Lesson 5 of 7 / Nutrition in humans
Hormones carry chemical messages
How can a gland affect an organ far away?
In this lesson: Define a hormone by its production, blood transport and effects on specific target organs.
About 4 min
The key ideaA hormone is a chemical substance produced by a gland, carried in the blood and affecting specific target organs.
Explore the idea
Which route carries the message?
A gland makes a hormone, blood carries it and specific target cells change their activity. Insulin is a signal, not the glucose being stored.
Arrows show a causal sequence. They do not mean that a hormone turns into the substance named in the next box.
Explanation
A hormone is a chemical substance produced by a gland, carried by the blood and changing the activity of one or more specific target organs. The gland and the target do not have to be beside each other because circulation connects them.
Blood carries a hormone past many tissues, but only suitable target cells respond. Their receptors allow them to recognise the signal. Transport around the body does not mean that every organ responds in the same way.
The pancreas produces insulin and glucagon and releases them into the blood. These hormones help regulate blood glucose. The pancreas also releases digestive enzymes into the small intestine through a duct. A hormone in blood and a digestive enzyme in the gut have different routes and jobs.
A hormone is a signal that changes activity. Insulin does not become glycogen or digest glucose. It promotes changes in target cells that affect glucose uptake and storage. This distinction lets us explain control without confusing the signal with the substance being controlled.
Step by step
- 1
Name the source
State that a gland produces the hormone.
- 2
Follow the route
Blood carries the hormone to its targets.
- 3
State specificity
Only suitable target organs change activity in response.
Worked example
Two pancreatic secretions
Insulin enters blood while pancreatic amylase enters the intestine. Explain which is a hormone and why.
One way to explain it
Insulin is a hormone: it is produced by the pancreas, carried in blood and changes the activity of specific target cells. Amylase is a digestive enzyme that acts on starch in the gut.
Why this answer works
- Use all parts of the hormone definition.
- Compare transport routes.
- Separate signalling from digestion.
Is this true? "Every organ responds equally because the blood carries a hormone everywhere."
A hormone affects suitable target cells with the appropriate receptors. Circulation and response are different things.