Properties and functions of hormones

May 23, 2018

A hormone(from the Greek participle “ὁρμῶ”, “to set in motion, urge on”) is any member of a class of signaling molecules produced by glands in multi cellular organisms that are transported by the circulatory system to target distant organs to regulate physiology and behaviour.

A) Properties

Regarded as “chemical messengers” of the body. They carry the message from the site of synthesis to the target organ.
Synthesized by ductless glands called endocrine glands.
Effective in extremely small amount which produces a marked effect.
Travel in blood to all parts of the body.
Affect only particular cells called target cells.
May be amino acid derivatives, peptides, proteins or steroids in nature chemically.
Have low molecular weight and can diffuse through the cell membranes.
Serious physiological disorders may result in excess and deficiency.
Have wide spread effects though some may have specific functions.
Cannot be stored in the body as they are rapidly altered or destroyed immediately after they have acted on the target organ.

Image source: newsmedical

B) Functions

Control the general metabolism of the body.
Regulate the growth of the organism, moulting, metamorphosis, regeneration and diapause of some animals.
Control the gametogenesis, development of secondary sexual characters, oviposition, implantation of the fertilized eggs, development of the embryo in the uterus and child birth.
Control the internal environment of the body including regulation of temperature, water and ionic balance of the body, blood sugar levels, etc.
Make adaptations to external factors including visual adaptation to light intensities and control of physiological color changes.