Differences between hypothyroidism and hyperthyroidism

Hypothyroidism

Hypothyroidism

Hypothyroidism is due to reduce hormone secretion by the thyroid gland for a prolonged time. Hypothyroidism is derived from the Greek words’ hypo-reduced, thyreos-shield, and eidos-‘form.’

Hypothyroidism is characterized by an increased level of TSH and the average level of T3 and T4. Subclinical hypothyroidism is more common than hypothyroidism.

Incidence of Hypothyroidism

About one billion people are suffering from iodine deficiency. But the incidence of hypothyroidism is not known.

Hypothyroidism occurs more in females than males.

People above 60 yrs are more commonly affected.

Causes

1. In developing countries, this is due to iodine deficiency.

2. In developed countries, hypothyreosis is due to the autoimmune disease Hashimoto’s thyroiditis.

3. Thyroid surgery

4. Radioactive iodine therapy

5. Congenital

6. Injury or diseases of the hypothalamus

7. Injury or diseases of the anterior lobe of the pituitary.

Types

The hypothalamo-pituitary-thyroid axis is responsible for the proper secretion of the thyroid hormones.

1. Primary hypothyroidism –The thyroid gland is not secreting hormones despite stimulation from ‘thyroid-stimulating hormone.’ This is the most typical type of hypothyroidism. Iodine deficiency is the commonest cause of primary hypothyroidism. Iodine deficiency is worldwide.

Thyroiditis of various causes, radioiodine treatment, thyroid surgery, thyroid dysgenesis.

2. Secondary hypothyroidism –The pituitary gland is not secreting ‘thyroid-stimulating hormone’ in an adequate amount. The causes are – pituitary adenoma, pituitary apoplexy, Sheehan syndrome, and subarachnoid hemorrhage.

3. Tertiary hypothyroidism: The hypothalamus does not secrete thyrotropin-releasing hormones in adequate amounts. This is an infrequent cause of hypothyroidism.

[Central hypothyroidism= Secondary hypothyroidism + Tertiary hypothyroidism]

https://blog.totalphysiology.com/2022/04/hypothyroidism-new-approach.html

Hyperthyroidism

Increased secretion by the thyroid gland increases levels of ‘tri-iodo-thyronine’ T3 and ‘tetra-iodo-thyronine’ T4 in circulation. The high levels of the hormones cause hyperthyroidism.

When thyroid gland secretion increases due to autoimmunity, it is known as thyrotoxicosis or exophthalmic goiter.

Thyrotoxicosis is an auto-immune disorder in which ‘Thyroid stimulation antibodies ‘are formed by plasma cells after activation by antigens.

Thyroid stimulation antibodies (TSA), Long-acting thyroid stimulator( LATS), or Thyroid stimulating immunoglobins (TSI) are formed. It acts like normal TSH. The Long-acting thyroid stimulator or thyroid stimulation antibody (LATS, TSA) is IgG.

LATS protectors are produced, which protect the inactivation of LATS, so LATS functions are prolonged.

Mechanism of action:

LATS binds with TSH receptors present on the cell membrane of the thyroid cells by displacing the TSH. After combining with the receptor stimulates adenyl cyclase through Gs to form cyclic adenyl cyclase and activates Phosphorylase C like TSH. The cyclic adenyl cyclase activated Phosphorylase C performs many functions.

1. Increase T3 and T4 secretion by increasing iodide (I- ) trapping and transport mechanism.

2. Binding of iodide (I- ) to tyrosine.

3. Increase thyroglobulin synthesis in the colloid. The colloid iodide (I- ) gets oxidized immediately by ‘thyroid peroxidase’ into Iodine. First, Iodine binds to the third position of tyrosine to form ‘mono-iodo- tyrosine( MIT ), and in the next step, ‘mono-iodo- tyrosine( MIT )’ is iodinated at the fifth position to form ‘di-iodo- tyrosine( DIT ).’

https://blog.totalphysiology.com/2022/04/hyperthyroidism-thyrotoxicosis-new.html

Differences between hypothyroidism and hyperthyroidism

polymenorrhea. Loss of libido in males and decreased libido in females.	Hypothyroidism	Hyperthyroidism
1.	Lassitude, undue fatigue, increased appetite but weight loss, diarrhea, hyperexcitable, hyperactive.weakness, nervousness, inability to sleep.	Lassitude, undue fatigue, weight gain, Decreased BMR, very sluggishness, muscular and mental sluggishness.
2.	Heat intolerance	Cold intolerance.
3.	Sweating increased, warm moist skin	Sweating decreased, dry skin, hair loss,
4.	Mild diarrhea	Constipation
5.	The reaction time of knee jerk decreased (normal is 20 seconds)	Delayed relaxation of ankle jerk.
6.	Increased heart rate, increased cardiac output	decreased heart rate decreased cardiac output
7.	Oligomenorrhea	polymenorrhea. loss of libido in males and decreased libido in females.
8.	Exophthalmos may develop	Myxedema may develop.