Table of Contents
Chemical messengers that control body functions #
Understanding Hormones: Think of hormones as the body’s chemical messengers. Just like you might send a text message to tell someone what to do, your body sends hormone messages through your bloodstream to tell different organs what to do. These chemical messages help coordinate many important body functions like growth, reproduction, and responding to emergencies.
The endocrine system works alongside the nervous system to control and coordinate body functions.
While the nervous system sends electrical signals through nerves for quick responses, the endocrine system sends chemical signals through the blood for longer-lasting effects.
Understanding how hormones work helps us understand many important body processes, from how we grow to how we respond to stress.
The endocrine system works alongside the nervous system to control and coordinate body functions.
While the nervous system sends electrical signals through nerves for quick responses, the endocrine system sends chemical signals through the blood for longer-lasting effects.
Understanding how hormones work helps us understand many important body processes, from how we grow to how we respond to stress.
What Are Hormones? #
A hormone is a chemical substance that acts as a messenger in your body. Hormones are produced by special glands called endocrine glands, and they travel through your bloodstream to reach their target organs. When a hormone reaches its target organ, it causes that organ to change its activity in some way.
Key Features of Hormones:
- Chemical substances: Hormones are made of different types of chemicals, but they all act as messengers
- Produced by glands: Special organs called endocrine glands make and release hormones
- Carried by blood: Hormones travel around the body in the bloodstream
- Target specific organs: Each hormone affects only certain organs that have the right receptors
- Alter activity: Hormones change how target organs work – they might speed up, slow down, or change their function
How Hormones Work – The Body’s Messaging System:
Think of hormones like messages on Viber or WhatsApp. The endocrine gland is like your phone when you type and send a message (hormone).
Your bloodstream is like the internet that carries your message around the body.
The target organ is like the specific person who receives your message – but just like on Viber, only organs with the right “phone number” (receptors) can receive and understand each specific hormone message.
Think of hormones like messages on Viber or WhatsApp. The endocrine gland is like your phone when you type and send a message (hormone).
Your bloodstream is like the internet that carries your message around the body.
The target organ is like the specific person who receives your message – but just like on Viber, only organs with the right “phone number” (receptors) can receive and understand each specific hormone message.
Major Endocrine Glands and Their Hormones #
Your body has several important endocrine glands, each producing specific hormones that control different body functions. For IGCSE Biology, you need to know five main glands and the key hormones they produce.- Adrenal Glands
- Pancreas
- Pituitary Gland
- Testes
- Ovaries
Adrenal Glands #
The adrenal glands are small, triangular-shaped glands that sit on top of your kidneys.
You have two adrenal glands – one on each kidney. These glands are like your body’s emergency response system, producing hormones that help you deal with stressful or dangerous situations.
You have two adrenal glands – one on each kidney. These glands are like your body’s emergency response system, producing hormones that help you deal with stressful or dangerous situations.
Location: On top of both kidneys
Main Hormone: Adrenaline
Main Function: Prepares the body for “fight or flight” responses during emergencies
Main Hormone: Adrenaline
Main Function: Prepares the body for “fight or flight” responses during emergencies
Pancreas #
The pancreas is a large gland located behind your stomach. It produces hormones that control blood sugar levels.
Location: Behind the stomach
Main Hormones: Insulin and Glucagon
Main Function: Controls blood glucose (sugar) levels
Main Hormones: Insulin and Glucagon
Main Function: Controls blood glucose (sugar) levels
Pancreatic Hormones:
- Insulin: Lowers blood glucose levels by helping cells absorb glucose from the blood
- Glucagon: Raises blood glucose levels by causing the liver to convert its stored Glucagon into Glocose and release it into the blood
Pituitary Gland #
The pituitary gland is often called the master gland because it controls many other glands in the body.
It’s about the size of a small bean and is located in the brain, just behind your eyes.
It’s about the size of a small bean and is located in the brain, just behind your eyes.
Location: Base of the brain
Hormones Produced: FSH and LH
Main Function: The hormones it produces mainly control other glands and also control the reproductive processes
Hormones Produced: FSH and LH
Main Function: The hormones it produces mainly control other glands and also control the reproductive processes
What FSH and LH Hormones do:
- FSH (Follicle-Stimulating Hormone):
- Triggers egg development in ovarie
- Triggers sperm production in testes
- LH (Luteinising Hormone):
- Triggers ovulation in females
- Triggers testosterone production in males
Testes (Male Reproductive Glands) #
The testes are the male reproductive glands. Besides producing sperm, they also act as endocrine glands by producing the male sex hormone testosterone.
