Human Circulatory System – Quick Revision Notes

Humans possess two transport systems that move materials to different parts of the body:

Blood circulatory system
Lymphatic system

Blood – The Transport Medium

Blood transports dissolved nutrients, gases, hormones, and wastes throughout the body. It consists of:

Plasma (55%)
Cells / cell-like bodies (45%) → RBCs, WBCs, Platelets

HUMAN CIRCULATORY SYSTEM

It includes blood, heart, and blood vessels (arteries, capillaries, veins).

Structure & Functioning of Human Heart

The heart is a strong, muscular pump located in the middle of chest cavity, between lungs.

Back surface → near vertebral column
Front surface → behind sternum
Appears left-sided because left side is larger and stronger
Left lung is smaller and has a cardiac notch to accommodate the heart.

Pericardium

The heart is enclosed in a protective sac called pericardium, which:

Separates heart from surrounding organs
Protects from shocks
Prevents excessive dilation

Layers of Pericardium

Fibrous pericardium (outer)

Strong connective tissue
Protects from external pressure

2.Serous pericardium (inner sac)

Has two layers:

Parietal pericardium (beneath fibrous layer)
Visceral pericardium / Epicardium (attached to heart surface)

Pericardial cavity lies between parietal and visceral layers.

Contains ~50 mL pericardial fluid → lubricates heart & prevents infections.

Wall of the Heart

The heart wall has three layers:

Epicardium
- Outer lining (visceral pericardium)
Myocardium

Thickest layer
Made of cardiac muscles (responsible for contraction)

Endocardium

Inner lining
Single layer of epithelial cells covering chambers

Chambers of Heart

The human heart has four chambers:

Upper chambers (Atria)

Thin-walled
Receive blood

Lower chambers (Ventricles)

Thick-walled
Pump blood out

Septums:

Interatrial septum → separates atria
Interventricular septum → separates ventricles (much thicker)
Atrioventricular septum → separates atria from ventricles

Heart Valves

Valves ensure one-way flow of blood.

Atrioventricular (AV) Valves

Located at entrances of ventricles:

Tricuspid valve

Between right atrium → right ventricle
Has three cusps

Bicuspid (Mitral) valve

Between left atrium → left ventricle
Has two cusps

Function:
When ventricles contract, these valves close to prevent backflow into atria.

Semilunar Valves

Located at exits of ventricles:

Pulmonary valve → base of pulmonary artery
Aortic valve → base of aorta

Function:
When ventricles relax, semilunar valves close, preventing backflow from arteries into ventricles

✔️ MCQs on Human Circulatory System (Heart, Pericardium, Valves, Walls, Chambers)

(More than 60 MCQs — high-yield + conceptual)

🩸 BASIC & DIRECT FACT MCQs

The human circulatory system consists of blood, heart, and ________.
a) Kidneys
b) Lungs
c) Blood vessels
d) Nerves
Ans: c
Plasma constitutes about ____% of total blood volume.
a) 35%
b) 45%
c) 55%
d) 65%
Ans: c
Blood cells constitute about ____% of blood.
a) 10%
b) 25%
c) 45%
d) 75%
Ans: c
The human heart is located between the:
a) Kidneys
b) Lungs
c) Vertebrae
d) Clavicles
Ans: b
The left lung is smaller because:
a) It has more lobes
b) It stores oxygen
c) It has a cardiac notch
d) It is less vascular
Ans: c
The sac covering the heart is called:
a) Endocardium
b) Myocardium
c) Pericardium
d) Pleura
Ans: c
The fibrous pericardium is made of:
a) Smooth muscle
b) Connective tissue
c) Epithelial tissue
d) Cardiac muscle
Ans: b
Serous pericardium consists of:
a) One layer
b) Two layers
c) Three layers
d) Four layers
Ans: b
Epicardium is also called:
a) Parietal pericardium
b) Visceral pericardium
c) Endocardium
d) Fibrous pericardium
Ans: b
Pericardial cavity contains about ____ mL fluid.
a) 10 mL
b) 20 mL
c) 30 mL
d) 50 mL
Ans: d

🩺 HEART WALL MCQs

The thickest layer of heart wall is:
a) Endocardium
b) Epicardium
c) Myocardium
d) Serosa
Ans: c
Myocardium is made of:
a) Smooth muscle
b) Skeletal muscle
c) Cardiac muscle
d) Connective tissue
Ans: c
Endocardium is made of:
a) Epithelial cells
b) Connective tissue
c) Nerve tissue
d) Smooth muscle
Ans: a
The layer that directly lines heart chambers is:
a) Epicardium
b) Myocardium
c) Endocardium
d) Pericardium
Ans: c
The outermost layer of the heart wall is the:
a) Myocardium
b) Endocardium
c) Epicardium
d) Serosa
Ans: c

