Thyroid disorders Flashcards
Where is the thyroid and what shape is it?
It is located at the back of the neck and has a shield shape.
How many lobes does the thyroid gland have?
2 lobes
Right and left
Tissue called isthmus holds the two lobes together, found at the centre.
Some people have a pyramidal lobe which is part of the extension from the back of the tongue
Where does the thyroid originate from?
The back of the tongue
Where is the foramen caecum?
The dimple at the back of the tongue, left by the disappearing thyroglossal duct
What are parathyroid glands? And what do they do?
They can be found embedded at the 4 corners of the thyroid (right top and bottom, left top and bottom) and they are involved in calcium control.
How much does the thyroid gland weigh?
20g
Why is there a chance that you may affect the patient’s voice after surgery on thyroid gland?
Left recurrent laryngeal nerve runs close (vocal cord supply)- small risk of damage there.
The recurrent laryngeal nerve innervates the larynx (voice box) allowing speech
Which lobe is the largest lobe?
Right lobe
What are the dimensions of an adult thyroid?
4cm x 2.5cm x 2.5cm
How should you draw the thyroid if asked to in an exam?
Describe the embryological development of the thyroid
Origin: midline outpouching of the floor of the pharynx (base of the tongue is the origin)
Outpouching forms a duct which elongates down (thyroglossal duct)
It migrates down the neck and divides into 2 lobes
The thyroid will be in its final position by week 7 of embryological development
Usually the thyroglossal duct disappears leaving only a dimple at the back of the tongur (foramen caecum)
The thyroid gland the develops
What are three problems that can occur with development of the thyroid?
- Thyroid agenesis- complete absence
- Incomplete descent- May not descend to the correct place ie, the base of tongue to the trachea. This can cause problems with delivery
- Thyroglossal cyst - segment of duct persists, forming cysts and presents as a lump years later
What is a lingual thyroid?
Where the thyroid tissue barely descends at all and remains very close to the back of the tongue- this can cause problems breathing.
What do we need thyroxine for?
Thyroxine is essential for brain development- neonates that have thyroxine deficiency and can get irreversible brain damage.
What does the term cretin refer to?
An individual with irreversible brain damage caused by lack of thyroxine.
What are some features of cretinism?
IQ is much lower than normal
Stunted growth
How is cretinism tested for?
All babies have a heel prick for blood test for thyroid function (measuring TSH) at the same time as the Gurthie test (for phenylketonuria) at 5-10 days of age.
The test isnt done immediately after birth as the neonate may have the mother’s thyroxine.
How is cretinism treated?
Thyroxine is immediately given if TSH is found to be high
What does the thyroid follicular cell do?
It is the site of thyroxine synthesis. Thyroid hormones are also stored and secreted.
Thyroid hormones regulate grwoth, development and BMR
Thyroglobulin vs thyroxine binding globulin
THEY ARE NOT THE SAME THING
Thyroxine binding globulin bonds 75% of thyroxine in the circulation whereas thyroglobulin is INSIDE the thyroid gland only.
Thyroid disease stats
Affects 5% of the population, and is much more common in females
F:M= 4:1
Overactive and underactive thyroid occurs at equal frequency.
What is primary hypothyroidism (myxoedema)?
It is due to autoimmune damage to the thyroid (or due to operation- thyroidectomy)
Thyroxine levels decline and TSH levels rise- to try and stimulate production of more thyroxine
Eventually, TSH levels will fall as it becomes exhausted.
Remember, when you are missing thyroxine you will have high TSH and high TRH as a negative feedback mechanism to make up for it.
Only TSH is measured because TRH is very much undetectable in the blood.
Describe the hypothalamo-pituitary- thyroidal axis
- Thyroxine will have direct negative feedback effect on the pituitary to inhibit production of more TSH
- It will also have an effect on the hypothalamus where itll inhibit the production of TRH
- The negative feedback loops makes sure that thyroxine levels in the blood remain constant.
Name some features of primary hypothyroidisim
- Deepening voice
- Depression and tiredness
- Cold intolerance
- Weight gain with reduced appetite
- Constipation (bowels slow down)
- Bradycardia
- Eventual myxoedema coma (brain stops functioning due to lack of thyroxine)
- Amenorrhoea may occur in late disease
- Heart enlargement - as it isn’t pumping properly
