Download thyroid gland

Endocrinology
• Introduction
• Dynamic function tests
• Hypothalamus and pituitary function
tests
• Adrenal function
• Thyroid function tests
• Other glands.
Thyroid gland
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Physiology of the thyroid gland.
T3 and T4.
Control of the thyroid gland.
Tests for thyroid function.
Hypothyroidism.
Hyperthyroidism.
Case 1
• Investigations of 63-year-old woman with effort angina
revealed a serum TSH of 96 mU/L and a serum free T4 of 3.7
pmol/L. An ECG showed some evidence of ischemia but was
not diagnostic of myocardial infarction. Further biological
investigations revealed:
Cholesterol
360 mmol/L less than 190
Creatinine kinase 290 U/L
less than 150
AST
35 U/L
12-48
1. How would theses results interpreted?
2. What is the importance of knowing about myocardial
ischemia?
Thyroid gland
• The thyroid gland is found in front of the
trachea.
• The thyroid gland secretes three
hormones: thyroxin (T4) and
triiodothyronine (T3), both of which are
iodinated derivatives of the amino acid
tyrosine, and calcitonine.
• T4 is ten time more than T3, most T3
(approximately 80%) being derived
from T4 by deiodination in peripheral
tissues, particularly the liver, kidneys
and muscle.
• T3 is more potent than T4.
Iodide
Control Of thyroid hormone
• The thyroid gland is under the control of the pituitary gland.
• When the level of thyroid hormones (T3 & T4) drops too
low, the pituitary gland produces Thyroid Stimulating
Hormone (TSH) which stimulates the thyroid gland to
produce more hormones.
• Under the influence of TSH, the thyroid will manufacture
and secrete T3 and T4 thereby raising their blood levels.
The pituitary senses this and responds by decreasing its
TSH production.
• The pituitary gland is regulated by the hypothalamus.
The hypothalamus produces TSH Releasing Hormone
(TRH) which stimulates the pituitary gland to releaseTSH
• Condition that increase ATP demand (cold environment,
pregnancy, hypoglycemia) increase the secretion of
thyroid hormones.
1. Thyroid hormones increase basal metabolic rate by
stimulating the use of cellular oxygen to produce ATP,
thus increase cellular metabolism of carbohydrate,
lipids and protein.
2. Stimulate the synthesis of additional Na+/K+ ATPase
which use large amount of ATP, more heat is given
off and lead to increase body temperature (calorigenic
effect) thus thyroid gland play major rule in
maintenance of normal body temperature.
3. Stimulate protein synthesis and increase the use of
glucose and fatty acid for ATP production, they
also increase lipolysis and enhance cholesterol
excretion thus reducing cholesterol level.
4. Enhance some action of the catecholamine (EP,
NE) because they upregulate β receptors for this
reason symptoms of hyperthyroidism include
increase heart rate and increased blood pressure.
5. With growth hormone and insulin, thyroid hormone
accelerates body growth (nervous and skeletal
system), deficiency of thyroid hormone during fetal
development or childhood causes severe mental
retardation.
Test Of thyroid function
1. Total thyroxin and triiodothyronine
 Measurement of plasma tT4 and tT3
concentration.
 Major disadvantage in that it is dependent on
binding protein concentration (TBG) as well
as thyroid activity (increase tT3 and tT4
compatible with hyperthyroidism can occur
with normal thyroid function if there is
increase in binding protein concentration).
2. Free thyroxin and triiodothyronine:
• Various techniques have been developed which
allow the estimation of fT4 and fT3
concentrations in plasma.
• Naturally occurring antibodies to thyroid
hormones are some times present in plasma and
give high result, measurement of TSH solve the
problem.
3. Thyroid-stimulating hormone (TSH)
4. TRH
5. Thyroid scan
Isotope Scan
Normal
Abnormal
Thyroid scan
A dose of isotope is given
and its distribution within
the thyroid is determined
using a gamma camera.
This technique allows the
identification of “hot,
active” or “cold, inactive”
nodules in a patient with
lumps in the thyroid gland
“malignant disease”.
Hypothyroidism and Hyperthyroidism
www.thyroid-disease.org.uk
Hyperthyroidism
Hypothyroidism
Too much thyroid hormone
Too little thyroid hormone
Metabolism speeds up
Metabolism slows down
Hypothyroidism
• Hypothyroidism: Underactive thyroid
glands which leads to decrease in the
thyroid hormone production.
• Incidence in ♀ > ♂ by 3x.
• Incidence increased with age (> 60
years).
• Hypothyroidism usually develops slowly.
• Types:
– Primary Hypothyroidism (more common).
– Secondary Hypothyroidism (uncommon, with
other pituitary insufficiency symptoms).
J. Dipiro, R. Talbert, et al. (2008),
Causes of hypothyroidism
• 90% of cases:
– Autoimmune destruction of the
thyroid gland (Hashimoto’s disease).
– Radiation or surgical treatment of
hyperthyroidism (Iatrogenic
hypothyroidism).