Location: In the scrotum
Main Hormone: Testosterone
Main Function: Controls male sexual development and characteristics
Main Hormone: Testosterone
Main Function: Controls male sexual development and characteristics
What Testosterone Does:
1) It controls the development of male puberty, such as deepening of the voice, growth of facial hair, muscle development.
2) It also causes the testes to produce sperms.
1) It controls the development of male puberty, such as deepening of the voice, growth of facial hair, muscle development.
2) It also causes the testes to produce sperms.
Ovaries (Female Reproductive Glands) #
The ovaries are the female reproductive glands. Overies have two jobs:
1) producing eggs
2) producing female sex hormones
– Oestrogen
– Progesterone
A woman has two ovaries that are located in the lower abdomen.
1) producing eggs
2) producing female sex hormones
– Oestrogen
– Progesterone
A woman has two ovaries that are located in the lower abdomen.
Location: Lower abdomen, on either side of the uterus
Main Hormones: Oestrogen and Progesterone
Main Function: Controls female sexual development and menstrual cycle
Main Hormones: Oestrogen and Progesterone
Main Function: Controls female sexual development and menstrual cycle
What Oestrogen and Progesterone do
- Oestrogen:
- Controls female sexual development during puberty
- Prepares the uterus lining to received a fertilised egg. This happens during the menstrual cycle
- Progesterone:
- Maintains the uterus lining during pregnancy
Adrenaline – The Emergency Hormone #
Adrenaline is one of the most important hormones to understand because it shows how the endocrine system helps us respond to emergencies.
When you’re scared, excited, or in danger, your adrenal glands release adrenaline into your bloodstream.
This hormone quickly prepares your body for action by making several important changes in your body.
When you’re scared, excited, or in danger, your adrenal glands release adrenaline into your bloodstream.
This hormone quickly prepares your body for action by making several important changes in your body.
What Adrenaline Does to Your Body #
What Does Adrenaline Do:
- Increases blood glucose concentration: Makes more energy available for muscles so that you can act quickly
- Increases heart rate: Pumps blood faster to deliver oxygen and glucose to muscles, do that your muscles have power to act quickly
Why Adrenaline Increases Blood Glucose: When you’re in danger, your muscles need extra energy to help you run away or fight.
Adrenaline tells the liver to convert the glycogen that it has stored, into glucose and release it into the blood. This gives your muscles the extra fuel they need for quick action.
Adrenaline tells the liver to convert the glycogen that it has stored, into glucose and release it into the blood. This gives your muscles the extra fuel they need for quick action.
Adrenaline Increases Heart Rate: Faster heart rate means your blood pumps around your body more quickly.
This delivers the extra glucose and oxygen to your muscles faster, helping them work more efficiently when you need to respond to danger.
This delivers the extra glucose and oxygen to your muscles faster, helping them work more efficiently when you need to respond to danger.
When Adrenaline Is Released #
Adrenaline is released in situations where your body needs to be prepared for quick action. These are often called “fight or flight” situations because your body is getting ready to either fight the danger or run away from it.
Examples of Situations That Trigger Adrenaline Release:
- Dangerous situations: Seeing a car coming toward you, hearing a loud crash, or being chased
- Exciting activities: Riding a roller coaster, bungee jumping, or playing in an important sports match
- Stressful events: Taking an important exam, giving a presentation, or performing on stage
- Sudden surprises: Someone jumping out to scare you or hearing unexpected loud noises
- Physical challenges: Intense exercise or athletic competitions
Real-Life Example: Imagine you’re walking down the street and suddenly a large dog starts barking and running toward you. Your brain recognizes this as a potential threat, and your adrenal glands immediately release adrenaline. Within seconds, your heart starts beating faster, and glucose floods into your bloodstream. This gives you the energy and blood flow you need to either run away quickly or stand your ground – classic “fight or flight” response.
Nervous vs Hormonal Control #
Your body has two main control systems: the nervous system (which sends electrical signals through nerves) and the endocrine system (which sends chemical signals through hormones). Both systems help coordinate body functions, but they work in very different ways. Understanding these differences helps explain why your body uses each system for different types of responses.
| Nervous System | Hormones System | |
|---|---|---|
| Speed of Action | Very fast (milliseconds) | Slower (seconds or even minutes) |
| Duration of Effect | Short-lasting (stops quickly when stimulus ends) | Long-lasting (continues for minutes to hours) |
| Type of Signal | Electrical impulses | Chemical messengers |
| How Signals Travel | Through nerve fibers | Through bloodstream |
| Target | Very specific (where the nerve ends) | Larger targets (organs with receptors) |
Speed of Action #
The nervous system is much faster than the hormonal system. Nerve impulses can travel at speeds up to 120 meters per second, allowing almost instant responses. For example, if you touch something hot, nerve signals reach your brain and send a signal back to your muscles in a fraction of a second, making you pull your hand away immediately.
