HORMONES ; are organic substances and protein in nature, that role in regulating physiological activities and maintenance of homeostasis, Hormones perform their function by evoking response from specific organ or tissue that are adapted to react minute quantities of them.
General characteristics of hormone
Not secreted at uniform rate .Exert their effects in biocatalytic amonuts.
Turnover is varied and usually rapid.
Exert multiple actions.
Exhibit high degree of specifity.
Different tissue may response diiferently to a given hormone .MECHANISM OF HORMONE ACTION
The hormone fall into two catagories ,based on their solubility into water .
Hydrophilic (water soluble hormone ) ;they are simply dissolved in blood.
For example :catecholamine (epinephrine or nor epinephrine) and peptide /protein hormones.
Lipophilic (they are poorly soluble in water ) so they cannot be dissolved in water blood. They bind to plasma protein and present in the blood in protein bound form. They are lipid soluble .
For example : the lipid soluble hormones include thyroid hormones, steroid hormone and vitamin D3 .
GENERAL PRINCIPLE OF HORMONE ACTIONS
A hormone that has its primarily function the regulation of hormone secretion by another endocrine gland
When different hormones work togather and have greater effect than individual hormone action .Permissiveness
A small amount of one hormone allow second hormone to have its full effect on a target cell i-e first hormone permit effect of second hormone.
One hormone produce the opposite effect of other .The processes involve in both positive and negative feedback mechanism.
CLASSIFICATION BASED ON MECHANISM OF ACTION
GROUP 1 ; Bind to intracellular receptor.
GROUP2 ; Bind to cell surface receptor
A- second messenger cAMP,ADH,ACTH ,FSH,LH and PTH
B- GMP as second messenger . ANF( atrial natrieuretic factor) , NO(nitric oxide)
C- calcium /phosphatadyl inositol as second messenger GnRH ,TRH ,PDGF substance
D- second messenger is kinase /phosphatase cascade.
Insulin , GH, Prolactin , insulin like growth factors . (IGF-1, IGF-2)
Signal amplification by 2nd messenger RNA
Initial signal is in the form of hormone which act as ligand whose concentration is just one per recceptor . the hormonal response has got multiple steps and each steps multiplies the signal (cascading effect )that finally leading to million fold of amplification ,i-e one hormone molecule mediated its effect through million of molecules .
This process is known as signal amplification .
Mode of hormone action
Synthesis of new molecule .Changing cell permeability .Lipid-soluble hormones involved in mobile receptor hypothesis .
Where as ,water soluble hormones involved in 2nd messenger mechanism .
Types of receptor
Receptor may be
External; in case of external there is involvment of cell membrane .
Internal ; in this case it may be nuclear or cytoplasmic.
Those receptors which occupies the place in the cell membrane or on the surface of cell membrane .Types
Ion channel linked receptor
G-protein coupled receptor
Enzyme linked receptor
for example protein ,peptide and catecholamine .
Those receptors which exist in cell cytoplasm .For example
Receptor present in the nucleus and there is direct association with one or more chromosomes .For example
Thyroid hormone and retinoid hormone
Impact of presence and absence of hormones in the body
There are many benefits of hormones existence in our body .Maintenance of homeostasis
Secretion of useful product in different circumstances for proper and healthy physioleogical activities .
There are many process which are controlled by hormones like growth controlled by growth hormone .Hunger and thirst also controlled by hormones.
Almost whole reproductive cycle is under the influence of multiple hormones ,wether peptid or steroid .
There are some harmful effect or disorders that emerge or caused due to less hormonal production or totally absence of hormones .;
If there is no secretion of TRH, then there is no production of T3 and T4 , consequently homeostasis is not regulated .
Similarly in reproduction ,if Astrogen or Androgen are not released then secondary sexual characteristics are not developed in the body .
Hormonal balance is very important for proper functioning because hormonal imbalance cause many diseases .
There is another factor that is imp for proper function of example of epinephrine and nor epinephrine which act under fight and flight situation , normally under stress condition it increase the level of glucose in blood ,now if this stress condition is too prolonged then continuously glucose level increases in the blood and unfortunately sufferers becomes diabetic patient . this abnormality in hormones
Hormones are blessing for our body that regulate our homeostasis , mood swings ,growth and development ,physiological as well as reproductive cyclicty.