Hi! My name is Rover B. Casey! You can call me RBC!  

I'm a positive guy and I love to go with the flow.

 I’m a red blood cell, a blood hound if you will, and I live inside a dog named Calypso! 

I have about 25 trillion brothers and sisters and we work hard all day! 

This is Calypso! She’s a five-year-old Bernese Mountain Dog. 

Today, I am going to take you on an adventure with me as I go through my home in the cardiovascular system.

What does a cardiovascular system look like? I'll show you! 

When I draw a picture of a simple Cardiovascular system, it looks like a tree with a heart at the base. 

 The trunk is made of the Aorta and Vena Cava, the arteries and veins are limbs, the arterioles and venules are branches and the capillaries are twigs. Cells are like leaves that grow on the twigs.  

Half of the system goes away from the heart and the other half goes towards it. Its filled with a fluid called Plasma.

But since dogs and other animals aren't shaped like trees, this is what it actually looks like, at least in Calypso.

It reminds me of a looping path through a park, but instead of people and dogs it has blood cells running along it. The whole system could be called the Cardio Trail! 

 But what does it do? Why is it important? 

Let’s take a closer look! We’ll start right here, near the lung.

There’s a lot of little air sacs called the Alveolus in the lungs that connect the lung to the blood stream. They look a bit like grapes. 

This is o2! He travelled through an Alveoli to be here. He is smaller than me, but he has a lot of nutrients that he needs to deliver. 

Today, he wants to visit Celly Pawpad, a cell who lives at the end of Calypso’s back leg.

I will carry him all the way there!  

As a red blood cell, I'm like a taxi, always carrying a passenger with me on the Cardio Trail. My riders are either Oyxgen (o2) or Carbon Dioxide. (Co2). 

We'll get to Co2 later. 

We’ll head for the heart via the Pulmonary Vein. Usually, veins don’t carry blood with oxygen, but this one does.

On the way, we go through a stent. 

A few years ago,  Calypso got really sick. Her pulmonary vein collapsed, and blood had a hard time getting through.

So, the vet put in a metal tube called a stent to keep the vein open. She made a full recovery. 

The stent ends at the left atrium of the heart. 

The heart, also called the Myocardium, is kind of like a visitor’s center for us blood hounds: a gathering place with two big entrance atriums and two big chambers called ventricles. It is powered by the coronaries. 

The heart is split up into left and right sections  by a wall called the septum. 

There is a constant beating in here.

The whole heart contracts and relaxes about 60 times a minute when Calypso isn’t running or playing. The contraction pushes blood through the Cardio trail. 

This contraction is called a systole. When it relaxes, it’s called diastole. The sound is kind of like a beating drum; ba-bump, 

ba-bump, ba-bump. 

Calypso's heart beats about 90,000 times a day. 

Each chamber also has a one-way exit door called a valve. Think of it like a turnstile. They take turns opening and shutting when the heart contracts. 

There’s no turning around once 

you’re through, since blood should only go in one direction.

The turnstile between the left atrium and ventricle is called the mirtal valve.     

The left ventricle leads into the Aorta, through the Aortic valve. The cane-shaped Aorta is the biggest artery in the body.

 It’s a smooth long tunnel, like a footpath in the woods covered by trees. 

There are lots of other paths that branch off the Aorta. These are also arteries, like the femoral artery.

These arteries branch off to the smaller arterioles. 

The arterioles are more flexible and snake through parts of the body that are too condensed for the arteries. 

There can be trouble on the Cardio trail. There’s a hole in this arteriole! 

It was caused by another dog biting Calypso on the leg. The platelets, clotting agents, work hard to patch up the hole. They are like little construction workers.

Oh no! Some bacteria got in! He could make Calypso sick. 

Thankfully, she has some incredible friends in her bloodstream that will try to protect her: the white blood cells! They are like guard dogs that patrol the Cardio Trail and get rid of any intruders.