❤️ HEART CHAMBERS MCQs

The heart contains how many chambers?
a) 2
b) 3
c) 4
d) 6
Ans: c
Atria are:
a) Thick-walled
b) Thin-walled
c) Muscular
d) Cartilaginous
Ans: b
Ventricles are thick-walled because they:
a) Receive blood
b) Pump blood out
c) Store blood
d) Filter blood
Ans: b
The thickest septum is:
a) Interatrial
b) Atrioventricular
c) Interventricular
d) None
Ans: c
The right atrium receives blood from:
a) Pulmonary veins
b) Pulmonary artery
c) Venae cavae
d) Aorta
Ans: c

🛑 HEART VALVES MCQs

Tricuspid valve is present between:
a) LA → LV
b) RA → RV
c) RV → Pulmonary artery
d) LV → Aorta
Ans: b
Bicuspid valve is also called:
a) Pulmonary valve
b) Aortic valve
c) Mitral valve
d) Semilunar valve
Ans: c
Number of cusps in tricuspid valve:
a) 1
b) 2
c) 3
d) 4
Ans: c
Semilunar valves are found at:
a) AV junctions
b) Veins
c) Arterial exits
d) Atria
Ans: c
Pulmonary valve is located at:
a) Base of aorta
b) Base of pulmonary artery
c) Base of vena cava
d) Base of pulmonary vein
Ans: b
Aortic valve prevents backflow into:
a) RA
b) RV
c) LA
d) LV
Ans: d
When ventricles contract, AV valves:
a) Open
b) Close
c) Tear
d) Inflate
Ans: b
When ventricles relax, semilunar valves:
a) Open
b) Close
c) Collapse
d) Harden
Ans: b
Bicuspid valve lies on:
a) Left side
b) Right side
c) Dorsal side
d) Ventral side
Ans: a
Semilunar valves resemble the shape of a:
a) Crescent moon
b) Star
c) Triangle
d) Circle
Ans: a

🧠 CONCEPTUAL MCQs

The heart appears towards left because:
a) Right side is weaker
b) Left side pumps to whole body
c) Right ventricle is smaller
d) Lungs push it
Ans: b
Pericardial fluid mainly helps in:
a) Increasing blood pressure
b) Lubrication
c) Pumping blood
d) Gas exchange
Ans: b
If interventricular septum is damaged, which function is most affected?
a) Atrial contraction
b) Blood separation
c) Hormone secretion
d) Lymph transport
Ans: b
Which layer protects the heart from mechanical shocks?
a) Epicardium
b) Fibrous pericardium
c) Myocardium
d) Endocardium
Ans: b
If AV valves fail, blood will leak into:
a) Arteries
b) Veins
c) Atria
d) Body tissues
Ans: c
Which valve closes during ventricular systole?
a) Aortic
b) Pulmonary
c) Tricuspid
d) Both a & b
Ans: c
Backflow from aorta is prevented by:
a) AV valves
b) Chordae tendineae
c) Aortic semilunar valve
d) Papillary muscles
Ans: c
The inner lining of heart chambers is smooth to:
a) Absorb nutrients
b) Reduce friction
c) Filter blood
d) Produce hormones
Ans: b
Cardiac notch is present in:
a) Right lung
b) Trachea
c) Left lung
d) Heart wall
Ans: c
Ventricles have thicker walls than atria because they:
a) Store blood
b) Contract more forcefully
c) Do not receive veins
d) Are protected
Ans: b

🔥 HARD / BS-LEVEL APPLICATION MCQs

Maximum pressure is generated by:
a) Right atrium
b) Right ventricle
c) Left atrium
d) Left ventricle
Ans: d
Failure of semilunar valves primarily affects:
a) Atrial filling
b) Ventricular filling
c) Arterial backflow
d) Venous return
Ans: c
Thick interventricular septum ensures:
a) Equal oxygen flow
b) Separation of oxygenated & deoxygenated blood
c) Smooth flow in atria
d) Heart lubrication
Ans: b
The layer directly involved in pumping action is:
a) Epicardium
b) Myocardium
c) Pericardium
d) Endocardium
Ans: b
Pericarditis affects mainly the:
a) Valves
b) Pericardial fluid
c) Coronary arteries
d) Atria
Ans: b
If pericardial fluid increases excessively, heart compresses due to:
a) Hypertension
b) Cardiac tamponade
c) Hypoxia
d) Vasodilation
Ans: b

🧪 MORE MCQs (High Quantity for Tests)

