1.3.12Structure and Functions in Living Organisms: Part 2
The Role of Hormones: Basic — Edexcel International GCSE Science Double Award (Modular) - Biology Unit 2 Revision Notes & Topical Questions
5 min read 6 parts Lesson 24 of 24
Part 1 of 5What a hormone is
Definition
- Definition A hormone is a chemical substance made by a gland and carried in the blood to one or more target organs, where it alters their activity.
- Hormones carry information from one part of the body to another and bring about a change.
Five to know
- Five to know The hormones to learn are adrenaline, insulin, testosterone, progesterone and oestrogen.
Part 2 of 5Adrenaline: fight or flight
Adrenaline
Faster heart and breathing
- Faster heart and breathing Delivers glucose and oxygen to muscle cells more quickly and removes carbon dioxide efficiently.
Blood redirected
- Blood redirected More blood goes to muscles and less to non-essential organs such as the gut.
Wider vessels in muscle
- Wider vessels in muscle Dilation of blood vessels in muscles lets more blood reach active tissues.
Glucose released
- Glucose released Stored glycogen in the liver and muscles is broken down to glucose, which muscle cells use in respiration.
Part 3 of 5Insulin and blood glucose
1Blood glucose rises
- Blood glucose rises After a meal the concentration of glucose in the blood goes above the normal range.
2Pancreas responds
- Pancreas responds Cells in the pancreas detect the rise and secrete insulin into the blood.
3Glucose is taken up
- Glucose is taken up Insulin makes muscles and the liver take glucose from the blood and store it as glycogen.
4Level returns to normal
- Level returns to normal Once blood glucose is back in range, the pancreas stops releasing insulin.
Part 4 of 5Why glucose must be controlled
Too high
- Too high Cells can lose water by osmosis, which is harmful.
Too low
- Too low The brain may not receive enough glucose for respiration, which can lead to coma or even death.
Pancreas with two roles
- Pancreas with two roles As an endocrine gland it secretes hormones into the blood, while separately it makes digestive enzymes that enter the gut.
Part 5 of 5Sex hormones and summary
| Hormone | Source | Main role |
|---|---|---|
| Adrenaline | Adrenal glands | Prepares the body for fight or flight |
| Insulin | Pancreas | Lowers blood glucose by promoting uptake and storage as glycogen |
| Testosterone | Testes | Development of male reproductive organs and male secondary sexual characteristics |
| Oestrogen | Ovaries | Female secondary sexual characteristics; repair of the uterus lining and control of ovulation |
| Progesterone | Ovaries | Maintains the uterus lining in pregnancy and prevents further ovulation |
Key terms
| Term | Meaning |
|---|---|
| Hormone | A chemical messenger made by a gland and carried in the blood to target organs. |
| Glycogen | A storage carbohydrate made of many glucose units, found in the liver and muscles. |
| Endocrine gland | A gland that secretes hormones directly into the bloodstream. |
| Secondary sexual characteristics | Features that develop at puberty, such as voice change in males and breast development in females. |
| Ovulation | The release of an egg cell from an ovary. |
Avoid these mistakes
1
Saying insulin raises blood glucose; it lowers it by causing glucose to be stored as glycogen.
2
Forgetting that adrenaline acts on the heart, blood vessels and liver together to prepare muscles for action.
3
Mixing up the sources of the sex hormones: testosterone from the testes, oestrogen and progesterone from the ovaries.
4
Confusing glucose with glycogen in explanations of storage.
Last updated: