39. Thyroid Flashcards
What AA is vital for making the thyroid hormones?
Where is the thyroid found?
Describe the internal structure of the thyroid gland.
How are T3 and T4 formed?
Tyrosine: tyr + iodine -> mono-iodotyrosine + I -> di-iodotyrosine. T3 = liothyronine. T4 = levothryroxine.
Anterior to 2nd - 4th rings of trachea, and lateral lobes extend upwards on either side of the trachea and larynx. R lobe slightly bigger than the L. Starts at back of tongue.
Epithelial cells (follicular cells) arranged into follicles around a lumen filled with colloid, containing thyroglobulin.
Na/I symporter pumps iodide into cell. Thyroperioxidase oxidises iodide -> iodine, iodinates tyrosyl residues in the thyroglobulin, and couples tyrosyl residues to produce T4 (80-90%) and T3.
What is A in the thyroid?
Colloid
What is the process of creating T3 and T4 controlled by?
How is T4 converted to T3?
Describe the mechanism of action and effects of thyroid hormones.
TSHR (thyroid stimulating hormone receptor). TSH binding increases prod of Na/I symptorter and transfers them to cell membrane. It has a number of effects on almost ALL elements of the pathway incl. activating DUOX2 and increasing production of thyroglobulin.
Occurs mainly in liver by type I (5’)-deiodinase. 3 types of deiodinases: D1 (liver, thyroid, kidney, muscle), D2 (brain and pituitary), D3 (brain, placenta, foetus)
Transported into cells, T3 acts on nuclear receptors (TRs) which act on response elements (TREs) in gene promotors -> stim or inhibition of production of diff mRNAs and thus proteins. Thyroid hormone acts on almost every tissue of the body = increase basal metabolic rate, which increases O2 use and heat production. Increase C.O., HR, stimulate gut motility, bone turnover and speed of muscle contraction.
How do T3 and T4 circulate the body?
What are the 3 types of hormone?
Distinguish between hyperthyroidism and thyrotoxicosis.
Bound to hormones e.g. thyroid binding globulin (TBG) or albumin (but T4 doesn’t bind that strong to)
Steroid (e.g. corisol), peptide (e.g. insulin), amine (e.g. thyroxine)
Hyperthyroidism = excessive production of thyroid hormone by thyroid gland.Thyrotoxicosis is excessive thyroid hormone of any cause and thus includes hyperthyroidism.
List how hyperthyroidism affects the following:
a) metabolism
b) nervous system
c) eyes
d) skin
e) GI tract
f) bones
g) haematological
h) reproduction
a) increased BMR, appetite and insulin turnover, heat intolerance, protein and lipid degradation, weight loss and myopathy, hyperglycaemia
b) nervousness, seizures
c) Graves’ disease: eyes wide and also inflammed behind eyes so stick out
d) plummer’s nails (autoimmune rash)
e) increased appetite and motility, weight loss, transaminitis (elevated liver enzymes)
f) accelereted osteoclast activity, hypercalcemia, osteoporosis
g) pernicious anaemia, B12 deficiency
h) decreases fertility, ED, gynecomastia
Compare these two images from the thyroid (normal = L). What can you deduce?
R = Graves’ thyroid - invaded by lymphocytes (autoimmune condition)
What are the risk factors of Graves’ disease?
Apart from Graves’ disease, what are some other causes of thyrotoxicosis?
What would T4, T3 and TSH levels be like in hyperthyroidism?
How is hyperthyroidism managed?
HLA status, infection, stress, female
Toxic multinodular goitre (mutation in TSHR - little nodules make too much thyroxine)[PIC]. Toxic adenoma. Excess iodine, amiodarone, HCG (human chorionic gondatrophin (looks alot like TSH so can get mild toxicosis when preg), thyroiditis, struma ovarii (ovary tumor), TSHoma (tumour of pituitary gland)
Elevated T4 and T3, supressed TSH
Thionamide drugs (propylthiouracil, carbimazole), radioactive iodine, thyroidectomy
List how hypothyroidism affects the following:
a) skin
b) cardiovascular
c) GI tract
d) nerves, muscle, bone
e) renal and haematological
f) endocrine and metabolism
a) dry, greasy, hair weak and falls out
b) sensitivity to cold, bradycardia, LDL chol increased
c) reduced appetite, constipation
d) impaired foetal brain development, dementia, slow relaxing reflexes, growth retardation
e) reduced GFR, mild hyponatraemia, normochromic normocytic anaemia
f) delayed puberty, reduced libido, ED, reduced BMR, decreased GLUT4 stim
List some causes of hypothyroidism.
What is the recommended iodine intake for pregnant/lactating women per day?
What causes cretinism?
What would T4 and TSH levels be like in hyperthyroidism?
How is hypothyroidism managed?
Hashimoto’s disease (organ-specific autoimmune disease with destruction of thyroid epithelial cells), endemic goitre, lithium (can affect iodine uptake), excess cabbage, infiltrative diseases, Pendred’s syndrome (EDS protein prob (normally gets iodine into colloid)), hypopituitarism (reduced TSH level)
250 micrograms(ug)/day
Born in areas of low iodine in soil - developing thyroid gland lacked iodine so produced less T4 -> stimulated gland to get bigger (goitre). Mental and growth retardation.
T4 = low, TSH = high
Levothyroxine
