colloid is abundant

Follicles are large

Cells lining them are flat

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36
Q

When gland is active

A

Follicle are smol

Cells cuboid or columnar

Edge of colloid is scalloped, forming many smol “reabsorption lacunae”

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37
Q

Thyroid gland arteries

A

Superior thyroid artery
Inferior thyroid artery
Thyroidea ima

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38
Q

A branch of the external carotid artery

Descends to the upper pole of each lobe, accompanied by external laryngeal nerve

A

Superior thyroid artery

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39
Q

A branch of the thyrocervical trunk, ascends behind the gland to the lvl of the cricoid cartilage

It then turns medially and downward to reavh the posterior border of the gland

The recurrent laryngeal nerve crosses either in front or behind the artery or pass between its branches

A

Inferior thyroid artery

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40
Q

If present, may arise from the brachiocephalic artery or arch of aorta

Ascends in front of trachea to the isthmus

A

Thyroidea ima

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41
Q

Thyroid gland veins

A

Superior thyroid - drains into internal jugular vein
Middle thyroid - drains into internal jugular vein
Inferior thyroid - receives its tributaries from the isthmus and the lower poles of the gland

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42
Q

Veins of the two sides anastomose w one another as they descend in front of the trachea

They drain into the left brachiocephalic vein in the thorax

A

Inferior thyroid vein

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43
Q

Lymphatic drainage of thyroid gland

A

Mainly laterally into the deep cervical LN

Few descend to the paratracheal nodes

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44
Q

Thyroid innervation

A

Both adrenergic and cholinergic NS via fivers arising from the cervical ganglia and vagus nerve, respectively

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45
Q

Afferent fibers pass thru the laryngealnerves and regulate an

A

Active vasomotor system

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46
Q

One fxn of neurogenic stimuli is to

A

regulate blood flow of thyroid

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47
Q

Major secretory product of thyroid gland is

A

3,5,3’,5’ - tetraiodothyronine (thyroxine) T4

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48
Q

Other thyroid hormone

A

T3

3,5,3’-triiodothyronine

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49
Q

Molar activity

A

T3 to T4

3-5:1

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50
Q

Secretory ratio

A

T4 to T3

10-20:1

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51
Q

Plasma conc ratio

A

Free T4 to free T3

2:1

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52
Q

Most T3 in plasma is derived from the monodeiodination of T4 by action of

A

Monodeiodinase (5’-deiodinase)

- found in peripheral tissues

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53
Q

Biologically inactive thyronine formed by peripheral conversion catalyzed by 5-deiodinase

A

rT3

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54
Q

Each thyroglobulin molecule contains approximately how many tyrosine residues?

A

120

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55
Q

Thyroid accumulates what from the plasma?

A

Inorganic iodide

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56
Q

In the US, Daily dietary iodine intake is about

A

500ug

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57
Q

How much iodide is required per week to maintain euthyroidism?

A

1mg of iodide or 150ug/day

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58
Q

Thyroid gland stored enuff thyroid hormone to maintain a euthyroid state for how many months w/o hormone synthesis?

A

3 months

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59
Q

Throid gland contains how much iodide?

A

5-7mg iodide

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60
Q

2/3 of total iodide content in the colloid is in the form of

A

biologically inactive iodothyrosines

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61
Q

1/3 of the colloid iodide content is in form of

A

biologically active thyronines t3t4

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62
Q

Also formed in the peripheral tissues by deiodination of T4

A

T3

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63
Q

More active hoe

A

T3 ayt

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64
Q

The naturally occurring forms of T4 and its congeners with asymmetric C atom are the

A

L isomers

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65
Q

Has only smol fraction of the activity of D form

A

D-thyroxine

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66
Q

Smol amts of rT3 are also found in

A

Thyroid venouse bld

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67
Q

Thyroglobulin glycoprotein is made up of two subunitsand has a MW of

A

660,000

10% carbs by wt
123 tyrosine residues (4-8 lang incorporated)

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68
Q

3 fxns of thyroid cells

A
  1. Collect abd transport iodine
  2. Synthesize Tg, secrete it into the colloid
  3. Remove thyroid hormones from Tg and secrete to circ
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69
Q

The normal plasma iodine lvl

A

0.3ug/dL

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70
Q

How much iodine enter the thyroid at normal rates?

