7.3 Flashcards
What are the 2 thyroid hormones?
T3= Triiodothyronine T4= Thyroxine
What is NIS
Na/I cotransporter
What can compete the I- on the NIS?
Thyocyanate (SCN-)
Pertechnate (TcO4-)
How does Iodine pumped ot to the colloid?
Pendrin- Cl/I antiporter
What oxidize I- to I2?
Thyroid Peroxidase (TOP) With the help of DUOX2
How does T3,T4 circulate in the blood?
80% bound to TBG
15% bound to Transthyretin
5% bound to Albumin
How much of T3, T4 is free?
- 5% of T3 is free
0. 02% of T4 is free
What happens to thyroid hormones in hepatic failure?
TBG levels drop -> increase in free thyroid hormones -> negative feedback -> less thyroid hormones are produced
When can an increase in TBG happen?
Pregnancy
What happens to T4when its absorbed by a tissue?
5’ Iodinase converts T3 to T4
When do 5’ Iodinase being inhibited?
During starvation in skeletal muscle to allow lower metabolic rate
What can decrease 5’ Iodinase activity?
Starvation Pregnancy Stress Hepatic failure Renal failure
What can increase 5’ Iodinase activity?
Obesity
Types of 5’ Iodinase
Type 1: T4->T3 in kidney, liver, skeletal muscle
Type 2: T4->T3 in CNS, Pituitary
Type 3: T4->rT3 Inactivation
What happens after the conversion of T4 to T3 inside the target cell?
T3 binds thyroid receptor on the nuclear membrane -> get inside nucleus and find Thyroid Responsive Element on DNA with RXE
(Thyroid Hormones Effects)
Effects on Basal Metabolic rate?
Increase O2 consumption (except brain, gonads, spleen)
This will increase body heat
(Thyroid Hormones Effects)
Metabolism?
Increase glucose absorption Gluconeogenesis Glycogenolysis Protein synthesis Protein degradation
General catabolic effect
(Thyroid Hormones Effects)
Cardiovascular?
Increase CO
Increase SV, HR
All by induce B1 adrenergic R in the heart (will increase sympathetic activity)
(Thyroid Hormones Effects)
Respiratory?
Rate and minute volume increases
Erythropoietin stimulated -> RBC synthesis increases
(Thyroid Hormones Effects)
Growth?
Thyroid hormones work with GH and Somatomedins to promote general growth
(Thyroid Hormones Effects)
CNS?
Myelination - childhood
Synapses formation - childhood
Cell migration - childhood
(Thyroid Hormones Effects)
Autonomic NS?
Induce expression of a and B adrenergic R
Structure of TSH
a subunit is non specific
B subunit is specific to TSH
How does TSH stimulate T3/T4 production?
- Increase NIS (I uptake, Iodination, TG endocytosis)
- mRNA synthesis for TPO, DUOX2, NIS
- Increase cell number and size (Goiterrr)
What will stimulate the Hypothalamus to secrete TRH
Increased food intake
Decreased temparture
What are the causes for Hypothyroidism?
Iodine deficiency
Genetic issues
Inflammation
Symptoms in infants of Hypothyroidism?
Cretinism (mental retardation, dwarfism, big tongue)
Symptoms in adults of Hypothyroidism?
- Myxoedema- proteoglycans and glycoproteins are high in CT (usually TH breaks them)
- Hoarse voice
- Dry skin
- Weight gain
- Sensitive to cold
- Slow speech
- Depression
What are the causes for Hyperthyroidism?
Increased TSH
TSH like antibodies (Graves disease)
Symptoms of Hyperthyroidism?
- Increased BMR
- Muscle weakness
- Anxiety
