Human Endocrine System - Hormones: An Introduction (GCSE Biology)

Hormones: An Introduction

Endocrine and Nervous Systems

Understanding the Endocrine System

• The endocrine system works with the nervous system. The endocrine system is part of the feedback mechanisms of the body. It works with the nervous system to maintain homeostasis. Sometimes the nervous system can activate the endocrine system – e.g. nerve impulses can stimulate glands to release hormones.
• The endocrine system uses hormones to transmit their signals. A hormone is a chemical substance, produced by a gland and secreted into and carried by the blood. It then alters the activity of one or more specific target organs by binding to specific receptors.
• The endocrine system works by negative feedback. Like the nervous system, the endocrine system aims to maintain homeostasis and resist change. Therefore it often works by negative feedback. For example, if water levels rise too high, then the endocrine system increases the level of a hormone (ADH) to counter the change and bring water levels back down.

Endocrine vs. Nervous Systems

This table discusses the key differences between the hormonal and nervous system. We touched on this in a previous tutorial, but it is good to re-cap:

The Pituitary Gland

Function of the Pituitary Gland

• The pituitary gland exists as a structure in the brain. It is possibly the most important gland involved in the endocrine system.
• The pituitary gland is key in homeostasis. It controls blood sugar, fertility, water levels, growth and so many other key features to life.
• However, the pituitary gland does not control all these things this directly. Instead, it works by secreting primary hormones that cause target organs to secrete secondary hormones.

Hormones Secreted by Pituitary Gland

There are different hormones secreted by the pituitary gland including:

• ACTH – Adrenocorticotrophic Hormone (ACTH) stimulates the adrenal glands, leading to release of adrenaline. Adrenaline is important during exercise, as it increases heart rate.
• ADH – Antidiuretic hormone (ADH) stimulates the kidneys. It works to control water levels in the blood. Less ADH is released when there is too much water and we want to increase the amount of water excreted via urines.

Location of the Pituitary Gland

The pituitary gland is located in the brain. Students always get mixed up and think the pituitary gland is located lower down the body because it influences the adrenal glands and kidneys, but in fact it is found just under the hypothalamus.

Examples of Endocrine Glands

You need to know the specific location of several glands in the body. We will study most of these in later tutorials.