Transcript The Thyroid - Metabolism

A BRIEF OVERVIEW OF THE
THYROID GLAND
By April Stoll
Anatomy of the Thyroid Gland
Thyroid Basics:
The main function of the
thyroid is to control the
body’s metabolism
Its sole function is to make
thyroid hormone
This hormone has an effect
on nearly all tissues of the
body where it increases
cellular activity
The Thyroid Produces and
Secretes 2 Metabolic Hormones
 The two principal hormones are:
Thyroxine (T4 ) and triiodothyronine (T3)
Required for homeostasis of all cells
Influence cell differentiation, growth, and
metabolism
Stimulate protein production in the body’s tissues
T4 is the most abundantly secreted, but T3 is
considerably more active
Considered the major metabolic hormones
because they target virtually every tissue
Thyroid Hormones Stimulate
Metabolic Activities in Most Tissues
Regulate the rate of overall body
metabolism (specifically T3)
T3 increases basal metabolic rate
Increases body heat production
Calorigenic effects
T3 increases oxygen consumption by most
peripheral tissues
The Chemistry of Thyroid
Hormones:
Thyroid hormones are derivatives of the amino
acid Tyrosine bound covalently to iodine
These hormones are basically two tyrosine's
linked together with the critical addition of iodine
at the three of four positions on the aromatic
rings
T4/T3 Conversion Sites
The liver is the major
extrathyroidal T4 conversion site
for production of T3
Some T4 to T3 conversion also
occurs in the kidney and other
tissues
Thyroid-Stimulating Hormone
(TSH)
 Also known as Thyrotropin
 Is secreted from cells, called thyrotrophs, in
the anterior pituitary, which in turn is
controlled by the hypothalamus
 Is the major regulator of the thyroid gland
 It Regulates thyroid hormone production,
secretion, and growth
 Is regulated by the negative feedback
action of T4 and T3
 Its synthesis and release is stimulated by
thyroid-releasing hormone (TRH)
TSH-cAMP
Thyroid-Stimulating Hormone-cyclic Adenosine
Monophosphate (cAMP)
Is the prime regulator of iodide uptake and
concentration
T3/T4 formation
Induces the expression and activation of the 3
necessary genes that encode proteins involved
in iodide uptake and thyroid hormone formation
Sodium-iodide symporter (NIS)
Thyroglobulin (Tg)
Thyroperoxidase (TPO)
Thyroid-Releasing Hormone (TRH)
Is secreted by hypothalamic neurons
Is only a tripeptide, with the basic
sequence of amino acids being
glutamic acid-histidine-proline
Is inhibited by high blood levels of
thyroid hormones in the negative
feedback loop
Is the major positive regulator of
TSH secretions
Hypothalamic-Pituitary-Thyroid Axis
Negative Feedback Mechanism
Thyroid Disorders
 Hypothyroidism
 Two common examples are:
 Iodine deficiency
 Primary thyroid disease
 Symptoms include:
 Lethargy
 Fatigue
 Cold-intolerance
 Weakness
 Hair loss
 Reproductive failure
 Hyperthyroidism
 The most common form
is Graves Disease
 Is less common than
Hypothyroidism
 Symptoms include:
 Nervousness
 insomnia
 high heart rate
 eye disease
 anxiety
http://www.methodisthealth.com/endocrin/thygland.htm
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