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Endocrinology -- Freedman > Exam 1 --Pt 3 Thyroid Gland-- Endocrinology > Flashcards

Exam 1 --Pt 3 Thyroid Gland-- Endocrinology Flashcards

1
Q

What do thyroid follicles in the thyroid hold that may be used to make active thyroid hormones for release? How it is “made”?

A

iodized thyroglobulin

import iodine; create thyroglobulin –> made iodize thyroglobulin (create and release thyroid hormones)

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2
Q

Where is the thyroid gland located?

A

below larynx on each side of trachea

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3
Q

T/F. The thyroid is one of the largest endocrine glands.

A

True

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4
Q

What hormones does the thyroid secrete?

A
  • Thyroxine (T4)
  • Triiodothyronine (T3)
  • Calcitonin
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5
Q

What two hormones does the thyroid secrete that increases the metabolic rate of the body? In what percentage?

A
  • Thyroxine (T4)–93%

- Triiodothyronine (T3)–7%

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6
Q

What happens to T4 when it gets to the tissues?

A

almost all is converted into T3

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7
Q

Which is more potent, T3 or T4? What is its half life?

A

T3 is about 4x more potent than T4, BUT it has a 6x shorter half life

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8
Q

What may interfere with T3 that is not biologically active?

A

Reverse triiodothryonie (rT3)

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9
Q

What does calcitonin do? What does it oppose?

A

secreted by thyroid; decrease blood Ca++

opposes action of PTH and activated vit. D (aka calcitriol–synthetic)

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10
Q

What is the form of activated Vit. D?

A

1,25 dihydroxycholicalciferol

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11
Q

The thyroid gland is composed of large number of ____ ____ with ____ and lined with ____ epithelial cells.

A

closed follicles; colloid; cuboidal

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12
Q

What is colloid?

A

secretory substance containing thyroglobulin (and thyroglobulin is the precursor for T3 and T4)

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13
Q

T/F. The Thyroid has very poor blood supply.

A

False— thyroid has rich blood flow (like all glands do)

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14
Q

What role does iodine have for the thyroid?

A

iodine is required for formation of T3 and T4

- need 1 mg of ingested iodine/wk to form normal qualities of thyroid hormones

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15
Q

Of the iodine absorbed how much is take up by the thyroid? What happens to the other part?

A

1/5 take up by thyroid

4/5 rapidly excreted by kidneys

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16
Q

Describe Iodine vs Iodide.

A 
Iodine = I (the element 53)
Iodide = I- (ion and cannot remain in free state; must combine with other elements to form compound)
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17
Q

How is iodide transported from blood into follicle of thyroid?

A

Sodium iodide symporter

  • co-transport 1 idodide along with 2 Na+ ions
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18
Q

What pump is the sodium iodide symporter coupled with?

A

Na+/K+ pump

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19
Q

What stimulates the sodium iodide symporter? What diminishes it?

A

stimulated by TSH

diminished by hypophysectomy (removemal of Ant. Pit.)–therefore no TSH made)

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20
Q

What are 4 things the follicular cells of the thyroid do?

A
  1. import iodide
  2. create thyroglobulin
  3. make thyroid hormones
  4. release thyroid hormones
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21
Q

What is the precursor for all thyroid hormones?

A

thyroglobulin

  • large glycoprotein
  • 70-130 tyrosine residues (~20% iodinated)–> only 5% become part of ACTIVE thyroid hormones
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22
Q

What are the stages/steps of the thyroglobulin molecule being made in the follicular cells?

A

Rough ER –> Golgi –> Vesicle –> lumen

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23
Q

What does organification of thyroglobulin mean?

A

tyrosine (which is the precursor for thyroid hormones) on thyroglobulin will combine with iodide

(this takes place after essential first step)

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24
Q

What is the first essential step in the formation of thyroid hormones?

A

oxidation of iodide; which requires preoxidase and H2O2 (hydrogen peroxide)

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25
Q

Is the thyroid gland capable of storing thyroid hormones?

A

yes, it can store large amounts (which is unusual among endocrine glands)
- usually 2-3 month supply at a time

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26
Q

Each thyroglobulin molecule contains up to ___ T4 and a few ___ molecules.

A

30 T4 and a few T3 molecules

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27
Q

What is the order of synthesis to T4? Which are not biologically active?

A

Tyrosine–> MIT (monoiodotyrosine) –> DIT (diiodotyrosine ) –> T3 –> T4

MIT and DIT are NOT biologically active

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28
Q

How many iodines does T4 have? How many does T3 have?

