thyroid & parathyroid tutorial

Question 1

Describe the histology of a hypoactive thyroid gland

Answer 1

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

Question 2

describe the histology of a hyperactive thyroid gland

Answer 2

• 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

Question 3

Describe the HPT axis

Answer 3

• 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

Question 4

what is cretinsim?

Answer 4

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

Question 5

what effects do the thyroid hormones have on the heart?

Answer 5

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

Question 6

what is the clinical presentation of hypothyroidism?

note symptoms

Answer 6

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

Question 7

what is the clinical presentation of hyperthyroidism

note symptoms

Answer 7

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

Question 8

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

Answer 8

• T3 and T4 will be reduced
• TSH will be increased

Question 9

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

Answer 9

• T3 and T4 will be decreased
• TSH will be decreased

Question 10

what is the treatment for hypothyroidism?

Answer 10

levothyroxine replacement therapy

Question 11

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

Answer 11

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

Question 12

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

Answer 12

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

Question 13

what are the main treatments for hyperthyroidism?

Answer 13

• 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

Question 14

what are the physiological roles of PTH - recap?

Answer 14

• 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

Question 15

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

Answer 15

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

Question 16

what are the main symptoms associated with hyperparathyroidism?

Answer 16

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

Question 17

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

Answer 17

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

Question 18

what are the main clinical symptoms associated with hypoparathyroidism?

Answer 18

• tetany
• wheezing
• dyspnea - shortness of breath

Question 19

what situations can cause hypoparathyroidism?

Answer 19

• trauma during thyroidectomy procedure
• idiopathic
• polyendocrine autoimmune disorder

Question 20

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?

Answer 20

• 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

Question 21

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

Answer 21

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

Question 22

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

Answer 22

• 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

Question 23

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

Answer 23

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

Question 24

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

Answer 24

• 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)

Question 25

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?

Answer 25

* PTH * parathyroid gland

Question 26

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

Answer 26

* alkaline phosphatase measures bone turnover * an elevated level would inidcate an increased bone turnover - which is consistent with primary hyperparathyroidism

Question 27

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

Answer 27

* 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+

Question 28

why were the patients urinary Ca2+ levels elevated?

Answer 28

* 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

Question 29

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

Answer 29

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

Question 30

Can primary hyperparathyroidism be assymptomatic?

Answer 30

* 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

Question 31

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

Answer 31

* 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+