A

120ug/d

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71
Q

Thyoid secretes how much iodine in T3 and 4

A

80ug/d

72
Q

How much iodine per day diffuses into the ECF?

A

40 micrograms

73
Q

The secreted t3&4 are metabolized in the liver and other tissues, w the release of how much in the ECF

A

60ug/d

74
Q

Net loss of iodine in the stool

A

20ug/d

75
Q

Normal thyroid iodide to plasma iodide conc ratio

A

25-40:1

76
Q

Biosynthetic steps that are stimulated by TSH

A
  1. Iodine uptake (Iodide Trapping)
  2. Oxidation of iodide; the role of thyroperoxidase
  3. Iodination of Tyrosine (Organification)
  4. Coupling (Condensation)
77
Q

Luminal iodide to follicular cell iodide conc ratio

A

5:1

78
Q

A useful therapeutic index of the fxnal statys of the thyroid gland

A

Radioactive iodide uptake by the thyroid gland

79
Q

A 24-hr uptake normally ranges between

A

10-35% of the administered dose

80
Q

In a nirmal gland, the iodide pump concentrates the iodide to abt

A

30x its conc in bld

81
Q

Active iodide forms

A

Iodinum ion (I+)
A free radixal of iodine (IO3-)
Iodine (I2)

82
Q

Denotes tge addition of iodide to the tyrosyl residues of thyroglobulin

A

Iodination of active iodide

83
Q

Substrate for iodination

A

Thyroglobulin

84
Q

Requires the fusion of two diiodotyrosine molecs

A

T4 synthesis

85
Q

Requires the condensation of monoiodotyrosine with a diiodotyrosine

A

T3 synthesis

86
Q

Also mediates the coupling rxn

A

Thyroid peroxidase

87
Q

The release of hormones involves the following rxns

A
  1. Hydrolysis of Tg by thyroid protease and peptidases
  2. Secretion of iodothyronines
  3. Pseudopod extensions –> pinocytic vesicles
  4. 3/4 of iodinated tyrosine in the Tg never become thyroid hormones but remain MIT abd DIT
88
Q

Freed from the Tg but they’re not secreted into the bld, instead their iodine is cleaved from them by a deiodinase enz (iodotyrosine deiodinase)

A

Iodinated tyrosines

89
Q

99.95% of T4 is bound to

A

Plasma proteins

90
Q

Binds about 75% of plasma T4

A

TBG (Thyroxine-binding globulin)

91
Q

In normal indivs, less than half of the available binding sites on TBH are saturated with

A

T4

92
Q

Binds abt 15-20% of the circulating T4

A

Thyroxine-binding prealbumin (TBPA or transthyretin)

93
Q

Abt 9% of T4 is bound to

A

Albumin

94
Q

Almost all (99.5%) of T3 is transported bound to

A

TBG

95
Q

Very little T3 us bound to

A

Albumin

96
Q

None is bound to

A

TBPA :

97
Q

Thyroid hormone is metabolized by

A

Deiodination
Deamination
By conjugation w glucoronic acid

98
Q

Is secreted via the bile duct into the intestine

A

Conjugate

99
Q

Catalysing the formation of T3 and rT3 (inactive)

A

5’-deiodinase

100
Q

In the liver, T4 & T3 are conjugated to form

A

Sulfates and glucoronides

101
Q

The thyroid conjugates are

A

Hydrolyzed
Reabsorbed (enterohepatic circ)
Excreted in the stool

102
Q

TSH secretion is infuenced by 4 factors:

A
  1. TRH secretion from the median eminence
  2. Bld lvl of unbound T4
  3. Bld lvl of unbound T3 generated by peripheral conversion of T4 to T3
  4. Peripheral conversion of T4 to T3 within the pituitary gland
103
Q

A tripeptide synthesized by the parvicellular peptidergic neurons in the hypothalamus

A

TRH

104
Q

Plays a major role in negative feedback in pituitary lvl

A

T3

105
Q

High conc of intrathyroidal inorganic iodide lead to

A

Inhibition of thyroid release

106
Q

High conc of organic iodide (thyroid hormone) lead to

A

Decrease in iodide uptake

107
Q

cAMP synthesis

A

TSH receptors -activate-> adenylcyclase -to form-> cAMP -activate-> protein kinase —> PHOSPHORYLATION

