Lesson 3 of 10 / Homeostasis and response
Hormones and endocrine glands
How can a gland affect an organ far away?
I can describe hormonal signalling and identify the islets of Langerhans as endocrine tissue.
I can describe a hormone and its specific targets.Syllabus
Syllabus K325, Topic 8(d). Describe a hormone and its specific targets.
I can describe endocrine glands using pancreatic islets.Syllabus
Syllabus K325, Topic 8(e). Describe endocrine glands using pancreatic islets.
About 4 min
Make a guess. You are not marked.
Insulin travels in the blood to every organ in your body. Does every organ respond to it?
Show the answer
No. Only target cells with the right receptors respond.
A hormone reaches everywhere but only acts where cells have matching receptors.
The key idea
A hormone is a chemical substance produced by a gland, carried in the blood and affecting specific target organs.
Green spot: endocrine islet tissue. The pancreas also contains ducted digestive tissue. The diagram compares routes, not anatomical scale.
Islet cells release insulin into blood without a duct. It circulates widely, but suitable target cells respond through specific receptors.
Explanation
An endocrine gland releases hormones directly into the blood. It has no duct carrying its hormone to a surface or cavity. Blood transports the hormone around the body, allowing it to act at a distance from the gland that produced it.
Only suitable target cells respond to a particular hormone because they have the appropriate receptors. A hormone circulating past many organs does not make all those organs perform the same response.
The islets of Langerhans are groups of endocrine cells in the pancreas. They produce hormones including insulin and glucagon, which regulate blood glucose. The pancreas also makes digestive secretions that travel through a duct to the small intestine; that is a different function.
Hormones change the activity of their targets. They are signals, not digestive enzymes, and are not usually the substances directly converted in the process they control. For example, insulin signals changes in glucose uptake and storage; it does not digest glucose.
Step by step
- 1
Name the source
Identify the endocrine gland or endocrine tissue.
- 2
Name the transport route
Hormones are carried in the blood, rather than along a neurone or through a gland duct.
- 3
Name the target and effect
Specify which organ changes activity and how that changes the internal condition.
Worked example
Two pancreatic functions
Insulin enters blood, while pancreatic juice enters the small intestine through a duct. Which release is endocrine?
One way to explain it
Insulin release by the islets of Langerhans is endocrine because the hormone enters the blood directly and acts on specific targets.
Why this answer works
- Identify insulin as a hormone.
- Use the blood route to explain endocrine.
- Do not classify the entire pancreas as having only one kind of secretion.
Watch out for this
A student says: "Every organ responds equally because the blood carries a hormone everywhere." What is wrong with this?
Show the answer
A hormone affects suitable target cells with the appropriate receptors. Circulation and response are different things.
Check your understanding
Which description identifies an endocrine function of the pancreas?
Show the answer
Islet cells release insulin directly into the blood.
A hormone entering the blood from ductless endocrine tissue is an endocrine secretion.
Quick recall
How can a gland affect an organ far away?