Which valve prevents backflow into RV?
Ans: Pulmonary valve
Which valve prevents backflow into LV?
Ans: Aortic valve
Which chamber has the thickest wall?
Ans: Left ventricle
Heart is enclosed within:
Ans: Mediastinum
Valve between atria & ventricles are called:
Ans: AV valves
Valves between ventricles & arteries are called:
Ans: Semilunar valves
Visceral pericardium =
Ans: Epicardium
Parietal pericardium is part of:
Ans: Serous pericardium
Right side of heart receives:
Ans: Deoxygenated blood
Left side of heart receives:
Ans: Oxygenated blood
“Cusps” are:
Ans: Flaps of valves
The heart pumps about ___ times per minute.
Ans: ~72
Myocardium gets blood supply from:
Ans: Coronary arteries
Inner lining of heart is smooth to prevent:
Ans: Clot formation
Tricuspid valve ensures flow from:
Ans: RA → RV
Bicuspid valve ensures flow from:
Ans: LA → LV
Aorta arises from:
Ans: Left ventricle
Pulmonary artery arises from:
Ans: Right ventricle

✔️ SHORT QUESTIONS (Beautifully Explained, Not One-Line)

1. Why is the left side of the heart stronger than the right side?

The left side of the heart, especially the left ventricle, has a much thicker myocardium because it pumps oxygenated blood to the entire body against high resistance, whereas the right side only pumps blood to the nearby lungs.

2. What is the pericardium? Describe its function.

The pericardium is a double-layered protective sac surrounding the heart. It reduces friction using pericardial fluid, anchors the heart in the chest cavity, and protects it from sudden mechanical shocks or over-stretching.

3. Differentiate between fibrous and serous pericardium.

The fibrous pericardium is the tough outer layer made of dense connective tissue that prevents over-dilation of the heart. The serous pericardium is the inner, thin double-layered membrane (parietal + visceral) that secretes lubricating pericardial fluid.

4. What is pericardial fluid and why is it important?

Pericardial fluid, present in the pericardial cavity, acts as a lubricant that allows smooth, frictionless heartbeats. It also protects the heart from infections and cushions it during rapid movements.

5. Describe the three layers of the heart wall.

The outer epicardium protects the heart and forms the visceral pericardium. The middle myocardium, composed of cardiac muscle, performs the actual pumping action. The inner endocardium is a smooth epithelial lining that reduces friction inside heart chambers.

6. Why is the interventricular septum thicker than the interatrial septum?

The interventricular septum must withstand and coordinate strong ventricular contractions, especially from the left ventricle, therefore it is much thicker. The atria generate very low pressure, so their septum is thin.

7. What is the function of atrioventricular valves?

Atrioventricular valves (tricuspid and bicuspid) ensure one-way blood flow from atria to ventricles. They close during ventricular contraction to prevent blood from flowing backward into the atria.

8. How do semilunar valves work?

Semilunar valves (pulmonary and aortic) open when ventricles contract and blood is pushed into arteries. When ventricles relax, these valves close immediately to prevent the arterial blood from returning to the ventricles.

9. Why are ventricles more muscular than atria?

Ventricles need strong forces to pump blood — right ventricle to lungs and left ventricle to the entire body. Atria only push blood a short distance to ventricles, requiring very little pressure.

10. What is the location of the human heart?

The heart lies in the thoracic cavity between the lungs, slightly tilted to the left side. Its back surface rests near the vertebral column while the front surface lies behind the sternum and rib cartilages.

11. Why is the left lung smaller than the right lung?

The left lung has a cardiac notch — a curved depression that provides space for the heart. Due to this adaptation, the left lung becomes smaller and has only two lobes.

12. What is the epicardium?

Epicardium is the outermost layer of the heart wall and also the visceral layer of the serous pericardium. It protects the heart and carries blood vessels that supply nutrients to the myocardium.

13. How does the endocardium help in heart function?

The endocardium is a smooth epithelial layer that reduces friction between flowing blood and heart walls, preventing clot formation and ensuring efficient blood flow through chambers.

14. Why is pericardial inflammation dangerous?

Inflammation can increase fluid in the pericardial cavity (pericardial effusion), which compresses the heart — a condition called cardiac tamponade — reducing the heart’s ability to fill and pump blood properly.

15. What is the functional role of the atria?

Atria act as receiving chambers for blood—right atrium from the body via venae cavae and left atrium from lungs via pulmonary veins—and gently push this blood into the ventricles.

16. What is the functional role of the ventricles?

Ventricles are the main pumping chambers: the right ventricle pumps deoxygenated blood to the lungs through the pulmonary artery, while the left ventricle pumps oxygenated blood to the entire body through the aorta.