108
Q

It inhibits TSH secretion and the response to TRH

A

Somatostatin

109
Q

Decrease the basal secretion of TSH

A

Dihydroxyphenylethylamine (dopamine)
Dopa
Bromocriptine

110
Q

Cause competitive inhibition of iodide transport into the cell, that is, inhibition of iodide-trapping mechanism

A

Thiocyanate in high enuff conc

111
Q

Deficiency of thyroid hormones leads to increased secretion of TSH by ant pit gland wc causes

A

Overgrowth of thyroid gland

112
Q

Block of thyroid secretion can lead to the ions to block thyroid secretion can lead to the development of an enlarged thyroid gland wc is called

A

Goiter

113
Q

Prevents formation of thyroid hormone from iodides and tyrosine

A

Propylthiouracil

Also methimazole and carbimazole

114
Q

The mild abd transient inhibition of organic binding of iodide and hence of hormone synthesis is known as the

A

Wolff-Chalkoff effect

115
Q

Vegetables of Brassicacae family, particularly rutabagas, cabbage and turnips, contain

A

Progoitrin

116
Q

Attached to the DNA genetic strands or in proximity to them

A

Thyroid hormone receptors

117
Q

Total membrane surface area of the mitochondria increases almost directly in proportion to the

A

Increased metabolic rate of the whole animal

118
Q

Enz that becomes increased in response to thyroid hormone is

A

Na-K-ATPase

119
Q

Thyroid hormone causes cell mem to be

A

Leaky to Na ions

- wc further activates the Na pump and further increase heat prodxn

120
Q

Normal BMR for adult euthyroid males is

A

35-40kcal/m^2 body surface/hr

121
Q

Normal BMR

A

6-10% lower in euthyroid females

122
Q

Marked decrease in the myelination abd arborization of neurons in the brain

A

Hypothyroidism

123
Q

What occurs if hypothyroidism it is untreated?

A

Mental retardation

124
Q

Thyroid hormone is necessary for

A

Normal lactation

125
Q

Thyroid hormone potentiates the glycogenolytic effevt of epinephrine, causing

A

Glycogen depletion

126
Q

In physiologic amounts, thyroid hormones has a

A

Potent protein anabolic effect

127
Q

In large doses, thyroid hormone has a

A

Protein catabolic effect

128
Q

Increased thyroid hormone

A

decreases the concentrations of cholesterol, phospholipids, and triglycerides in the plasma, even though it increases the free fatty acids.

129
Q

The large increase in circulating plasma cholesterol in prolonged hypothyroidism is often associated with

A

severe atherosclerosis

130
Q

One of the mechanisms by which thyroid hormone decreases plasma cholesterol concentration is to

A

Increase significantly cholesterol secretion in the bile and consequent loss in the feces

131
Q

A possible mechanism for the increased cholesterol secretion is that thyroid hormone induces increased numbers of

A

low-density lipoprotein
receptors on the liver cells, leading to rapid removal of low-density lipoproteins from the plasma by the liver and
subsequent secretion of cholesterol in these lipoproteins by the liver cells

132
Q

relative vitamin deficiency can occur when

A

excess thyroid hormone is secreted

133
Q

A greatly increased amount of thyroid hormone almost always

A

decreases body weight

134
Q

mean arterial pressure usually remains normal. Because of

A

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.

135
Q

lack of thyroid hormone can cause

A

constipation

136
Q

diarrhea

A

Hyperthyroidism

137
Q

lack of thyroid hormone

A

decreases rapidity of cerebration

138
Q

extremely nervous and have many psychoneurotic tendencies, such as anxiety complexes, extreme worry, and paranoia

A

hyperthyroidism

139
Q

makes the muscles react with vigor, but when the quantity of hormone becomes excessive, the muscles become weakened because of excess protein catabolism

A

hyperthyroidism

140
Q

it causes the muscles to become sluggish, and they relax slowly after a contraction.

A

hypothyroidism

141
Q

resting hand tremors, wt loss, palpitations, DoB, complaining of lack of sleep

A

hyperthyroidism

142
Q

feeling of constant tiredness, but because of the excitable effects of thyroid hormone on the synapses, it is difficult to sleep

A

hyperthyroidism

143
Q 
extreme somnolence (Sleepiness, the state of feeling drowsy, ready to fall asleep) is
characteristic of
A

hypothyroidism

144
Q

is likely to cause loss of libido

A

lack of thyroid hormone

145
Q

sometimes causes impotence

A

a great excess of the hormone

146
Q

menorrhagia and polymenorrhea

amenorrhea

A

lack of thyroid hormone

147
Q

the production of heat via the digestion of food, or by the action of hormones.

