Ch. 11 Endocrine pt. 3- Thyroid gland

all about thyroid gland & its hormones

Where is the thyroid gland located? How big is this gland?

below the larynx

-the largest of the pure endocrine glands

Why is T3 and T4 named the way they are? What type of cells secrete T3 & Thyroxin(T4)

T3→has 3 iodine atoms

T4→has 4 iodine atoms

-both secreted by follicular cells

Are T3 & T4 soluble in plasma? What receptors do they usually bind to?

NO because they are thyroid hormones & are amphipathic

-they bind to nuclear receptors to activate gene transcription but need membrane transporters

Which 3 plasma protein carriers do T3 & T4 need?

1) TBG
2) Transthyretin

3) Albumin

What are the 2 primary ingredients needed to create T3 and T4?

1) Iodide

2) Tyrosine

How is Iodide used to create the Thyroid hormones?

Iodide cotransported w/ Na+ →goes thru follicle cell→goes thru Pendrin into the colloid→Thyroid Peroxidase(TPO) oxidizes Iodide into Iodine→Iodine binds to tyrosine residues within the Thyroglobulin(TG)→T3 & T4 in the thyroglobulin are then endocytose→T3 and T4 released out cell

What is organification?

its when Iodine attaches to Tyrosines within Thyroglobulin

-1 iodine attachment=MIT

-2 iodine attachement=DIT

MIT+DIT=T3

2 DIT= T4

Metabolic Actions of Thyroid hormones

1) stimulate carb absorption from small intestine & increase fatty acid release from adipocytes

2) stimulate Na/P ATP-ases to increase metabolism+heat production

Permissive Actions of Thyroid hormones?

increase beta-adrenergic receptors= increases Catechalomines(Epinephrine & NE)

How do thyroid hormones contribute to growth and development?

1) T3 required for production of Growth Hormones

low T3=decreased growth in kids

2) T3 influence central nervous system during development

-underdeveloped CNS=retardness

3) T3 help preserve nerve/muscle reflex & alertness

Hypothyroidism: what is it caused by? Example? Symptoms? Treatment?

-caused by iodine deficiency or nonfunctional thyroid tissue

ex// Hashimoto’s thyroiditis(autoimmune)

Symptoms: weight gain, cold sensitivity, lethargy, mental fatigue

Treatment: Synthetic T4(Levothyroxine) →becomes T3 in body

Hyperthyroidism: what is it caused by? Example? Symptoms?

-caused by antibodies activating TSH receptors=increased T3/T4 OR thyroid nodules issue

Ex// Grave’s disease

Symptoms: weight loss, heat sensitivity, increased appetite, increase heart rate, tremors, nervousness

Treatment options for Hyperthyroidism?

1) inhibitor drugs

2) surgical removal of thyroid

3) destroy thyroid w/ radioactive iodine

4) beta blockers=decrease heart rate

Goiter

caused by iodine deficiency BUT Grave’s disease can also cause this