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Endocrine physiology > thyroid & parathyroid tutorial > Flashcards

thyroid & parathyroid tutorial Flashcards

1
Q

Describe the histology of a hypoactive thyroid gland

A
  • follicular epithelium is squamous (smaller)
  • colloid is abundant
  • average follicule sie is relatively large
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2
Q

describe the histology of a hyperactive thyroid gland

A
  • follicular epithelial cells are very large - more columnar
  • colloid in the follicles is depleted, suggesting that it has been taken up rapidly for conversion to thyroid hormone to be secreted
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3
Q

Describe the HPT axis

A
  • TRH released from the hypothalamus
  • TSH released from the anterior pituitary gland
  • TSH stimulates the production and secretion of T3/T4 in the follicular cells
  • T3/T4 have a negative feedback effect on TSH and TRH
  • note that T4 is converted to T3 in target cells
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4
Q

what is cretinsim?

A
  • congenital hypothyroidism
  • happens due to untreated thyroid deficiency
  • mostly caused by maternal hypothyroidism
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5
Q

what effects do the thyroid hormones have on the heart?

A
  • increase HR
  • increase contractility of the heart
  • increase stroke volume & cardiac output
  • cause local vasodilatation
  • decrease peripheral resistance and lower diastolic BP
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6
Q

what is the clinical presentation of hypothyroidism?

note symptoms

A
  • weight gain - due to low BMR
  • lethargy - due to low BMR
  • brady cardia
  • constipation
  • thick tongue - slowed speech
  • menstrual disturbances
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7
Q

what is the clinical presentation of hyperthyroidism

note symptoms

A
  • weight loss
  • tachycardia
  • increase in systolic BP
  • muscle wasting
  • enlarged thyroid - goitre
  • intolerance to heat
  • bulging eyes
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8
Q

Describe the levels of TSH, T3 and T4 in primary hypothyroidism

A
  • T3 and T4 will be reduced
  • TSH will be increased
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9
Q

Describe the levels of TSH, T4 and T3 in secondary hypothyroidism

A
  • T3 and T4 will be decreased
  • TSH will be decreased
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10
Q

what is the treatment for hypothyroidism?

A

levothyroxine replacement therapy

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11
Q

Describe the levels of TSH, T3 and T4 in primary hyperthyroidism eg graves disease

A
  • increased T3 and T4
  • decreased TSH (as a result of increased negative feedback)
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12
Q

Describe the levels of TSH, T3 and T4 in** secondary hyperthyroidism**

A
  • T3 and T4 are increased
  • TSH is increased - pituitary dysfunction/ abnormality
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13
Q

what are the main treatments for hyperthyroidism?

A
  • thyrostatic drugs - ie antithyroid hormone agent (antagonist)
  • thyroidectomy - removing some of the thyroid during surgery
  • Iodine 131 radiation - it damages and destroys thyroid cells that are overactive or cancerous
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14
Q

what are the physiological roles of PTH - recap?

A
  • PTH is released when plasma Ca2+ is low
  • its function is to inrease Ca2+ levels
  • it acts directly on the bone to increase bone resroption
  • it acts directly on the kidney to increase Ca2+ reabsorption and decrease phosphate reabsorption
  • it also stimulates the production of 1,25-(OH)2-D in the kidney
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15
Q

What are Ca2+, PTH, phosphate & vit d levels like in hyperparathyroidism?

A
  • HIGH PTH
  • HIGH CA2+
  • low or normal phosphate (as PTH decreases it)
  • low vit D
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16
Q

what are the main symptoms associated with hyperparathyroidism?

A
  • kidney stones - due to high Ca2+ in plasma
  • unexpected fractures of bone - due to bone loss
  • osteopenia and osteoporosis
17
Q

what are PTH, Ca2+ & phosphate like in hypoparathyroidism?

A
  • low PTH
  • low Ca2+ - can become dangerously low and cause tetany - increases permebaility to Na+
  • normal to high phosphate
18
Q

what are the main clinical symptoms associated with hypoparathyroidism?

