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Chemical Coordination and Integration

Introduction to Human Endocrine System

Hormones are the organic chemicals produced by the body, which are released into the blood.

The key feature of the hormones is that they are secreted by the ductless glands. The glands that secrete hormones do not have ducts. Hormones are released directly into the blood stream and reach the target organ.

Differences between Hormonal Control and Nervous Control

Hormonal Control Nervous Control
Transmitted chemically through blood Transmitted electro-chemically through nerve fibres 
Transmitted slowly Transmitted rapidly
Affects different organs     Affects specific organs
Is not affected by previous experience Is affected by previous experience
Has both long lasting and short lasting effects Has short lasting effect

The endocrine system works in association with nervous system to control and coordinate our bodies. They contribute to the maintenance of homeostasis in our bodies.

Homeostasis is the capacity of an organism to adjust itself and cope up with external stress to maintain a steady state.


A cell, tissue, or an organ that secretes chemical messengers required for coordinating a specific function is called a gland. Glands are mainly divided into two broad categories - endocrine and exocrine.

Exocrine gland

Endocrine gland

These glands possess ducts for discharging their secretions on the body surface. The sebaceous glands present in the skin, salivary glands present in the buccal cavity, and gastric glands present in the walls of the stomach etc. are a few examples of exocrine glands.

These glands do not discharge their secretions through ducts. Hence, they are also known as ductless glands. They discharge their secretions directly into the bloodstream. Their secretions are known as hormones. The pituitary gland, thyroid gland, adrenal gland etc. are a few examples endocrine glands.

Characteristics of Hormones

  • Hormones are the organic chemicals that are secreted in response to environmental changes in or outside the body.
  • Hormones are secreted by ductless glands and transported along with the blood stream to the site of their action. The site of their production and the organ of their influence are different.
  • They can be amino-acid derivatives, proteins, or steroids.
  • Being low molecular weight substances, they can easily diffuse through the cell membrane.
  • They are produced in small quantities and are effective in extremely lower concentrations.
  • Abnormal production of hormones (be it less or more) affects the body in a negative manner.

Some of the ductless glands that secrete hormones are thyroid gland, adrenal gland, pituitary gland, parathyroid gland, gonads, etc.

Human Endocrine System
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