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Endo/Repro Exam 1 > Thyroid Gland > Flashcards

Thyroid Gland Flashcards

1
Q

_ is the prohormone of the thyroid gland

_ is the active hormone produced by the thyroid gland

The newly synthesized thyroid hormones are bound to _ and located in the _ of the thyroid gland

_ cells are also present in addition to follicular cells and are responsible for the productions of _

A
  • T4
  • T3
  • Thyroglobulun, Colloid
  • C cells, calcitonin
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2
Q

The secretory products of the thyroid glands are _

Thyroid hormones contain large amounts of _

Part of synthesis is _ and some is extracellular

_ is the major secretory product

A
  • Iodothyronines
  • Iodine
  • Intracellular
  • T4
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3
Q
  • Iodide is added to peroxide to produce _
  • Adding iodine to tyrosine produces what two products?
  • Are these products biologically active?
A
  • Iodine
  • MIT and DIT
  • Not biologically active, but used to synthesize T3 and T4
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4
Q
  • Two molecules of _ are used to make T4
  • One molecule of _ and one molecule of _ are used to make T3
  • T4 synthesis is 10x _ than T3 synthesis
A
  • DIT
    MIT, DIT
  • Greater (T4 is made much faster)
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5
Q
  • The enzyme _ is responsible for the peripheral conversion of T4 to T3 (80-90%)
  • 10% of T3 comes from _
A
  • Iodinase (different types of iodinase enzymes depending on where you are in the body)
    • Type I-skeletal muscle
    • Type II-provides feedback to anterior pituitary
  • Direct secretion of T3 from thyroid
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6
Q
  • What are some clinical conditions where the conversion from T4 to T3 is reduced?
A

Fasting

Medical and surgical stress

Catabolic disease

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7
Q
  • How is thyroid hormone synthesized?
A
  1. Thyroglobulin is transported from Golgi/ReR into apical/luminal membrane of the follicular cell
  2. “Iodide trap”-iodide enters cell on basolateral surface using 2Na+/I- transporter
  3. I- is transported out of apical membrane via Peroxidase/TPO
  4. Peroxidase catalyzes addition of I- to thyroglobulin to make MIT and DIT (still bound to TG)
  5. Peroxidase reaction occurs again to make TG with bound MIT, DIT, T3 and T4 (stored as colloid)
  6. Endocytosis into cell from TSH stimulation
  7. Proteases in lysosomes cleave T3 and T4 off of TG and send them into circulation; MIT and DIT are recycled
  8. MIT and DIT are converted to tyrosine and TG via deiodinase
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8
Q
  • When the availability of iodide is restriction, the formation of _ is favored
  • Deficiency of _ mimics dietart I- deficiency
  • _ is an effective treatment for hyperthyroidism by inhibiting Na+/I- cotransporter on basolateral surface of follicular cell in thyroid
  • High levels of _ inhibit organification and synthesis of thyroid hormone (WOLFF-CHAIKOFF EFFECT)
A
  • T3
  • deiodinase
  • PTU
  • I-
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9
Q
  • Enough hormone is stored as _ in the follicular colloid to last the body 2-3 months
A
  • Iodinated TG
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10
Q
  • The activity of the thyroid gland can be assessed by _
  • Identify the following
A
  • Radioactive iodine uptake
  • 1) Hyperthyroidism
  • 2) Normal
  • 3) Hypothyroidism
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11
Q
  • What are the main binding proteins that carry thyroid hormones in the blood?
  • There is an _ between bound and free circulating T3 and T4 in the bloodstream
  • What percentage of thyroid hormones are bound to proteins?
A
  • TBG (Thyroxine binding globulin)
    • ​HIGHER AFFINITY FOR T4
    • Made in liver
  • TTR (Transthyretin)
  • Albumin​

