Thyroid t4,t3,tsh

1. THYROID T4,T3,TSH
OMAR ALJABRI

2. introduction
The thyroid hormones are tyrosine-based hormones produced by the
thyroid gland that are primarily responsible for regulation of metabolism

3. THYROID GLAND

4. Biosynthesis
Two biologically active thyroid hormones:
1)Tetraiodothyronine(T4 -thyroxine)
2)Triiodothyronine (T3)
Derived from modification of tyrosine
• Thyroglobulin
Pituitary produces Thyroid-
Stimulating Hormone -TSH-
which binds to follicle cell
receptors.
The follicle cells of the thyroid
produce thyroglobulin.

6. REGULATION
Thyroid hormones are lipid-soluble.
found in the circulation associated with
binding proteins:
1. Thyroid Hormone-Binding Globulin(70%)
2. Pre-albumin (transthyretin) (14%)
3. Albumin (~15%)
4. Less than 1% free
 Only free and albumin-bound thyroid
hormone is biologically available to
tissues.

7. Thyroid-Stimulating Hormone TSH
TSH is produced by the anterior pituitary.
TSH is a glycoprotein hormone composed of two subunits:
I. alpha subunit: (common to LH, FSH)
II. TSH beta subunit: which gives specificity of receptor binding and
biological activity.

8. ROLE AND REGULATION OF TSH
TSH acts on follicular cells of
thyroid.
1. Increases iodide transport into
follicular cells
2. Increases production of
thyroglobulin
3. Increases endocytosis of colloid
from lumen into follicular cells
Thyroid-Stimulating Hormone
release is influenced by:
1. hypothalamic TRH
2. thyroid hormones themselves.
Thyroid hormones exert
negative feedback on TSH
release at the level of the anterior
pituitary.
 inhibition of TSH synthesis
decrease in pituitary receptors for TRH

9. CONVERSION OF T4 TO T3
The thyroid secretes about 80mg of T4, but only 5mg of T3 per day.
T3 has much greater biological activity than T4.
A large amount of T4 (25%) is converted to T3 in peripheral tissues.
In addition to T3, an equal amount of “Reverse T3” also formed.
This conversion takes place mainly in the
liver and kidneys.

10. Normal values
Thyroid Test Reference Range
TSH 0.5-4.70 µIU/mL
Total T4 4.5-12.5 µg/dL
Free T4 0.8-1.8 ng/dL
Total T3 80 -200 ng/dL
Free T3 2.3- 4.2 pg/mL
RT3 10-24 ng/dL

11. Physiological and metabolic effect
A-Metabolism:
Thyroid hormones stimulate metabolic activities most tissues, leading to an increase in
basal metabolic rate. increase body heat production, increased oxygen consumption and
rates of ATP hydrolysis.
1. Lipid metabolism:
 Increased thyroid hormone stimulate fat mobilization.
 Enhance oxidation of fatty acids in many tissues.
 Plasma concentrations of cholesterol are inversely correlated with thyroid hormone levels - one
diagnostic indiction of hypothyroidism is increased blood cholesterol concentration.
2. Carbohydrate metabolism:
 Enhancement of insulin-dependent entry of glucose into cells
 Increased gluconeogenesis and glycogenolysis.

12. Physiological and metabolic effect
B-Growth&Development
Thyroid hormones necessary for normal growth in children as evidenced by the growth-
retardation observed in thyroid deficiency. Normal levels of thyroid hormone are essential to
the development of the fetal and neonatal brain.
Lack of thyroid hormone during development results in short stature and mental deficits
(cretinism).
C-Other Effects
• Cardiovascular system: Thyroid hormones increases heart rate, cardiac output. They also
promote vasodilation, which leads to enhanced blood flow to many organs.
• Central nervous system: Both decreased and increased concentrations of thyroid hormones
lead to alterations in mental state.
• Reproductive system:. Hypothyroidism in particular is commonly associated with infertility.

13. TSH FREE T4 FREE T3 PROBABLE INTERPRETATION
High Normal Normal Mild (subclinical) hypothyroidism
High Low Low Hypothyroidism
Low Normal Normal Mild (subclinical) hyperthyroidism
Low High High Hyperthyroidism
Normal High High Thyroid hormone resistance syndrome
(a mutation in the thyroid hormone receptor
decreases thyroid hormone function)

14. Symptoms of hypothyroidism& hyperthyroidism

16. disease related to thyroid hormone
THYROID GOITER
A goiter is an abnormal enlargement of
thyroid gland.
The most common cause of goiters
worldwide is a lack of iodine.
1. During iodine deficiency, thyroid hormone
production decreases.
2. This results in increased TSH release.
3. TSH acts on thyroid, increasing blood flow, and
stimulating follicular cells and increasing colloid
production. then thyroid gland enlarges.

17. disease related to thyroid hormone
GRAVES' DISEASE
is an autoimmune disorder in which
antibodies against the TSH receptor
act to stimulate the thyroid in the
absence of TSH. (hyperthyroidism)
HASHIMOTO’S THYROIDITIS
 is an autoimmune disease in which the
thyroid gland is attacked by a variety
of cell- and antibody-mediated
immune processes, causing primary
(hypothyroidism)
 This form of thyroid disease may also
be referred to as chronic lymphocytic
thyroiditis .