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PinkMonkey Online Study Guide-Biology


22.0 Introduction

All animals contain chemical components produced by exocrine or endocrine glands. Exocrine glands release their chemicals into ducts. The endocrine glands (Figure 22.1) release their secretions, the hormones, directly into the blood-stream.

These hormones are then carried to other parts of the body (target organs), where in extremely minute quantities, they elicit cellular responses. E.H.Starling (1902) suggested the name ’hormone’ (Greek meaning "to stimulate" or "to excite") for these chemical messengers or transmitters.

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Figure 22.1 The position of the main endocrine glands in the human body

Hormones are specifically-acting organic compounds with varying chemical compositions, usually steroids, proteins, peptides or amino acids. Based on their general roles, hormones are metabolic (stimulate or retard metabolic activities), trophic (regulate rate and secretion of other endocrine glands) and morphogenetic (affect rate and development of various parts).

Hormones are an additional means of coordination and communication. Together with the nervous system, the endocrine system forms a combined neuro-endocrine system. The hormone pathway is by the blood stream, while nervous pathway is by the neuron-reflex arc.

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Table of Contents

22.0 Introduction
22.1 Pituitary gland
22.2 Thyroid gland

Chapter 23


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