A
  • tetany
  • wheezing
  • dyspnea - shortness of breath
19
Q

what situations can cause hypoparathyroidism?

A
  • trauma during thyroidectomy procedure
  • idiopathic
  • polyendocrine autoimmune disorder
20
Q

a 50 year old women visitied her GP complaining of progessive weight gain of 20 pounds in 1 year, fatigue, postural dizziness, slow speech, dry skin and constipation. On physical examination she was hypotensive and her heart rate had a pulse of 58bpm…. what are the key symptoms here and describe how they came about?

A
  • progessive weight gain - hypothyroidism - causes low BMR which causes less calories to be burnt and therefore more cholesterol and fat build up
  • fatigue - caused by low BMR also
  • slow speech- due to thickening of the tongue
  • constipation - thyroid hormones are important for digestion and bowel contractions
  • hypotensive and low HR - thyroid hormone acts to increase heart contractility and HR
21
Q

why is measuring T4 a better indicator of thyroid function than T3?

A
  • as T4 represents 90% of all thyroid hormone secreted
  • a measurement of T3 could be misleading
22
Q

the women (who has classic hypothyroidism) was put through a TRH stimulation test - what can we conclude? also what does the red line mean?

A
  • pituitary function seems normal as it responded to TRH - therefore it is defo not secondary hypothyroidism
  • baseline TSH is elevated as a result of TRH administeration
  • the red line would indicate that the patient has seondary hypothyroidism as the TSH levels didnt rise upon TRH admin
23
Q

why is T4 analogue (levothyroxine) given instead of T3 for treatment of hypothyroidism?

A
  • more stable
  • longer half life
  • can be converted to T3 in target cells and tissues
24
Q

how might one assess what is the correct dosage for the T4 analogue?

A
  • test TSH levels - if the dose is appropriate the TSH levels should go down (ie the levels of thyroid hormone increase and have a negative feedback effect on TSH)
25
Q

a 33 year old women is brought to A&E as she passes bright red urine and has several ureteal stones after scanning the renal pelvis. She has also been feeling fatigued, lethargic, constipated. She has been taking a high strength Vit D supplement and she also had a spontaneous fracture of her tibia. What hormone and gland might be affacted based on these observations?

A
  • PTH
  • parathyroid gland
26
Q

what is the significance of the elevated alkaline phosphatase in the womens blood reading?

A
  • alkaline phosphatase measures bone turnover
  • an elevated level would inidcate an increased bone turnover - which is consistent with primary hyperparathyroidism
27
Q

why was serum albumin measured in the PTH woman’s blood test?

A
  • approx 40% of total plasma Ca2+is bound to plasma proteins such as albumin
  • since serum albumin was normal, we can exclude the fact that the hypercalcemia might have been due to an increase in the protein bound fraction
  • as her reading was normal, her hypercalcemia was due to an increase in free ionized Ca2+
28
Q

why were the patients urinary Ca2+ levels elevated?

A
  • although PTH normally stimulates Ca2+ reabsorbtion in the renal tubules
  • when the Ca2+ load is chronically elevated , eventually the tubular reabsorptive capacity is exceeded and increased Ca2+ excretion occurs leading to hypercalciuria
  • chronic hypercalciuria leads to the formation of kidney stones
29
Q

is the patients high strength vit D supplement relevant, if so why?

A
  • The high strength vitamin D supplement could potentially increase Ca2+ absorption from the gut and contribute to the hypercalcemia and hypercalciuria
30
Q

Can primary hyperparathyroidism be assymptomatic?

A
  • primary hyperparathyroidism may not present symptoms for years as the increased renal excretion may compensate for the increase in plasma Ca2+ levels
  • however with sustained renal loading, uretal stones will eventually appear
31
Q

As the patient was exercising on a hot day leading up to the A&E admission, is this relevant ?

A
  • exercising on a hot day would lead to dehydration
  • this would stimulate the release of ADH which would make the urine even more concentrated and therefore this would increase her urinary output of Ca2+

Endocrine physiology (19 decks)

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