MECHANISM OF HORMONE ACTION NEET

22.4 MECHANISM OF HORMONE ACTION NCERT, NEET/PMT

  • Hormones produce their effects on target tissues by binding to specific proteins called hormone receptors located in the target tissues only.
  • Hormone receptors present on the cell membrane of the target cells are called membrane-bound receptors and the receptors present inside the target cell are called intracellular receptors, mostly nuclear receptors (present in the nucleus).
  • Binding of a hormone to its receptor leads to the formation of a hormone-receptor complex 
  • Each receptor is specific to one hormone only and hence receptors are specific. 
  • Hormone-Receptor complex formation leads to certain biochemical changes in the target tissue. 
  • Target tissue metabolism and hence physiological functions are regulated by hormones. 
  • On the basis of their chemical nature, hormones can be divided into groups :
          
peptide
gastrin, secretin, cholecystokinin (CCK) and gastric inhibitory peptide (GIP), atrial natriuretic factor (ANF), insulin, glucagon
polypeptide, protein hormones
pituitary hormones, hypothalamic hormones
steroids
cortisol, testosterone, estradiol and progesterone
iodothyronines
thyroid hormones
 amino-acid derivatives 
Epinephrine, nor-epinephrine

  • Hormones which interact with membrane-bound receptors normally do not enter the target cell, but generate second messengers (e.g., cyclic AMP (Adenosine mono-phosphate), IP3 (inositol 1,4,5-trisphosphate) , Ca++ etc) which in turn regulate cellular metabolism 
       

  • Hormones which interact with intracellular receptors (e.g., steroid hormones, iodothyronines, etc.) mostly regulate gene expression or chromosome function by the interaction of hormone-receptor complex with the genome. 
  • Cumulative biochemical actions result in physiological and developmental effects.
         


On the above text and diagram try to answer the following questions-
1. how do a hormone produce its action?
2. what are receptors? what are they made up of? are they specific or non-specific? where do they present?
3. what are the different chemical nature of hormones?
4. make a list of hormone which can bind to intra-cellular receptor.
5. write down the flow of direction of hormone action from the above diagrams.
6. what kind hormone action is performed by idothyronine?

plz post your queries in case  of doubt--- 



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