17. What is atrioventricular septum?

The atrioventricular septum is a fibrous wall that separates atria from ventricles and houses the AV valves. It maintains proper structural separation for the flow of blood between upper and lower chambers.

18. What is the significance of chordae tendineae?

Chordae tendineae are tendon-like cords attached to AV valves. They prevent valve flaps from turning backward during ventricular contraction, ensuring one-direction blood flow.

19. Why is smooth flow inside the heart important?

Smooth flow reduces turbulence, prevents clot formation, ensures efficient filling of chambers, and keeps blood pressure stable. The smooth endocardial surface plays a major role in this.

20. Why does the heart need its own blood supply?

The heart muscle is extremely active and requires constant oxygen and nutrients. Coronary arteries supply this blood directly to the myocardium because blood inside chambers cannot diffuse adequately into thick cardiac muscle.

21. What happens if aortic valve becomes weak?

A weak aortic valve allows backflow of blood from aorta to left ventricle, causing volume overload, enlargement of the left ventricle, and reduced efficiency of body-wide blood circulation.

22. Why does the heart never fatigue?

Cardiac muscle cells contain abundant mitochondria, rich blood supply, and a rapid supply of oxygen. They work rhythmically and continuously without tetanus, allowing the heart to function lifelong.

23. What is the significance of having four chambers?

Four chambers allow complete separation of oxygenated and deoxygenated blood, enabling efficient double circulation and maintaining high metabolic efficiency in warm-blooded organisms like humans.

24. Why is the pumping capacity of the heart considered efficient?

The heart pumps around 5 liters of blood per minute at rest due to synchronized contraction of atria and ventricles, regulated valves, and powerful myocardium, ensuring all body tissues receive constant supply.

25. What protects the heart from shocks?

The fibrous pericardium, rib cage, sternum, and surrounding lungs collectively protect the heart from external mechanical shocks and allow safe beating even during body movements.

✔️ LONG QUESTIONS (Only Questions, Well-Structured & Comprehensive)

1. Describe in detail the structure of the human heart, including its location, coverings, chambers, and associated major blood vessels.

2. Explain the structure and functions of the pericardium. Why is pericardial fluid essential for heart functioning?

3. Discuss the three layers of the heart wall. How does each layer contribute to the efficient working of the heart?

4. Explain the structure and functioning of atrioventricular valves and semilunar valves. How do they maintain unidirectional flow of blood?

5. Describe the internal structure of the right and left atria and ventricles. How do their structural differences relate to their functions?

6. What is the cardiac cycle? Discuss its phases in detail, highlighting the sequence of changes in atria, ventricles, and valves.

7. Explain the conduction system of the heart, including SA node, AV node, bundle of His, and Purkinje fibers. How does this system produce rhythmic heartbeat?

8. Describe the path of blood circulation through the heart, starting from the vena cava and ending at the aorta.

9. Discuss the structure and functioning of the human circulatory system. How is it adapted for efficient transport of materials?

10. Explain pulmonary circulation and systemic circulation. How do both work together to form double circulation in humans?

11. What is blood pressure? Explain the mechanism of its regulation and the factors that influence it.

12. Describe the composition of blood in detail. Explain the structure and functions of RBCs, WBCs, plasma, and platelets.

13. Discuss the role of lymphatic system in circulation. How does it complement the blood circulatory system?

14. Compare the structure, functions, and locations of arteries, veins, and capillaries. How do these vessels support circulation?

15. What is coronary circulation? Explain how coronary arteries and veins supply blood to the heart muscle.

16. Describe the process of heartbeat regulation. How do neural, hormonal, and intrinsic factors control heart rate?

17. Explain the disorders of the circulatory system such as atherosclerosis, hypertension, angina, and heart attack.

18. Discuss the structural and functional differences between the right and left sides of the heart. Why is the left side more muscular?

19. Explain the role of valves in preventing backflow of blood. Describe the mechanism of opening and closing of valves.

20. Describe the mechanism of exchange of materials between blood and tissues at the capillary level.

21. Explain the importance of the interventricular and interatrial septa. What would happen if these septa were absent or damaged?

22. Discuss how exercise affects heart rate and blood circulation. What physiological changes occur during physical activity?

23. Explain how the heart is adapted for continuous functioning throughout life. Discuss structural and physiological features.

24. Describe cardiac output. What factors alter cardiac output and how does the body maintain it?

25. Discuss the role of the autonomic nervous system in controlling the activities of the heart.

🌿 Human Circulatory System Quiz 🌿

Time: 30s

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Human Circulatory System: Structure, Location & Valves of the Human Heart | Class 11 Biology