Endocrinology



The branch of biology deals with the study of the endocrine system and its physiology. FATHER OF ENDOCRINOLOGY:-THOMAS ADDISON. 
Endocrine glands:- Glands that pour their secretion directly into blood are called endocrine glands. Substances secreted by endocrine glands are called hormones(To excite = hormaein {Greek word}. Hormones are also called "Primary messengers" or chemical messengers. 


HUMAN ENDOCRINE SYSTEM


Organized endocrine gland:- Where hormone-producing cells are present in cluster/tissue form. 
Examples:- Pituitary, Pancreas, Parathyroid, Pineal, Thyroid, Thymus, Adrenal, and Gonads.

Non-organized endocrine gland:- Where hormone-producing cells are present in scattered/ diffused form. 
Examples:- Heart, Liver, Kidney, Gastrointestinal tract. 





HORMONE


Classical Definition:-
Chemicals produced by endocrine glands and released into the blood and transported to a distantly located target organ. 





Current Scientific Definition:- 
Hormones are non-nutrient chemicals that act as intercellular messengers and are produced in trace amounts. 


PROTEINACEOUS HORMONE

(i) Amino Acid Derivatives

Hormone:- Thyroxine, Epinephrine, Nor-Epinephrine 

Glands:- Thyroid Gland Adrenal Medulla Adrenal Medulla

(ii) Short Peptides 

Hormone:-  Oxytocin, Vasopressin, MSH 

Glands:- Hypothalamus, Adenohypophysis 

(iii) Long Peptides 

Hormone:- Parathyroid Hormone, ACTH, Thyrocalcitonin, Insulin 

Glands:- Parathyroid Gland, Adenohypophysis, Thyroid Gland, Pancreas

(iv) Glycoproteins
Hormone :- TSH,FSH,LH 
Glands:- Adenohypophysis



STEROIDS HORMONE


STEROIDS:- 
Hormone:-  Mineralocorticoids, Glucocorticoids, Testosterone, Oestrogen, Progesterone 
Glands:- Adrenal Cortex,  Testis, Ovary




PHYSICAL & CHEMICAL SPECIALITIES OF HORMONES


Hormones are small and their molecular weight is low. Most hormones are soluble in water, while a few are soluble in fat and are easily diffusible in tissues. Their secretion always occurs in very small quantities as they are highly reactive substances.  Hormones are destroyed after use, i.e. hormones cannot be stored in the body. 

Thyroxine is an exception in this regard. The liver and kidneys separate hormones from blood and decompose them. The products formed after decomposition are excreted with urine, i.e.Hormones cannot be reutilized. Hormones are Non-antigenic & Non-species specific. Usually, hormones do not participate in the metabolic activities of target cells, but they affect and control the activity level of these target cells

MECHANISM OF HORMONE ACTION

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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.



PROTEIN (WATER-SOLUBLE) HORMONE



STEROID (LIPID-SOLUBLE) HORMONE




The action of lipid-soluble hormones is slower but long-lasting than that of the water-soluble hormones. 



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