# Blood Circulation in Human Body - Grade 10 (SEE) Science
## Complete Chapter Notes with All Exercises - NEB Curriculum
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## 🎯 Chapter Overview
**Think of your body as a bustling city. The roads are your blood vessels, the vehicles are your blood cells, and the central transport hub is your heart.** This chapter, "Blood Circulation in Human Body," explores this incredible transport system that keeps you alive. These notes will make understanding this complex network simple and fascinating.
**This is a vital chapter in biology with high importance in the SEE exam, especially the diagram of the heart and the concept of double circulation.** We'll break down the components—blood, blood vessels, and the heart—and trace the journey of blood as it delivers oxygen and nutrients and removes waste. Every exercise from your textbook is solved here, with clear, easy-to-follow explanations.
**Weightage:** 7-9 marks in SEE examination
**Time Required:** 15-20 periods
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## 📚 Learning Objectives
After studying this chapter, you will be able to:
- Identify the three main components of the circulatory system.
- Describe the composition and functions of blood, including plasma and blood cells.
- Differentiate between arteries, veins, and capillaries.
- Draw a labeled diagram of the human heart and describe its structure.
- Explain the mechanism of double circulation (pulmonary and systemic).
- Understand concepts like heartbeat and blood pressure.
- Identify the causes, symptoms, and preventive measures of some circulatory disorders.
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##🩸 1. BLOOD: The Fluid of Life
**Blood** is a vital red fluid connective tissue that circulates throughout our body. An average adult has about 5-6 litres of blood. It's composed of two main parts: Plasma and Blood Corpuscles.

### A. Plasma (55% of Blood)
Plasma is the pale-yellow, liquid matrix of the blood. It consists of about 90% water and 10% dissolved substances.
- **Function:**
  1.  **Transport:** Carries digested food, hormones, waste products (like urea), and proteins.
  2.  **Regulation:** Helps in regulating body temperature.
  3.  **Clotting:** Contains proteins like fibrinogen, which are essential for blood clotting.

### B. Blood Corpuscles/Cells (45% of Blood)
These are the cells suspended in the plasma.

| Cell Type | Other Name | Key Features | Main Function |
|---|---|---|---|
| **RBCs** | Erythrocytes | Biconcave discs, no nucleus at maturity, red due to **hemoglobin**. Most numerous blood cell. | Transport oxygen from lungs to body tissues. |
| **WBCs** | Leucocytes | Irregular shape, have a nucleus, larger than RBCs. Can move like an amoeba. | **Body's defense system.** They engulf germs and produce antibodies to fight infections. |
| **Platelets**| Thrombocytes| Tiny, irregular cell fragments, no nucleus. | Help in **blood clotting** at the site of an injury to prevent excessive bleeding. |


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## 🛣️ 2. BLOOD VESSELS: The Body's Highway Network
Blood vessels are a network of tubes that transport blood throughout the entire body.

| Feature | Arteries | Veins | Capillaries |
|---|---|---|---|
| **Function** | Carry blood **AWAY** from the heart. | Carry blood **TOWARDS** the heart. | Connect arteries to veins; site of exchange. |
| **Blood Type** | **Oxygenated** (except Pulmonary Artery). | **Deoxygenated** (except Pulmonary Veins). | Exchange of gases and nutrients occurs here. |
| **Wall** | **Thick**, muscular, and elastic to withstand high pressure. | **Thin** and less muscular. | **Extremely thin** (one-cell thick) for easy diffusion. |
| **Pressure** | Blood flows under **high pressure** and speed. | Blood flows under **low pressure** and speed. | Pressure is very low. |
| **Valves** | Absent (pressure from the heart prevents backflow). | **Present** to prevent the backflow of blood. | Absent. |

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## ❤️ 3. THE HEART: The Super Pump
The heart is a muscular organ, about the size of a fist, that pumps blood continuously. It has four chambers.
**Analogy:** Think of the heart as a two-story house with two rooms on each floor. The upper floors are **Atria (Auricles)** and the lower floors are **Ventricles**.



### Chambers and Valves
- **Right Atrium (RA):** Receives deoxygenated blood from the body.
- **Right Ventricle (RV):** Pumps deoxygenated blood to the lungs.
- **Left Atrium (LA):** Receives oxygenated blood from the lungs.
- **Left Ventricle (LV):** Pumps oxygenated blood to the entire body. **(Has the thickest wall)**.

- **Valves:** These are like one-way doors that prevent blood from flowing backward.
  - **Tricuspid Valve:** Between the right atrium and right ventricle.
  - **Bicuspid (Mitral) Valve:** Between the left atrium and left ventricle.
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## 🔄 4. DOUBLE CIRCULATION: The Two-Circuit Journey
In humans, blood passes through the heart **twice** to make one complete circuit. This efficient system is called **double circulation**. It consists of two loops:

### A. Pulmonary Circulation (The "Lungs" Loop)
This circuit carries deoxygenated blood from the heart to the lungs and brings oxygenated blood back.
**Path:** **Right Ventricle** $\rightarrow$ Pulmonary Artery (deoxygenated blood) $\rightarrow$ **Lungs** (blood gets oxygenated) $\rightarrow$ Pulmonary Veins (oxygenated blood) $\rightarrow$ **Left Atrium**.

### B. Systemic Circulation (The "Body" Loop)
This circuit carries oxygenated blood from the heart to all body parts and brings deoxygenated blood back.
**Path:** **Left Ventricle** $\rightarrow$ Aorta (oxygenated blood) $\rightarrow$ **All Body Parts** (oxygen is delivered) $\rightarrow$ Vena Cava (deoxygenated blood) $\rightarrow$ **Right Atrium**.