Causes of hypothyroidism
• Rare cases:
1. Drugs induced: e.g. amiodarone.
2. TSH deficiency such in case of hypopituitarism.
3. Congenital defects such as blocks in the
synthesis of T4 and T3 , end organ resistance to
their action or even borne without a gland or
with a part of gland (1:4000).
4. Severe iodine deficiency: daily requirement of
Iodide is 75mcg which found in 10gm of
ionized salt (one teaspoon).
Clinical presentation of hypothyroidism
1. General:
• Adults: varied & nonspecific symptoms
(So need for lab analysis of TSH, T4
&T3 for confirmation).
• Children (called Cretinism): failure to
thrive.
Clinical presentation of hypothyroidism
2. Symptoms:
• Dry skin.
• Cold intolerance (always feeling colder than
others).
• Weight gain (despite loss of appetite).
• Constipation.
• Weakness.
• Lethargy.
• Fatigue.
Clinical presentation of hypothyroidism
3. Signs:
• Coarse hair/dry skin.
• Peri-orbital puffiness→
• Slow Relaxing Reflex.
• Bradycardia.
• Slow hoarse speech.
Signs and symptoms of hypothyroidism
Tiredness
Puffy Eyes
Forgetfulness/Slower Thinking
Moodiness/ Irritability
Depression
Hoarseness/
Deepening of Voice
Persistent Dry or Sore Throat
Inability to Concentrate
Difficulty Swallowing
Thinning Hair or Hair Loss
Loss of Body Hair
Dry, Patchy Skin
Weight Gain
Slower Heartbeat
Menstrual Irregularities/
Heavy Period
Infertility
Cold Intolerance
Constipation
Elevated Cholesterol
Muscle Weakness or Cramps
Diagnosing hypothyroidism
• Primary hypothyroidism:
1.↑ TSH.
2.↓ (Free ± Total T4 & T3).
3.Thyrotropin receptor antibodies (Hashimoto).
• Secondary hypothyroidism:
1.Normal or ↓ TSH.
2.↓ (Free ± Total T4 & T3).
Hyperthyroidism
• Excess thyroid hormone from over-activity of
thyroid gland, appeared with symptoms.
• Causes of Hyperthyroidism:
1. Grave’s disease (most common).
2. Thyroiditis.
3. Drug induced: Iodine toxicity, Amiodarone
and L-thyroxine overdose.
4. Pituitary-hypothalamus origin (adenomas).
Clinical presentation of hyperthyroidism
1. Symptoms:
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Nervousness.
Anxiety.
Palpitations
Easy fatigability.
Menstrual disturbances.
Heat intolerance.
Loss of weight despite increased appetite.
2. Signs:
• Warm, smooth and moist skin.
• Exophthalmos →
• Unusually fine hair.
• Separation of the end
of the fingernails
from the nail beds.
2.
Signs:
• Retraction of the eyelids and lagging of the upper
lid behind the globe when the patient looks
downward (Lid Lag)→
• Tachycardia at rest.
• Rapid pulse.
• Arrhythmia such as atrial fibrillation (specially in
elders).
Signs and symptoms of hyperthyroidism
Nervousness
Irritability
Difficulty Sleeping
Bulging Eyes/Unblinking Stare
Hoarseness or
Deepening of Voice
Persistent
Sore or Dry Throat
Difficulty Swallowing
Rapid or Irregular Heartbeat
Infertility
Menstrual Irregularities or
Weight Loss
Light Period
Heat Intolerance
Frequent Bowel Movements
Warm, Moist Palms
Excessive Vomiting in Pregnancy
Increased Sweating
First-Trimester Miscarriage
Family History of
Thyroid Disease
or Diabetes
Diagnosis of hyperthyroidism
1. Physical examination:
• Enlargement thyroid gland.
• Rapid pulse.
• Look for moist and smooth skin.
• Tremor of finger trips.
• Fast relaxing reflex →
Diagnosis of hyperthyroidism
2. Lab data:
• ↓ TSH.
• ↑ Free ± total T3 & T4.
• Thyroid stimulating antibodies
(Grave’s).
• Thyroid biopsy.
Diagnosis of hyperthyroidism
3. ↑ Radioactive Iodine Uptake (RAIU):
• True Hyperthyroidism.
• Thyroid gland actively overproducing T3 ±
T4.
4. ↓ Radioactive Iodine Uptake (RAIU):
• Indicate that high levels of thyroid hormone
are not a consequence of thyroid gland
hyperfunction but by thyroiditis or hormone
ingestion (toxicity).
Hyperthyroidism treatment
• Non-pharmacological:
– Surgery.
• Pharmacological:
– Anti-thyroid drugs.
– Radioactive Iodine (RAI).
Calcitonin
• A thyroid hormone.
• Produced by C-cells.
• Physiological effects are
opposite to those of
PTH, lowers plasma Ca.
• Rapid acting, short term
regulator of plasma Ca
levels.
• Stimulates osteoblasts, inhibits osteoclasts which causes
removal of Ca from plasma to calcify new bone.
• Minor role in adult due to PTH feedback, major role in
children due to the rapid nature of bone remodeling and
its effect on osteoclastic activity.
The End