A

T4 has 4 on 3,5,3’,5’

T3 has 3 on 3,5,3’

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29
Q

What stimulates the uptake of Thyroglobulin into follicular cells from follicular lumen? What does this also then stimulate

A

TSH—> to go through MIT –> DIT –> T3 –> T4 and secrete into extracellular fluids

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30
Q

Describe how thyroid hormones are doubly secreted?

A
  • precursor molecule thyroglobulin is released from apical surface of follicular cell into follicular lumen
  • Thyroglobulin is taken back up by follicular cells and degraded to release T4 and T3 which are secreted from basal surfaces into blood
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31
Q

What is the primary thyroid hormone secreted?

Which is the major biologically active form?

A

T4

T3

(most T4 transformed to T3 at target sites)

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32
Q

Biosynthesis of thyroid hormones depends on the products of three genes expressed primarily in thyroid follicular cells–what do these three genes code for?

A
  1. Sodium iodide symporter
  2. Thyroglobulin
  3. Thyroid peroxidase
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33
Q

Prior to release of thyroid hormones, what must occur? How much of T4 and T3 are released?

A

must be cleaved form thyroglobulin

93% T4 (1/2 of T4 converted to T3)

7% T3

34
Q

How is over 99% of T3 and T4 transported in blood?

A

bound to plasma proteins (synthesized by liver)–> providing controlled slow release to tissues

35
Q

What type of onset do thyroid hormones have? What type of duration?

A

slow onset; but long duration of action

36
Q

What impact will high serum levels of T4 have on TSH? What about T3?

A

TSH secretion will be inhibited

T3 has lesser impact

37
Q

What is TRH? What releases it?

A

Thyrotropin-releasing hormone; released by hypothalmus

38
Q

What is TSH controlled by?

A

TRH (thyrotropin-releaseing hormone) released by hypothalamus – it will bind to TRH receptors on anterior pituitary

39
Q

What impacts the sensitivity of the pituitary to TRH?

A

depends on intrapituitary T3 levels:
- when T4 serum levels drop, intrapituitary T3 also drops
- TRH receptors on pituitary increase due to the results of low T3
(need to secrete more TSH in order to make more Thyroid hormones)

40
Q

What stimulates release of TRH? What does this do to BMR?

A

exposure to cold; noticed by thermoregulation by hypthalamic centers

increase BMR up to 50%

41
Q

Where are TSH receptors located? What does it work with?

A

on surface of thyroid follicular cells

- works with cAMP

42
Q

What enzyme is used to create AMP from cAMP? Why is this important?

A

phosphodiesterase

(used along with TSH receptors on thyroid follicular cells)

therefore this enzyme inhibits the effects of thyroid hormones b/c cAMP cannot go phosphorylate things

43
Q

T/F. TSH increases all known secretory activities of the thyroid glandular cells.

A

True

44
Q

What is responsible for mediating TSH effects?

A

cAMP

45
Q

What secretory activities of the thyroid glandular cells does TSH increase?

A
  • proteolysis of thyroglobulin
  • activity of iodide pump
  • iodination of tyrosine
  • size and secretory activity of thyroid cells
  • number of thyroid cells (cubdoidal to columnar)
46
Q

What is the major transporter for T4 (thyroxine)?

A

Thyroxine-binding globulin (TBG)

47
Q

What transport molecule has the highest affinity for T3 and T4?

A

Thyroxine-binding globulin (TBG)

- 77% of T4 bound to TBG

48
Q

What transport molecule has a lesser affinity for T4 and does not effectively bind T3?

A

Transthyretin (aka TTR or Thyroxine-binding preablumin)

49
Q

How does T4 get turned into T3 once it gets to the tissues?

A

5’ monodeidoninase (takes off 5’ iodine)

50
Q

Can thyroid hormones activate nuclear receptors?

A

yes, and they increase transcription of a large number of genes

51
Q

What type of nongenomic cellular effects do thyroid hormones have on cells?

A
  • regulation of ion channels
  • regulation of oxidative phosphorylation
  • probably involves cAMP-protein kinase activation
52
Q

How do thyroid hormones affect cellular metabolic activity?

A

increases it;

  • increases number and activity of mitochondria
  • increase active transport of ions through cell membranes (Na+/K+ pump
53
Q

How do thyroid hormones affect grow? What impact does this have?

A

promote growth
- Hyperthyroid children grow faster (but epiphyseal plates may close sooner and therefore duration of growth is shortened)

54
Q

What if there is a lack of thyroid function at birth?

A

intellectual development disorder occurs

thyroid’s affect on growth is very important on the brain, esp. during fetal and neonatal period

55
Q

What do thyroid hormones decrease the concentration plasma of?

A
  • cholesterol
  • phospholipids
  • triglycerides
56
Q

What will an increase in thyroid hormones (T3/T4) have on cholesterol?

