5.1.4 Ch14 Hormonal Communication
, 14.1 The Endocrine System
• Like the nervous system, the endocrine system is a form of cell signalling that helps us to respond to our
environment
• The endocrine system sends information as chemical signals (rather than electrical signals)
• It is made up of:
• Glands (called endocrine glands)
• Hormones (chemical messengers)
• Target cells/tissues
• Endocrine glands are groups of cells that are specialised to secrete chemicals
• These chemicals are known as hormones
Secretion of hormones
• Hormones are secreted directly into the bloodstream when a gland is stimulated. This can occur as a result
of a nerve impulse, another hormone, or a change in concentration of a particular substance, such as blood
glucose concentration
• Once secreted, the hormones are transported in the blood plasma all over the body
• Hormones will diffuse out of the bloodstream all over the body but each hormone will only bind to specific
receptors for that hormone, found on the membranes, or in the cytoplasm of some cells, called target cells
• Tissues that contain target cells are called target tissues
• The hormones trigger a response in the target cells (the effectors)
Stimuli to response pathway
Stimulus → Receptor → Hormone release → Effectors → Response
, 14.1 The Endocrine System
• Like the nervous system, the endocrine system is a form of cell signalling that helps us to respond to our
environment
• The endocrine system sends information as chemical signals (rather than electrical signals)
• It is made up of:
• Glands (called endocrine glands)
• Hormones (chemical messengers)
• Target cells/tissues
• Endocrine glands are groups of cells that are specialised to secrete chemicals
• These chemicals are known as hormones
Secretion of hormones
• Hormones are secreted directly into the bloodstream when a gland is stimulated. This can occur as a result
of a nerve impulse, another hormone, or a change in concentration of a particular substance, such as blood
glucose concentration
• Once secreted, the hormones are transported in the blood plasma all over the body
• Hormones will diffuse out of the bloodstream all over the body but each hormone will only bind to specific
receptors for that hormone, found on the membranes, or in the cytoplasm of some cells, called target cells
• Tissues that contain target cells are called target tissues
• The hormones trigger a response in the target cells (the effectors)
Stimuli to response pathway
Stimulus → Receptor → Hormone release → Effectors → Response
