The term Hormone (hormaoG= to excite) was first used by ‘William M.Bayliss’ and his brother-in-law ‘Ernest H.Starling’, both of London University college, in 1904, who showed that a chemical stimulate the action of a pancreatic secretion. These substances were then called “Chemical Messengers”.
Definition:
According to Went & Thimann (1937),
“A substance which produced in any one part of an organism, is transferred to another part and there influences a specific physiological process”.
Properties:
A hormone is a Chemical messengers. It has the following properties:
- ·It travels in the blood.
- It has its effect at a site different from the site where it is made, called the “Target”, hence the term “Messenger”.
- It fits precisely into receptor molecules in the target like a key in a lock-it is therefore Specific for a particular target.
- It is a small soluble organic molecule.
- It is effective in low concentrations.
- These have low molecular weight & diffuse readily.
Location of principal endocrine glands:
a) Two in the head region --> The pineal & the Pitutary
b) Three in the neck region --> The Thymus, the Thyroid & Parathyroid
c) Four in the abdominal region –> The Pancreas, The Gastrointesinal mucosa,
The adrenals & The Gonads
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ENDOCRINOLOGY
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