A

increases rate of cholesterol secretion into bile and increase fecal loss

increases LDL receptors on liver cells and promotes rapid removal of LDL from plasma by the liver

57
Q 
What are thyroid hormones affect on:
vitamins?
BMR?
Body weight?
Digestive system?
A
  • increase requirement for vitamins
  • increase BMR
  • decrease body weight
  • increase appetite, food intake, GI tract motility, secretion of digestive juices
58
Q

What are the effects of thyroid hormones on the cardiovascular system?

A
  • increase blood flow
  • increase cardiac output (direct and indirect)
  • increase HR and strength of contraction
  • increase systolic and decrease diastolic due to decrease Total Peripheral Resistance–> causing mean arterial pressure to be unchanged
59
Q

What effects do thyroid hormones have on the CNS?

A

increase rapidity of cerebration (thought)

60
Q

What effect does hyperthyroidism have on the CNS?

A
  • extreme nervousness/hyperexcitability
  • incrase startle response
  • psychoneurotic tendencies (anxiety, worry, paranoia, irritability)
  • hyperreflexia
61
Q

What effect does T3/T4 have on skeletal muscle at normal levels?

A

enhances muscle contraction

62
Q

What effect does T3/T4 have on skeletal muscle when in excess?

A

weakens muscle contraction due to excessive protein catabolism

63
Q

What effect does T3/T4 have on skeletal muscle in hypothyroidism?

A

cause molecules to be sluggish and they contract slowly after a contraction

64
Q

What is a characteristic sign of hyperthyroidism dealing with skeletal muscle?

A

is fine muscle tremor (10-15Hz)*

65
Q

What effect does hypothyroidism have on sexual function?

A

in both men and women leads to loss of libido (sex drive)

- in excess for men may cause impotence

66
Q

What do hypothyroid women usually have that relates to sexual function?

A

menorrhagia (excessive uterine bleeding) or polymenorrhea (diminished menstrual flow)

67
Q

What do hyperthyroid women have that relates to sexual function?

A

oligomenorrhea (diminished menstrual flow) and occasionally amenorrhea (no menses)

68
Q

How do thyroid hormones have on effect the gonads?

A

both direct and indirect acting through feedback effects on the anterior pituitary

69
Q

Describe the effects/actions on metabolism that thyroid hormones have.

A
  1. control BMR
  2. stimulate anabolic and catabolic pathways
  3. increase O2 consumption and heat production
  4. mitoch. increase in size and number (hyperth.)
  5. membrane more permeable = Na+/K+ ATPase pumps run harder
70
Q

What part of the ANS do thyroid hormones interact with?

A

Sympathetic nervous system

71
Q

Increase secretion of thyroid hormones will exaggerate mediated responses of what (when related to ANS)?

A

of NTs NE and Epi from both SNS and adrenal medulla

72
Q

What do many symptoms of hyperthyroidism resemble?

A

sympathicotonia (excessive sympathetic activity)–> increase HR, tremor, sweating

increase SNS mimics hyperthyroidism too (NE and Epi ass. with T3/T4)

73
Q

How do T3/T4 affect Beta-receptors? What about G proteins?

A

increases beta-receptors for NE/Epi in myocardium and other tissues

increase Gs proteins and decrease Gi proteins

74
Q

What effect does SNS have on local convertion of T4–> T3?

A

it accelerates the local conversion

75
Q

If someone was on pharmacologic blockage of beta-receptors, what are you thinking they may have?

A

they are useful to lessen effects of hyperthyroidism

76
Q

When someone has excitement and anxiety that is stimulating the SNS, how does this affect thyroid function?

A

cause an acute decrease in TSH secretion due in part to increase in metabolic rate and body heat production —> which suppresses TSH release via inhibition of TRH

77
Q

What happens if the hypophysial stalk (infundibulum stalk) is cut?

A

effects are abolished of thyroid hormones; demonstrating hypthalamic control

78
Q

What affect do thyroid hormones have on skeletal muscle?

A
  • increased Na+/K+ ATPase membrane pumps
  • increase Ca++ into sarcoplasmic reticulum
  • increased muscle mass
  • increase glycogen synthesis
  • diminishes glycogen breakdown (therefore glycogen accumulates)
79
Q

What affect do thyroid hormones have on cardiac muscle?

A

increased HR, contractability and cardiac output

- increased Na+/K+ ATPase membrane pumps

80
Q

The action of hypothyroid is to _____ physiological action, while the action of hyperthyroid is to ______ physiological action. What is the one exception that hyperthyroid with decrease?

A

decrease; increase; hyperthyroid will decrease serum levels of cholesterol*

Endocrinology -- Freedman (14 decks)

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