CIE iGCSE Biology-14.3 Hormones- Study Notes- New Syllabus
CIE iGCSE Biology-14.3 Hormones- Study Notes – New syllabus
CIE iGCSE Biology-14.3 Hormones- Study Notes -CIE iGCSE Biology – per latest Syllabus.
Key Concepts:
Core
- Describe a hormone as a chemical substance, produced by a gland and carried by the blood, which alters the activity of one or more specific target organs
- Identify in diagrams and images specific endocrine glands and state the hormones they secrete, limited to:
(a) adrenal glands and adrenaline
(b) pancreas and insulin
(c) testes and testosterone
(d) ovaries and oestrogen - Describe adrenaline as the hormone secreted in ‘fight or flight’ situations and its effects, limited to:
(a) increased breathing rate
(b) increased heart rate
(c) increased pupil diameter - Compare nervous and hormonal control, limited to speed of action and duration of effect
Supplement
- State that glucagon is secreted by the pancreas
- Describe the role of adrenaline in the control of metabolic activity, limited to:
(a) increasing the blood glucose concentration
(b) increasing heart rate
Definition of a Hormone
What is a Hormone?
A hormone is a:
- Chemical substance
- Produced by an endocrine gland
- Carried in the blood
- That alters the activity of one or more specific target organs
📌 Key Characteristics of Hormones
- Chemical messengers that help regulate body functions
- Secreted directly into the bloodstream by endocrine glands (e.g. pituitary, pancreas, adrenal)
- Travel throughout the body in the blood but act only on specific target organs with matching receptors
- Cause longer-lasting, slower responses compared to the nervous system
- Help control processes like growth, metabolism, mood, and reproduction
📍 Examples of Hormones:
| Hormone | Gland | Target Organ | Function |
|---|---|---|---|
| Insulin | Pancreas | Liver, muscles | Lowers blood glucose level |
| Adrenaline | Adrenal gland | Heart, muscles, liver | Prepares body for ‘fight or flight’ |
| Oestrogen | Ovaries | Uterus, other cells | Controls female sexual development |
🧾 Summary:
Hormones are chemical messengers secreted by glands into the blood that bring about specific changes in target organs to help maintain internal balance and control body functions.
Hormones are chemical messengers secreted by glands into the blood that bring about specific changes in target organs to help maintain internal balance and control body functions.
Identifying Endocrine Glands & Their Hormones
The endocrine system consists of glands that secrete hormones directly into the bloodstream. Below are 4 key glands to recognize in diagrams and exams:
(a) Adrenal Glands → Adrenaline
| Location | On top of each kidney (one on each side) |
| Shape | Small, triangular or cap-like |
| Hormone | Adrenaline |
| Function | Prepares body for “fight or flight” (increases heart rate, breathing rate, etc.) |
(b) Pancreas → Insulin
| Location | Behind the stomach, in the upper abdomen |
| Shape | Leaf-shaped or elongated |
| Hormone | Insulin |
| Function | Lowers blood glucose levels by helping cells absorb glucose |
(c) Testes → Testosterone
| Location | Inside the scrotum (male reproductive system) |
| Shape | Oval organs |
| Hormone | Testosterone |
| Function | Controls male secondary sexual characteristics (e.g., voice deepening, muscle growth) |
(d) Ovaries → Oestrogen
| Location | One on each side of the uterus (in females) |
| Shape | Small, oval |
| Hormone | Oestrogen |
| Function | Controls female secondary sexual characteristics and menstrual cycle |
📘 Quick Recap Table:
| Gland | Location | Hormone | Function Summary |
|---|---|---|---|
| Adrenal | On kidneys | Adrenaline | Fight or flight response |
| Pancreas | Near stomach | Insulin | Lowers blood glucose |
| Testes | Male reproductive | Testosterone | Male characteristics |
| Ovaries | Female reproductive | Oestrogen | Female characteristics, menstrual cycle |
🗒️Note:
Endocrine glands = Hormone factories
No ducts → hormones go straight into blood
Learn location + hormone + function for each gland
Endocrine glands = Hormone factories
No ducts → hormones go straight into blood
Learn location + hormone + function for each gland
Adrenaline – The ‘Fight or Flight’ Hormone
✅ What is Adrenaline?
Adrenaline is a hormone secreted by the adrenal glands, located just above the kidneys.
It is released into the bloodstream in response to stressful, fearful, or emergency situations.
Adrenaline prepares the body to deal with sudden danger – this is called the ‘fight or flight’ response.
📝 Note:
Adrenaline is not under conscious control – it is part of the automatic hormonal response to stress.
