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Neuroendocrine Exam 3 > Thyroid Gland Physiology > Flashcards

Thyroid Gland Physiology Flashcards

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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

Study These Flashcards
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

Study These Flashcards
A

TSH
Thyroid- stimulating Igs
High TBG (pregnant women)

24
Q

Factors that decrease T3/T4 secretion

Study These Flashcards
A

LOW I, TBG
X: deiodinase

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

25
THYROID HORMONES (T4/T3) FUNCTIONS in other organs
``` 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
Thyroid H.s increase what in metabolism
BMR Due to increased Na+/K+ = high O2 consumption and heat made (Long-lasting effect) ``` Hyperthyroidism = HIGH BMR Hypothyroidism = LOW BMR ```
27
T3/T4 on Lipid metabolism
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
T3/T4 on cardiovascular effects
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
How B1 get effected by TH.s
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
T3/T4 effects on Growth
Act with GH to promote growth | Act with somatomedins to promote bone formation
31
Somatostatin
Inhibits GH and TSH from AP Inhibits pancreatic Hs. Like insulin and glucagon Inhibits gastric enzymes from secretion
32
T3/T4 effects on CNS
Important in prenatal synapse formation and myelination and dendrite formation Low TH during prenatal= cretinism (learning disability, dumb/foolish)
33
EXCESS TH on the Metabolism and Bone and CNS
Metabolism: Heat intolerance (prefers cold) Weight loss HIGH BMR Bone: Osteoporosis CNS: Agitation, anxiety, ADD, Hyperreflexia
34
DEFICIENT TH on the Metabolism and Bone and CNS
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
EXCESS TH on Skin, CV system, and GI
Skin: Sweating CV: Tachycardia, palpitations, atrial fibrillations, high CO failure GI: Diarrhea
36
DEFICIENT TH on Skin, CV system, and GI
Skin: Dry Myedema CV: Bradycardia Low CO, and contraction Heart failure GI: Constipation
37
Primary Hyperthyroidism
``` Thyrotoxicosis Graves Disease (most common) ```
38
Secondary Hyperthyroidism
HIGH TSH from AP Despite the high T3 trying to negative feedback and ——I AP
39
Graves Disease | Cause
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
Grave’s Disease Sx: Dx:
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
Graves Disease | Tx:
PTU Thyroidectomy High I- B1 blocking agents
42
Hypothyroidism causes Tx:
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
Hypothyroidism | Tx:
``` T4 replacement (Higher dosage needed in younger patients, since 1/2-life increases with age) ``` *overprescribing T4 in post-menopause women= osteoporosis
44
Hashimoto’s Thyroditis
Thyroglobulin can’t make T4/T3 = LOW T3/T4 =HIGH TSH =growth of thyroid gland GOITER
45
GOITER
HIGH TSH
46
Hyperpigmentation
HIGH ACTH
47
Hypothyroidism congenital causes Sx:
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
IF I IS LOW ——> hypothyroidism and why
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
Sheehan Syndrome
AP necrosis X: lactation, hypothyroidism, amenorrhea (no periods) other endocrine dysfunctions, postpartum hemorrhage can cause it, or other reasons LOW TSH, T3/T4
50
GOITER happens during:
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
Thyroiditis in hyperthyroidism
low I found High T3/T4 low TSH
52
Hyperthyroidism | Sx:
Weight loss, sweating, tremor, muscle spasm, hot feeling, Goiter, EXOPHTHALMOS, increased CO, high BMR
53
Hyperthyroidism causes
``` 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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