A

Calorigenesis

148
Q

the basal metabolic rate falls to almost one-half normal

A

when no thyroid hormone is produced

149
Q

Chronotropic effevt on heart

A

Increase number and affinity of B-adrenergic receptors

150
Q

Inotropic effect on heart ❤️

A

Enhance responses to circulating catecholamines

Increase proportion to a-myosin heavy chain (w highger ATPase activity)

151
Q

Effect of adipose and muscle

A

Catabolic

152
Q

Metabolic effects of the gut

A

Increase rate of carbohydrate absorption

153
Q

Metabolic effects og lipoprotein

A

Stimulate formation of LDL receptors

154
Q

Stimulate O2 consumption by metabolically active tissues and inc metabolic rate

Tissue exceptions: testes, uterus, LN, spleen, ant pit

A

Calorigenic

155
Q

Characterized by nervousness, wt loss, hyperphagia, heat tolerance, increased pulse p, fine tremor of outstretched fingers, warm soft skin, sweating, BMR +10 to as high as +100

A

Hyperthyroidism (thyrotoxicosis)

156
Q

Hyperthyroidism most common cause is

A

Graves’ dse (exophthalmic goiter)

157
Q

Autoimmune dse in wc circulating Ab formed against the TSH receptor activate the receptor, making glands hyperactive

A

Graves’ dse

158
Q

Immunity that destroys the gland rather than stimulates it

A

Hypothyroidism

159
Q

Hypothyroidism pt first have this

A

Thyroiditis - inflammation

160
Q

Goitrous glands may secrete normal quantities of thyroid hormones, but more frequently, the secretion of hormone is depressed

A

Idiopathic nontoxic colloid goiter

161
Q

Iodine is not pumped adequately into the thyroid cells

A

Deficient iodide-trapping mechanism

162
Q

Iodides aren’t oxidized to the iodine state

A

Deficient peroxidase system

163
Q

Final thyroid hormones cannot be formed

A

Deficient coupling of iodinated tyrosines in the thyroglobulin molecule

164
Q

Prevents recovery of ipdine from the iodinated tyrosines that are not coupled to form the thyroid hormones thus leading to iodine deficiency

A

Enz deiodinase deficiency

165
Q

Prevents recovery of ipdine from the iodinated tyrosines that are not coupled to form the thyroid hormones thus leading to iodine deficiency

A

Enz deiodinase deficiency

166
Q

Are substance s that block the synthesis of thyroid hormone

They hav a propylthiouracil-type of antithyroid activity

TSH secretion is enhanced

A

Goitrogens

167
Q

Goiterogenic agents include

A

Perchiorate, thiocyanate, pertechnetate
Thionamides (propylthiouracil and methimazole)
Iodide def
Excess iodide
Turnips, rutabagas, cabbages, veggies of fam Brassicacae

168
Q

Monovalent anions that block iodide-trapping

A

Perchiorate, thiocyanate, pertechnetate

169
Q

Block coupling of iodotyrosines

A

Thionamides (prophylthiouracil and methimazole)

170
Q

Physiologic characteristics of hypothyroidism

A

Depressed growth of hair and scaliness of skin
Frog like husky voice
Edematous appearance throughout the body (myxedema)

171
Q

Wc can result in peripheral vascular dse, deafness, coronary artery dse w consequent early death

D/t increase in quantity of blood CHOL bcs of altered fat and CHOL metabolism and diminished liver excretion of cholesterol in bile

A

Atherosclerosis

172
Q

Hypothyroidism tx

A

Daily ingestion of tablet or more containing thyroxine to maintain a steady lvl if thyroid hormone activity

173
Q

Conc of binding proteins in hyperthyroidism and hypothyroidism

A

Normal

174
Q

Conc of binding proteins in Euthyroid: estrogens, methadone, heroin, major tranquilizers, clofibrate

A

High

Also high total plasma T4, T3 abd RT3

Normal: fT3 fT4 and frT3 also plasma TSH

175
Q

Conc of binding proteins in Euthyroid: glucocorticoids, androgens, danazol, asparaginase

A

Low

Also low total plasma T4, T3 abd RT3

Normal: fT3 fT4 and frT3 also plasma TSH

ENDOCRINE SYSTEM (6 decks)

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