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PY365 AF > AF and the Thyroid > Flashcards

AF and the Thyroid Flashcards

1
Q

Describe the incidence of AF

A

Most common abnormal heart rhythm and age increases risk

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2
Q

Give examples of risk factors for AF

A

CHF, male gender, CAD, HT, LVH, DM, age, BMI, alcohol consumption, cigarette smoking

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3
Q

What does CHF stand for

A

congestive heart failure

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4
Q

What does LVH stand for

A

Left ventricular hypertrophy

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5
Q

What does CAD stand for

A

Coronary artery disease

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6
Q

What does HT stand for

A

Hypertension

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7
Q

What does RR stand for

A

Relative risk

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8
Q

Give examples of modifiable risk factors associated with AF

A

cigarette smoking, BMI, alcohol

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9
Q

Give examples of non modifiable risk factors associated with AF

A

age, gender

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10
Q

What happens if more than one risk factor is present?

A

Risk factors are additive, so if more than 1 risk factor us present, this increases the risk of AF

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11
Q

What are the symptoms of AF

A
  1. Shortness of breath, difficulty breathing
  2. Dizziness, lightheaded, feeling faint
  3. heart palpitations
  4. tiredness/weakness
  5. chest discomfort
  6. difficulty exercising
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12
Q

Why do these symptoms of AF occur

A

Due to an impairment of cardiac output and insufficient blood supply (angina)

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13
Q

Describe the signs of AF

A
  1. absent P waves (atrial depolarisation)
  2. QRS complex irregular (ventricular depolarisation)
  3. T wave (ventricular repolarisation)
  4. Reduced atrial contraction
  5. Irregularly irregular rhythm
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14
Q

Why can atrial repolarisation not be seen on an ECG

A

because it happens around the same time as QRS complex

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15
Q

What does reduced atrial contraction lead to

A

Leads to risk of thrombus/embolic event which can break off and travel to brain causing a stroke

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16
Q

What are the characteristics of a normal ECG

A
  1. clearly defined p wave- all muscle fibres are receiving a stimulus to depolarise at the same time, leading to a coordinated electrical event
  2. all complexes are roughly the same distance apart
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17
Q

What does the absence of p waves suggest

A

Suggests atrial depolarisation is not synchronous

18
Q

What does an irregular QRS complex suggest

A

Suggests action potentials are not making it through the AVN at regular time points

19
Q

Describe the anatomy of the thyroid gland

A

Butterfly shaped gland surrounding the trachea (rings of cartilage)
- follicular cells are surrounded by an area of colloid
- lots of follicles come together to form the thyroid gland

20
Q

What is the role of the thyroid gland?

A

Releases a number of hormones: calcitonin, T3 and T4 (thyroid hormones)
- controls release of thyroid hormones due to the hypothalamus and pituitary gland

21
Q

explain how the thyroid hormones are released

A

hypothalamus will stimulate thyrotrophin releasing hormone, which drives the release of thyrotrophin stimulating hormone from the pituitary gland.
This stimulates the thyroid gland to release thyroid hormones

22
Q

What is the role of calcitonin

A

Regulates calcium homeostasis

23
Q

What occurs as the levels of thyroid hormones rise

A

As levels of thyroid hormones rise and reach optimum level, they feedback and inhibit TRH and TSH, allowing levels in the blood not to rise too high

24
Q

What does the thyroid gland require

A

needs a good blood supply
- there are blood capillaries close to follicles

25
Q

what are the primary hormones secreted by the thyroid gland

A

Tri-iodothyronine (T3) and tetra-iodothyronine (T4, thyroxine)

26
Q

Describe the 1st step in the process of production of T3 and T4 in thyroid follicles

A
  1. Follicular cell synthesises enzymes and thyroglobulin for colloid
    - thyroglobulin is a protein which has lots of tyrosine moieties attached to it
    - together, these proteins are exocytosed, so vesicle will fuse with the membrane and release its contents into colloid
27
Q

Describe the 2nd step in the process of production of T3 and T4 in thyroid follicles

