Thyroid Flashcards
The thyroid gland consists of two lobes connected by a _________.
isthmus
The thyroid gland is anterior to what structures?
larynx
trachea
What is the arterial supply for the thyroid gland?
superior thyroid artery (ECA)
Inferior thyroid artery (SC)
External carotid artery, subclavian artery
The thyroid is extremelt vascular
What vessels provide venous drainage to the thyroid gland?
- superior and middle thyroid veins (IJV)
- inferior thyroid vein (BCV)
Internal jugular vein, brachiocepahlic vein
What nerves provide autonomic supply to the thyroid gland?
- sympathetic chain
- parasympathetic - recurrent laryngeal nerve, superior laryngeal nerve
Structural units of the thyroid gland are referred to as __________.
follicles
What is a thyroid follicle?
they are simple epithelium enclosing a colloid filled cavity
colloid- mixture of microscopic particles that are suspended in another mixture
What structures surround the thyroid follicle?
- blood vessels
- connective tissue
The thyroid also contains scattered parafollicular cells (C-cells); what is their function?
secrete calcitonin
What cells surround the thyroid follicle and what is their function?
- follicular cells
- secrete thyroid hormones
What is the basic function of the thyroid gland?
regulates basal metabolic rate
List the functions of the thyroid gland
- respiratory
- regulation of digestion
- cardiovascular- heart rate and heart structure
- calcium regulation
- catecholamine sensitivity (response to NA, A)
- sexual function
- metabolism- basal metabolic rate, heat generation (mitochondrial activity), macronutrient metabolism
- growth- cell differentiation, bone maturation, nerve development, brain maturation in foetus
- congenital hypothyroidism can lead to birth defects
The initial instruction for thyroid hormone synthesis comes from the __________. What hormone does it produce?
- hypothalamus
- thyroid releasing hormone (TRH)
What is the function of TRH?
stimulates the release of thyroid stimulating hormone (TSH) from the anterior pituitary gland
What is the function of TSH?
stimulates thyroid to produce thyroxine (T4) and triiodithyronine (T3) from follicular cells using iodine
What mechanism controls release of TRH/TSH from the hypothalamus and pituitary?
T3 and T4 have a negative feedback mechanism on hypothalamus and pituitary
More T3&T4 cause less TSH and TRH to be released from anterior pituitary and hypothalamus and vice versa
Briefly outline the synthesis of T3 and T4 hormones
- follicular cells synthesise enzymes and thyroglobulin for the thyroid colloid
- iodine is cotransported into the cell with Na+ and transported into the colloid
- thyroglobulin then enters the colloid from the follicular cells and enzymes add iodine to thyroglobulin to make T3 and T4
- thyroglobulin [modified with iodine] is then taken back into the follicular cell where intracellular enzymes seperate T3 and T4 from the protein
- free T3 and T4 enter circulation
What are the levels of TSH, T3 and T4 in a euthyroid ?
- normal TSH
- normal T3
- normal T4
What are the levels of TSH, T3 and T4 in subclinical hypothyroidism ?
- high TSH
- normal T3
- normal T4
this is an early warning sign for hypothyroidism; low thyroid has been detected so hypothalamic-pituitary axis aims to compensates and secretes more TSH so normal levels of thyroid hormones are produced
What are the levels of TSH, T3 and T4 in hypothyroidism ?
- high TSH
- low T3
- low T4
What are the levels of TSH, T3 and T4 in subclinical hyperthyroidism ?
- low TSH
- normal T3
- normal T4
less TSH released as higher than normal levels of thyroid hormone detected
What are the levels of TSH, T3 and T4 in hyperthyroidism?
- low TSH
- high T3
- high T4
List primary causes of hypothyroidism
- hashimotos autoimmune thyroiditis
- iodine deficiency (developing world)
- postpartum thyroiditis
- iatrogenic (medically caused)
- drugs amiodarone and lithium
Outline some central causes of hypothyroidism
- pituitary lesions
- infiltrative diseases- massive lymphocyte infiltration in the thyroid
What is the most common cause of hypothyroidism in the UK?
hashimotos disease
What is the presentation of hashimotos diseases? Why is this?
Goitre- swelling in the neck/ swollen thyroid gland
Lymphocyte infiltration in thyroid endemic goitre
What are the main types of hypothyroidism?
- primary
- central
- congenital
Briefly describe the effect of amiodarone on the thyroid gland
usually causes a hyperthyroid effect before a hypothyroid effect because of the damage and scarring caused to the thyroid
What are the levels of TSH, T3 and T4 in central hypothyroidism ?
