thyroid & parathyroid tutorial Flashcards
Describe the histology of a hypoactive thyroid gland
- follicular epithelium is squamous (smaller)
- colloid is abundant
- average follicule sie is relatively large
describe the histology of a hyperactive thyroid gland
- 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
Describe the HPT axis
- 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
what is cretinsim?
- congenital hypothyroidism
- happens due to untreated thyroid deficiency
- mostly caused by maternal hypothyroidism
what effects do the thyroid hormones have on the heart?
- increase HR
- increase contractility of the heart
- increase stroke volume & cardiac output
- cause local vasodilatation
- decrease peripheral resistance and lower diastolic BP
what is the clinical presentation of hypothyroidism?
note symptoms
- weight gain - due to low BMR
- lethargy - due to low BMR
- brady cardia
- constipation
- thick tongue - slowed speech
- menstrual disturbances
what is the clinical presentation of hyperthyroidism
note symptoms
- weight loss
- tachycardia
- increase in systolic BP
- muscle wasting
- enlarged thyroid - goitre
- intolerance to heat
- bulging eyes
Describe the levels of TSH, T3 and T4 in primary hypothyroidism
- T3 and T4 will be reduced
- TSH will be increased
Describe the levels of TSH, T4 and T3 in secondary hypothyroidism
- T3 and T4 will be decreased
- TSH will be decreased
what is the treatment for hypothyroidism?
levothyroxine replacement therapy
Describe the levels of TSH, T3 and T4 in primary hyperthyroidism eg graves disease
- increased T3 and T4
- decreased TSH (as a result of increased negative feedback)
Describe the levels of TSH, T3 and T4 in** secondary hyperthyroidism**
- T3 and T4 are increased
- TSH is increased - pituitary dysfunction/ abnormality
what are the main treatments for hyperthyroidism?
- 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
what are the physiological roles of PTH - recap?
- 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
What are Ca2+, PTH, phosphate & vit d levels like in hyperparathyroidism?
- HIGH PTH
- HIGH CA2+
- low or normal phosphate (as PTH decreases it)
- low vit D
what are the main symptoms associated with hyperparathyroidism?
- kidney stones - due to high Ca2+ in plasma
- unexpected fractures of bone - due to bone loss
- osteopenia and osteoporosis
what are PTH, Ca2+ & phosphate like in hypoparathyroidism?
- low PTH
- low Ca2+ - can become dangerously low and cause tetany - increases permebaility to Na+
- normal to high phosphate
what are the main clinical symptoms associated with hypoparathyroidism?
- tetany
- wheezing
- dyspnea - shortness of breath
what situations can cause hypoparathyroidism?
- trauma during thyroidectomy procedure
- idiopathic
- polyendocrine autoimmune disorder
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?
- 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
why is measuring T4 a better indicator of thyroid function than T3?
- as T4 represents 90% of all thyroid hormone secreted
- a measurement of T3 could be misleading
the women (who has classic hypothyroidism) was put through a TRH stimulation test - what can we conclude? also what does the red line mean?
- 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
why is T4 analogue (levothyroxine) given instead of T3 for treatment of hypothyroidism?
- more stable
- longer half life
- can be converted to T3 in target cells and tissues
how might one assess what is the correct dosage for the T4 analogue?
- 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)
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?
- PTH
- parathyroid gland
what is the significance of the elevated alkaline phosphatase in the womens blood reading?
- alkaline phosphatase measures bone turnover
- an elevated level would inidcate an increased bone turnover - which is consistent with primary hyperparathyroidism
why was serum albumin measured in the PTH woman’s blood test?
- 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+
why were the patients urinary Ca2+ levels elevated?
- 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
is the patients high strength vit D supplement relevant, if so why?
- The high strength vitamin D supplement could potentially increase Ca2+ absorption from the gut and contribute to the hypercalcemia and hypercalciuria
Can primary hyperparathyroidism be assymptomatic?
- 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
As the patient was exercising on a hot day leading up to the A&E admission, is this relevant ?
- 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+