Hormonal control is slower because hormones have to be produced by glands, released into the bloodstream, travel through the circulatory system, and then reach their target organs. This process takes much longer – from several seconds to several minutes.
Speed Example: When you accidentally touch a hot stove, your nervous system makes you pull your hand away in less than a second. But if you’re scared by the same situation, it takes several seconds for adrenaline to be released and affect your heart rate and blood glucose levels.
Duration of Effect #
Nervous system effects are usually short-lasting. As soon as the stimulus stops or the nerve impulse ends, the response stops too. This is perfect for quick, temporary responses like moving away from danger or adjusting your balance.
Hormonal effects last much longer because hormones remain in the bloodstream for extended periods. Even after the original stimulus is gone, the hormones continue to affect target organs until they are broken down or removed from the blood.
Duration Example: If someone startles you by jumping out, your nervous system makes you jump immediately, but this reaction stops as soon as you realize what happened. However, the adrenaline released during this scare will keep your heart racing and maintain high blood glucose levels for several minutes afterward.
Why Both Systems Are Important #
When to Use Each System: The nervous system is perfect for situations that need immediate, precise responses – like reflexes, movement, and sensory responses. The hormonal system is ideal for processes that need to be coordinated over longer periods – like growth, reproduction, and maintaining steady blood glucose levels.
Examples of When Each System Is Used:
- Nervous control examples: Pulling hand away from heat, adjusting balance when walking, focusing your eyes on an object
- Hormonal control examples: Growing taller during puberty, maintaining blood sugar levels throughout the day, preparing the body for pregnancy
- Both systems working together: During exercise, nerves control immediate muscle movements while hormones like adrenaline provide sustained energy and increased heart rate
Summary: Key Points About Mammalian Hormones #
Essential Understanding: Hormones are chemical messengers that coordinate body functions over longer time periods.
They are produced by endocrine glands, travel in the blood, and affect specific target organs.
The hormonal system works together the nervous system to control body functions.
Hormones are slower-acting and longer-lasting than nerve signals.
They are produced by endocrine glands, travel in the blood, and affect specific target organs.
The hormonal system works together the nervous system to control body functions.
Hormones are slower-acting and longer-lasting than nerve signals.
Key Endocrine Glands and Hormones to Remember:
- Adrenal glands: Produce adrenaline for emergency responses
- Pancreas: Produces insulin and glucagon to control blood glucose
- Pituitary gland: Produces FSH and LH for reproductive control
- Testes: Produce testosterone for male characteristics
- Ovaries: Produce oestrogen and progesterone for female characteristics
Adrenaline’s Key Effects:
- Increases blood glucose concentration: Provides more energy for muscles
- Increases heart rate: Delivers oxygen and glucose faster to muscles
- Released during: Dangerous, exciting, stressful, or surprising situations
Quick Comparison: Nervous vs Hormonal Control
| Nervous System | Hormonal System |
|---|---|
| Fast action (milliseconds) | Slower action (seconds to minutes) |
| Short duration | Long duration |
| Electrical signals through nerves | Chemical signals through blood |
Exam Tips: Remember that hormones are always chemical substances, they always travel in the blood, and they always have specific target organs.
When describing adrenaline’s effects, focus on the two main changes:
1) increased blood glucose
2) increased heart rate
For nervous vs hormonal comparisons, think “fast but brief” for nervous control and “slow but lasting” for hormonal control.
When describing adrenaline’s effects, focus on the two main changes:
1) increased blood glucose
2) increased heart rate
For nervous vs hormonal comparisons, think “fast but brief” for nervous control and “slow but lasting” for hormonal control.
Real-World Connections: Understanding hormones helps explain many everyday experiences –
– Why you feel energetic after being scared, why teenagers go through growth spurts
– Why people with diabetes need insulin injections
– Why athletes’ hearts beat faster during competitions.
The endocrine system plays a crucial role in keeping our bodies functioning properly and responding appropriately to different situations.
– Why you feel energetic after being scared, why teenagers go through growth spurts
– Why people with diabetes need insulin injections
– Why athletes’ hearts beat faster during competitions.
The endocrine system plays a crucial role in keeping our bodies functioning properly and responding appropriately to different situations.
