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1. MSCDFSM
BIOCHEMISTRY
HORMONES

2. THE ENDOCRINE SYSTEM : It is composed of the endocrine gland whose secreation pass directly into blood
stream ,the secreation is called hormone. .
HORMONE : it is substance that is synthesized in one organ and transported to circulatory system to act on other
tissue.since hormones carry signals or messeges ,they are also called messangers or specifically first messangers .
REGULATION OF ENDOCRINE SYSTEM :
1. The regulation originates in blood /central nervous system .it receives inputs for many internal and external
sensation like hunger , danger ,dietary intake etc .this is called hormonal cascade system that shows chain of
command in hormonal signaling hirerarchy .
2. The signal first originates in external environment and transmitted aselectric pulse to hypothalamus..then
hypothalamus release hormone in nanogram .the reeasing hormone is carried by blood to anterior pituitary .this
is the first target .
3. Anterior pituitary secrete tropic hormone or tropin in microgram ,this is then carried out to endocrine gland to
get stimulated .
4. Now endocrine gland synthesize its specific hormone in mg .then this hormone travel to targets tissue through
blood.
5. So the starting point is hypothalamus and ending is target tissue and hypothalamus is coordinator ,it receives and
integrate messages from central nervous system.

3. Infection in body : suppose a person is suffering from infection or haemmorage ,the person perceives fear or pain
.electrical chemical signals are generated that are received by the CNS .CNS the paas signal to hypothalamus it
realeses corticotropin releasing hormone .that goes to anterior pituitary it inturn secrete adrenocorticotropic
hormone (ACTH) that goes to adrenal cortex .and triggers cortisol .Cortisol alter metabolism .in liver cels
hepatocytes ,cortisol increases the rate of gluconeogenesis .this ensures that the body gets enough fuel to overcome
adverse action .
It is clear that in hormonal signaling hierarchy .at each level , a small signal elicits a large response the electrical signal
releases CRH that inturn release corticotropin .corticotropin act on adrenal cortex to release Cortisol .it is called
hormonal cascade system .cascade mechanism means that small amount of extracellular compound can effect large
number of intracellular enzyme without crossing the plasma membrane or binding to each target protein.
Whenever there is increased level of products at any stage ,feedback inhibition is initiated and this ensures that a
product is made only until the necessary concentration is reached.
MACHANISM OF HORMONE ACTION :
1. The target cell concept :
There are 200 types of differentiated cells in human .only few produce hormones .all cells are target of one or more
of more than 50 hormones.
2.Hormone receptor:
Hormone are present at very low concentration in extracellular fluid .this concentration is lower than sterols ,amino
acid and peptides.hence target cell must distinguish not only between different hormones but also between given

4. This high degree of discrimination is provided by cell associated recognisition molecules called receptor .target call has
ability to selectively bind a given hormone to specific receptor. Hormone binds to specific receptors . Hormone
induced actions are terminated when hormone dissociates from receptors.
Characterstics of receptors :
1. All receptors have two functional domains: , Recognition domain that bind the hormone and aregion that generate
s signal that couples hormone recognition to intracelular function.
2. The coupling occurs in two ways depending on chemical nature of hormone
3. Polypeptide and protein hormone and catecholamine bind to receptors located in plasma membrane and then
generate a signal that regulates intracellular function that changes the enzyme activity .
4. Steroid , retinoid and thyroid hormone react with intracellular receptor and hormone receptor complex directly
provides the signal to genes who transcription rate is affected.These hormone receptor have functional domains :
• That binds the hormone ,
• that bind to specific DNA regions ,
• that is involved in the interaction with other coregulator protein result in activation of gene transcription ,
• That bind to one ormore protein that influence intracellular trafficking of the receptor.
Both recognition and coupling domains occur on receptor .
CLASSIFICATION OF HORMONES
1.There are different type of hormone according to mechanism of action :

5. GROUP I : Hormones that bind to intracellular receptor
• Thyroid hormone
• Glucocorticoid ‘
• Mineralocorticoid
• Retenoic acid
• Calcitriol
• Androgens
• Oesterogens
Group II : Hormones that bind to cell surface receptors
A – The second messanger is Camp
• Glucagon
• Calcitonin
• Parathyroid hormone
• a2 adrenergenic catecholamines
• adrenergenic catecholamines
• Thyrod stimulating hormone
• Antiduretic hormone
• Adrenocorticotropic hormone
• Human chorionic gonadotropin

6. B .The second messanger is cGMP
Atrial natriuretic factor
C .The second messanger is calcium or phosphatidyl inositol or both.
• Acetyl choline
• A1 –adrenergic catecholamine
• Oxytocin
• Antiduretic hormone
• Cholecystokinin
D.The second messanger is a kinase or phosphatase cascade
• Insulin
• Growth hormone
• Prolactin
GROUP I HORMONE:
1.They are lipophilic
2.They are fat soluble
3. These hormone associate with plasma transport or carrier protein this overcomes the problem of their insolubility
in aqueous medium of plasma .At the same time it prolongs thr plasma half life of hormone since they cannot be
eliminated easily when bound to protein .bonding capacity andbinding affinity determine the relative percentage of
bound and free hormone .

7. The free hormone in the active form crosses the lipophilic plasma membrqne of cell.the receptors for Group I
hormone are present in cytosol or nucleus of target cells then hormone receptor complex is formed .this complex
theligand receptor complex is formed is the intracellular messanger that conveys the message brought from CNS to
specific cells .
GROUP II : they are hydrophillic or water soluble .they cannot cross the hydrophilic plasma membrane .they bind to
plasma membrane of target cells .their receptor are located in plasma membrane .such hormone that bind to surface
of cells communicate with intracellular metabolic process through intermidiatory molecular called second messanger.
The hormone is called first messanger .and second messanger are generated as concequences of the ligand receptor
interaction .When epinephrine bind the plasma membrane of certain cells ,the concentration of cyclic AMP
increases.
CHARACTERSTICS GROUP I GROUP II
Types of hormone Steroids,retenoids Polypeptide ,protein
solubilty lipophilic hydrophillic
Transport protein yes no
Plasma half line long short
Rreceptor Intracellular Plasma membrane
mediator Receptor hormone complex Second messanger-Camp