6.1.1 Hormone As A Chemical Messenger

A hormone is a small soluble organic molecule which is effective in low concentration. It is essentially a chemical messenger that transports a signal from one cell to another. It has its effect at a site where specific receptors are present, called the target; hence it is termed as messenger.

Definition

Hormone as a Chemical Messenger: A hormone is a small soluble organic molecule which is effective in low concentration. It is essentially a chemical messenger that transports a signal from one cell to another. It has its effect at a site where specific receptors are present, called the target; hence it is termed as messenger.

Main Idea

• A hormone is a small soluble organic molecule.
• It is effective in low concentration.
• It is a chemical messenger.
• It transports a signal from one cell to another.
• It has its effect at a site where specific receptors are present.
• This site is called the target.
• Hormones affect and manage hundreds of processes occurring in the body.
• Often, a bodily process involves a chain reaction of several different hormones.
• A hormone will only act on a part of the body if the cells in the target tissue have receptors that receive the message of the hormone.
• Its action is like the lock and key model of enzyme action.
• The body uses hormones for two types of communication.

Core Concept

• Hormone = chemical messenger
• Effective in low concentration
• Target = site with specific receptors
• Lock and key model = hormone fits receptor
• Two types of communication:

Detailed Explanation

Hormone as a Chemical Messenger

• A hormone is a small soluble organic molecule which is effective in low concentration.
• It is essentially a chemical messenger that transports a signal from one cell to another.
• It has its effect at a site where specific receptors are present, called the target; hence it is termed as messenger.
• Hormones are chemical messengers that affect and manage hundreds of processes occurring in the body.
• Often, a bodily process involves a chain reaction of several different hormones.
• A hormone will only act on a part of the body, if the cells in the target tissue have receptors that receive the message of the hormone.
• Its action is like the lock and key model of enzyme action.
• Think of a hormone as a key and the cells of its target tissue, as specially shaped locks.
• If the hormone fits the lock (receptor) on the cell membrane, then it'll work; the hormone will deliver a message that causes the target site to take a specific action.

Two Types of Communication

The body uses hormones for two types of communication.

1. Communication Between Two Endocrine Glands

• One gland releases a hormone, which stimulates another gland to change the levels of hormones that it's releasing.
• An example of this is the communication between pituitary gland and thyroid.
• The pituitary gland releases thyroid-stimulating hormone (TSH), which triggers thyroid gland to release its hormones, which then affect various aspects of body.

2. Communication Between an Endocrine Gland and a Target Organ

- An example of this is when the pancreas releases insulin, which then acts on the muscles and liver to help analyse glucose.

Science Titbits

• In 1902, Bayliss and Starling, prepared an extract from the duodenum which stimulated secretion of pancreatic digestive juices when it was injected into the bloodstream.
• They called the product 'secretin', and coined the term 'hormone', meaning 'to excite' or 'to set in motion.'

Summary Table of Hormone as Chemical Messenger

Intermediate Level

Hormone as a Chemical Messenger

Two Types of Communication

Lock and Key Model

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. A hormone is a small soluble organic molecule.
• 2. It is effective in low concentration.
• 3. It is a chemical messenger.
• 4. It transports a signal from one cell to another.
• 5. It acts on target cells with specific receptors.
• 6. The target site has specific receptors.
• 7. Its action is like the lock and key model.
• 8. Hormones affect and manage hundreds of processes.
• 9. A bodily process involves a chain reaction of several hormones.
• 10. A hormone only acts if the target tissue has receptors.
• 11. The body uses hormones for two types of communication.
• 12. First type: between two endocrine glands.
• 13. Second type: between an endocrine gland and a target organ.
• 14. Example of gland-to-gland communication: pituitary releases TSH → thyroid releases hormones.
• 15. Example of gland-to-organ communication: pancreas releases insulin → acts on muscles and liver.
• 16. Bayliss and Starling coined the term hormone.
• 17. Secretin was the first hormone discovered.
• 18. Hormone means 'to excite' or 'to set in motion'.
• 19. Hormones are essential for body functions.
• 20. Hormones work through chain reactions.

Remember

• - Hormone = chemical messenger
• - Effective in low concentration
• - Target = site with specific receptors
• - Lock and key model = hormone fits receptor
• - Two types of communication:
• 1. Between two endocrine glands
• 2. Between an endocrine gland and a target organ
• - Example = pituitary releases TSH → thyroid releases hormones
• - Example = pancreas releases insulin → acts on muscles and liver
• - Bayliss and Starling = coined the term hormone
• - Secretin = first hormone discovered

Common Mistakes

• 1. Confusing hormones and neurotransmitters — Hormones travel through blood; neurotransmitters cross synapses.
• 2. Thinking hormones act on all cells — They act on target cells with specific receptors.
• 3. Forgetting the lock and key model — Hormone fits receptor like a key fits a lock.
• 4. Mixing up the two types of communication — Gland-to-gland; gland-to-organ.
• 5. Forgetting the role of receptors — Receptors are essential for hormone action.
• 6. Thinking hormones are effective at high concentrations — They are effective at low concentrations.
• 7. Mixing up the examples — Pituitary-thyroid; pancreas-insulin.
• 8. Believing hormones work alone — They often work in chain reactions.
• 9. Thinking hormones are not specific — They are highly specific.
• 10. Confusing hormone and secretin — Secretin is a hormone.

Quick Revision

A hormone is a small soluble organic molecule which is effective in low concentration. It is essentially a chemical messenger that transports a signal from one cell to another. It has its effect at a site where specific receptors are present, called the target; hence it is termed as messenger. Hormones are chemical messengers that affect and manage hundreds of processes occurring in the body. Often, a bodily process involves a chain reaction of several different hormones. A hormone will only act on a part of the body, if the cells in the target tissue have receptors that receive the message of the hormone. Its action is like the lock and key model of enzyme action. Think of a hormone as a key and the cells of its target tissue, as specially shaped locks. If the hormone fits the lock (receptor) on the cell membrane, then it'll work; the hormone will deliver a message that causes the target site to take a specific action. The body uses hormones for two types of communication. The first type is communication between two endocrine glands. One gland releases a hormone, which stimulates another gland to change the levels of hormones that it's releasing. An example of this is the communication between pituitary gland and thyroid. The pituitary gland releases thyroid-stimulating hormone (TSH), which triggers thyroid gland to release its hormones, which then affect various aspects of body. The second type of communication is between an endocrine gland and a target organ. An example of this is when the pancreas releases insulin, which then acts on the muscles and liver to help analyse glucose. In 1902, Bayliss and Starling, prepared an extract from the duodenum which stimulated secretion of pancreatic digestive juices when it was injected into the bloodstream. They called the product 'secretin', and coined the term 'hormone', meaning 'to excite' or 'to set in motion.'

60-Second Revision

• Hormone = chemical messenger
• Effective in low concentration
• Target = site with specific receptors
• Lock and key model = hormone fits receptor
• Two types of communication = gland-to-gland; gland-to-organ
• Example = pituitary releases TSH → thyroid releases hormones
• Example = pancreas releases insulin → acts on muscles and liver
• Bayliss and Starling = coined the term hormone
• Secretin = first hormone discovered
• Warning: Hormones act only on target cells with specific receptors