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ENDOCRINE > Thyroid Physiology > Flashcards

Thyroid Physiology Flashcards

1
Q

Describe the general anatomical appearance of the thyroid gland

A
  • 2 lobes usually joined by an isthmus

- sits in front of the trachea

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2
Q

What hormones does the thyroid secrete?

A

T3
T4
Calcitonin

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3
Q

What do the parathyroid glands secrete?

A

Parathyroid hormone

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4
Q

What vertebrae does the thyroid sit in front of?

A

C5-T1

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5
Q

What tracheal cartilage rings does the thyroid sit in front of?

A

2-4

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6
Q

The thyroid decreases in size during pregnancy. TRUE/FALSE?

A

FALSE

It increases in size during pregnancy

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7
Q

What nerve has the potential to be damaged during thyroid surgery?

A

Recurrent Laryngeal Nerve

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8
Q

What cells are responsible for synthesising thyroid hormones?

A

Follicular cells

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9
Q

Where can thyroid hormones be stored if the do not need released immediately/

A

Large Colloid in centre of follicles

Enclosed by follicular cells

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10
Q

What cells are responsible for the synthesis of Calcitonin

A

Parafollicular C cells

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11
Q

What ion is required from the bloodstream in order to make thyroid hormones?

A

Iodine

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12
Q

How are thyroid hormones synthesised?

A

Iodine in from blood
Added to tyrosine molecules
Via pinocytosis and assistance from ribosomes
Hormones then released into bloodstream

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13
Q

Explain the naming process when each iodine is added to a tyrosine unit

A

1 iodine = Monoiodotyrosine
2 iodines = Di-iodotyrosine
3 iodines = Triiodothyronine
4 iodines = Thyroxine

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14
Q

Drugs to target HYPERthyroidism (e.g. carbimazole and propyluracil) target what stage of thyroid hormone production?

A

Creation of mono/di-iodotyrosines

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15
Q

What percentage of hormone secreted by the thyroid is T3 and what percentage is T4?

A 
T3  = 10% 
T4  = 90%
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16
Q

T4 is a more potent thyroid hormone than T3. TRUE/FALSE?

A

FALSE

T3 = more potent

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17
Q

Which of the thyroid hormones is the most biologically active?

18
Q

If thyroid hormones are hydroPHOBIC, what plasma proteins are required for their transport?

A

thyroxine binding globulin (70%)
thyroxine binding prealbumin (20%)
Albumin (5%)

19
Q

Unbound thyroid hormones are considered to be biologically active. TRUE/FALSE?

20
Q

Give examples of cases where a patient would have increased TBG and therefore increased bound T4?

A 
Pregnancy/Oral Contraceptive
Newborn
Hepatitis
Biliary Cirrhosis
Drug related e.g. clofibrate/heroin
21
Q

Give examples of cases where a patient may have decreased TBG and therefore less bound T4?

A 
Large glucocorticoid dose
Active acromegaly
Chronic Liver Disease
Nephrotic syndrome
Drug related e.g. Phenytoin/Carbamazepine
22
Q

What processes are thyroid hormones known to increase?

A
  • Basal metabolic rate
  • Thermogenesis
  • Carbohydrate/Lipid/Protein Metabolism
23
Q

What aspects of growth require thyroid hormone?

A
  • Growth hormone releasing hormone (GHRH) production and secretion requires thyroid hormones
  • Myelinogenesis and axonal growth in foetus requires thyroid hormones
24
Q

What effect can an under or overactive thyroid have on the CNS?

A

Hypothyroidism - slow intellectual functions

Hyperthyroidism – nervousness, hyperkinesis and emotional lability

25
Q

What medication can be used to decrease the symptoms of hyperthyroidism?

A

beta-blocker e.g. PROPRANOLOL

26
Q

Explain the process of thyroid hormone release starting from the hypothalamus

A

Thyrotrophin releasing hormone (TRH) from hypothalamus
STIMULATES
Thyroid stimulating hormone (TSH) release from anterior pituitary
STIMULATES
T3 and T4 release from thyroid gland

27
Q

What part of the thyroid hormone pathway can T3 and T4 negatively feedback on?

A

Both TRH and TSH

28
Q

What are the role of de-Iodinases in thyroid hormone activation?

A

Converts T4 -> T3 or rT3 (reverse T3)

29
Q

What de-iodinases are most important in converting T4 -> T3?

A

De-iodinase 1 and 2

30
Q

What de-iodinase converts T4 to revers T3 (rT3)?

A

De-iodinase 3

31
Q

Where is de-iodinase 1 usually found?

A

liver and kidney

32
Q

Where can de-iodinase 2 be found?

A 
Heart 
Skeletal muscle
CNS
Fat 
Thyroid
Pituitary
33
Q

Where is de-iodinase 3 found?

A

fetal tissue
placenta
brain (except pituitary)

34
Q

Why may a patient be deficient in thyroid hormones?

A

Primary (gland) failure – may be associated
with goitre

Secondary to TRH or TSH (no goitre)

Lack of iodine in diet (may be associated with goitre)

35
Q

What are the symptoms of hypothyroidism?

A 
Reduced BMR
Slow pulse rate 
Fatigue, lethargy, slow response times and mental sluggishness
Cold-intolerance
Tendency to put on weight easily
36
Q

What symptom of hypothyroidism in adults is characterised by a puffy face, hands and feet?

37
Q

What do babies with hypothyroidism sometimes present with?

A

Cretinism:

- dwarfism and limited mental functioning due to deficiency of thyroid hormones present at birth

38
Q

What is Grave’s disease?

A

Autoimmune disease
Causes HYPERthyroidism
Thyroid stimulating immunoglobulin (TSI) acts like TSH but unchecked by T3 and T4

39
Q

What can Grave’s disease cause?

A

Goitre

Exopthalmus - bulging eyes due to water retaining carbohydrate build up behind eyes

40
Q

What are the symptoms of HYPERthyroidism?

A
  • Increased BMR
  • Very fast pulse rate
  • Increased nervousness and excessively emotional
  • insomnia
  • Sweating / heat intolerance
  • Tendency to lose weight easily

ENDOCRINE (22 decks)

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