Here's something amazing: you are mostly water. About 50-60% of your total body weight is water! If you weigh 70 kg, that's roughly 40 liters of water flowing through your cells, tissues, and blood vessels right now.

Think of your body like a city with an elaborate water system. Just like a city needs water mains, pipes, and drainage to function, your body needs a way to move this precious fluid around. That's where blood comes in.

Blood is your body's liquid delivery service. It carries oxygen from your lungs, nutrients from your gut, hormones from your glands, and removes waste products — all while zipping through about 96,000 km of blood vessels. That's like driving around the Earth twice!

Fluid compartments: Your body water lives in two main neighborhoods. About two-thirds is inside your cells (intracellular fluid), and one-third is outside your cells (extracellular fluid) — this includes blood plasma and the fluid between your cells.

Blood is like a busy highway system with different types of vehicles serving different purposes. Let's meet the fleet:

Red Blood Cells (Erythrocytes): These are your oxygen delivery trucks. They contain hemoglobin, a protein that grabs oxygen in your lungs and drops it off at your tissues. There are about 5 million of these in every tiny drop of blood!

White Blood Cells (Leukocytes): Your security patrol. They cruise through your bloodstream looking for invaders like bacteria and viruses. When they find trouble, they attack.

Platelets (Thrombocytes): The repair crew. When you get a cut, these tiny cell fragments rush to the scene and form a plug to stop the bleeding.

Plasma: The river itself — the yellowish liquid that carries all the cells plus nutrients, hormones, and proteins. It's about 90% water.

Your blood also maintains a delicate acid-base balance. Your blood pH needs to stay between 7.35 and 7.45 — that's slightly alkaline. Even small deviations can be dangerous because enzymes and proteins only work properly at the right pH.

Your body has two fluid transport systems that work together like a tag team:

The Cardiovascular System: This is your main circulation — the heart pumping blood through arteries, capillaries, and veins. Think of it as the express delivery service, constantly moving at high speed.

The Lymphatic System: This is like the drainage department. While blood circulates, some fluid leaks out into your tissues. The lymphatic system collects this excess fluid (now called lymph), filters it through lymph nodes, and returns it to your bloodstream. It's also crucial for your immune system.

This week, we'll dive deep into:

• The composition and functions of blood
• Different types of blood vessels and their roles
• How to interpret blood test results
• The lymphatic system's structure and function
• How your body maintains acid-base balance