🫀 Human Circulatory System
Primary 5 Science — Summary Notes
Created by Miss Clarissa Ng · www.clartutors.com
1. Parts of the Circulatory System
The circulatory system consists of three basic components:
- Heart — a muscular pump.
- Blood vessels — a set of tubes through which blood is transported.
- Blood — a circulatory fluid.
2. Functions of the Circulatory System
- Transports digested food, oxygen and water to all parts of the body.
- Transports waste materials like carbon dioxide away from the body.
- Protects the body from infection.
3. The Heart, the Blood and the Blood Vessels
| Component | What you need to know |
|---|---|
| Heart | The heart is made of heart muscles that pump blood to all parts of the body by continuously contracting and relaxing. The heart is located between the lungs, and is protected by the ribcage. |
| Blood | The blood carries digested food, oxygen, water and waste substances around our body. Blood is made up of plasma, red blood cells, white blood cells and platelets. The red blood cells carry oxygen to all parts of our body. |
| Blood vessels | Blood vessels are tubes that carry blood to all parts of the body. The three main types of blood vessels are the arteries, the veins and the capillaries. |
4. Flow of Blood
- Blood rich in oxygen flows from the lungs to the heart.
- The heart then pumps the oxygen-rich blood to the other parts of the body.
- The body cells take in oxygen and digested food from the blood to carry out respiration.
- Carbon dioxide and other waste substances produced by the body cells enter the blood.
- The blood becomes poor in oxygen and flows back to the heart.
- The heart then pumps the oxygen-poor blood back to the lungs, where the carbon dioxide in the blood is exchanged for oxygen.
- The blood becomes rich in oxygen again and the whole cycle repeats.
⭐️ KEY POINT
Lungs → heart → body → heart → lungs. Blood is rich in oxygen on the way out to the body, and poor in oxygen on the way back.
5. Heart Beat
- The heart contracts and relaxes in a rhythmic cycle.
- One complete cycle of contraction and relaxation is known as a heartbeat.
- The heart rate is the number of heartbeats in a minute. It is expressed as "beats per minute" (bpm).
- The heart rate changes according to a person's activity.
6. Effects of Exercising on Heart Rate
MEMORISE! (BE PORED)
When we exercise, our Body needs more Energy. Thus, our heart Pumps faster to transport more Oxygen and digested food in the blood to other parts of our body faster, to undergo a greater rate of Respiration to release more Energy. This also allows carbon Dioxide given out during respiration to be removed faster.
| Letter | Stands for | The answer, in full |
|---|---|---|
| B | Body | Our body needs more energy. |
| E | Energy | Our body needs more energy. |
| P | Pumps | The heart pumps faster. |
| O | Oxygen | To transport more oxygen and digested food in the blood to other parts of our body faster. |
| R | Respiration | To undergo a greater rate of respiration. |
| E | Energy | To release more energy. |
| D | Dioxide | Carbon dioxide given out during respiration is removed faster. |
7. Fish vs Human — Circulatory Systems
Humans — Double Circulation
The human circulatory system is described as having double circulation as blood passes through the heart twice in one complete circuit around the body.
Fish — Single Circulation
In fish, blood only passes through the heart once. As such, fish are described as having a single circulatory system.
Blood flows in two loops in the circulatory system of humans:
- First loop: blood flows from the heart to the lungs and back to the heart.
- Second loop: blood also flows from the heart to the other parts of the body and back to the heart.
Blood flows in one loop in the circulatory system of fish:
- Blood flows from the heart to the gills and then to the other parts of the body before returning to the heart.
👀 SIMILARITIES
- Both circulatory systems consist of the heart, blood and blood vessels.
- In both systems, a heart is present to pump blood to all parts of the organism.
- In both systems, blood is transported in blood vessels.
8. How Our Body Systems Work Together
- The digestive system and the respiratory system are two organ systems that work closely together with the circulatory system.
- Digested food and water from the digestive system enter the circulatory system to be circulated around the body.
- Oxygen from the respiratory system enters the circulatory system to be circulated.
- Carbon dioxide from oxygen-poor blood leaves the circulatory system and enters the respiratory system to be removed out of the body.
9. Humans vs Plants
| Differences | Similarities |
|---|---|
| Humans have a heart to pump substances, while plants do not have a heart. | Both systems consist of tubes for the transportation of substances. |
| Humans have blood vessels to transport substances, while plants have food-carrying tubes and water-carrying tubes. | In both systems, water and nutrients are transported through the tubes to all parts of the organism. |
| In humans, digested food, oxygen, water and waste substances are all transported by blood in blood vessels, while different substances are carried in different tubes in plants. |
10. Common Question — Removing Carbon Dioxide
How does our body remove carbon dioxide produced during respiration?
- Carbon dioxide enters the blood, which flows to the heart.
- The heart then pumps the blood rich in carbon dioxide to the lungs.
- Carbon dioxide leaves the blood and enters the lungs.
- Carbon dioxide is removed from the human body through the nose when a person exhales.
11. Effects of Narrowed Blood Vessels
- The fatty deposits result in a smaller opening for blood to flow through, reducing the amount of blood flowing through the blood vessels.
- Hence, the heart of Person Y with narrowed blood vessels has to pump faster to transport the same amount of oxygen and digested food in the blood to other parts of the body for respiration.
🧪 EXAM TIP
Narrower vessels → less blood flows through per pump → the heart must pump faster to deliver the same amount of oxygen and digested food.