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Neuroendocrine Exam 3 > Thyroid Gland Physiology > Flashcards

Thyroid Gland Physiology Flashcards

1
Q

Prohormone and active hormone

The Thyroid follicle

C-cells

A 
T4 = prohormone 
T3 = active hormone

Functional unit of thyroid (filled with colloid

Parafollicular cells —secrete calcitonin

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2
Q

Where are thyroid hormones made

A

In the follicular lumen (colloid)= new synthesized Thyroid H. Attached to thyroglobulin
Follicle= surrounded by epithelium
These follicular epithelial cells make TH.

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3
Q

How TH is made

A

New TH-thryroglobulin is released into the lumen (colloid)
IODINE absorbed from the ECF into the thyroid gland and into the colloid is iodinated on thyroglobulin
= T3 and T4 (MORE T4)

Thyroglobulin leaves when TH gets Iodinated

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4
Q

T4—>T3 where

A

Outer ring deiodination by DEIODINASES
80-90% converted in the periphery
10% converted in the Thyroid Gland
T3 = active and taken up by tissues that need it

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5
Q

How T4–> T3 is lowered

A

Fasting
Medical/surgical stress
Catabolic disease

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6
Q

TH synthesis detailed version

A
  1. Tyrosine ——> Tyroglobulin + ER/Golgi modifications (epithelial cell) goes to the colloid exported out of epithelial cell
  2. I —> NIS——> Pendrin into the colloid
  3. Tyroglobulin gets Iodinated (peroxidased)
  4. TSH stimulates pinocytosis of tyroblobulin-iodinated to back in to the follicular epithelial cell
  5. Proteases break it down to Tyrosine and T3 and T4
  6. T3 and T4 are exported out to the circulation
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7
Q

I trap

A

I enters the epithelial thyroid cell with 2 Na+ ions with the NIS transporter, from the blood

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8
Q

When there is low I

A

T3 is favored

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9
Q

Deiodinase deficiency

A

Low T3 and T4 made from tyroblobulin

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10
Q

PENDRIN mutation

A

Cl-/I pump
(I use NIS to get into epithelial cell——>Pendrin to get into colloid)
Gene SLC26A4= PDS = I can’t get to colloid
=Hypothyroidism + Goiter
=sensorineural hearing loss in cochlea

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11
Q

Wolff-Chaikoff effect

A

High levels of [I] ———I Thyroid hormones synthesis

Hypothyroidism

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12
Q

PTU

A

TX: for hyperthyroidism

Inhibits NIS, Pendrin, Peroxidases

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13
Q

T3 and T4 circulate in the blood how

A 
99% bond to plasma proteins 
1. Thyroxine-binding globulin (TGB)-made in liver
2. Transthyretin (TTR)
3. Albumin
1% free
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14
Q

How to test TH levels

A

T4 has higher affinity for TBG

TEST: TBG(most bond to T4) + T3 rein uptake (antibody for T3)

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15
Q

RESULTS

High T4, T3 resin uptake

A

Hyperthyroidism

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16
Q

RESULTS

LOW T4, T3 resin uptake

A

Hypothyroidism

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17
Q

RESULTS
HIGH T4,
LOW T3 resin uptake

A

HIGH TBG

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18
Q

RESULTS
LOW T4,
HIGH T3 resin uptake

A

LOW TBG

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19
Q

RESULTS
HIGH TBG
LOW T3 resin uptake

A

Pregnancy

(Low amount of free T3 and T4)———> HIGH stimulation to synthesize T3/T4 (negative feedback)
= HIGH T3/T4 levels, however, NORMAL free T3/T4 -physiologically active
=CLINICALLY EUTHYROID

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20
Q

RESULTS
LOW TBG
HIGH T3 resin uptake

A

Hepatic Failure

More free T3 and T4 found) ———I synthesis of T3/T4 (negative feedback

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21
Q

Control and regulation of TH synthesis and secretion

A

T4/T3 ———I AP (TSH) + HYPO paraventricular Nucleus(TRH)

TSH———> secretion of T3/T4 + growth of thyroid gland (trophic effect)
TSH is secreted at a steady rate

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22
Q

LOW TSH

A

Goiter and Thyroid grows to large = Hypothyroidism

Because TSH ——> Thyroglobulin-iodinated(stored in colloid) to pinocytosis into follicular cells to breakdown and release T4/T3
NoTSH= increased storage in colloid

23
Q

Factors that increase T3/T4 secretion

A

TSH
Thyroid- stimulating Igs
High TBG (pregnant women)

24
Q

Factors that decrease T3/T4 secretion

A

LOW I, TBG
X: deiodinase

EXCESSIVE I = Wolff-Chaikoff effect
Perchorate Thiocynate——I NIS
PTU———I Peroxidase enzymes

25
Q

THYROID HORMONES (T4/T3) FUNCTIONS in other organs

A 
NA+/K+ ATPase
Transport/ structural proteins
B1 receptors (adrenergic) -E
Myosin
Lypolysis/gluconeogenesis/gycogenolysis/O2 consumption
Protein synthesis/ heat production 
GROWTH, bone maturation 
Other key metabolic enzymes
26
Q

Thyroid H.s increase what in metabolism

A

BMR
Due to increased Na+/K+ = high O2 consumption and heat made
(Long-lasting effect)

Hyperthyroidism = HIGH BMR
Hypothyroidism = LOW BMR
27
Q

T3/T4 on Lipid metabolism

A

Fat mobilization = HIGH FA oxidation
Lowers cholesterol and TAG (lowers fat)
Carotene——> VIT A (eyes)
make free glucose (gluconeogenesis/glycogenolysis)+ increase glucose storage by insulin

