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Unlock This CourseBlood is amazing stuff! It's constantly flowing around your body, delivering everything your cells need to stay alive. Think of it as your body's delivery service - it brings oxygen, food and removes waste. But what exactly is blood made of?
Blood isn't just a red liquid. It's actually made up of four main parts, each with a special job to do. About 55% of your blood is a yellowish liquid called plasma, whilst the remaining 45% consists of different types of cells floating around in it.
Key Definitions:
If you looked at a drop of blood under a microscope, you'd see thousands of tiny red discs floating in a clear liquid. These are red blood cells in plasma. You'd also spot some larger, oddly-shaped white blood cells and tiny fragments called platelets.
Red blood cells are the most numerous cells in your blood - you have about 25 trillion of them! They're perfectly designed for one main job: carrying oxygen from your lungs to every cell in your body.
Red blood cells have some brilliant adaptations that make them excellent at their job:
They're biconcave discs - like doughnuts without holes. This shape gives them a large surface area for absorbing oxygen and makes them flexible enough to squeeze through tiny blood vessels.
Mature red blood cells don't have a nucleus. This leaves more room for haemoglobin - the special protein that carries oxygen.
This iron-containing protein gives blood its red colour. Each haemoglobin molecule can carry up to four oxygen molecules.
Red blood cells live for about 120 days before they're broken down and recycled. Your bone marrow is constantly making new ones - about 2 million every second!
Athletes often train at high altitudes where there's less oxygen in the air. Their bodies respond by making more red blood cells to capture as much oxygen as possible. When they return to sea level, they have extra oxygen-carrying capacity, giving them an advantage in competitions.
White blood cells are like your body's army - they patrol your bloodstream looking for invaders like bacteria, viruses and other harmful substances. Although they're called 'white' cells, they're actually colourless.
There are several different types of white blood cells, each with special roles in keeping you healthy:
These cells literally eat harmful microorganisms! They engulf bacteria and viruses in a process called phagocytosis. Think of them as cellular vacuum cleaners, sucking up anything that shouldn't be there.
These cells make antibodies - special proteins that stick to specific germs and mark them for destruction. They also remember past infections, which is why you don't usually get the same disease twice.
White blood cells can change shape and squeeze through blood vessel walls to reach infected tissues. When you have an infection, your body makes more white blood cells, which is why a blood test can help doctors diagnose illness.
Platelets aren't actually whole cells - they're tiny fragments of larger cells made in your bone marrow. But don't let their size fool you - they have a crucial job in stopping bleeding when you're injured.
When you cut yourself, platelets spring into action in a carefully coordinated process:
Platelets detect damage to blood vessel walls and become sticky, clumping together at the injury site.
More platelets stick to the first ones, forming a temporary plug to slow down bleeding.
Platelets release chemicals that trigger a cascade of reactions, forming fibrin threads that create a strong, permanent clot.
Without platelets, even a small cut could be life-threatening because the bleeding wouldn't stop. People with low platelet counts bruise easily and may bleed for longer than normal.
Plasma makes up about 55% of your blood volume and is roughly 90% water. But this isn't just any water - it's packed with dissolved substances that are essential for life.
Plasma is like a busy motorway, carrying all sorts of important cargo around your body:
Glucose from digested food, amino acids from proteins and fatty acids from fats are all transported in plasma to cells that need energy and building materials.
Carbon dioxide from cellular respiration and urea from protein breakdown are carried in plasma to organs that can remove them from the body.
Plasma also contains hormones (chemical messengers), antibodies for fighting disease and proteins that help maintain blood pressure and clotting. It even helps regulate your body temperature by distributing heat around your body.
When you donate blood, you're giving about 470ml of whole blood. Your body quickly replaces the plasma within 24 hours by absorbing water from your tissues. Red blood cells take longer to replace - about 4-6 weeks. This is why there's a minimum 12-week gap between blood donations to ensure your red blood cell levels return to normal.
All four blood components work as a team to keep your body functioning properly. Red blood cells couldn't do their job without plasma to carry them around. White blood cells need plasma to transport their antibodies. Platelets require plasma proteins to form effective clots.
This teamwork makes blood one of the most efficient transport systems in nature. Every minute, your heart pumps about 5 litres of blood around your entire body, ensuring that every cell gets what it needs to survive and thrive.
Understanding blood composition helps explain many medical procedures and conditions. Blood tests can reveal infections (high white cell count), anaemia (low red cell count), or clotting disorders (low platelet count). It's truly remarkable how much information this red liquid can tell us about our health!