Thyroid Hormone - Biology notes - Physiology Notes

 Thyroid Gland:

Thyroid Gland is present in front of the larynx. It has two lobes and one is isthmus.

Thyroid gland is made up of many follicles. Follicles are filled with Colloid

They are lined by cuboidal epithelial cells, which secrete into the interior of the follicle.

Colloid contains thyroglobulin, a glycoprotein its main function is to collect iodine from blood and transport it into the colloid for hormone synthesis. Synthesized villains.

To synthesize thyroglobulin.

Removal of thyroid hormone from thyroglobulin and then to secrete them into blood.

Thyroid gland secretes three hormones: Thyroxine T4,Triiodothyronine T3 and Calcitonin.

T3 and T4 synthesized by follicular cells.Calcitonin is synthesized by parafollicular cells.

Function of thyroid hormones.

  1. Effect on growth.

Thyroid hormone are important for growth and skeletal maturity, its action is important in growing children. It promotes the growth and development of the brain during fetal life and first few years. It helps in tissue differentiation and maturation (Thyroid hormones muscle, bones aur brain ke development ke liye important hai).

  1. Effect of carbohydrate metabolism.

Carbohydrate ke metabolism ko badhata hai thyroid hormone. Yad rakhen Ek Bhukha hormone hai Jo Har chij ko Khata rahata Hai Har energy source ko khata hai.

  1. Rapid uptake of glucose by cells (cells Jyada energy use karte hain Jiske vajah se glucose cell ke andar jaldi ghus jaege).

  2. increase glycolysis

(Glycolysis  se cells mein energy production Hoti Hai Jiski vajah se yah usko badhata hai).

  1. increases gluconeogenesis (gluconeogenesis matlab naya glucose Banna non carbohydrate source se jaise Pyruvate, Lactate aur Amino acids aur enzymes ki activity ki badha deta hai).

  2. Increases absorption of Carbohydrates from GIT (carbohydrates ki absorption GIT se badh jata hai kyunki use energy zyada chahie). 

  3. Increase insulin secretion: insulin action badne ki wajah se carbohydrates ko Cells ke andar dalta hai Jaise muscle cells, fat cells aur liver.

3.  Effect on fat metabolism: it increases fat metabolism, it decreases fat stores. Lipids are removed from fatty tissues. It increases fatty acid levels in plasma and increases breakdown of free fatty acids by cells (Jaise Humne pahle Pada ki yah Bhukha hormone Hai To yah fatty tissues se fat ko nikalega aur use fat ko blood Mein Dal dega free fatty acid ke form mein phir Inka free fatty acid ka concentration blood Mein badhane lagega aur free fatty acid cell Mein Jaenge aur use Honge energy keliye). 

  • It decreases cholesterol phospholipid and triglyceride levels in plasma.

4. Protein metabolism:

  • Normally as a physiological action it has an anabolic effect where it increases protein synthesis, (thyroid hormone ka positive nitrogen balance rahata hai, matlab yah proteins ko banayega muscle mass ko stimulate Karega aur banne mein).

  •  Pharmacological doses has a catabolic action It utilizes protein for energy. hence decreasing muscle mass due to increase in basal metabolic rate or BMR

(Thyroid hormone energy ke liye proteins ko bhi use kar sakta hai, agar Thyroid hormones ki matra badh jayegi to muscle mass ko kam kar deta hai).

5. Metabolic action on vitamins:

  • It increases the reabsorption of vitamins as they act as enzymes for various reactions. (body ki energy requirement or enzyme requirement badhane ki vajah se yah vitamins quamate bhi badh Jaati Hai).

6.  Metabolic rate: Thyroid hormones increase our metabolic rate in almost all the cells of our body. They have a calorigenic and thermogenic action with increased consumption of oxygen hence increase in BMR.( Thyroid hormone accelerator Ki Tarah hai, Jab accelerator dubbta hai phir car ya machine teji se bhagata hai ya kam karti hai. Aur Jyada energy petrol ko use Karti hai,yahan per thyroid hormone body ki Raftar ko Badha deta Hai Jiski vajah se energy jyada use hogi energy ke sath oxygen use hoga aur sath mein garmi Paida karega).i

7. Body weight: thyroid hormones always decrease body weight and increase appetite

8. Cardiovascular system:

  • Increase in utilisation of oxygen, increase in activity of heart leads to increase in cardiac output. Increase in stroke volume and blood flow to heart (Heart ki Jyada kam karne ki vajah Se usmein Jyada blood flow Hoti Hai sath mein heart Jyada kam Karta Hai Jiski vajah se uski cardiac output badh jati Hai aur stroke volume badh jata hai).

  • It increases the force of contraction of heart.

  • There is an increase in systolic blood pressure but diastolic blood pressure decreases.

(Cardiac output aur stroke volume ke badhne ki vajah se systolic blood pressure badh Jata Hai Kyunki systolic blood pressure cardiac output per depend karta hai. Diastolic blood pressure isliye kam hota hai Kyunki peripheral vessels jo Dur ki Blood vessels hain jaise arterioles, metaarterioles relax ho jati hai Jiski vajah se Unka pressure kam ho jata hai.

10. Gastrointestinal System:

  • Increase in activity of GIT leads to increase in appetite and thirst.

  • Increase in secretion of digestive juices, increase motility of GIT.

(Yahan per patient ko Jyada Bhookh Lagi Jyada Pyas Lagegi, juices Jaise gastric juice, pancreatic juice Inki secretion badh Jayegi, GIT ki contraction bhi badh Jayegi).

11. Respiration: 

increase in rate and depth of respiration


(body ki oxygen ki requirement badhane ki vajah se metabolism badhane ke jaise oxygen ki demand bhi pad Jaati Hai Jiski vajah se respiration activity increase ho jayegi)

12.  Reproductive system:

It affects spermatogenesis in males and menstrual cycle in females

(thyroid hormone males mein spermatogenesis ko maintain karta hai, spermatogonia se mature sperm banne ki process Mein important hai aur sath mein female mein menstrual cycle Mein important hai). 

13. Kidneys

it increases renal blood flow increases glomerular filtration rate increases reabsorption of substances

14. CNS

  • Thyroid hormone important for normal development and maintaining normal activity of central nervous system. It maintains the rate of conduction of impulse in nerve fibres.

  • Thyroid hormone deficiency after birth upto the age of 2 years can lead to defective myelination of axons of Brain.

  • Decrease in branching and development of dendrites of neurons leading to abnormal or less synapse.

  • Decrease in blood supply to brain.


(Thyroid hormone brain or central nervous system ki development ke liye important hai bacche ke Paida hone se lekar do Sal Tak Inki kamiyon ke hone ke vaje se axon ki myelination kharab ho Jaati Hai. Dendrites ka divide Hona branching kam ho jata hai aur neurones ke sath synapse kum ho jata hai Sath hi brain ki blood supply kam ho sakti hai isliye yah brain ke intellectual activities, Memory, activeness etc ke liye important Ban jaati hai).

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