⚙️ Effects of Adrenaline (limited to syllabus):
| Effect | How It Helps in ‘Fight or Flight’ Situations |
|---|---|
| Increased breathing rate | Increases oxygen intake to supply muscles with more oxygen |
| Increased heart rate | Pumps more oxygenated blood quickly to muscles and vital organs |
| Increased pupil diameter | Allows more light into the eyes to improve vision and alertness |
📚Key Points:
- Adrenaline is a fast-acting hormone, and its effects are almost immediate.
- It works alongside the nervous system for a rapid coordinated response.
- After the situation passes, the hormone level falls, and the body returns to normal.
🧾 Summary:
Adrenaline is a hormone released in stressful situations that increases breathing rate, heart rate, and pupil size to help the body respond quickly and efficiently.
Adrenaline is a hormone released in stressful situations that increases breathing rate, heart rate, and pupil size to help the body respond quickly and efficiently.
Comparison: Nervous vs Hormonal Control
Nervous Control
- Involves electrical impulses sent through neurones
- Target: Specific muscles or glands
- Used for quick, immediate responses
- Example: Pulling hand away from something hot
Hormonal Control
- Involves chemical messengers (hormones) carried in the bloodstream
- Target: Specific organs with receptors
- Used for longer-term adjustments
- Example: Adrenaline release during stress
| Feature | Nervous Control | Hormonal Control |
|---|---|---|
| Speed of action | Very fast (almost instant) | Slower (carried in the bloodstream) |
| Duration of effect | Short-lived | Long-lasting |
📝Note:
Nervous = Fast but brief
Hormonal = Slow but lasting
Nervous = Fast but brief
Hormonal = Slow but lasting
🧾 Summary:
Nervous control is rapid and short-lived, ideal for immediate actions. Hormonal control is slower but longer-lasting, suitable for regulating body processes over time.
Nervous control is rapid and short-lived, ideal for immediate actions. Hormonal control is slower but longer-lasting, suitable for regulating body processes over time.
Glucagon and the Pancreas
What is Glucagon?
- Glucagon is a hormone.
- It is secreted by the pancreas, specifically by the alpha cells in the islets of Langerhans.
🎯 Function of Glucagon:
Glucagon helps to increase blood glucose levels when they are too low. It does this by:
- Stimulating the conversion of glycogen (stored in the liver) into glucose.
- Releasing that glucose into the bloodstream.
Note: Glucagon works opposite to insulin. Insulin lowers blood sugar, glucagon raises it!
🧾 Summary:
Glucagon is a hormone secreted by the pancreas that raises blood sugar levels by converting stored glycogen into glucose.
Glucagon is a hormone secreted by the pancreas that raises blood sugar levels by converting stored glycogen into glucose.
Adrenaline and Its Role in Metabolic Activity
What is Adrenaline?
- Adrenaline is a hormone.
- It is secreted by the adrenal glands, which are located just above the kidneys.
- Released especially during ‘fight or flight’ situations – i.e., when a person is scared, excited, angry, or in danger.
🟨 Adrenaline’s two key actions:
1. Liver: Glycogen → Glucose ↑ (more fuel)
2. Heart: Beats faster and stronger ↑ (better delivery)
1. Liver: Glycogen → Glucose ↑ (more fuel)
2. Heart: Beats faster and stronger ↑ (better delivery)
🔁 Main Functions of Adrenaline in Metabolism:
(a) Increasing Blood Glucose Concentration
- Adrenaline acts on the liver.
- It causes the breakdown of glycogen (a stored form of glucose in the liver) into glucose.
- This glucose is then released into the bloodstream, so that more energy is quickly available to body cells, especially muscles.
- This is important during emergencies when muscles need energy for rapid movement.
(b) Increasing Heart Rate
- Adrenaline increases the rate and strength of heart contractions.
- As a result, blood is pumped more rapidly around the body.
- This ensures that more oxygen and glucose are delivered to muscles and the brain, enabling quicker reactions and physical responses.
🧠 Why These Actions Matter
- These two effects – more glucose in blood and faster blood flow – prepare the body for sudden activity like running away or fighting.
- Together, they help the body respond quickly and powerfully in stressful or dangerous situations.
📌 Summary Point:
Adrenaline increases blood glucose concentration and heart rate during stress. This helps deliver more energy and oxygen to the muscles, enabling a fast and efficient ‘fight or flight’ response.
Adrenaline increases blood glucose concentration and heart rate during stress. This helps deliver more energy and oxygen to the muscles, enabling a fast and efficient ‘fight or flight’ response.