Describe the general anatomical appearance of the thyroid gland
- 2 lobes usually joined by an isthmus
- sits in front of the trachea
What hormones does the thyroid secrete?
What do the parathyroid glands secrete?
What vertebrae does the thyroid sit in front of?
What tracheal cartilage rings does the thyroid sit in front of?
The thyroid decreases in size during pregnancy. TRUE/FALSE?
It increases in size during pregnancy
What nerve has the potential to be damaged during thyroid surgery?
Recurrent Laryngeal Nerve
What cells are responsible for synthesising thyroid hormones?
Where can thyroid hormones be stored if the do not need released immediately/
Large Colloid in centre of follicles
Enclosed by follicular cells
What cells are responsible for the synthesis of Calcitonin
Parafollicular C cells
What ion is required from the bloodstream in order to make thyroid hormones?
How are thyroid hormones synthesised?
Iodine in from blood
Added to tyrosine molecules
Via pinocytosis and assistance from ribosomes
Hormones then released into bloodstream
Explain the naming process when each iodine is added to a tyrosine unit
1 iodine = Monoiodotyrosine
2 iodines = Di-iodotyrosine
3 iodines = Triiodothyronine
4 iodines = Thyroxine
Drugs to target HYPERthyroidism (e.g. carbimazole and propyluracil) target what stage of thyroid hormone production?
Creation of mono/di-iodotyrosines
What percentage of hormone secreted by the thyroid is T3 and what percentage is T4?
T3 = 10% T4 = 90%
T4 is a more potent thyroid hormone than T3. TRUE/FALSE?
T3 = more potent
Which of the thyroid hormones is the most biologically active?
If thyroid hormones are hydroPHOBIC, what plasma proteins are required for their transport?
thyroxine binding globulin (70%)
thyroxine binding prealbumin (20%)
Unbound thyroid hormones are considered to be biologically active. TRUE/FALSE?
Give examples of cases where a patient would have increased TBG and therefore increased bound T4?
Pregnancy/Oral Contraceptive Newborn Hepatitis Biliary Cirrhosis Drug related e.g. clofibrate/heroin
Give examples of cases where a patient may have decreased TBG and therefore less bound T4?
Large glucocorticoid dose Active acromegaly Chronic Liver Disease Nephrotic syndrome Drug related e.g. Phenytoin/Carbamazepine
What processes are thyroid hormones known to increase?
- Basal metabolic rate
- Carbohydrate/Lipid/Protein Metabolism
What aspects of growth require thyroid hormone?
- Growth hormone releasing hormone (GHRH) production and secretion requires thyroid hormones
- Myelinogenesis and axonal growth in foetus requires thyroid hormones
What effect can an under or overactive thyroid have on the CNS?
Hypothyroidism - slow intellectual functions
Hyperthyroidism – nervousness, hyperkinesis and emotional lability
What medication can be used to decrease the symptoms of hyperthyroidism?
beta-blocker e.g. PROPRANOLOL
Explain the process of thyroid hormone release starting from the hypothalamus
Thyrotrophin releasing hormone (TRH) from hypothalamus
Thyroid stimulating hormone (TSH) release from anterior pituitary
T3 and T4 release from thyroid gland
What part of the thyroid hormone pathway can T3 and T4 negatively feedback on?
Both TRH and TSH
What are the role of de-Iodinases in thyroid hormone activation?
Converts T4 -> T3 or rT3 (reverse T3)
What de-iodinases are most important in converting T4 -> T3?
De-iodinase 1 and 2
What de-iodinase converts T4 to revers T3 (rT3)?
Where is de-iodinase 1 usually found?
liver and kidney
Where can de-iodinase 2 be found?
Heart Skeletal muscle CNS Fat Thyroid Pituitary
Where is de-iodinase 3 found?
brain (except pituitary)
Why may a patient be deficient in thyroid hormones?
Primary (gland) failure – may be associated
Secondary to TRH or TSH (no goitre)
Lack of iodine in diet (may be associated with goitre)
What are the symptoms of hypothyroidism?
Reduced BMR Slow pulse rate Fatigue, lethargy, slow response times and mental sluggishness Cold-intolerance Tendency to put on weight easily
What symptom of hypothyroidism in adults is characterised by a puffy face, hands and feet?
What do babies with hypothyroidism sometimes present with?
- dwarfism and limited mental functioning due to deficiency of thyroid hormones present at birth
What is Grave’s disease?
Thyroid stimulating immunoglobulin (TSI) acts like TSH but unchecked by T3 and T4
What can Grave’s disease cause?
Exopthalmus - bulging eyes due to water retaining carbohydrate build up behind eyes
What are the symptoms of HYPERthyroidism?
- Increased BMR
- Very fast pulse rate
- Increased nervousness and excessively emotional
- Sweating / heat intolerance
- Tendency to lose weight easily