Hypothyroidism= high cholesterol levels, blindness and jaundice

28
Q

T3/T4 on cardiovascular effects

A

T4–> T3
T3=
1. Tissue thermogenesis
2. Decrease Systemic vascular resistance
LOWER Diastole BP = decrease Afterload = HIGH CO
LOWER Diastole BP= cause aldosterone to release= increase Preload= HIGH CO
= Increase blood volume

Also makes B1 adrenergic receptors (NE) which cause increase heart myocardial cells constriction

29
Q

How B1 get effected by TH.s

A

They make B1 adrenergic receptors (NE) which cause increase heart myocardial cells constriction (sympathetic)

This overtakes the M2 receptors (ACH) which decreases CO and heart contraction (parasympathetic)

30
Q

T3/T4 effects on Growth

A

Act with GH to promote growth

Act with somatomedins to promote bone formation

31
Q

Somatostatin

A

Inhibits GH and TSH from AP
Inhibits pancreatic Hs. Like insulin and glucagon
Inhibits gastric enzymes from secretion

32
Q

T3/T4 effects on CNS

A

Important in prenatal synapse formation and myelination and dendrite formation

Low TH during prenatal= cretinism (learning disability, dumb/foolish)

33
Q

EXCESS TH on the Metabolism and Bone and CNS

A

Metabolism:
Heat intolerance (prefers cold)
Weight loss
HIGH BMR

Bone:
Osteoporosis

CNS:
Agitation, anxiety, ADD, Hyperreflexia

34
Q

DEFICIENT TH on the Metabolism and Bone and CNS

A

Metabolism:
Cold intolerance (prefer heat)
Weight gain
Low BMR

Bone:
Stunted growth

CNS:
Cretinism, slow movements, impaired memory, low mental capacity, somnolence, listlessness, tiredness

35
Q

EXCESS TH on Skin, CV system, and GI

A

Skin:
Sweating

CV:
Tachycardia, palpitations, atrial fibrillations, high CO failure

GI:
Diarrhea

36
Q

DEFICIENT TH on Skin, CV system, and GI

A

Skin:
Dry
Myedema

CV:
Bradycardia
Low CO, and contraction
Heart failure

GI:
Constipation

37
Q

Primary Hyperthyroidism

A 
Thyrotoxicosis
Graves Disease (most common)
38
Q

Secondary Hyperthyroidism

A

HIGH TSH from AP

Despite the high T3 trying to negative feedback and ——I AP

39
Q

Graves Disease

Cause

A

Primary hyperthyroidism

Thyroid Stimulating Ig ——> TSH R. On Thyroid gland
= increases T3/T4 continuously
(T3——I TSH at AP, which does nothing)
LOW TSH

40
Q

Grave’s Disease
Sx:
Dx:

A

EXOPHTHALMOS = protrusion of the eyeballs
Periorbital edema

Dx: high T3/T4 free and bonded, TSI (TS Igs)- not tumor in this case
Goiter + ophthalmophaty
High I also found

41
Q

Graves Disease

Tx:

A

PTU
Thyroidectomy
High I-
B1 blocking agents

42
Q

Hypothyroidism
causes

Tx:

A
  1. Gland destruction - Hashimoto’s Tyroditis:
  2. I deficiency——I TH synthesis and release
  3. Drugs
  4. Defected enzymes
  5. Hypothalamic disease or AP disease (Sheehan’s syndrome)
  6. TH resistance
  7. Low TSH/TRH

TH replacement therapy

43
Q

Hypothyroidism

Tx:

A 
T4 replacement 
(Higher dosage needed in younger patients, since 1/2-life increases with age)

*overprescribing T4 in post-menopause women= osteoporosis

44
Q

Hashimoto’s Thyroditis

A

Thyroglobulin can’t make T4/T3
= LOW T3/T4
=HIGH TSH
=growth of thyroid gland GOITER

45
Q

GOITER

A

HIGH TSH

46
Q

Hyperpigmentation

A

HIGH ACTH

47
Q

Hypothyroidism congenital
causes
Sx:

A

X: I
Mom takes anti-thyroid medication
Thyroid gland did not develop
LOW T3/T4

Sx:
Feeding problems, resp. Probs, protruding tongue, ,growth stunted, mental slowness, Jaundice, dry skin, hypotonia

48
Q

IF I IS LOW ——> hypothyroidism and why

A

Low T4/T3 made on the Thyroglobulin
= HIGH TSH made
= growth of thyroid gland GOITER

  1. If normal levels of T4/T3 can still be made with this elevated TSH= EUTHYROID and ASYMPTOMATIC (with goiter)
  2. If normal levels of T4/T3 can’t be reached despite TSH increase= HYPOTHYROIDISM
49
Q

Sheehan Syndrome

A

AP necrosis
X: lactation, hypothyroidism, amenorrhea (no periods) other endocrine dysfunctions,
postpartum hemorrhage can cause it, or other reasons

LOW TSH, T3/T4

50
Q

GOITER happens during:

A
  1. Hyperthyroidism = Grave’s disease, AP tumor in TSH producing area
  2. Primary Hypothyroidism = low I in diet, autoimmune thyroid disease, Hishimoto’s disease, random cause
51
Q

Thyroiditis in hyperthyroidism

A

low I found
High T3/T4
low TSH

52
Q

Hyperthyroidism

Sx:

A

Weight loss, sweating, tremor, muscle spasm, hot feeling, Goiter, EXOPHTHALMOS, increased CO, high BMR

53
Q

Hyperthyroidism causes

A 
Graves’ disease
Thyroid neoplasm 
High TSH
Exogenous T3/T4
Defected AP or tumor of the AP

Neuroendocrine Exam 3 (18 decks)

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