The thyroid in health and disease Flashcards
What are the follicles in the thyroid filled with
colloid
what epithelial is in the thyroid
cuboidal epithelial cells
what is special about the thyroid
stores and secretes hormones
what do the parafollicular cells produce
Calcitonin
what do the follicular cells produce
T3 and T4
what controls the release of thyroid hormones
Hypothalamo-pituitary axis
HPA for thyroid =
releases TRH from hypothalamus
Anterior pituitary releases TSH
TSH stimulates the thyroid to release T3 and T4
T3 and T4 negative feedback
TRH=
thyrotropin releasing hormone
from the hypothalamus
TSH=
Thyroid stimulating hormone
released from the anterior pituitary
T3=
Triodothyronine
T4=
Thyroxin
T3 is made up of
2 tyrosine with 3 iodine
T4 is made up of
2 tyrosine with 4 iodine
overall function of thyroid hormone (3)
increase metabolic rate
positive inotropic and chronotropic
growth and development
bc Thyroid hormone increases metabolism and heat production what is it
calorigenic
how does thyroid hormone increase growth in children
stimulates GH secretion and promotes GH effects
lack of growth hormone=
growth retardation
in foetal and postnatal life thyroid hormone deficiency =
mental retardation
where does synthesis of thyroid hormone take place
in the follicles on the thyroglobulin molecule
what ion is needed in producing thyroid hormone
iodine
1st step in thyroid hormone production
iodine atoms are actively transported across follicular cells and trapped in the colloid
what happens to iodine in the colloid
it is oxidised to iodine I2 by thyroid peroxidase
what enzyme oxidises iodine
thyroid peroxidase
what does I2 attach to in the thyroglobulin molecule
tyrosine
1 iodine + tyrosine=
MIT (monoiodotyrosine)
2 iodine + tyrosine=
DIT (di-iodotyrosine)
how do MIT and DIT combine
via thyroid peroxidase enzyme
T3 combo=
MIT+ DIT
T4 combo=
DIT + DIT
what happens to any MIT/DIT that hasn’t formed T3/T4
recycled back into process
where is all the bodies t4 produced
thyroid gland
where is the main source of T3
deiodination of T4 in liver and kidneys
Actions of TSH (4)
- causes active uptake of iodine
- stimulates other reactions involved in thyroid hormone synthesis
- stimulates the uptake of colloid
- induces growth of the thyroid
majority of T3 and T4 bound to
TBG (thyroid binding globulin)
thyroid hormone mechanism of action
bind to transmembrane receptor and directly alter gene expression in cells that regulate metabollic rate
3 hypothyroid diseases
primary
secondary
tertiary
2 types of primary hypothyroidism
congenital
acquired
congenital hypothyroidism is usually due to
absence of thyroid or ectopic thyroid
acquired hypothyroidism is due to (2)
iodine deficiency
autoimmune
levels in primary hypothyroidism
High TSH
High TRH
low T4/T3
symptoms of hypothyroidism
fatigue
cold intolerance
depression
Myxedema (retention of water)
Hashimoto’s disease=
autoimmune thyroiditis
most common cause of hypothyroidism=
hashimoto’s disease (autoimmune)
what is hashimoto’s disease associated with
thyroid peroxidase and thyroglobulin antibodies
what happens on the thyroglobulin molecule
MIT and DIT are combined to make T3 and T4
levels in secondary hypothyroidism
Decreased TSH
Decreased T3/ T4
example of a secondary hypothyroidism
pituitary tumour
2 main causes of hyperthyroidism
autoimmune
toxic nodular goitre
what happens in autoimmune hyperthyroidism
produce antibodies similar shape to TSH
what do antibodies similar to TSH cause
turns on T3 and T4 production process uncontrollably
primary hyperparathyroid levels=
very little TSH, very high T3 and T4
symptoms of hyperthyroidism (5)
weight loss lack of energy heat intolerance Anxiety increase appetite
Giotre=
enlarged thyroid
graves disease=
hyperthyrodism
treatment for hyperthyroidism
medical
radioactive iodine
surgical
drug treatment for hyperthyroidism
Thionamindes
Beta blockers
e.g 2 thionamindes
Carbimazole
Propylthiouracil
what do Thioamindes do
inhibit iodide oxidation by thyroid peroxidase
beta blockers
alleviate sympathetic manifestations rapidly
what is the surgical procedure for hyperthyroidism
thyroidiectomy
