Thyroid Flashcards
Thyroid function control interaction with hypothalamus and pitutitary and pathologies
describe location and shape of thyroid gland
Sits on trachea, two lobes joined by isthmus
what do parathyroid glands do
Parathyroid glands make: Parathyroid hormone (PTH) – involved in Ca2+ metabolism
What does thyroid gland make
T3/T4/calcitonin
describe the thyroid pituitary hypothalamus axis
Hypothalamus releases
THYROTROPIN RELEASING HORMONE (TRH)
3aa pyro-Glu-His-Pro-NH2
TRH stimulates thyrotrophs in anterior pituitary to
produce THYROID STIMULATING HORMONE (TSH) or
THYROTROPIN
TSH stimulates thyroid gland to synthesize and release
thyroid hormones
What is the main hormone released by thyroid
mainly T4 metabolised to T3 in periphery
At thyroid receptors which is more potent t3 or t4
t3
Which hormone is involved in negative feedback of thyroid
T3 acts on the thyrotrophs to decrease release of TSH
and to decrease release of TRH from hypothalamus
briefly describe organisation of thyroid gland
follicles formed by throid cells, inside each follicle is a colloid. in between follicles are c cells.
outline how thyroid hormone is synthesised
Active uptake of iodine Synthesis of glycoprotein THYROGLOBULIN contains about 115 tyrosine residues Organification of iodine by THYROID PEROXIDASE in the presence of H2O2 Addition of iodine to TYROSINE Monoiodotyrosine (MIT) Di-iodotyrosine (DIT) MIT + DIT ------→ tri-iodothyronine (T3 ) DIT + DIT ------→ thyroxine (T4 )
what is the role of TPO (thyroid peroxidase)
Organification of iodine by
THYROID PEROXIDASE in the presence of
H2O2
Addition of iodine to TYROSINE
how does T4 travel in blood
majority is bound to TBG 75%,tbpa 20%, albumin 10%, small small amount is free
How does T3 travel in blood
TBG majority then albumin then minority 4% is free
How do thyroid hormones interact with target cells
Thyroid hormones interact with nuclear receptors
Thyroid hormone enters cells by diffusion or by specific
carrier
T3 enters the nucleus and binds to the thyroid receptor
Hormone-receptor complex binds to thyroid hormone
responsive element (TRE) on DNA
What physiological changes does T3 result in
Increased mRNA production Increased protein synthesis Increased Na+/K+-ATPase levels Increased ATP turnover Increased O2 consumption Increased number of adrenoceptors
What does thyroid hormone conc increase do to cardiac muscle
Increase cardiac muscle contractility tachycardia
What does thyroid hormone conc increase do to cholesterol
Increase cholesterol degradation
What does thyroid hormone conc increase do to bones
Increase bone turnover
What does thyroid hormone conc increase do to gut
Increase gut motility
What does thyroid hormone conc increase do to blood
Increase erythropoeisis
What does thyroid hormone conc increase do to respiratory centre
Maintenance of hypoxic and hypercapnic drive in
respiratory centre
What does thyroid hormone conc increase do to heat and 02 consumption
Increased O2 consumption and heat production
What does thyroid hormone conc increase do to metabolism
Increase metabolic turnover of hormones and drugs
what are the effects of a hypothyroid state
increase bodyweight, decrease oxygen consumption, heat production, bmr, cns decreased (drowsy), reflexes decreased, sns (decreased), cardiac bradycardia decreased cardiac output and bp, gut effects decreased
Signs of hypothyroidism
weight gain, constipated,slow reflexes, Hypercholesterolaemia
hyperprolactinaemia
