Week 2 Flashcards
THYROID + sole function
is the biggest gland in the neck. It is
situated in the anterior (front) neck
below the skin and muscle layers.
gland takes the shape of a butterfly with
the two wings being represented by the
left and right thyroid lobes which wrap
around the trachea.
sole function of the thyroid is to make
thyroid hormone. The function of the
thyroid therefore is to regulate the
body’s metabolism.
function of the thyroid gland
The function of the thyroid gland is to take
iodine, found in many foods, and convert it
into thyroid hormones: thyroxine (T4) and
triiodothyronine (T3).
These cells combine iodine and the amino
acid tyrosine to make T3 and T4. T3 and
T4 are then released into the blood stream
and are transported throughout the body
where they control metabolism (conversion
of oxygen and calories to energy).
Metabolic Function (Thyroid)
Energy metabolism – Oxygen/Heat
Carbohydrate metabolism
Protein metabolism
Lipid Metabolism
Cardiovascular- increases heart rate,
output, systolic volume and
contractility
Beta adrenergic effects
Bone growth
GI tract motility
Erythropoietin production
Receptors related to the Thyroid hormone
The thyrotropin (TSH) receptor
plays a preeminent role in thyroid
physiology.
TSH, acting through the TSH
receptor, is the major stimulator of
thyroid cell growth, differentiation
and function.
Thyroid hormone receptors (TRs)
are members of the nuclear
receptor superfamily that exhibit a
dual role as activators or
repressors of gene transcription in
response to thyroid hormone (T3).
Receptor isoforms
Modulate various physiological
functions in many organ systems.
The TRα and TRβ isoforms and
TRα1 and TRβ1 isoforms.
Have genomic or non-genomic
effects
Genomic signaling pathway
directly influences
gene transcription and translation
Non-genomic pathway involves
more rapid, cellular changes,
some of which also regulate gene
expression through more indirect
signaling.
What are the key players for
Thyroid hormone regulation?
Hypothalamus: Thyrotropin-
releasing hormone (TRH)
control of thyroid stimulating
hormone (TSH)
Pituitary: Thyroid stimulating
hormone (TSH)
controls production of the thyroid
hormones by binding to TSH
receptors located on cells in the
thyroid gland.
Thyroid: triiodothyronine (T3) and
thyroxine (T4)
Binding proteins
The major serum thyroid hormone-
binding proteins are:
-Thyroxine-binding globulin [TBG
or thyropexin],
binds thyroid hormones in
circulation
Transthyretin
a transport protein in the
serum and cerebrospinal fluid
that carries the thyroid
hormone thyroxine (T4)
Albumin (HAS, human serum
albumin)
CONTROL AND REGULATION
Is under the control of the pituitary gland, a
small gland the size of a peanut at the base of
the brain.
When the level of thyroid hormones (T3 & T4)
drops too low, the hypothalamus is part of the
brain and produces TSH Releasing Hormone
(TRH) which tells the pituitary gland to
stimulate the thyroid gland (release TSH).
The pituitary gland produces Thyroid
Stimulating Hormone (TSH) which stimulates
the thyroid gland by binding to the TSH
receptors to produce more hormones.
The pituitary senses this and responds by
decreasing its TSH production.
Thyroid Autoantibodies
Thyroid peroxidase antibodies
(TPO). These antibodies can be a sign of:
Hashimoto disease, also known as
Hashimoto thyroiditis.
This is an autoimmune disease and
the most common cause
of hypothyroidism. Hypothyroidism is
a condition in which the thyroid
doesn’t make enough thyroid
hormones.
Graves’ disease.
This is also an autoimmune disease
and the most common cause
of hyperthyroidism. Hyperthyroidism
is a condition in which the thyroid
makes too much of certain thyroid
hormones.
Thyroglobulin antibodies (Tg).
These antibodies can also be a sign of
Hashimoto disease. Most people with
Hashimoto disease have high levels of
both Tg and TPO antibodies.
Thyroid-stimulating hormone
(TSH) receptor.
These antibodies can be a sign of
Grave’s disease.
Common Thyroid Problems
- Those concerning the production
of hormone (too much, or too
little), - Those due to increased growth
of the thyroid causing
compression of important neck
structures or simply appearing
as a mass in the neck, - The formation of nodules or
lumps within the thyroid which
are worrisome for the presence
of thyroid cancer, and - Those which are cancerous.
Laboratory Diagnosis
Measurement of serum thyroid-stimulating
hormone (TSH): Measuring serum TSH is
the best way to determine thyroid dysfunction
Direct measurement of free T4 and T3:
Since free thyroid hormones are
available to peripheral tissues, directly
measuring serum free hormones avoids
the pitfalls of interpreting total levels,
which are influenced by the level of the
binding proteins. Thus, serum free
levels more accurately diagnose true
thyroid function.
Measurement of thyroid
autoantibodies:
Autoantibodies to thyroid
peroxidase and, less commonly, to
thyroglobulin are present in almost
all patient’s thyroid autoimmune
disease,
Thyroid peroxidase autoantibodies
are usually detected in patients with
Graves’ disease.
Both these antibodies are
commonly measured by enzyme
immunoassays
Measurement of thyroglobulin:
The principle use of serum
thyroglobulin is mostly used as a
tumour marker test to help guide
thyroid cancer treatment
Hypothyroidism types
There are 3 types of hypothyroidism:
Primary hypothyroidism – when your
thyroid gland becomes diseased and
cannot produce sufficient hormones
Subclinical hypothyroidism- early and mild
form of hypothyroidism
Secondary hypothyroidism – when your
pituitary gland isn’t stimulating your
thyroid to produce enough hormones.
Etiology PRIMARY HYPOTHYROIDISM
Hashimoto’s thyroiditis-most common (most common)
Iodine deficiency
Drug therapy
Signs and Symptoms hypothyroidism
Non-specific.
May be confused with other
conditions especially in postpartum
depression and elderly.
Fatigue.
Increased sensitivity to cold.
Constipation.
Dry skin.
Weight gain.
Puffy face.
Hoarseness.
Muscle weakness.
Auto antibodies in hypothyroidism
Autoantibodies:
Thyroid autoantibodies
are antibodies that develop when a
person’s immune system mistakenly
targets components of the thyroid gland
or thyroid proteins, leading
to chronic inflammation of the thyroid
Anti thyroid peroxidase [anti
microsomal] antibodies
Anti thyroglobulin antibodies.
Anti bodies against T3 and T4 in
auto immune hypothyroid disease.