A
  1. I- will enter follicular cells using co-transporter and Na+
    - net neutral charge (+ ion coin in for every - ion)
    - doesn’t change potential within the cell
    Then, I- is pumped out across basal membrane of follicular cells into colloid
28
Q

Describe the 3rd step in the process of production of T3 and T4 in thyroid follicles

A
  1. Iodine binds with tyrosines and combine to form T3 and T4 and the molecule is now endocytosed back into follicular cells
29
Q

Describe the 4th step in the process of production of T3 and T4 in thyroid follicles

A
  1. Enzymes work on that molecule to free up thyroglobulin, so it can be exocytosed back into colloid
30
Q

Describe the 5th step in the process of production of T3 and T4 in thyroid follicles

A
  1. Intracellular enzymes separate T3 and T4 from the protein
31
Q

Describe the final step in the process of production of T3 and T4 in thyroid follicles

A
  1. Free T3 and T4 then pass out of the follicular cell, into the bloodstream, where they are transported to their site of action
32
Q

Describe the 2 ways iodide combines with tyrosine

A
  1. Tyrosine combines with a single iodide atom to form mono-iodotyrosine
  2. or it combines 2 iodide atoms to form di-iodotryrosine
    - if you combine one that’s bound 2 with another that’s bound 2, you can form T4
33
Q

Describe the solubility of thyroid hormones and how they are transported

A

Thyroid hormones are insoluble in water, so are transported in blood bound to plasma proteins

34
Q

Which thyroid hormone is mostly released from follicular cells into the bloodstream

A

T4

35
Q

Describe the percentages of the thyroid hormones that are protein bound

A

over 99% of circulating thyroid hormones are protein bound and 95% is T4 as half life in plasma is 6-8 days (more stable) and T3 is only 1 day

36
Q

What does T4 mainly bind to

A

Majority of T4 binding is to thyroxine binding globulin (TBG)
- 15-20% is bound to thyroxine binding pre albumin (TBPA)
- 5-10% is bound to albumin (tends to be biologically inactive, so we need to free up that hormone for it to become biologically active)
- only free (unbound) hormone is biologically active

37
Q

Describe the mechanism of thyroid hormone action

A
  1. T3 and T4 are pumped into cells using carrier mediated transport
  2. T4 is generally biologically inactive and so once its inside the cell, it is converted to T3 by an enzyme that removes 1 of the iodide ions
  3. That T3 then gets transported into the nucleus where it binds to thyroid hormone receptors that can then affect gene transcription and translation
  4. Beta adrenergic receptor is affected as stimulation of beta receptors increases heart rate
38
Q

Outline the effects the thyroid has on the body

A
  1. increases protein synthesis and metabolic activity in cells
  2. Increases body metabolism and body heat
  3. Increases Beta 1 receptors
  4. Increases heart rate and stroke volume
  5. Increases cardiac output and blood pressure
  6. Increases GI motility and GI secretions
  7. Increases Neurogenesis, myelination and synaptogenesis
  8. Increases dendrite formation and sympathetic activity
  9. INcreases proliferation of skin cells and sweat and skin secretions
  10. Increases hair and nail growth
39
Q

what are the biological effects of thyroid hormones

A
  1. the main effect of thyroid hormones is to increase basal metabolic rate
  2. causes increase in carbohydrate metabolism
  3. increases synthesis, mobilisation and degradation of lipids
  4. increases protein synthesis
  5. essential for the normal development of the CNS, especially myelination of nerve fibres
40
Q

What is the primary mechanism of thyroid hormone action

A

an increase in the number and size of mitochondria and an increased activity of metabolically important enzymes
-so respiratory chain, ATP production and metabolic rate is increased

41
Q

What aspects of carbohydrate metabolism are increased by thyroid hormone action

A

all aspects of carbohydrate metabolism are increased
- glycogenesis and glucose uptake by muscle cells and adipose cells
- potentiation of the effects of insulin
- potentiation of the effects of the catecholamines
- increase in glucose absorption by the GIT

PY365 AF (19 decks)

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