How do the circulatory and respiratory systems work together?
Think of it as a delivery business. The lungs are the warehouse where oxygen comes in and waste goes out. The blood vessels are the roads. The heart is the engine that keeps every van moving.
What are the organs of the circulatory system?
This is a common surprise on tests: Cleveland Clinic notes the heart is the system’s only organ. Everything else is a vessel. The lungs belong to the respiratory system, even though blood passes through them.
| Part | Job |
|---|---|
| Heart | The muscular pump that moves your blood |
| Arteries | Carry blood away from the heart, including the aorta, the largest |
| Veins | Bring blood back to the heart, including the vena cava |
| Capillaries | Thin-walled tiny vessels where oxygen, carbon dioxide, nutrients and waste are exchanged |
What is the path of blood through the heart and lungs?
- Back from the bodyOxygen-poor blood enters the right side of the heart through the vena cava.
- To the lungsThe right ventricle pumps it through the pulmonary artery.
- The swapIn capillaries around the alveoli, blood gives up carbon dioxide and collects oxygen.
- Back to the heartOxygen-rich blood returns to the left side through the pulmonary veins.
- Out to the bodyThe left ventricle pushes it through the aorta, and the loop starts over.
Doctors split the trip in two: the pulmonary circulation is the heart-to-lungs part, and the systemic circulation is the heart-to-body part. Yes, the pulmonary artery carries oxygen-poor blood and the pulmonary veins carry oxygen-rich blood, the opposite of the rest of the body. Arteries lead away from the heart and veins lead back. That’s the rule to remember.
Circulatory vs respiratory system: what’s the difference?
| Respiratory | Circulatory | |
|---|---|---|
| Moves | Air | Blood |
| Main parts | Airways, lungs, diaphragm | Heart, arteries, veins, capillaries |
| Job | Brings oxygen in, sends carbon dioxide out | Takes oxygen and nutrients around, collects waste |
| Where they meet | Around the alveoli | |
Explaining the circulatory system to kids? The delivery-van version works well: the heart is the engine, blood is the van, oxygen is the parcel, and every part of your body is an address. Our respiratory system for kids guide has an experiment you can do with a timer.
Why does your heart rate change when you breathe?
Your heart rate rises a little as you breathe in and falls a little as you breathe out. The name for this is respiratory sinus arrhythmia. Despite the scary word, it’s normal. Try it: find your pulse at your wrist, breathe slowly, and see if you can catch it.
A 2018 systematic review found that slow breathing increases both this effect and heart-rate variability. It also says the evidence is limited: only 15 studies qualified, and most were small. So: a real, measurable link between the two systems, and one to be modest about.
Feel the two systems talk
Fingers on your wrist. Breathe in for 5, out for 5. Your pulse may ease as you breathe out.
5 in · 5 out
Follow the orb: in as it grows, out as it shrinks.
Seconds per phase: 5 in · 5 out. Turn on JavaScript to use the timer.
Runs in your browser: nothing is saved or sent. For haptic taps with your eyes closed, or on your wrist, use ATHA on iPhone or Apple Watch.
Common questions
What organs are in the circulatory system?
The heart is the only organ. The rest of the system is blood vessels: arteries, veins and capillaries. The lungs are part of the respiratory system.
Where do the circulatory and respiratory systems meet?
In the lungs, at the capillaries wrapped around the alveoli. That is where oxygen enters the blood and carbon dioxide leaves it.
Which side of the heart pumps blood to the lungs?
The right side. The left side pumps oxygen-rich blood to the rest of the body.
What happens if one of the systems stops working well?
The other is affected, because the two depend on each other. Conditions affecting the lungs can put a strain on the heart, and the reverse can be true. Ongoing breathlessness or chest symptoms are worth checking with a doctor.
Does breathing slowly lower your heart rate?
Your heart rate falls a little on each out-breath, and slow breathing is linked in studies with higher heart-rate variability. The evidence is limited, and breathing exercises don’t treat heart conditions.
Where does ATHA fit in?
That pulse-and-breath link is the reason ATHA has a Coherence pattern: 5 seconds in, 5 out, about six breaths a minute. The app doesn’t measure your heart or claim to change it. It keeps the rhythm, so all you have to do is follow along.
Thanks for reading all the way to the veins and arteries. Tell me what to explain next.
Indie iOS developer, and the maker of ATHA. Say hello on Instagram or at solostaseraofficial@gmail.com.
Sources
Checked on 3 November 2026.
- NHLBI: How blood flows through the heart · Last updated 25 June 2025.
- Cleveland Clinic: Circulatory system · Last updated 4 September 2024.
- NHLBI: The respiratory system · Last updated 24 March 2022.
- Zaccaro A et al. How breath-control can change your life: a systematic review on psycho-physiological correlates of slow breathing. Frontiers in Human Neuroscience, 2018
ATHA is a breathing and mindfulness app, not a medical device, and this guide is general information, not medical advice. It doesn’t diagnose or treat any condition. For a symptom that is persistent, severe or worrying, talk to a doctor. In an emergency, call your local emergency number.