Equilibrium

99%

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12
Q
  • TBG has a higher affinity for _, making the half life of this hormone longer
A
  • T4 (half life is 6 days v. 1 day half life for T3)
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13
Q
  • Circulating levels of TGG can be measured with what test?
  • How does this test work?
A
  • T3 resin uptake test
  • STEPS
    • TGB with bound T4 is taken from serum
    • Unbound and labeled T3 is added
    • If there are binding sites available on TGB, T3 will bind
    • Whatever is left over or unable to bind TGB will bind T3 resin and precipitate
    • TGB with bound T3/4 is in solution
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14
Q
  • How are blood levels of TGB and free thyroid hormones affected in hyperthyroidism?
A
  • TGB should not change
  • Increase in T4 (thyroid is making excess)
  • Increase in resin uptake of T3 (T4 taking up binding sites on TGB and T3 is also being made in excess)
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15
Q
  • How are blood levels of TGB and free thyroid hormones affected in a patient with hypothyroidism?
A
  • TGB unchanged
  • Decrease in T4 (thyroid isnt making as much)
  • Decrease in T3 resin uptake (less T4 means more open binding sites on TGB for T3)
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16
Q
  • How are blood levels of TGB and free thyroid hormones affected in patients with High TGB?
A
  • TGB elevated (obvi)
  • Increase in T4 *
  • Decrease in T3 resin uptake (more TGB-more binding sites for T3)
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17
Q
  • How are blood levels of TGB and free thyroid hormones affected in patients with Low TGB?
A
  • TGB is low
  • Decrease in bound T4
  • Increase in T3 resin uptake (Less TGB for T3 to bind)
18
Q
  • How are TGB and thyroid hormone concentrations altered in the blood during hepatic failure?
A
  • Hepatic failure-decreases TGB (its made there)
  • Increase in level of FREE T3 and T4
    • Followed by inhibition of synthesis of T3 and T4 (via negative feedback on anterior pituitary)
19
Q
  • How does pregnancy affect TGB and thyroid hormone levels in the blood?
A
  • Pregnancy-increase in TGB levels
  • Increase in bound T3 and T4
  • Decrease in free T3 and T4
  • Decrease in free T3 and T4 causes an increase in synthesis of T3 and T4
  • Levels of free, physiologically active hormones increased, total thyroid hormones normal (clinically euthyroid)
20
Q
  • HPT axis :
    • TRH _ anterior pituitary to release _ which stimulates the thyroid gland to release thyroid hormones
    • TSH is regulated by _ and _ (which one stimulates and which one inhibits?)
    • _ secretion occurs at a steady rate, unlike GH
A
  • TRH stimulates TSH release from anterior pituitary
  • TSH is regulated by TRH (stimulatory) and Free T3 (Inhibitory)
  • TSH secretion occurs at a steady rate
21
Q

_ enzyme has an indirect inhibitory effect on the hypothalamus and a direct inhibitory effect on the anterior pituitary

A
  • Deiodinase
22
Q

_ is the second messenger for TSH

What are the two actions of TSH on the thyroid gland?

A
  • cAMP
  • Trophic effects on thyroid gland
  • Thyroid hormone secretion
23
Q
  • Stimulatory factors of thyroid hormone secretion
  • Inhibitory factors of thyroid hormone secretion
A
  • Stimulatory factors:
    • ​TSH
    • Increased TBG (ex: pregnancy)
    • Thyroid Stimulating IGs
  • Inhibitory factors:
    • ​I- deficiency
    • Diodenase deficiency
    • Excessive I- intake (inhibits TPO activity)
    • Drugs inhibiting Na+/I- cotransport (Perchlorate, thiocyanite)
    • Drugs inhibiting peroxidase enzyme (PTU)
    • Decreased TGB levels (Liver Disease)
24
Q
  • Thyroid hormone is responsible for the synthesis of new _
  • In the liver and adipose tissue, TH helps with synthesis of _
A
  • Proteins
    • Beta 1 adrenergic receptors
    • Na+/K+ ATPase
    • Transport proteins
    • Lysosomal/Proteolytic enzymes
    • Structural proteins
    • Cariac proteins (myosin, beta adrenergic receptor, Ca2+ ATPase)
  • Metabolic enzymes
25
Q
  • The receptor for thyroid hormone is located in the _ and has _ and _ domains

It is more sensitive to which thyroid hormone?