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## 🩺 5. HEARTBEAT, BLOOD PRESSURE & DISORDERS

- **Heartbeat:** One complete contraction (systole) and relaxation (diastole) of the heart muscle. The normal rate for a resting adult is about **72 beats per minute**. This rate increases during exercise, fear, or excitement.
- **High Blood Pressure (Hypertension):** A condition where the force of the blood against the artery walls is too high.
  - **Causes:** Smoking, excessive alcohol consumption, stress, obesity, lack of exercise.
  - **Prevention:** Maintaining a healthy weight, regular exercise, balanced diet, avoiding smoking.
- **Uric Acid:** High levels can cause joint pain (gout). Prevention includes drinking plenty of water and consuming dairy products.
- **Diabetes:** A condition affecting blood sugar levels. Symptoms include frequent urination and slow healing of wounds.

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## 📋 6. COMPLETE EXERCISE SOLUTIONS

### **1. Differentiate Between:**
**a. Artery and Vein**
| Artery | Vein |
|---|---|
| Carries blood **away** from the heart. | Carries blood **towards** the heart. |
| Has **thick**, muscular, and elastic walls. | Has **thin**, less muscular walls. |
| Carries oxygenated blood (except pulmonary artery). | Carries deoxygenated blood (except pulmonary vein). |
| Blood pressure is high. | Blood pressure is low. |
| Valves are absent. | Valves are present to prevent backflow. |

**b. RBCs and WBCs**
| RBCs (Red Blood Corpuscles) | WBCs (White Blood Corpuscles) |
|---|---|
| Are biconcave and have no nucleus. | Are irregular in shape and have a nucleus. |
| Contain hemoglobin and are red. | Do not contain hemoglobin and are colorless. |
| Function is to transport oxygen. | Function is to protect the body from diseases. |
| They are more numerous. | They are less numerous (but increase during infection). |

**c. Auricles and Ventricles**
| Auricles (Atria) | Ventricles |
|---|---|
| The two **upper** chambers of the heart. | The two **lower** chambers of the heart. |
| Have **thin** muscular walls. | Have **thick** muscular walls (especially the left). |
| They **receive** blood from the body and lungs. | They **pump** blood to the lungs and body. |

### **2. Give Reasons:**
**a. The wall of the left ventricle is thicker than the right ventricle.**
**Answer:** The left ventricle has to pump oxygenated blood to all parts of the body, which requires a much greater force and higher pressure. The right ventricle only has to pump deoxygenated blood to the nearby lungs, which requires less force. Therefore, the left ventricle has a thicker, more muscular wall.

**b. Blood is red in colour.**
**Answer:** Blood is red due to the presence of a pigment called **hemoglobin** in the Red Blood Cells (RBCs). Hemoglobin contains iron, which binds with oxygen and gives blood its characteristic red colour.

**c. Arteries have thick and elastic walls.**
**Answer:** Arteries receive blood directly from the heart's powerful pumping action. Their thick, muscular, and elastic walls are necessary to withstand the **high pressure** of the blood flow without bursting.

**d. The number of WBCs in the blood increases during an infection.**
**Answer:** WBCs are the "soldiers" of the body's immune system. When the body is attacked by pathogens like bacteria or viruses, it produces more WBCs to fight off the infection and destroy the invaders.

**e. Donated blood is mixed with sodium citrate.**
**Answer:** Sodium citrate is an **anticoagulant**. It prevents the blood from clotting by binding with calcium ions, which are essential for the clotting process. This keeps the blood in a liquid state and suitable for storage and transfusion.

### **3. Answer the following questions:**
**a. What is the importance of blood circulation?**
**Answer:** Blood circulation is vital because it transports oxygen and nutrients to all body cells, removes waste products like carbon dioxide, helps regulate body temperature, and circulates WBCs and antibodies to fight diseases.

**b. What exchange takes place between blood capillaries and tissues?**
**Answer:** In the capillaries, oxygen and nutrients diffuse from the blood into the body tissues. At the same time, carbon dioxide and other waste products diffuse from the tissues into the blood to be carried away.

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## ✅ 7. CHAPTER CHECKLIST & EXAM TIPS
**Exam Hotspots 🔥:**
-   **Diagram of the Heart:** Practice drawing a neat, well-labeled diagram of the human heart. This is a very common question.
-   **Double Circulation:** Be able to draw a flowchart and explain the paths of both pulmonary and systemic circulation.
-   **Differences:** The difference between arteries and veins is a classic and frequently asked question.
-   **Give Reasons:** The reasons for the thick wall of the left ventricle and the thick walls of arteries are very important.

**Your Pre-Exam Checklist:**
- [ ] I can draw and label the four chambers and main vessels of the human heart.
- [ ] I can differentiate between an artery and a vein based on 3-4 points.
- [ ] I can describe the function of RBCs, WBCs, and platelets.
- [ ] I can explain the path of blood in both pulmonary and systemic circulation.
- [ ] I can explain why the left ventricle wall is the thickest.
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## 🎊 CONCLUSION
The human circulatory system is a masterpiece of engineering, working tirelessly every second of your life. Understanding how this system functions not only helps in your exams but also empowers you to appreciate your own body and make healthier life choices.
**Key to Success:** Master the Heart Diagram + Trace the Blood Flow + Understand the "Why" Questions = A Healthy Score!