- low TSH
- low T3
- low T4
disorder to pituitary, hypothalamus or hypothalamic pituitary portal circulation
Remember central hypothyroidism involves lesions to the pituitary
What is the presentation of hypothyroidism ?
- weakness
- lethargy
- sensitive to cold
- constipation
- weight gain
- depression
- menstrual irregulariy
- dry skin
- eyelid/facial oedema
- myxoedema- thickening of skin
- macroglossia- swollen tongue
- bradycardia
A serum sample for a hypothyroidism will confirm … (levels of hormones)
- high TSH
- low T3&4
How is hypothyroidism managed?
- levothyroxine
- regular monitoring of levels- people respond to thyroid replacement differently
List the causes of hyperthyroidism
- graves disease (autoimmune)
- toxic multi-modular goitre
- thyroid adenoma (single nodule)
- iatrogenic
- amiodarone
- post-partum
What is the presentation of hyperthyroidism?
- heat intolerance
- sweating
- weight loss
- anxiety
- palpitations
- fine tremor
- tachycardia (atrial fibrillation)
- pretibial myxoedema
- orbitopathy- lid retraction, exopthalamus, chemosis, EOM involvment, sight loss
Lid retraction- thyroid gland stimulating mullers muscle; you should not see the whites of the eyes above the iris; this is an indication of lid retraction
EOM -extraocular muscle
What is myxoedema?
this is the presence of an increased ground substance in subcutaneous tissue which leads to thickening of the skin
How is hyperthyroidism diagnosed?
- serum samples; low TSH, high T3&4; presence of TSH receptor antibodies
- thyroid ultrasound
- radioactive iodine uptake
What is graves disease ?
- autoimmune condition
- antibodies that mimic TSH and bind to TSH receptors on the thyroid gland are produced
What is the treatment of hyperthyroidism?
- anti-thyroid drugs such as carbimazole
- symptomatic managment ; propanolol - beta blocker for tachycardia
- radioactive iodine- taken up by the gland and damage the gland
- methylprednisolone for orbitopathy
- surgical resection
What is the MOA of carbimazole?
- interferes with cascade of enzyme that synthesise thyroid hormones
Overproduction of hormones in endocrine glands is usually due to…
- adenoma (benign)
- adenocarcinoma (malignant)
- hyperplasia
What are the dental considerations for hyperthyroidism?
- increased susceptibility to caries
- periodontal disease
- maxillary or mandibular osteoporosis (mobilisation of calcium in the bone)
- accelerated dental eruption
- burning mouth syndrome
- increased incidence of sjogrens syndrome (remember autoimmune diseases travel in packs)
What are some dental considerations of congenital hypothyroidism?
- macroglossia
- thick lips
- malocclusion
- delayed eruption of teeth
What are some long term dental considerations for hypothyroidism?
- impaction of second molars due to lack of space for proper eruption (due to incomplete resorption)
- dysgeusia - foul, salty, rancid or metallic taste sensation
- poor wound healing
How are thyroid cancers mostly presented? How is it ususally detected?
- asymptomatic thyroid nodule
- palpitation or ultrasound in a woman in her 30s or 40s
What is the diagnostic test for thyroid cancers?
- fine needle aspiration
What is the treatment for thyroid cancers?
total thyroidectomy followd by radioactive iodine ablation and TSH suppression
What are the 4 types of malignan thyroid cancers?
Papillary
Follicular
Anaplastic
Medullary
80% of thyroid cancer cases are papillary, what is the prognosis for these types of cancers?
excellent prognosis
What kind of malignant thyroid cancer has the worst prognosis?
Anaplastic
What kind of malignant thyroid cancer is associated with multiple endocrine neoplasia?
Medullary
Medullary thyroid cancer is a cancer of what cells?
Parafollicular cells
What are multiple endocrine neoplasias?
hereditary tumour syndromes with distinct patterns of organ development
What is the pattern of inheritance for multiple endocrine neoplasia (MEN)?
autosomal dominant mutations (inherited or sporadic)
What are the two types of MEN syndromes?
MEN1
MEN2
90% of people with MEN1 syndromes will develop …
primary hyperthyroidism
30-70% of people with MEN1 syndromes will develop…
pancreatic neuroendocrine tumours
10% of people with MEN1 syndromes will develop …
pituitary adenomas
> 90% of people with MEN2 syndrome will develop…
medullary thyroid tumour (parafollicular dells)
50% of people with MEN2 syndrome will develop…
phaeochromocytoma
30% of people with MEN2 syndrome will develop…
parathyroid adenoma
What gene has been implicated in MEN2 syndromes?
RET- oncogene (if given the chance will predipose individual to a malignancy)