A
  • Nucleus
  • Retinoid X and Thyroid hormone receptor domains
  • T3
26
Q
  • Systemic actions of thyroid hormone
A
27
Q
  • How does TH increase BMR?
  • Hypothyroid patients will have a _ BMR
  • Hyperthyroid patients will have a _ BMR
A
  • Increases activity of Na+/K+
    • Increase in O2 consumption and heat generation
  • Single dose of T4 can last 6 hours in increasing BMR
  • Low
  • High
28
Q
  • How does thyroid hormone affect metabolism?
A
  • Lipids:
    • Stimulates fat mobilization (increase FFAs in plasma)
    • Stim beta oxidation
    • Plasma concentration of cholesterol and triglycerides are inversely correlated to thyroid hormones (High triglycerides and cholesterol in HYPOthyroidism)
    • Helps with conversion of Carotine to Vit A
  • Carbs:
    • Increased glycogenolysis and gluconeogenesis
    • Increased insulin-dependent entry of glucose into cells
29
Q
  • Cardiovascular effects of thyroid hormones
A
30
Q
  • How does thyroid hormone affect growth and the CNS?
A
  • Thyroid hormone acts synergistically w/ GH and somatomedins-helps with bone formation
  • CNS:
    • Important for CNS maturation (dendritic branching, myelination)
31
Q
  • Thyroid Pathophysiology Summary
A
32
Q
  • Hyperthyroidism
    • Primary
    • Secondary
    • How are TSH levels affected?
A
  • Primary (Grave’s)-problem with the thyroid gland itself
    • ​Low TSH levels-T3 being produced is inhibiting TSH secretion from the anterior pituitary
  • Secondary (TSH secreting pituitary)
    • High TSH
33
Q

Grave’s disease

A
  • Exopthalmos-abnormal protrusion of the eyeballs and periobital edema
  • Dx:
    • Elevated serum free and total T3 or T4
    • Presence of circulating TSI (thyroid stumulating immunoglobulins)-helps distinguish grave’s disease from adenoma of pituitary thyrotrophs (secondary hyperthyroidism)
34
Q
  • Causes of hypothyroidism
    • Primary
    • Other causes
A
  • Primary
    • Agenesis
    • Gland destruction (Hashimoto’s thyroditis-AID)
    • Inhibition of TH synthesis and release (iodine def, enzyme defects, drugs)
    • Transient
  • Other:
    • Hypothalamic disease (tertiary)
    • Pituitary disease (Sheehans’s Syndrome-2ndary)
    • Resistance to thyroid hormones
35
Q
  • Treatment for hypothyroidism
A
  • T4 (longer 1/2 life than T3 because it binds TGB with more affinity and can just be converted to T3)
  • Be careful w/ postmenopausal women -osteoporosis
36
Q
  • Hashimoto’s Thyroiditis
    • How are TH levels affected?
    • How is TSH affected?
A
  • Thyroglobulin or TPO Abs attack thyroid gland
  • T3 and T4 levels are low, so TSH levels are high
37
Q
  • Cretinism
    • ​Causes
    • Symptoms
A
  • Causes:
    • Iodide def
    • Maternal intake of anti-thyroid meds
    • Impaired development of thyroid gland
    • Inherent defects in the synthesis of thyroid hormones
  • Symptoms:
    • Feeding problems
    • Resp difficulty
    • Protruding tongue
    • Curse facial features
    • Growth retardation
    • Mental retardation
    • Jaundice
    • Dry Skin
    • Hypotonia
38
Q
  • Hypothyroidism d/t iodine deficiency
  • How can this lead to goiter formation?
A
  • Goiter:
    • Gland maintains normal levels of thyroid hormones, patient is euthyroid and asymptomatic
    • If gland cannot maintain normal BGLs of thyroid hormones, patient will be hypothyroid
39
Q

Goiter can be caused by _ and _

A
  • Hyperthyroidism
    • Graves disease
    • TSH producing tumor
  • Primary hypothyroidism
    • Lack of adequate iodine in the diet
    • Sporadic hypothyroidism of unknown etiology
    • Chronic thyroiditis
40
Q
  • _ test is used for the diagnosis of thyroid disorders?
A

Endo/Repro Exam 1 (12 decks)

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